@article{rosenthal_hughes_laggner_odstrcil_bortolon_wilks_mordijck_miller_sciortino_2024, title={Pedestal main ion particle transport inference through gas puff modulation with experimental source measurements}, volume={64}, ISSN={["1741-4326"]}, url={https://doi.org/10.1088/1741-4326/ad17f5}, DOI={10.1088/1741-4326/ad17f5}, abstractNote={Abstract}, number={3}, journal={NUCLEAR FUSION}, author={Rosenthal, A. M. and Hughes, J. W. and Laggner, F. M. and Odstrcil, T. and Bortolon, A. and Wilks, T. M. and Mordijck, S. and Miller, M. A. and Sciortino, F.}, year={2024}, month={Mar} }
@article{leuthold_suttrop_paz-soldan_dunne_fischer_hinson_knolker_laggner_logan_osborne_et al._2024, title={Progress towards edge-localized mode suppression via magnetic perturbations in hydrogen plasmas}, volume={64}, ISSN={["1741-4326"]}, url={https://doi.org/10.1088/1741-4326/ad1625}, DOI={10.1088/1741-4326/ad1625}, abstractNote={Abstract}, number={2}, journal={NUCLEAR FUSION}, author={Leuthold, N. and Suttrop, W. and Paz-Soldan, C. and Dunne, M. G. and Fischer, R. and Hinson, E. and Knolker, M. and Laggner, F. and Logan, N. C. and Osborne, T. and et al.}, year={2024}, month={Feb} }
@article{chaban_mordijck_rosenthal_bortolon_hughes_knolker_laggner_osborne_schmitz_thome_et al._2024, title={The role of isotope mass on neutral fueling and density pedestal structure in the DIII-D tokamak}, volume={64}, ISSN={["1741-4326"]}, DOI={10.1088/1741-4326/ad2113}, abstractNote={Abstract}, number={4}, journal={NUCLEAR FUSION}, author={Chaban, R. A. and Mordijck, S. and Rosenthal, A. M. and Bortolon, A. and Hughes, J. W. and Knolker, M. and Laggner, F. M. and Osborne, T. H. and Schmitz, L. and Thome, K. E. and et al.}, year={2024}, month={Apr} }
@article{effenberg_abe_sinclair_abrams_bortolon_wampler_laggner_rudakov_bykov_lasnier_et al._2023, title={In-situ coating of silicon-rich films on tokamak plasma-facing components with real-time Si material injection}, volume={63}, ISSN={["1741-4326"]}, url={https://doi.org/10.1088/1741-4326/acee98}, DOI={10.1088/1741-4326/acee98}, abstractNote={Abstract}, number={10}, journal={NUCLEAR FUSION}, author={Effenberg, F. and Abe, S. and Sinclair, G. and Abrams, T. and Bortolon, A. and Wampler, W. R. and Laggner, F. M. and Rudakov, D. L. and Bykov, I. and Lasnier, C. J. and et al.}, year={2023}, month={Oct} }
@article{rosenthal_hughes_laggner_odstrcil_bortolon_wilks_sciortino_2023, title={Inference of main ion particle transport coefficients with experimentally constrained neutral ionization during edge localized mode recovery on DIII-D}, volume={63}, ISSN={["1741-4326"]}, url={https://doi.org/10.1088/1741-4326/acb95a}, DOI={10.1088/1741-4326/acb95a}, abstractNote={Abstract}, number={4}, journal={NUCLEAR FUSION}, author={Rosenthal, A. M. and Hughes, J. W. and Laggner, F. M. and Odstrcil, T. and Bortolon, A. and Wilks, T. M. and Sciortino, F.}, year={2023}, month={Apr} }
@article{chen_jian_brower_haskey_yan_groebner_wang_rhodes_laggner_ding_et al._2023, title={Micro-tearing mode dominated electron heat transport in DIII-D H-mode pedestal}, url={https://doi.org/10.1088/1741-4326/accafb}, DOI={10.1088/1741-4326/accafb}, abstractNote={Abstract}, journal={Nuclear Fusion}, author={Chen, J. and Jian, X. and Brower, D.L. and Haskey, S.R. and Yan, Z. and Groebner, R. and Wang, H.Q. and Rhodes, T.L. and Laggner, F. and Ding, W. and et al.}, year={2023}, month={Jun} }
@article{parsons_mateja_messer_abrams_allain_bortolon_byrne_donovan_effenberg_herfindal_et al._2023, title={Tungsten erosion and divertor leakage from the DIII-D SAS-VW tungsten-coated divertor in experiments with neon gas seeding}, volume={37}, ISSN={["2352-1791"]}, DOI={10.1016/j.nme.2023.101520}, abstractNote={Collector probes have been used to examine tungsten divertor leakage in a variety of scenarios with low-Z impurity seeding during operation with the new tungsten-coated SAS-VW divertor in DIII-D. Measurements of tungsten deposition on collector probes inserted into the far Scrape-off-Layer (SOL) are used to deduce how efficiently tungsten leaks out of the closed, V-shaped divertor after it is eroded from the target surfaces. Qualitative differences in the tungsten deposition patterns across the collector probes provide clear experimental evidence that the SOL conditions depend on the low-Z impurity seeding conditions. These measurements show that in scenarios where neon gas is injected into the plasma, the tungsten divertor leakage and SOL transport depend on the poloidal location from which the neon is injected. In particular, neon injection from the Inner Midplane and Outer Midplane appear to each result in higher divertor leakage by a factor of 2 to 3 compared to cases with neon injection from either the SOL Crown or from the SAS-VW divertor itself.}, journal={NUCLEAR MATERIALS AND ENERGY}, author={Parsons, Matthew S. and Mateja, Jeremy D. and Messer, Seth H. and Abrams, Tyler and Allain, Jean Paul and Bortolon, Alessandro and Byrne, Patrick and Donovan, David C. and Effenberg, Florian and Herfindal, Jeffrey L. and et al.}, year={2023}, month={Dec} }
@article{krieger_balden_bortolon_dux_griener_hegele_laggner_rohde_wampler_team_2023, title={Wall conditioning effects and boron migration during boron powder injection in ASDEX Upgrade}, volume={34}, ISSN={["2352-1791"]}, url={https://doi.org/10.1016/j.nme.2023.101374}, DOI={10.1016/j.nme.2023.101374}, abstractNote={The efficacy of boron powder injection as a wall conditioning tool method in terms of its ability to create a sufficiently uniform boron layer on plasma-facing surfaces has been studied in ASDEX Upgrade. Boron powder was injected in two series of dedicated plasma discharges at varied injection rates and total amount injected. The resulting boron deposition was determined quantitatively by exposure of witness samples followed by ex-situ surface analysis of the retrieved samples. In both experiments, isotopically enriched boron was used to distinguish the deposition of the newly injected material from the residual boron fraction in the machine originating from previous glow discharge boronisations. It could be confirmed that the injected boron is migrating and re-deposited across plasma-facing wall surfaces already within one discharge. At erosion dominated divertor areas, the boron influx from the main chamber results in formation of a mixed tungsten–boron surface layer with a boron area density of O(1nm) whereas at deposition dominated areas closed boron layers grow with ongoing boron injection to a thickness of up to O(1μm). Extrapolating the radial boron deposition profile on the samples exposed in the main chamber to the limiter front yields a similar boron coverage of O(1μm), which is about ten times higher than typical values for glow discharge boronisation. Together with the observed reduction of oxygen level and improved wall pumping, the surface analysis results demonstrate that boron powder injection provides a suitable means to refresh the wall conditioning effect of a preceding glow discharge boronisation.}, journal={NUCLEAR MATERIALS AND ENERGY}, author={Krieger, K. and Balden, M. and Bortolon, A. and Dux, R. and Griener, M. and Hegele, K. and Laggner, F. and Rohde, V. and Wampler, W. R. and Team, ASDEX Upgrade}, year={2023}, month={Mar} }
@article{fenstermacher_abbate_abe_abrams_adams_adamson_aiba_akiyama_aleynikov_allen_et al._2022, title={DIII-D research advancing the physics basis for optimizing the tokamak approach to fusion energy}, volume={62}, url={http://dx.doi.org/10.1088/1741-4326/ac2ff2}, DOI={10.1088/1741-4326/ac2ff2}, abstractNote={Abstract}, number={4}, journal={Nuclear Fusion}, publisher={IOP Publishing}, author={Fenstermacher, Max and Abbate, J. and Abe, S. and Abrams, Tyler and Adams, M. and Adamson, B. and Aiba, N. and Akiyama, T. and Aleynikov, P. and Allen, E. and et al.}, year={2022}, month={Apr}, pages={042024} }
@article{garofalo_ding_solomon_grierson_jian_osborne_holland_knolker_laggner_chrystal_et al._2022, title={Deconvolving the roles of E × B shear and pedestal structure in the energy confinement quality of super H-mode experiments}, volume={62}, url={http://dx.doi.org/10.1088/1741-4326/ac4d63}, DOI={10.1088/1741-4326/ac4d63}, abstractNote={Abstract}, number={5}, journal={Nuclear Fusion}, publisher={IOP Publishing}, author={Garofalo, Andrea M. and Ding, Siye and Solomon, W.M. and Grierson, Brian and Jian, X. and Osborne, T.H. and Holland, Christopher and Knolker, Matthias and Laggner, F.M. and Chrystal, Colin and et al.}, year={2022}, month={May}, pages={056008} }
@article{xu_nagy_bortolon_shafer_laggner_2022, title={Design of a Novel Variable Geometry Divertor for Tokamaks}, url={https://doi.org/10.1109/TPS.2022.3194847}, DOI={10.1109/TPS.2022.3194847}, abstractNote={The divertor is a key component of fusion reactors, allowing exhaust of gas, impurities, and helium ash to preserve plasma purity. The divertor geometry strongly affects plasma performance, and it is designed to be compatible with different plasma shapes in present-day fusion experiments. We present a novel concept for a variable geometry divertor, in which the divertor baffle tiles are reorientable by external actuation. Implementation of this concept in a medium-sized research tokamak would uniquely provide the flexibility to tailor divertor geometry to the plasma configuration and also enable study of the effect of divertor closure on plasma performance. To ensure compatibility with typical tokamak operations, the adjustable divertor must withstand the effects of significant mechanical and thermal stresses such as MW/m2-scale heat fluxes and large electromagnetic fields, e.g., disruption forces. The technological solutions for actuation mechanisms, cooling system, gas baffling and plasma-facing components are assessed. A functional reduced-scale model with movable outer divertor target baffle tiles is developed and the actuation mechanism is tested.}, journal={IEEE Transactions on Plasma Science}, author={Xu, Chongdu and Nagy, Alexander and Bortolon, Alessandro and Shafer, Morgan and Laggner, Florian M.}, year={2022}, month={Sep} }
@article{haskey_grierson_stagner_chrystal_bortolon_laggner_2022, title={Details of the neutral energy distribution and ionization source using spectrally resolved Balmer-alpha measurements on DIII-D}, url={https://doi.org/10.1063/5.0101854}, DOI={10.1063/5.0101854}, abstractNote={Spectrally resolved passive Balmer-α (D-α, H-α) measurements from the DIII-D 16 channel edge main-ion charge exchange recombination system confirm the presence of higher energy neutrals (“thermal” neutrals) in addition to the cold neutrals that recycle off the walls in the edge region of DIII-D plasmas. Charge exchange between thermal ions and edge neutrals transfers energy and momentum between the populations giving rise to thermal neutrals with energies approximating the ions in the pedestal region. Multiple charge exchange events in succession allow an electron to effectively take a random walk, transferring from ion to ion, providing a pathway of increasing energy and velocity, permitting a neutral to get deeper into the plasma before a final ionization event that contributes to the ion and electron particle fueling. Spectrally resolved measurements provide information about the density and velocity distribution of these neutrals, which has been historically valuable for validating Monte Carlo neutral models, which include the multi stage charge exchange dynamics. Here, a multi-channel set of such measurements is used to specifically isolate the details of the thermal neutrals that are responsible for fueling inside the pedestal top. Being able to separate the thermal from the cold emission overcomes several challenges associated with optical filter-based neutral density measurements. The neutral dynamics, deeper fueling by the thermal neutrals, and spectral measurement are modeled with the FIDASIM Monte Carlo collisional radiative code, which also produces synthetic spectra with a shape that is in close agreement with the measurements. By scaling the number of neutrals in the simulation to match the intensity of the thermal emission, we show it is possible to obtain local neutral densities and ionization source rates.}, journal={Review of Scientific Instruments}, author={Haskey, S. R. and Grierson, B. A. and Stagner, L. and Chrystal, C. and Bortolon, A. and Laggner, F. M.}, year={2022}, month={Oct} }
@article{logan_hu_paz-soldan_nazikian_rhodes_wilks_munaretto_bortolon_laggner_scotti_et al._2022, title={Improved Particle Confinement with Resonant Magnetic Perturbations in DIII-D Tokamak H-Mode Plasmas}, url={https://doi.org/10.1103/PhysRevLett.129.205001}, DOI={10.1103/PhysRevLett.129.205001}, abstractNote={Experiments on the DIII-D tokamak have identified a novel regime in which applied resonant magnetic perturbations (RMPs) increase the particle confinement and overall performance. This Letter details a robust range of counter-current rotation over which RMPs cause this density pump-in effect for high confinement (H mode) plasmas. The pump in is shown to be caused by a reduction of the turbulent transport and to be correlated with a change in the sign of the induced neoclassical transport. This novel reversal of the RMP induced transport has the potential to significantly improve reactor relevant, three-dimensional magnetic confinement scenarios.}, journal={Physical Review Letters}, author={Logan, N. C. and Hu, Q. and Paz-Soldan, C. and Nazikian, R. and Rhodes, T. and Wilks, T. and Munaretto, S. and Bortolon, A. and Laggner, F. and Scotti, F. and et al.}, year={2022}, month={Nov} }
@article{haskey_ashourvan_banerjee_barada_belli_bortolon_candy_chen_chrystal_grierson_et al._2022, title={Ion thermal transport in the H-mode edge transport barrier on DIII-D}, volume={29}, url={http://dx.doi.org/10.1063/5.0072155}, DOI={10.1063/5.0072155}, abstractNote={The power balance ion heat flux in the pedestal region on DIII-D increases and becomes increasingly anomalous (above conventional neoclassical) in experiments with higher temperature and lower density pedestals where the ion collisionality (νi*) is lowered toward values expected on ITER. Direct measurements of the main-ion temperature are shown to be essential on DIII-D when calculating the ion heat flux due to differences between the temperature of D+ and the more commonly measured C6+ impurity ions approaching the separatrix. Neoclassical transport calculations from NEO and non-linear gyrokinetic calculations using CGYRO are consistent with these observations and show that while neoclassical transport plays an important role, the turbulent ion heat flux due to ion scale electrostatic turbulence is significant and can contribute similar or larger ion heat fluxes at lower collisionality. Beam emission spectroscopy and Doppler backscattering measurements in the steep gradient region of the H-mode pedestal reveal increased broadband, long-wavelength ion scale fluctuations for the low νi* discharges at the radius where the non-linear CGYRO simulations were run. Taken together, increased fluctuations, power balance calculations, and gyrokinetic simulations show that the above neoclassical ion heat fluxes, including the increases at lower νi*, are likely due to weakly suppressed ion scale electrostatic turbulence. These new results are based on world first inferred ion and electron heat fluxes in the pedestal region of deuterium plasmas using direct measurements of the deuterium temperature for power balance across ion collisionalities covering an order of magnitude from high νi* values of 1.3 down to ITER relevant νi* ∼0.1.}, number={1}, journal={Physics of Plasmas}, publisher={AIP Publishing}, author={Haskey, S. R. and Ashourvan, Arash and Banerjee, S. and Barada, K. and Belli, E. A. and Bortolon, A. and Candy, J. and Chen, J. and Chrystal, C. and Grierson, B. A. and et al.}, year={2022}, month={Jan}, pages={012506} }
@article{burke_fonck_mckee_burrell_haskey_knolker_laggner_osborne_victor_yan_2022, title={Local measurements of the pedestal magnetic field profile throughout the ELM cycle on DIII-D}, url={https://doi.org/10.1063/5.0102610}, DOI={10.1063/5.0102610}, abstractNote={New high speed localized measurements of the pedestal magnetic field during the edge localized mode (ELM) cycle of a DIII-D High confinement mode (H-mode) discharge indicate a temporally and spatial complex redistribution of the edge current density profile, jedge. The measurement technique extracts the magnetic field magnitude, B, via the spectral separation of Stark-split neutral beam radiation in the pedestal. Single spatial channel measurements from a novel spatial heterodyne spectrometer are validated in discharges with core current profile changes. The technique measures Stark-splitting changes that imply B changes as small as 1 mT with high time resolution (50 μs). At normalized poloidal flux ψn=1.0, B appears saturated in the inter-ELM period and then rapidly decreases in <200 μs by ∼1%, before edge recycling emission begins to increase. Radially inboard of jedge, B increases at the ELM crash. The behavior is consistent with a rapid collapse of jedge at the ELM crash and subsequent pedestal recovery. In some discharges, at ψn<0.96, changes in B are observed throughout the ELM cycle. In others, B recovers and is relatively stable until a few ms leading up to the next crash. Measurements of B during the H-mode transition show a large increase at ψn=1 with little change at ψn=0.9, consistent with the formation of the edge bootstrap current density peak. The ψn=0.9 spectrum is complicated by predicted changes to the Stark component intensities with density at the L–H transition.}, journal={Physics of Plasmas}, author={Burke, M. G. and Fonck, R. J. and McKee, G. R. and Burrell, K. H. and Haskey, S. R. and Knolker, M. and Laggner, F. M. and Osborne, T. H. and Victor, B. S. and Yan, Z.}, year={2022}, month={Oct} }
@article{effenberg_bortolon_casali_nazikian_bykov_scotti_wang_fenstermacher_lunsford_nagy_et al._2022, title={Mitigation of plasma–wall interactions with low-Z powders in DIII-D high confinement plasmas}, volume={62}, url={http://dx.doi.org/10.1088/1741-4326/ac899d}, DOI={10.1088/1741-4326/ac899d}, abstractNote={Abstract}, number={10}, journal={Nuclear Fusion}, publisher={IOP Publishing}, author={Effenberg, Florian and Bortolon, Alessandro and Casali, Livia and Nazikian, Raffi and Bykov, Igor and Scotti, Filippo and Wang, Huiqian and Fenstermacher, Max and Lunsford, Robert and Nagy, Alexander and et al.}, year={2022}, month={Oct}, pages={106015} }
@article{guttenfelder_battaglia_belova_bertelli_boyer_chang_diallo_duarte_ebrahimi_emdee_et al._2022, title={NSTX-U theory, modeling and analysis results}, volume={62}, url={http://dx.doi.org/10.1088/1741-4326/ac5448}, DOI={10.1088/1741-4326/ac5448}, abstractNote={Abstract}, number={4}, journal={Nuclear Fusion}, publisher={IOP Publishing}, author={Guttenfelder, W. and Battaglia, D.J. and Belova, E. and Bertelli, N. and Boyer, M.D. and Chang, C.S. and Diallo, A. and Duarte, V.N. and Ebrahimi, F. and Emdee, E.D. and et al.}, year={2022}, month={Apr}, pages={042023} }
@article{stroth_aguiam_alessi_angioni_arden_parra_artigues_asunta_balden_bandaru_et al._2022, title={Progress from ASDEX Upgrade experiments in preparing the physics basis of ITER operation and DEMO scenario development}, volume={62}, url={http://dx.doi.org/10.1088/1741-4326/ac207f}, DOI={10.1088/1741-4326/ac207f}, abstractNote={Abstract}, number={4}, journal={Nuclear Fusion}, publisher={IOP Publishing}, author={Stroth, Ulrich and Aguiam, D. and Alessi, E. and Angioni, C. and Arden, N. and Parra, R. Arredondo and Artigues, V. and Asunta, O. and Balden, M. and Bandaru, V. and et al.}, year={2022}, month={Apr}, pages={042006} }
@article{schmitz_wilcox_shiraki_rhodes_yan_mckee_callahan_chrystal_haskey_liu_et al._2022, title={Reducing the L-H transition power threshold in ITER-similar-shape DIII-D hydrogen plasmas}, volume={62}, url={http://dx.doi.org/10.1088/1741-4326/ac94e1}, DOI={10.1088/1741-4326/ac94e1}, abstractNote={Abstract}, number={12}, journal={Nuclear Fusion}, publisher={IOP Publishing}, author={Schmitz, Lothar and Wilcox, Robert and Shiraki, Daisuke and Rhodes, Terry and Yan, Zheng and McKee, George and Callahan, Kyle and Chrystal, Colin and Haskey, Shaun and Liu, Yueqiang and et al.}, year={2022}, month={Dec}, pages={126050} }
@article{odstrcil_laggner_rosenthal_bortolon_hughes_spendlove_wilks_2022, title={Robust identification of multiple-input single-output system response for efficient pickup noise removal from tokamak diagnostics}, url={https://doi.org/10.1063/5.0100988}, DOI={10.1063/5.0100988}, abstractNote={Electromagnetic pickup noise in the tokamak environment imposes an imminent challenge for measuring weak diagnostic photocurrents in the nA range. The diagnostic signal can be contaminated by an unknown mixture of crosstalk signals from coils powered by currents in the kA range. To address this issue, an algorithm for robust identification of linear multi-input single-output (MISO) systems has been developed. The MISO model describes the dynamic relationship between measured signals from power sources and observed signals in the diagnostic and allows for a precise subtraction of the noise component. The proposed method was tested on experimental diagnostic data from the DIII-D tokamak, and it has reduced noise by up to 20 dB in the 1–20 kHz range.}, journal={Review of Scientific Instruments}, author={Odstrcil, T. and Laggner, F. M. and Rosenthal, A. M. and Bortolon, A. and Hughes, J. W. and Spendlove, J. C. and Wilks, T. M.}, year={2022}, month={Oct} }
@article{rosenthal_hughes_bortolon_laggner_wilks_vieira_leccacorvi_marmar_nagy_freeman_et al._2021, title={A 1D Lyman-alpha profile camera for plasma edge neutral studies on the DIII-D tokamak}, volume={92}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85102316556&partnerID=MN8TOARS}, DOI={10.1063/5.0024115}, abstractNote={A one dimensional, absolutely calibrated pinhole camera system was installed on the DIII-D tokamak to measure edge Lyman-alpha (Ly-α) emission from hydrogen isotopes, which can be used to infer neutral density and ionization rate profiles. The system is composed of two cameras, each providing a toroidal fan of 20 lines of sight, viewing the plasma edge on the inboard and outboard side of DIII-D. The cameras’ views lie in a horizontal plane 77 cm below the midplane. At its tangency radius, each channel provides a radial resolution of ∼2 cm full width at half maximum (FWHM) with a total coverage of 22 cm. Each camera consists of a rectangular pinhole, Ly-α reflective mirror, narrow-band Ly-α transmission filter, and a 20 channel AXUV photodetector. The combined mirror and transmission filter have a FWHM of 5 nm, centered near the Ly-α wavelength of 121.6 nm and is capable of rejecting significant, parasitic carbon-III (C-III) emission from intrinsic plasma impurities. To provide a high spatial resolution measurement in a compact footprint, the camera utilizes advanced engineering and manufacturing techniques including 3D printing, high stability mirror mounts, and a novel alignment procedure. Absolutely calibrated, spatially resolved Ly-α brightness measurements utilize a bright, isolated line with low parasitic surface reflections and enable quantitative comparison to modeling to study divertor neutral leakage, main chamber fueling, and radial particle transport.}, number={3}, journal={Review of Scientific Instruments}, publisher={AIP Publishing}, author={Rosenthal, A. M. and Hughes, J. W. and Bortolon, A. and Laggner, F. M. and Wilks, T. M. and Vieira, R. and Leccacorvi, R. and Marmar, E. and Nagy, A. and Freeman, C. and et al.}, year={2021}, pages={033523} }
@article{laggner_bortolon_rosenthal_wilks_hughes_freeman_golfinopoulos_nagy_mauzey_shafer_2021, title={Absolute calibration of the Lyman-α measurement apparatus at DIII-D}, volume={92}, url={https://doi.org/10.1063/5.0038134}, DOI={10.1063/5.0038134}, abstractNote={The LLAMA (Lyman-Alpha Measurement Apparatus) diagnostic was recently installed on the DIII-D tokamak [Rosenthal et al., Rev. Sci. Instrum. (submitted) (2020)]. LLAMA is a pinhole camera system with a narrow band Bragg mirror, a bandpass interference filter, and an absolute extreme ultraviolet photodiode detector array, which measures the Ly-α brightness in the toroidal direction on the inboard, high field side (HFS) and outboard, low field side (LFS). This contribution presents a setup and a procedure for an absolute calibration near the Ly-α line at 121.6 nm. The LLAMA in-vacuum components are designed as a compact, transferable setup that can be mounted in an ex situ vacuum enclosure that is equipped with an absolutely calibrated Ly-α source. The spectral purity and stability of the Ly-α source are characterized using a vacuum ultraviolet spectrometer, while the Ly-α source brightness is measured by a NIST-calibrated photodiode. The non-uniform nature of the Ly-α source emission was overcome by performing a calibration procedure that scans the Ly-α source position and employs a numerical optimization to determine the emission pattern. Nominal and measured calibration factors are determined and compared, showing agreement within their uncertainties. A first conversion of the measured signal obtained from DIII-D indicates that the Ly-α brightness on the HFS and LFS is on the order of 1020 Ph sr−1 m−2 s−1. The established calibration setup and procedure will be regularly used to re-calibrate the LLAMA during DIII-D vents to monitor possible degradation of optical components and detectors.}, number={3}, journal={Review of Scientific Instruments}, publisher={AIP Publishing}, author={Laggner, F. M. and Bortolon, A. and Rosenthal, A. M. and Wilks, T. M. and Hughes, J. W. and Freeman, C. and Golfinopoulos, T. and Nagy, A. and Mauzey, D. and Shafer, M. W.}, year={2021}, month={Mar}, pages={033522} }
@article{wilks_knolker_snyder_eldon_scotti_chrystal_laggner_lasnier_mclean_osborne_et al._2021, title={Development of an integrated core–edge scenario using the super H-mode}, volume={61}, url={https://doi.org/10.1088/1741-4326/ac34d6}, DOI={10.1088/1741-4326/ac34d6}, abstractNote={Abstract}, number={12}, journal={Nuclear Fusion}, publisher={IOP Publishing}, author={Wilks, T.M. and Knolker, M. and Snyder, P.B. and Eldon, D. and Scotti, F. and Chrystal, C. and Laggner, F.M. and Lasnier, C. and Mclean, A. and Osborne, T. and et al.}, year={2021}, month={Dec}, pages={126064} }
@article{hammond_laggner_diallo_doskoczynski_freeman_funaba_gates_rozenblat_tchilinguirian_xing_et al._2021, title={Initial operation and data processing on a system for real-time evaluation of Thomson scattering signals on the Large Helical Device}, volume={92}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85108713985&partnerID=MN8TOARS}, DOI={10.1063/5.0041507}, abstractNote={A scalable system for real-time analysis of electron temperature and density based on signals from the Thomson scattering diagnostic, initially developed for and installed on the NSTX-U experiment, was recently adapted for the Large Helical Device and operated for the first time during plasma discharges. During its initial operation run, it routinely recorded and processed signals for four spatial points at the laser repetition rate of 30 Hz, well within the system’s rated capability for 60 Hz. We present examples of data collected from this initial run and describe subsequent adaptations to the analysis code to improve the fidelity of the temperature calculations.}, number={6}, journal={Review of Scientific Instruments}, publisher={AIP Publishing}, author={Hammond, K. C. and Laggner, F. M. and Diallo, A. and Doskoczynski, S. and Freeman, C. and Funaba, H. and Gates, D. A. and Rozenblat, R. and Tchilinguirian, G. and Xing, Z. and et al.}, year={2021}, pages={063523} }
@article{hammond_laggner_diallo_doskoczynski_freeman_funaba_gates_rozenblat_tchilinguirian_xing_et al._2021, title={Initial operation and data processing on a system for real-time evaluation of Thomson scattering signals on the Large Helical Device}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85108679563&partnerID=MN8TOARS}, journal={arXiv}, author={Hammond, K.C. and Laggner, F.M. and Diallo, A. and Doskoczynski, S. and Freeman, C. and Funaba, H. and Gates, D.A. and Rozenblat, R. and Tchilinguirian, G. and Xing, Z. and et al.}, year={2021} }
@article{nelson_xing_izacard_laggner_kolemen_2021, title={Interpretative SOL modeling throughout multiple ELM cycles in DIII-D}, volume={26}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85097735876&partnerID=MN8TOARS}, DOI={10.1016/j.nme.2020.100883}, abstractNote={Coupling between the UEDGE (edge fluid model), GINGRED (grid generation) and CAKE (equilibrium reconstruction) codes opens the door for automated interpretative scrape-off-layer (SOL) analysis over entire discharges, providing information that is essential in efforts to couple the SOL to core transport codes. In this work, we utilize new developments in the autoUEDGE code (Izacard et al. 2018) to investigate the behavior of the DIII-D SOL during the temporal evolution of an edge-localized mode (ELM) cycle. Modeled temperature and density profiles in UEDGE are automatically matched to experimental measurements by iteratively and self-consistently adjusting transport coefficient profiles in the plasma edge. This analysis is completed over multiple ELM cycles of a well-diagnosed discharge with long (∼100ms) inter-ELM periods. Directly after the ELM crash, a short period of high-density, low-temperature conditions is observed in Langmuir probe measurements at the outer divertor. This regime is associated with enhanced Dα emission and incident particle flux, suggesting that the divertor enters a period of high recycling after an ELM crash. After about ∼25ms, divertor conditions return to their pre-ELM conditions and remain there for several tens of milliseconds. Using the autoUEDGE code, the SOL is modeled as a function of ELM cycle using upstream profiles as input. The 2D modeling successfully reproduces both divertor Thomson scattering measurements and the experimentally observed divertor dynamics. Though the recycling is kept fixed throughout the modeling, changes in particle fluxes are consistent with local experimental recycling changes induced by ELMs. Agreement between modeling and observation suggests a strong link between upstream profiles and the high-recycling divertor conditions directly following large type-I ELMs.}, journal={Nuclear Materials and Energy}, publisher={Elsevier BV}, author={Nelson, A.O. and Xing, Z.A. and Izacard, O. and Laggner, F.M. and Kolemen, E.}, year={2021}, pages={100883} }
@article{barada_rhodes_haskey_groebner_diallo_banerjee_zeng_yan_chen_laggner_et al._2021, title={New understanding of inter-ELM pedestal turbulence, transport, and gradient behavior in the DIII-D tokamak}, volume={61}, url={https://doi.org/10.1088/1741-4326/ac3020}, DOI={10.1088/1741-4326/ac3020}, abstractNote={New observations of pedestal localized turbulence in the inter-ELM period of H-mode plasmas in DIII-D show that ion temperature gradient mode scale (ITG-scale) density fluctuation (ñ) increases immediately after each ELM crash and is quickly suppressed during the increase in local E × B shear. This excitation and subsequent suppression of ITG-scale ñ can explain the previously reported anomalous ion heat flux, Q i during the ELM (Viezzer et al 2017 Nucl. Fusion 57 022020). Shorter wavelength trapped electron mode scale (TEM-scale) ñ starts to increase at a critical pedestal temperature gradient (∇T e,ped ) and saturates as local E × B shear, TiC6+/Te ratio, and ∇T e,ped saturate. This TEM-scale ñ, which has the potential to cause electron (and also ion) heat transport, is consistent with driving an anomalous electron heat flux Q e, where Q e is estimated between ELMs using experimental profiles and power balance. Both ITG- and TEM-scale ñ amplitude variations with background T i/T e and ∇n e,ped are found to be consistent with theoretical predictions of these measured density fluctuations being ITG and TEM instabilities respectively. These new and unique observations on the nature of turbulence and their potential contributions to electron and ion heat fluxes at different ELM periods (i.e. collapse, recovery, and saturation phases of pedestal gradients) can significantly test and improve our pedestal predictive capabilities for ITER and other future fusion devices.}, number={12}, journal={Nuclear Fusion}, publisher={IOP Publishing}, author={Barada, K. and Rhodes, T.L. and Haskey, S.R. and Groebner, R. and Diallo, A. and Banerjee, S. and Zeng, L. and Yan, Z. and Chen, J. and Laggner, F. and et al.}, year={2021}, month={Dec}, pages={126037} }
@article{nelson_laggner_diallo_xing_smith_kolemen_2021, title={Perturbative determination of plasma microinstabilities in tokamaks}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85101949633&partnerID=MN8TOARS}, journal={arXiv}, author={Nelson, A.O. and Laggner, F.M. and Diallo, A. and Xing, Z.A. and Smith, D.R. and Kolemen, E.}, year={2021} }
@article{zeger_laggner_bortolon_rea_meneghini_saarelma_sammuli_smith_zhao_2021, title={Prediction of DIII-D Pedestal Structure from Externally Controllable Parameters}, volume={49}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85117398817&partnerID=MN8TOARS}, DOI={10.1109/TPS.2021.3114608}, abstractNote={The sharp increase of pressure at the edge of a high confinement mode (H-mode) plasma, the pedestal, strongly impacts overall plasma performance. Predicting the pedestal is a necessity to control and optimize tokamak operations. An experimental data-driven machine learning (ML) approach is presented, which predicts the pedestal heights and widths of electron density ( $n_{\mathrm {e}}$ ) and electron temperature ( $T_{\mathrm {e}}$ ) profiles as well as the separatrix $n_{\mathrm {e}}$ from externally controllable parameters such as the plasma shape, heating method and power, and gas puff rate and integrated gas puff. The one modeling framework for integrated tasks (OMFIT) framework was used with DIII-D data to efficiently, robustly, and automatically build a database of pedestal parameters to train ML models. Database creation was enabled by the search engine tool for DIII-D data, TokSearch, which parallelizes data fetching, enabling fast searches through basic signals of thousands of DIII-D shots and selection of relevant time intervals. Principal component analysis (PCA) separated the database into three clusters that represent classes of plasma shapes that are regularly used in DIII-D. The most important parameters for setting the pedestal structure were plasma current ( $I_{\mathrm {p}}$ ), toroidal magnetic field ( $B_{\phi }$ ), neutral beam heating power ( $P_{{\mathrm {NBI}}}$ ), and shaping quantities. The deep jointly informed neural networks (DJINNs) algorithm was applied to identify suitable neural network (NN) architectures that appropriately capture the features of the pedestal database. Separate NNs were implemented for each pedestal parameter, and ensembling methods were used to improve the prediction accuracy and allowed estimation of the prediction uncertainty. The pedestal predictions of the test dataset lie within the measurement uncertainties of the pedestal parameters. The NN outperformed simple linear regression (LR) analysis, indicating nonlinear dependencies in the pedestal structure. The presented achievements illustrate a promising path for future research, using feature extraction to infer experimental trends and thereby improve pedestal models as well as deploying NN for a fast pedestal prediction in DIII-D scenario development.}, number={10}, journal={IEEE Transactions on Plasma Science}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Zeger, Emi U. and Laggner, Florian M. and Bortolon, Alessandro and Rea, Cristina and Meneghini, Orso and Saarelma, Samuli and Sammuli, Brian S. and Smith, Sterling P. and Zhao, Jinjin}, year={2021}, pages={3212–3227} }
@article{diallo_laggner_2021, title={Review: Turbulence dynamics during the pedestal evolution between edge localized modes in magnetic fusion devices}, volume={63}, url={https://doi.org/10.1088/1361-6587/abbf85}, DOI={10.1088/1361-6587/abbf85}, abstractNote={Abstract}, number={1}, journal={Plasma Physics and Controlled Fusion}, publisher={IOP Publishing}, author={Diallo, A and Laggner, F M}, year={2021}, month={Jan}, pages={013001} }
@article{nelson_laggner_diallo_smith_xing_shousha_kolemen_2021, title={Time-dependent experimental identification of inter-ELM microtearing modes in the tokamak edge on DIII-D}, volume={61}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85118558080&partnerID=MN8TOARS}, DOI={10.1088/1741-4326/ac27ca}, abstractNote={In a series of discharges on the DIII-D tokamak, fast vertical plasma jogs are used to induce current perturbations in the steep gradient region of the H-mode edge. These current perturbations directly influence the edge q profile, decoupling the resonant location and instability drive of pedestal-localized microtearing modes (MTMs). By exploiting this effect, we develop and apply a new experimental technique to track the dynamical frequency evolution of MTMs in the pedestal region, providing a compelling validation of the MTM model. The frequency of potential MTMs is calculated as the Doppler-shifted electron diamagnetic frequency at rational q = m/n surfaces, showing remarkable agreement with chirped frequency behavior of n = 3, 4 and 5 modes detected with fast magnetics. Data is collected throughout multiple ELM cycles in order to build robust statistics describing the time-dependent frequency evolution of MTMs, which can be explained by examining the recovery of pedestal gradients after an ELM event. MTMs have a dominant transport contribution in the electron thermal channel, so the presented results indicate that reduced models of pedestal transport must be electromagnetic in nature and constructed with accurate calculations of MTM stability; inclusion of this physics is essential for accurate predictions of the electron temperature pedestal profile. Supporting measurements of mode saturation, propagation direction and transport fingerprints are made to support the dynamic frequency determination, unambiguously and experimentally identifying MTMs in the pedestal region of DIII-D.}, number={11}, journal={Nuclear Fusion}, publisher={IOP Publishing}, author={Nelson, A.O. and Laggner, F.M. and Diallo, A. and Smith, D. and Xing, Z.A. and Shousha, R. and Kolemen, E.}, year={2021}, pages={116038} }
@article{willensdorfer_viezzer_cavedon_cano-megias_fable_wolfrum_cruz-zabala_david_dux_fischer_et al._2020, title={Dynamics of the pedestal transport during edge localized mode cycles at ASDEX Upgrade}, volume={62}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85081390193&partnerID=MN8TOARS}, DOI={10.1088/1361-6587/ab5b1d}, abstractNote={Abstract}, number={2}, journal={Plasma Physics and Controlled Fusion}, author={Willensdorfer, M. and Viezzer, E. and Cavedon, M. and Cano-Megias, P. and Fable, E. and Wolfrum, E. and Cruz-Zabala, D.J. and David, P. and Dux, R. and Fischer, R. and et al.}, year={2020} }
@article{réfy_solano_vianello_zoletnik_dunai_tál_brix_gomes_birkenmeier_wolfrum_et al._2020, title={Identity of the JET M-mode and the ASDEX Upgrade I-phase phenomena}, volume={60}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85082864260&partnerID=MN8TOARS}, DOI={10.1088/1741-4326/ab7594}, abstractNote={An H-mode plasma state free of edge-localized mode (ELM), close to the L-H transition with clear density and temperature pedestal has been observed both at the Joint European Torus (JET) and at the ASDEX Upgrade (AUG) tokamaks usually identified by a low frequency (LFO, 1–2 kHz), m = 1, n = 0 oscillation of the magnetics and the modulation of pedestal profiles. The regime at JET is referred to as M-mode while at AUG as intermediate phase or I-phase. This contribution aims at a comparative analysis of these phenomena in terms of the density and temperature pedestal properties, the magnetic oscillations and symmetries. Lithium beam emission spectroscopy (Li-BES) and reflectometer measurements at JET and AUG show that the M-mode and the I-phase modulates the plasma edge density. A high frequency oscillation of the magnetics and the density at the pedestal is also associated with both the M-mode and the I-phase, and its power is modulated with the LFO frequency. The power modulation happens simultaneously in every Mirnov coil signal where it can be detected. The bursts of the magnetic signals and the density at the pedestal region are followed by the flattening of the density profile, and by a radially outward propagating density pulse in the scrape-off layer (SOL). The analysis of the helium line ratio spectroscopy (He-BES) signals at AUG revealed that the electron temperature is modulated in phase with the density, thus the I-phase modulates the pressure profile gradient. This analysis gave opportunity to compare Li-BES and He-BES density profiles at different locations suggesting a toroidal and poloidal symmetry of the density modulation. The presented results indicate that the regimes, the AUG I-phase and the JET M-mode, exhibit similar characteristics, which leads to the conclusion that the regimes are likely the same.}, number={5}, journal={Nuclear Fusion}, author={Réfy, D.I. and Solano, E.R. and Vianello, N. and Zoletnik, S. and Dunai, D. and Tál, B. and Brix, M. and Gomes, R. and Birkenmeier, G. and Wolfrum, E. and et al.}, year={2020} }
@article{réfy_solano_vianello_zoletnik_dunai_tál_brix_gomes_birkenmeier_wolfrum_et al._2020, title={Identity of the JET M-mode and the ASDEX upgrade I-phase phenomena}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85095263972&partnerID=MN8TOARS}, journal={arXiv}, author={Réfy, D.I. and Solano, E.R. and Vianello, N. and Zoletnik, S. and Dunai, D. and Tál, B. and Brix, M. and Gomes, R. and Birkenmeier, G. and Wolfrum, E. and et al.}, year={2020} }
@article{knolker_snyder_evans_wilks_eldon_grierson_jaervinen_jian_laggner_mcclenaghan_et al._2020, title={Optimizing the Super H-mode pedestal to improve performance and facilitate divertor integration}, volume={27}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85092727633&partnerID=MN8TOARS}, DOI={10.1063/5.0011008}, abstractNote={Access to Super H-mode is demonstrated for moderately shaped plasmas in agreement with EPED [Snyder et al., Phys. Plasmas 16, 056118 (2009)] predictions. In particular, Super H-mode is realized in a DIII-D shape that is accessible to the JET tokamak. The reduced triangularity of the JET-compatible shape compared to previous Super H-mode plasma shapes does not prevent deep ascension into the so-called Super H-mode “channel.” Operationally, access is enabled and optimized by delaying the neutral beam power injection and, thus, protracting the L–H transition. In highly shaped DIII-D plasmas, the injection of nitrogen sufficient for the establishment of a radiative divertor is shown to be possible during Super H-mode without pedestal degradation. Due to its increased stored energy and radiative divertor integration capabilities, Super H-mode is a promising candidate as operating regime for JET, ITER, and future fusion reactors.}, number={10}, journal={Physics of Plasmas}, publisher={AIP Publishing}, author={Knolker, M. and Snyder, P. B. and Evans, T. E. and Wilks, T. and Eldon, D. and Grierson, B. and Jaervinen, A. and Jian, X. and Laggner, F. and McClenaghan, J. and et al.}, year={2020}, pages={102506} }
@article{laggner_eldon_nelson_paz-soldan_bortolon_evans_fenstermacher_grierson_hu_humphreys_et al._2020, title={Real-time pedestal optimization and ELM control with 3D fields and gas flows on DIII-D}, volume={60}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85086600626&partnerID=MN8TOARS}, DOI={10.1088/1741-4326/ab88e1}, abstractNote={The capabilities of the DIII-D tokamak’s plasma control system (PCS) were expanded to allow for pedestal optimization and edge localized mode (ELM) control. Three proof of principle control schemes are presented that were successfully implemented and tested. These use multiple inputs from real-time (RT) diagnostics like a Dα based ELM monitor and edge profile measurements from Thomson scattering (TS) as well as 3D, i.e. non-axisymmetric, magnetic fields and gas puffs as actuators to regulate the density pedestal. The first scheme targets to optimize the access of ELM suppression induced by non-axisymmetric magnetic perturbations (MPs). The conducted set of experiments identifies a path dependence of plasma confinement on the applied MP amplitude. The controller aims to transition into ELM suppression at the minimum 3D field amplitude and reduces it further afterwards, allowing for partial confinement recovery. Another pedestal control scheme is deployed to compensate the density ‘pump-out’ in MP ELM suppression by regulating the gas puff. This uses RT TS diagnostic data, extracting the pedestal height from the electron density ( ne) profiles and enables studies of the transition into and out of MP ELM suppression at constant density. A limit cycle behavior of edge rotation and MP amplitude persists under these conditions. The third control scheme combines MPs and gas puffs as actuators to perform pedestal density trajectory control to access Super high confinement mode (H-mode) and furthermore, allowing the integration of a radiative divertor in this regime. While MPs mainly impact the pedestal top density, the control scheme allows to loosen the tight coupling of pedestal top and separatrix density evolution. With respect to ITER, the achieved results emphasize the need for an advanced control system to keep MP amplitude close to but above the ELM suppression threshold at all times, enabling high confinement and, respectively, at high fusion energy gain factor (Q). Furthermore, pedestal control enables detailed physics studies in present-day tokamaks and allows the exploration of core-edge integrated plasma scenarios.}, number={7}, journal={Nuclear Fusion}, publisher={IOP Publishing}, author={Laggner, F.M. and Eldon, D. and Nelson, A.O. and Paz-Soldan, C. and Bortolon, A. and Evans, T.E. and Fenstermacher, M.E. and Grierson, B.A. and Hu, Q. and Humphreys, D.A. and et al.}, year={2020}, pages={076004} }
@article{nelson_laggner_groebner_grierson_izacard_eldon_shafer_leonard_shiraki_sontag_et al._2020, title={Setting the H-mode pedestal structure: Variations of particle source location using gas puff and pellet fueling}, volume={60}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85082308637&partnerID=MN8TOARS}, DOI={10.1088/1741-4326/ab5e65}, abstractNote={Experiments in DIII-D show that a particle source location inside the top of the H-mode pedestal (pellets) maintains a higher pedestal pressure than an edge source (gas fueling) through a widening of the electron temperature pedestal with reduction of the temperature gradient. The effect of these two fueling schemes on the H-mode pedestal structure was examined in DIII-D by comparing controlled pellet-fueled and gas-fueled discharges across a fueling scan up to 40 torr l s−1. High resolution electron profiles reveal that gas fueling lowers the pedestal pressure as the density profile shifts radially outwards and the separatrix density increases, while pellet fueling maintains a constant pedestal pressure. The neutral source locations from pellets and gas are determined with the PELLET and UEDGE codes, respectively, and quantify the particle source localization. Pellets provide significant ionization inside the pedestal top while gas puffing localizes ionization in the scrape-off-layer and pedestal foot, broadly consistent with the density profile structure influenced by the source. ELMs are observed to increase in frequency and reduce impurity content as fueling is increased. Stability analysis with ELITE shows that both conditions are near the type-I ELM corner of the peeling–ballooning stability diagram, which is altered significantly by the introduction of pellets. Since transport mechanisms are not observed to change substantially with particle source location, wider pedestals allow the pellet-fueled discharges to retain higher pedestal temperatures at similar pedestal densities. EPED1 is tested to capture the pedestal pressure, under-predicting the height with pellets and over-predicting the height with gas by ∼15%. These results have important implications for future reactors where pellet fueling will be the primary particle source due to an opaque scrape-off-layer by showing that the neutral source location plays a role in setting the structure of the H-mode pedestal.}, number={4}, journal={Nuclear Fusion}, publisher={IOP Publishing}, author={Nelson, A.O. and Laggner, F.M. and Groebner, R. and Grierson, B.A. and Izacard, O. and Eldon, D. and Shafer, M.W. and Leonard, A. and Shiraki, D. and Sontag, A.C. and et al.}, year={2020}, pages={046003} }
@article{laggner_diallo_leblanc_rozenblat_tchilinguirian_kolemen_2019, title={A scalable real-time framework for Thomson scattering analysis: Application to NSTX-U}, volume={90}, url={http://dx.doi.org/10.1063/1.5088248}, DOI={10.1063/1.5088248}, abstractNote={A detailed description of a prototype setup for real-time (RT) Thomson scattering (TS) analysis is presented and implemented in the multi-point Thomson scattering (MPTS) diagnostic system at the National Spherical Torus Experiment Upgrade (NSTX-U). The data acquisition hardware was upgraded with RT capable electronics (RT-analog digital converters and a RT server) that allow for fast digitization of the laser pulse signal of eight radial MPTS channels. In addition, a new TS spectrum analysis software for a rapid calculation of electron temperature (Te) and electron density (ne) was developed. Testing of the RT hardware and data analysis software was successfully completed and benchmarked against the standard, post-shot evaluation. Timing tests were performed showing that the end-to-end processing time was reproducibly below 17 ms for the duration of at least 5 s, meeting a 60 Hz deadline by the laser pulse repetition rate over the length of a NSTX-U discharge. The presented RT framework is designed to be scalable in system size, i.e., incorporation of additional radial channels by solely adding additional RT capable hardware. Furthermore, it is scalable in its operation duration and was continuously running for up to 30 min, making it an attractive solution for machines with long discharges such as advanced, non-inductive tokamaks or stellarators.}, number={4}, journal={Review of Scientific Instruments}, publisher={AIP Publishing}, author={Laggner, F. M. and Diallo, A. and LeBlanc, B. P. and Rozenblat, R. and Tchilinguirian, G. and Kolemen, E.}, year={2019}, month={Apr}, pages={043501} }
@article{lunsford_rohde_bortolon_dux_herrmann_kallenbach_mcdermott_david_drenik_laggner_et al._2019, title={Active conditioning of asdex upgrade tungsten plasma-facing components and discharge enhancement through boron and boron nitride particulate injection}, volume={59}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85076618975&partnerID=MN8TOARS}, DOI={10.1088/1741-4326/ab4095}, abstractNote={The injection of boron (B) and boron nitride (BN) powders into ASDEX Upgrade H-mode discharges have demonstrated effective control of tungsten influx in low density/collisionality operational regimes, similar to conventional boronization methods. Sub-mm powder particles are gravitationally accelerated into the upper edge of a lower single null H-mode plasma with a boundary shape roughly conforming to the shape of the poloidal midplane limiters. Visible spectroscopy measurements at one of the outer limiter showed increases in both B and N signal levels, as well as elevated B levels in the divertor, and an increase in total radiated power by greater than a factor of two during BN injection. Globally the BN injection improved energy confinement by 10%–20%, associated with improvements in pedestal performance similar to gaseous N injection. Following conditioning discharges with B powder injection, three low gas-fueling discharges with magnetic perturbations for ELM suppression were successfully conducted. These first results suggest that the application of B containing powders can be used to both improve plasma performance in real-time, and to improve overall wall conditions for subsequent discharges.}, number={12}, journal={Nuclear Fusion}, author={Lunsford, R. and Rohde, V. and Bortolon, A. and Dux, R. and Herrmann, A. and Kallenbach, A. and McDermott, R.M. and David, P. and Drenik, A. and Laggner, F. and et al.}, year={2019} }
@article{petty_abadie_abrams_ahn_akiyama_aleynikov_allcock_allen_allen_anderson_et al._2019, title={DIII-D research towards establishing the scientific basis for future fusion reactors}, volume={59}, ISSN={["1741-4326"]}, url={https://publons.com/wos-op/publon/21450552/}, DOI={10.1088/1741-4326/AB024A}, abstractNote={Abstract}, number={11}, journal={NUCLEAR FUSION}, author={Petty, C. C. and Abadie, L. and Abrams, T. W. and Ahn, J. and Akiyama, T. and Aleynikov, P. and Allcock, J. and Allen, E. O. and Allen, S. and Anderson, J. P. and et al.}, year={2019}, month={Nov} }
@article{dependence on plasma shape and plasma fueling for small edge-localized mode regimes in tcv and asdex upgrade_2019, volume={59}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85070909412&partnerID=MN8TOARS}, DOI={10.1088/1741-4326/ab2211}, abstractNote={Within the EUROfusion MST1 work package, a series of experiments has been conducted on AUG and TCV devices to disentangle the role of plasma fueling and plasma shape for the onset of small ELM regimes. On both devices, small ELM regimes with high confinement are achieved if and only if two conditions are fulfilled at the same time. Firstly, the plasma density at the separatrix must be large enough (ne,sep/nG ∼ 0.3), leading to a pressure profile flattening at the separatrix, which stabilizes type-I ELMs. Secondly, the magnetic configuration has to be close to a double null (DN), leading to a reduction of the magnetic shear in the extreme vicinity of the separatrix. As a consequence, its stabilizing effect on ballooning modes is weakened.}, number={8}, journal={Nuclear Fusion}, year={2019} }
@article{rozenblat_kolemen_laggner_freeman_tchilinguirian_sichta_zimmer_2019, title={Development of Real-Time Software for Thomson Scattering Analysis at NSTX-U}, volume={75}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85073835505&partnerID=MN8TOARS}, DOI={10.1080/15361055.2019.1658037}, abstractNote={Abstract The Thomson scattering (TS) diagnostic on the National Spherical Tokamak eXperiment Upgrade (NSTX-U) has been an essential system for many operational campaigns due to its function of measuring plasma electron density and temperature. Constructive feedback to improve the next plasma discharge, however, has been limited because of in-between shots analysis. Plasma control, therefore, desires a diagnostic system that is real-time capable. This contribution presents the development of software that demonstrates the feasibility of a real-time TS diagnostic system for NSTX-U. The developed software is able to evaluate the electron temperature and density within 2.5 ms. The overall system requirement is specified by a 60-Hz timing cycle, which is driven by the TS laser pulse rate. The real-time software processes the peak amplitudes of the detected photons, evaluates the electron temperature and density, and then outputs them to an analog output card that is used to interface with the NSTX-U control. The real-time software is implemented in an object-oriented architecture using C++11. C++11 software components include Abstract class, Atomic data types for synchronization, and a Hash data structure. The software application makes use of multiple threads that run concurrently: a thread to acquire the photon peak amplitude and feed a circular buffer, threads to evaluate the electron density and temperatures, and a thread that supplies corresponding output voltages and feeds the output card. In summary, the new real-time TS system has been proven to meet the 60-Hz system requirement. For this reason, the software implementation was deemed successful. In future NSTX-U campaigns, this diagnostic will be a great asset enabling real-time plasma density and temperature control.}, number={8}, journal={Fusion Science and Technology}, author={Rozenblat, R. and Kolemen, E. and Laggner, F.M. and Freeman, C. and Tchilinguirian, G. and Sichta, P. and Zimmer, G.}, year={2019}, pages={835–840} }
@article{knolker_evans_wingen_bortolon_laggner_moyer_nazikian_zohm_2019, title={Divertor currents during type-I edge-localized modes on the DIII-D tokamak}, volume={59}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85076731355&partnerID=MN8TOARS}, DOI={10.1088/1741-4326/ab3e9a}, abstractNote={Measurements of divertor currents on DIII-D lead to new insights in nonlinear edge-localized mode (ELM) dynamics and a possible mechanism to explain their explosive growth. Rapidly oscillating currents flowing into the divertor before a significant increase in divertor heat flux occurs are measured with an array of shunted tiles and characterized. Extrapolation results in total n = 0 currents of 5–10 kA flowing into a concentric circle near the strike point. The detected Fourier harmonics appear consistent with a mix of low-n modes (n < 4) with currents up to 4 kA. A heuristic framework for ELM currents is developed based on thermoelectric origin of the tile currents with flow through regions inside of the nominal separatrix and found consistent with the current measurements. A current flow through the confined plasma leading to increased stochasticity and transport at the plasma edge could provide a mechanism for additional nonlinear growth as sought for in computational ELM simulations. Results also imply that ELM currents may open the possibility to manipulate the ELM character by perturbations through non-axisymmetric divertor bias or tile insulation.}, number={12}, journal={Nuclear Fusion}, publisher={IOP Publishing}, author={Knolker, M. and Evans, T.E. and Wingen, A. and Bortolon, A. and Laggner, F.M. and Moyer, R.A. and Nazikian, R. and Zohm, H.}, year={2019}, pages={126020} }
@article{snyder_hughes_osborne_paz-soldan_solomon_knolker_eldon_evans_golfinopoulos_grierson_et al._2019, title={High fusion performance in Super H-mode experiments on Alcator C-Mod and DIII-D}, volume={59}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85070818533&partnerID=MN8TOARS}, DOI={10.1088/1741-4326/ab235b}, abstractNote={Abstract}, number={8}, journal={Nuclear Fusion}, author={Snyder, P.B. and Hughes, J.W. and Osborne, T.H. and Paz-Soldan, C. and Solomon, W.M. and Knolker, M. and Eldon, D. and Evans, T. and Golfinopoulos, T. and Grierson, B.A. and et al.}, year={2019} }
@article{laggner_diallo_cavedon_kolemen_2019, title={Inter-ELM pedestal localized fluctuations in tokamaks: Summary of multi-machine observations}, volume={19}, url={http://dx.doi.org/10.1016/j.nme.2019.02.030}, DOI={10.1016/j.nme.2019.02.030}, abstractNote={A variety of experimental studies on pedestal localized fluctuations appearing in between crashes of edge localized modes (ELMs) across several tokamaks have been reviewed and summarized. The onset of the inter-ELM fluctuations is correlated with the evolution of the pedestal gradients. Three profile recovery phases are extracted, which are interlinked with the onsets of different kinds of pedestal fluctuations. Across machines it is found that the pedestal fluctuations can be assorted into at least three categories. These are determined by the fluctuation onset in the ELM cycle, observed frequency range and radial location in the pedestal. Further, the categories might be also related to different instabilities. Similar observations at various machines may point to a underlying generation mechanism that acts similarly for presently accessible pedestal parameter ranges.}, journal={Nuclear Materials and Engergy}, publisher={Elsevier BV}, author={Laggner, F.M. and Diallo, A. and Cavedon, M. and Kolemen, E.}, year={2019}, month={May}, pages={479–486} }
@article{knolker_evans_wingen_bortolon_chrystal_laggner_moyer_nazikian_zohm_2019, title={Observation of divertor currents during type-I ELMs on the DIII-D tokamak}, volume={18}, url={https://doi.org/10.1016/j.nme.2019.01.003}, DOI={10.1016/j.nme.2019.01.003}, abstractNote={In DIII-D, large currents flowing into the divertor floor during edge-localized modes (ELMs) have been measured by an array of shunt current resistors before an increase of heat flux is measured by IR thermography. The diagnostic consists of 40 tiles distributed in five concentric circles in the lower divertor with sampling rates range between 50 and 500 kHz. Typically, the current measured by a single tile during an ELM can reach 500 A. This amounts to 5–25 kA flowing in the divertor tiles. The temporal evolution of the ELM currents shows a first phase with large amplitude oscillations, occurring before the heat flux increase measured by infrared thermography at the same location, lasting between 0.05 ms and 0.3 ms. A second phase follows where the time evolution of the divertor current mimics the evolution of the divertor heat flux. These currents could affect the plasma edge stability in the nonlinear ELM phase and provide a mechanism leading to explosive growth of edge stochasticity, the need of which and existence is predicted in contemporary nonlinear ELM simulations.}, journal={Nuclear Materials and Energy}, publisher={Elsevier BV}, author={Knolker, M. and Evans, T.E. and Wingen, A. and Bortolon, A. and Chrystal, C. and Laggner, F. and Moyer, R.A. and Nazikian, R. and Zohm, H.}, year={2019}, month={Jan}, pages={222–226} }
@article{cavedon_dux_pütterich_viezzer_wolfrum_dunne_fable_fischer_harrer_laggner_et al._2019, title={On the ion and electron temperature recovery after the ELM-crash at ASDEX upgrade}, volume={18}, url={https://doi.org/10.1016/j.nme.2018.12.034}, DOI={10.1016/j.nme.2018.12.034}, abstractNote={The access to fast measurements, i.e. Δt ≈ 100 µs, of the ions and the electrons during an entire edge localized cycle (ELM) reveals asymmetries in the recovery of the maximum edge gradients. Different magnetic fluctuations are found to correlate with the saturation of the edge ion temperature (Ti), electrons temperature (Te) and density (ne) gradients. In particular, while ∇Ti and ∇ne clamp roughly 3.0 ms after the ELM-crash together with the onset of mid-frequency (f ≲ 50 kHz) magnetic fluctuations, ∇Te recovers to the pre-ELM conditions only after 7.0 ms and saturates with the appearance of high frequency fluctuations (f ≈ 200 kHz). The effect of electron temperature gradient modes (ETGs) and of energy losses induced by ionization of neutrals are discussed as possible reasons for the delayed recovery of ∇Te. The onset and the suppression of ETGs qualitatively follow the requirements of an increased electron heat transport. However, gyro-kinetic simulations are necessary to quantify the impact of ETGs. On the other hand, the impact of the neutral ionization during the density build-up as an electron energy loss channel is measured to be small compared to the total electron energy. The dominant terms in the electron energy balance are instead the radiative power and the ion-electron heat exchange.}, journal={Nuclear Materials and Energy}, publisher={Elsevier BV}, author={Cavedon, M. and Dux, R. and Pütterich, T. and Viezzer, E. and Wolfrum, E. and Dunne, M. and Fable, E. and Fischer, R. and Harrer, G.F. and Laggner, F.M. and et al.}, year={2019}, month={Jan}, pages={275–280} }
@article{overview of physics studies on asdex upgrade_2019, volume={59}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85072124840&partnerID=MN8TOARS}, DOI={10.1088/1741-4326/ab18b8}, abstractNote={Abstract}, number={11}, journal={Nuclear Fusion}, year={2019} }
@article{laggner_keerl_gnilsen_wolfrum_bernert_carralero_guimarais_nikolaeva_potzel_cavedon_et al._2018, title={Divertor, scrape-off layer and pedestal particle dynamics in the ELM cycle on ASDEX Upgrade}, volume={60}, url={https://doi.org/10.1088/1361-6587/aa90bf}, DOI={10.1088/1361-6587/aa90bf}, abstractNote={In addition to the relaxation of the pedestal, edge localised modes (ELMs) introduce changes to the divertor and scrape-off layer (SOL) conditions. Their impact on the inter-ELM pedestal recovery is investigated, with emphasis on the electron density (ne) evolution. The typical ELM cycle occurring in an exemplary ASDEX Upgrade discharge interval at moderate applied gas puff and heating power is characterised, utilising several divertor, SOL and pedestal diagnostics. In the studied discharge interval the inner divertor target is detached before the ELM crash, while the outer target is attached. The particles and power expelled by the ELM crash lead to a re-attachment of the inner target plasma. After the ELM crash, the outer divertor target moves into a high recycling regime with large ne in front of the plate, which is accompanied by high main chamber neutral fluxes. On similar timescales, the inner target fully detaches and the high field side high density region (HFSHD) is formed reaching up to the high field side midplane. This state evolves again to the pre-ELM state, when the main chamber neutral fluxes are reduced later in the ELM cycle. Neither the timescale of the appearance of the HFSHD nor the increase of the main chamber neutral fluxes fit the timescale of the ne pedestal, which is faster. It is found that during the ne pedestal recovery, the magnetic activity at the low field side midplane is strongly reduced indicating a lower level of fluctuations. A rough estimation of the particle flux across the pedestal suggests that the particle flux is reduced in this period. In conclusion, the evolution of the ne pedestal is determined by a combination of neutral fluxes, HFSHD and reduced particle flux across the pedestal. A reduced particle flux explains the fast, experimentally observed re-establishment of the ne pedestal best, whereas neutrals and HFSHD impact on the evolution of the SOL and separatrix conditions.}, number={2}, journal={Plasma Physics and Controlled Fusion}, publisher={IOP Publishing}, author={Laggner, F M and Keerl, S and Gnilsen, J and Wolfrum, E and Bernert, M and Carralero, D and Guimarais, L and Nikolaeva, V and Potzel, S and Cavedon, M and et al.}, year={2018}, month={Feb}, pages={025002} }
@article{vanovac_wolfrum_denk_mink_laggner_birkenmeier_willensdorfer_viezzer_hoelzl_freethy_et al._2018, title={Effects of density gradients and fluctuations at the plasma edge on ECEI measurements at ASDEX Upgrade}, volume={60}, url={https://doi.org/10.1088/1361-6587/aaa7ac}, DOI={10.1088/1361-6587/aaa7ac}, abstractNote={Electron cyclotron emission imaging (ECEI) provides measurements of electron temperature (Te) and its fluctuations (δTe). However, when measuring at the plasma edge, in the steep gradient region, radiation transport effects must be taken into account. It is shown that due to these effects, the scrape-off layer region is not accessible to the ECEI measurements in steady state conditions and that the signal is dominated by the shine-through emission. Transient effects, such as filaments, can change the radiation transport locally, but cannot be distinguished from the shine-through. Local density measurements are essential for the correct interpretation of the electron cyclotron emission, since the density fluctuations influence the temperature measurements at the plasma edge. As an example, a low frequency 8 kHz mode, which causes 10%–15% fluctuations in the signal level of the ECEI, is analysed. The same mode has been measured with the lithium beam emission spectroscopy density diagnostic, and is very well correlated in time with high frequency magnetic fluctuations. With radiation transport modelling of the electron cyclotron radiation in the ECEI geometry, it is shown that the density contributes significantly to the radiation temperature (Trad) and the experimental observations have shown the amplitude modulation in both density and temperature measurements. The poloidal velocity of the low frequency mode measured by the ECEI is 3 km s–1. The calculated velocity of the high frequency mode measured with the magnetic pick-up coils is about 25 km s–1. Velocities are compared with the E × B background flow velocity and possible explanations for the origin of the low frequency mode are discussed.}, number={4}, journal={Plasma Physics and Controlled Fusion}, publisher={IOP Publishing}, author={Vanovac, B and Wolfrum, E and Denk, S S and Mink, F and Laggner, F M and Birkenmeier, G and Willensdorfer, M and Viezzer, E and Hoelzl, M and Freethy, S J and et al.}, year={2018}, month={Apr}, pages={045002} }
@article{krieger_balden_coenen_laggner_matthews_nille_rohde_sieglin_giannone_göths_et al._2018, title={Experiments on transient melting of tungsten by ELMs in ASDEX Upgrade}, volume={58}, url={https://doi.org/10.1088/1741-4326/aa9a05}, DOI={10.1088/1741-4326/aa9a05}, abstractNote={Repetitive melting of tungsten by power transients originating from edge localized modes (ELMs) has been studied in ASDEX Upgrade. Tungsten samples were exposed to H-mode discharges at the outer divertor target plate using the divertor manipulator II (DIM-II) system (Herrmann et al 2015 Fusion Eng. Des. 98–9 1496–9). Designed as near replicas of the geometries used also in separate experiments on the JET tokamak (Coenen et al 2015 J. Nucl. Mater. 463 78–84; Coenen et al 2015 Nucl. Fusion 55 023010; Matthews et al 2016 Phys. Scr. T167 7), the samples featured a misaligned leading edge and a sloped ridge respectively. Both structures protrude above the default target plate surface thus receiving an increased fraction of the parallel power flux. Transient melting by ELMs was induced by moving the outer strike point to the sample location. The temporal evolution of the measured current flow from the samples to vessel potential confirmed transient melting. Current magnitude and dependency from surface temperature provided strong evidence for thermionic electron emission as main origin of the replacement current driving the melt motion. The different melt patterns observed after exposures at the two sample geometries support the thermionic electron emission model used in the MEMOS melt motion code, which assumes a strong decrease of the thermionic net current at shallow magnetic field to surface angles (Pitts et al 2017 Nucl. Mater. Energy 12 60–74). Post exposure ex situ analysis of the retrieved samples show recrystallization of tungsten at the exposed surface areas to a depth of up to several mm. The melt layer transport to less exposed surface areas leads to ratcheting pile up of re-solidified debris with zonal growth extending from the already enlarged grains at the surface.}, number={2}, journal={Nuclear Fusion}, publisher={IOP Publishing}, author={Krieger, K. and Balden, M. and Coenen, J.W. and Laggner, F. and Matthews, G.F. and Nille, D. and Rohde, V. and Sieglin, B. and Giannone, L. and Göths, B. and et al.}, year={2018}, month={Feb}, pages={026024} }
@article{asdex upgrade team_viezzer_cavedon_fable_laggner_mcdermott_galdon-quiroga_dunne_kappatou_angioni_et al._2018, title={Ion heat transport dynamics during edge localized mode cycles at ASDEX Upgrade}, volume={58}, url={https://doi.org/10.1088/1741-4326/aaa22f}, DOI={10.1088/1741-4326/aaa22f}, abstractNote={The edge ion heat transport is analyzed in ASDEX Upgrade (AUG) by combining a comprehensive set of pedestal measurements with both interpretive and predictive modelling. The experimentally determined ion heat diffusivities, χi, are compared with neoclassical theory and the impact of edge localized modes (ELMs) on the edge ion heat transport level is studied in detail. Pedestal matching experiments in deuterium and hydrogen plasmas show that the inter-ELM pedestal χi remains close to the neoclassical value. The additional power needed in hydrogen to get similar pedestal temperatures as in deuterium plasmas mostly affects the electron heat channel, i.e. the electron heat diffusivity increases while the ion heat diffusivity stays at the same level within the uncertainties. Sub-ms measurements of the edge ion temperature allows us to extend the analysis to the entire ELM cycle. During the ELM crash, the ion heat transport is increased by an order of magnitude. The perturbed heat flux increases first at the separatrix, i.e. first the separatrix ion temperature increases, leading to a flatter ion temperature gradient, followed by a decrease of the whole pedestal profile. The ion heat transport returns to its pre-ELM neoclassical level 3–4 ms after the ELM crash.}, number={2}, journal={Nuclear Fusion}, publisher={IOP Publishing}, author={Asdex Upgrade Team, T. and Viezzer, E. and Cavedon, M. and Fable, E. and Laggner, F.M. and McDermott, R.M. and Galdon-Quiroga, J. and Dunne, M.G. and Kappatou, A. and Angioni, C. and et al.}, year={2018}, month={Feb}, pages={026031} }
@article{mink_hoelzl_wolfrum_orain_dunne_lessig_pamela_manz_maraschek_huijsmans_et al._2018, title={Nonlinear coupling induced toroidal structure of edge localized modes}, volume={58}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85040697092&partnerID=MN8TOARS}, DOI={10.1088/1741-4326/aa98f7}, abstractNote={Edge localized modes (ELMs) are magnetohydrodynamic (MHD) instabilities that cause fast periodic relaxations of the strong edge pressure gradient in tokamak fusion plasmas. A novel diagnostic method allows the extraction of toroidal mode numbers, rotation velocities and spatial information during the ELM cycle including the crash. While mode number branches n=3–6 and n=8–10 are dominant just before the ELM crash, during the ELM crash n=2–5 are observed in typical discharges with type-I ELMs in the tokamak experiment. These findings are compared to results from nonlinear MHD simulations. Although n=6 is linearly dominant, nonlinear coupling in which n=1 is particularly important leads to the dominance of n=3–5 during the ELM crash, in excellent agreement with experimental observations. The simultaneous occurrence of these modes over a wide radial region leads to high stochasticity and thus increased transport.}, number={2}, journal={Nuclear Fusion}, author={Mink, A.F. and Hoelzl, M. and Wolfrum, E. and Orain, F. and Dunne, M. and Lessig, A. and Pamela, S. and Manz, P. and Maraschek, M. and Huijsmans, G.T.A. and et al.}, year={2018} }
@article{harrer_wolfrum_dunne_manz_cavedon_lang_kurzan_eich_labit_stober_et al._2018, title={Parameter dependences of small edge localized modes (ELMs)}, volume={58}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85054770714&partnerID=MN8TOARS}, DOI={10.1088/1741-4326/aad757}, abstractNote={The development of small edge localized mode (ELM) scenarios is important in order to reduce the strain on plasma facing components. One such scenario can be found at high densities, in highly shaped, close to double-null plasmas in ASDEX Upgrade, showing small ELMs characterized by a frequency Hz and a low power loss. Changing from gas fuelling to pellet fuelling results in edge profiles in which the collisionality of pedestal top and separatrix are decoupled. While the pedestal top values remain unchanged, only the phases with low separatrix and scrape-off layer (SOL) density show large ELMs with small ELMs in between. In phases with high separatrix density the small ELMs increase in amplitude and large ELMs do not occur. Similarly, a change in vertical plasma position by only ∼2 cm downwards, at constant reduces the size of small ELMs while the large ELMs appear more intense. A possible explanation of this behaviour could be the influence of the drive and the stabilization of modes positioned close to the separatrix. When these small ELM modes cause enough transport, they flatten the gradient region around the separatrix and thereby consequently narrow the effective pedestal width. Because a narrower pedestal is more stable against global PB modes, the stability boundary is shifted towards higher pressure gradients and type-I ELMs do not occur. It is shown that a higher increases the amplitude of small ELMs and, in agreement with basic ballooning mode theory, a higher local magnetic shear reduces their amplitude.}, number={11}, journal={Nuclear Fusion}, author={Harrer, G.F. and Wolfrum, E. and Dunne, M.G. and Manz, P. and Cavedon, M. and Lang, P.T. and Kurzan, B. and Eich, T. and Labit, B. and Stober, J. and et al.}, year={2018} }
@article{asdex upgrade team_laggner_wolfrum_cavedon_dunne_birkenmeier_fischer_willensdorfer_aumayr_2018, title={Plasma shaping and its impact on the pedestal of ASDEX Upgrade: edge stability and inter-ELM dynamics at varied triangularity}, volume={58}, url={https://doi.org/10.1088/1741-4326/aaaa43}, DOI={10.1088/1741-4326/aaaa43}, abstractNote={The plasma shape, in particular the triangularity (δ), impacts on the pedestal stability. A scan of δ including a variation of heating power (Pheat) and gas puff was performed to study the behaviour of edge localised modes (ELMs) and the pre-ELM pedestal stability for different plasma shapes. Generally, at higher δ the pedestal top electron density (ne) is enhanced and the ELM repetition frequency (fELM) is reduced. For all δ, the pedestal top ne is already fully established to its pre-ELM value during the initial recovery phase of the ne pedestal, which takes place immediately after the ELM crash. The lowering of the fELM with increasing δ is related to longer pedestal recovery phases, especially the last pre-ELM phase with clamped pedestal gradients (after the recovery phases of the ne and electron temperature (Te) pedestal) is extended. In all investigated discharge intervals, the pre-ELM pedestal profiles are in agreement with peeling–ballooning (PB) theory. Over the investigated range of δ, two well-separated fELM bands are observed in several discharge intervals. Their occurrence is linked to the inter-ELM pedestal stability. In both kinds of ELM cycles the pedestal evolves similarly, however, the ‘fast’ ELM cycle occurs before the global plasma stored energy (WMHD) increases, which then provides a stabilising effect on the pedestal, extending the inter-ELM period in the case of the ‘slow’ ELM cycle. At the end of a ‘fast’ ELM cycle the ne profile is radially shifted inwards relative to the ne profile at the end of a ‘slow’ ELM cycle, leading to a reduced pressure gradient. The appearance of two fELM bands suggests that the pedestal becomes more likely PB unstable in certain phases of the inter-ELM evolution. Such a behaviour is possible because the evolution of the global plasma is not rigidly coupled to the evolution of the pedestal structure on the timescales of an ELM cycle.}, number={4}, journal={Nuclear Fusion}, publisher={IOP Publishing}, author={Asdex Upgrade Team, T. and Laggner, F.M. and Wolfrum, E. and Cavedon, M. and Dunne, M.G. and Birkenmeier, G. and Fischer, R. and Willensdorfer, M. and Aumayr, F.}, year={2018}, month={Apr}, pages={046008} }
@article{carralero_madsen_artene_bernert_birkenmeier_eich_fuchert_laggner_naulin_manz_et al._2017, title={A study on the density shoulder formation in the SOL of H-mode plasmas}, volume={12}, url={https://publons.com/wos-op/publon/1120030/}, DOI={10.1016/J.NME.2016.11.016}, abstractNote={The term “shoulder formation” refers to an increase of the density decay length in the scrape-off layer (SOL) observed in many tokamaks during L-mode operation when a density threshold is reached. Recent experiments in ASDEX Upgrade (AUG) and JET have shown that the shoulder forms when the divertor collisionality in the divertor electrically disconnects filaments from the wall. This leads to a transition from the sheath limited to the inertial regime and to an enhancement of radial particle transport, in good agreement with analytical models. In the present work, the validity of such a mechanism is investigated in the more reactor-relevant H-mode regime. For this, a cold divertor H-mode scenario is developed in AUG using different levels of D puffing and N seeding, in which inter-ELM filaments and SOL density profiles are measured. The basic relation between filament size and divertor collisionality is still valid in H-mode plasmas, albeit an additional condition related to the gas fueling rate has been found for the formation of the shoulder.}, journal={Nuclear Materials and Energy}, author={Carralero, D. and Madsen, J. and Artene, S.A. and Bernert, M. and Birkenmeier, G. and Eich, T. and Fuchert, G. and Laggner, F. and Naulin, V. and Manz, P. and et al.}, year={2017}, pages={1189–1193} }
@article{frassinetti_dunne_beurskens_wolfrum_bogomolov_carralero_cavedon_fischer_laggner_mcdermott_et al._2017, title={ELM behavior in ASDEX Upgrade with and without nitrogen seeding}, volume={57}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85010953617&partnerID=MN8TOARS}, DOI={10.1088/0029-5515/57/2/022004}, abstractNote={Abstract}, number={2}, journal={Nuclear Fusion}, author={Frassinetti, L. and Dunne, M.G. and Beurskens, M. and Wolfrum, E. and Bogomolov, A. and Carralero, D. and Cavedon, M. and Fischer, R. and Laggner, F.M. and McDermott, R.M. and et al.}, year={2017} }
@article{dunne_frassinetti_beurskens_cavedon_fietz_fischer_giannone_huijsmans_kurzan_laggner_et al._2017, title={Global performance enhancements via pedestal optimisation on ASDEX Upgrade}, volume={59}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85010366313&partnerID=MN8TOARS}, DOI={10.1088/1361-6587/59/2/025010}, abstractNote={Results of experimental scans of heating power, plasma shape, and nitrogen content are presented, with a focus on global performance and pedestal alteration. In detailed scans at low triangularity, it is shown that the increase in stored energy due to nitrogen seeding stems from the pedestal. It is also shown that the confinement increase is driven through the temperature pedestal at the three heating power levels studied. In a triangularity scan, an orthogonal effect of shaping and seeding is observed, where increased plasma triangularity increases the pedestal density, while impurity seeding (carbon and nitrogen) increases the pedestal temperature in addition to this effect. Modelling of these effects was also undertaken, with interpretive and predictive models being employed. The interpretive analysis shows a general agreement of the experimental pedestals in separate power, shaping, and seeding scans with peeling-ballooning theory. Predictive analysis was used to isolate the individual effects, showing that the trends of additional heating power and increased triangularity can be recoverd. However, a simple change of the effective charge in the plasma cannot explain the observed levels of confinement improvement in the present models.}, number={2}, journal={Plasma Physics and Controlled Fusion}, author={Dunne, M.G. and Frassinetti, L. and Beurskens, M.N.A. and Cavedon, M. and Fietz, S. and Fischer, R. and Giannone, L. and Huijsmans, G.T.A. and Kurzan, B. and Laggner, F. and et al.}, year={2017} }
@article{lang_maingi_mansfield_mcdermott_neu_wolfrum_arredondo parra_bernert_birkenmeier_diallo_et al._2017, title={Impact of lithium pellets on plasma performance in the ASDEX Upgrade all-metal-wall tokamak}, volume={57}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85009813254&partnerID=MN8TOARS}, DOI={10.1088/0029-5515/57/1/016030}, abstractNote={Abstract}, number={1}, journal={Nuclear Fusion}, author={Lang, P.T. and Maingi, R. and Mansfield, D.K. and McDermott, R.M. and Neu, R. and Wolfrum, E. and Arredondo Parra, R. and Bernert, M. and Birkenmeier, G. and Diallo, A. and et al.}, year={2017} }
@article{cavedon_pütterich_viezzer_birkenmeier_happel_laggner_manz_ryter_stroth_2017, title={Interplay between turbulence, neoclassical and zonal flows during the transition from low to high confinement mode at ASDEX Upgrade}, volume={57}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85009756530&partnerID=MN8TOARS}, DOI={10.1088/0029-5515/57/1/014002}, abstractNote={Abstract}, number={1}, journal={Nuclear Fusion}, author={Cavedon, M. and Pütterich, T. and Viezzer, E. and Birkenmeier, G. and Happel, T. and Laggner, F.M. and Manz, P. and Ryter, F. and Stroth, U.}, year={2017} }
@article{viezzer_fable_cavedon_angioni_dux_laggner_bernert_burckhart_mcdermott_pütterich_et al._2017, title={Investigation of inter-ELM ion heat transport in the H-mode pedestal of ASDEX Upgrade plasmas}, volume={57}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85010982941&partnerID=MN8TOARS}, DOI={10.1088/0029-5515/57/2/022020}, abstractNote={Abstract}, number={2}, journal={Nuclear Fusion}, author={Viezzer, E. and Fable, E. and Cavedon, M. and Angioni, C. and Dux, R. and Laggner, F.M. and Bernert, M. and Burckhart, A. and McDermott, R.M. and Pütterich, T. and et al.}, year={2017} }
@inproceedings{krieger_sieglin_balden_coenen_göths_laggner_marne_matthews_nille_rohde_et al._2017, title={Investigation of transient melting of tungsten by ELMs in ASDEX Upgrade}, volume={2017}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85056587618&partnerID=MN8TOARS}, DOI={10.1088/1402-4896/aa8be8}, abstractNote={Repetitive melting of tungsten by power transients originating from edge localized modes (ELMs) has been studied in the tokamak experiment ASDEX Upgrade. Tungsten samples were exposed to H-mode discharges at the outer divertor target plate using the Divertor Manipulator II system. The exposed sample was designed with an elevated sloped surface inclined against the incident magnetic field to increase the projected parallel power flux to a level were transient melting by ELMs would occur. Sample exposure was controlled by moving the outer strike point to the sample location. As extension to previous melt studies in the new experiment both the current flow from the sample to vessel potential and the local surface temperature were measured with sufficient time resolution to resolve individual ELMs. The experiment provided for the first time a direct link of current flow and surface temperature during transient ELM events. This allows to further constrain the MEMOS melt motion code predictions and to improve the validation of its underlying model assumptions. Post exposure ex situ analysis of the retrieved samples confirms the decreased melt motion observed at shallower magnetic field line to surface angles compared to that at leading edges exposed to the parallel power flux.}, number={T170}, booktitle={Physica Scripta}, publisher={IOP Publishing}, author={Krieger, K and Sieglin, B and Balden, M and Coenen, J W and Göths, B and Laggner, F and Marne, P and Matthews, G F and Nille, D and Rohde, V and et al.}, year={2017}, pages={014030} }
@article{overview of asdex upgrade results_2017, volume={57}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85028458117&partnerID=MN8TOARS}, DOI={10.1088/1741-4326/aa64f6}, abstractNote={Abstract}, number={10}, journal={Nuclear Fusion}, year={2017} }
@article{overview of progress in european medium sized tokamaks towards an integrated plasma-edge/wall solution_2017, volume={57}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85028471890&partnerID=MN8TOARS}, DOI={10.1088/1741-4326/aa6084}, abstractNote={Integrating the plasma core performance with an edge and scrape-off layer (SOL) that leads to tolerable heat and particle loads on the wall is a major challenge. The new European medium size tokamak task force (EU-MST) coordinates research on ASDEX Upgrade (AUG), MAST and TCV. This multi-machine approach within EU-MST, covering a wide parameter range, is instrumental to progress in the field, as ITER and DEMO core/pedestal and SOL parameters are not achievable simultaneously in present day devices. A two prong approach is adopted. On the one hand, scenarios with tolerable transient heat and particle loads, including active edge localised mode (ELM) control are developed. On the other hand, divertor solutions including advanced magnetic configurations are studied. Considerable progress has been made on both approaches, in particular in the fields of: ELM control with resonant magnetic perturbations (RMP), small ELM regimes, detachment onset and control, as well as filamentary scrape-off-layer transport. For example full ELM suppression has now been achieved on AUG at low collisionality with n = 2 RMP maintaining good confinement . Advances have been made with respect to detachment onset and control. Studies in advanced divertor configurations (Snowflake, Super-X and X-point target divertor) shed new light on SOL physics. Cross field filamentary transport has been characterised in a wide parameter regime on AUG, MAST and TCV progressing the theoretical and experimental understanding crucial for predicting first wall loads in ITER and DEMO. Conditions in the SOL also play a crucial role for ELM stability and access to small ELM regimes.}, number={10}, journal={Nuclear Fusion}, year={2017} }
@article{asdex upgrade team_cavedon_pütterich_viezzer_laggner_burckhart_dunne_fischer_lebschy_mink_et al._2017, title={Pedestal andErprofile evolution during an edge localized mode cycle at ASDEX Upgrade}, volume={59}, url={https://doi.org/10.1088/1361-6587/aa7ad0}, DOI={10.1088/1361-6587/aa7ad0}, abstractNote={The upgrade of the edge charge exchange recombination spectroscopy diagnostic at ASDEX Upgrade has enabled highly spatially resolved measurements of the impurity ion dynamics during an edge-localized mode cycle (ELM) with unprecedented temporal resolution, i.e. 65 μs. The increase of transport during an ELM induces a relaxation of the ion, electron edge gradients in impurity density and flows. Detailed characterization of the recovery of the edge temperature gradients reveals a difference in the ion and electron channel: the maximum ion temperature gradient ∇ T i is re-established on similar timescales as ∇ n e , which is faster than the recovery of ∇ T e . After the clamping of the maximum gradient, Ti and Te at the pedestal top continue to rise up to the next ELM while ne stays constant which means that the temperature pedestal and the resulting pedestal pressure widen until the next ELM. The edge radial electric field Er at the ELM crash is found to reduce to typical L-mode values and its maximum recovers to its pre-ELM conditions on a similar time scale as for ne and Ti. Within the uncertainties, the measurements of Er align with their neoclassical predictions E r , neo for most of the ELM cycle, thus indicating that Er is dominated by collisional processes. However, between 2 and 4 ms after the ELM crash, other contributions to E × B flow, e.g. zonal flows or ion orbit effects, could not be excluded within the uncertainties.}, number={10}, journal={Plasma Physics and Controlled Fusion}, publisher={IOP Publishing}, author={Asdex Upgrade Team, T. and Cavedon, M. and Pütterich, T. and Viezzer, E. and Laggner, F.M. and Burckhart, A. and Dunne, M. and Fischer, R. and Lebschy, A. and Mink, F. and et al.}, year={2017}, month={Oct}, pages={105007} }
@article{laggner_wolfrum_cavedon_mink_bernert_dunne_schneider_kappatou_birkenmeier_fischer_et al._2017, title={Pedestal structure and inter-ELM evolution for different main ion species in ASDEX Upgrade}, volume={24}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85014548681&partnerID=MN8TOARS}, DOI={10.1063/1.4977461}, abstractNote={In tokamak plasmas with different main ion species, a change in confinement occurs, known as the isotope effect. Experiments comparing hydrogen (H), deuterium (D), and helium (4He) plasmas have been performed to identify processes that define the pedestal structure and evolution in between the crashes of edge localized modes (ELMs). The pedestal top electron densities and temperatures have been matched to compare the pedestal shape and stability. In the D and H discharges, the pedestal electron temperature profiles do not differ, whereas the density profile in H has shallower gradients. Furthermore, the heat flux across the pedestal in H is roughly a factor of two higher than in D. In 4He plasmas at similar stored energy, the pedestal top electron density is roughly a factor of 1.5 larger than in the references owing to the larger effective charge. The peeling-ballooning theory, which is independent of the main ion species mass, can sufficiently describe the pedestal stability in the hydrogenic plasmas. The inter-ELM pedestal evolution has the same sequence of recovery phases for all investigated species, giving evidence that similar mechanisms are acting in the pedestals. This is further supported by a similar evolution of the inter-ELM magnetic signature and the corresponding toroidal structure.}, number={5}, journal={Physics of Plasmas}, author={Laggner, F.M. and Wolfrum, E. and Cavedon, M. and Mink, F. and Bernert, M. and Dunne, M.G. and Schneider, P.A. and Kappatou, A. and Birkenmeier, G. and Fischer, R. and et al.}, year={2017} }
@article{dunne_potzel_reimold_wischmeier_wolfrum_frassinetti_beurskens_bilkova_cavedon_fischer_et al._2017, title={The role of the density profile in the ASDEX-Upgrade pedestal structure}, volume={59}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85006134930&partnerID=MN8TOARS}, DOI={10.1088/0741-3335/59/1/014017}, abstractNote={Experimental evidence for the impact of a region of high density localised in the high-field side scrape-off layer (the HFSHD) on plasma confinement is shown in various dedicated experiments on ASDEX Upgrade (AUG). Increasing main ion fuelling is shown to increase the separatrix density and shift the density profile outwards. Predictive pedestal modelling of this shift indicates a 25% decrease in the attainable pedestal top pressure, which compares well with experimental observations in the gas scan. Since the HFSHD can be mitigated by applying nitrogen seeding, a combined scan in fuelling rate, heating power, and nitrogen seeding is presented. Significant increases in the achievable pedestal top pressure are observed with seeding, in particular at high heating powers, and are correlated with inward shifted density profiles and a reduction of the HFSHD and separatrix density. Interpretive linear stability analysis also confirms the impact of a radially shifted pressure profile on peeling-ballooning stability, with an inward shift allowing access to higher pressure gradients and pedestal widths.}, number={1}, journal={Plasma Physics and Controlled Fusion}, author={Dunne, M.G. and Potzel, S. and Reimold, F. and Wischmeier, M. and Wolfrum, E. and Frassinetti, L. and Beurskens, M. and Bilkova, P. and Cavedon, M. and Fischer, R. and et al.}, year={2017} }
@article{parra_quicios_ploeckl_birkenmeier_herrmann_kocsis_laggner_lang_lunt_macian-juan_et al._2016, title={A compact lithium pellet injector for tokamak pedestal studies in ASDEX Upgrade}, volume={87}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85013956452&partnerID=MN8TOARS}, DOI={10.1063/1.4942122}, abstractNote={Experiments have been performed at ASDEX Upgrade, aiming to investigate the impact of lithium in an all-metal-wall tokamak and attempting to enhance the pedestal operational space. For this purpose, a lithium pellet injector has been developed, capable of injecting pellets carrying a particle content ranging from 1.82 × 1019 atoms (0.21 mg) to 1.64 × 1020 atoms (1.89 mg). The maximum repetition rate is about 2 Hz. Free flight launch from the torus outboard side without a guiding tube was realized. In such a configuration, angular dispersion and speed scatter are low, and a transfer efficiency exceeding 90% was achieved in the test bed. Pellets are accelerated in a gas gun; hence special care was taken to avoid deleterious effects by the propellant gas pulse. Therefore, the main plasma gas species was applied as propellant gas, leading to speeds ranging from 420 m/s to 700 m/s. In order to minimize the residual amount of gas to be introduced into the plasma vessel, a large expansion volume equipped with a cryopump was added into the flight path. In view of the experiments, an optimal propellant gas pressure of 50 bars was chosen for operation, since at this pressure maximum efficiency and low propellant gas flux coincide. This led to pellet speeds of 585 m/s ± 32 m/s. Lithium injection has been achieved at ASDEX Upgrade, showing deep pellet penetration into the plasma, though pedestal broadening has not been observed yet.}, number={2}, journal={Review of Scientific Instruments}, author={Parra, R. Arredondo and Quicios, R. Moreno and Ploeckl, B. and Birkenmeier, G. and Herrmann, A. and Kocsis, G. and Laggner, F. M. and Lang, P. T. and Lunt, T. and Macian-Juan, R. and et al.}, year={2016} }
@article{laggner_wolfrum_cavedon_mink_viezzer_dunne_manz_doerk_birkenmeier_fischer_et al._2016, title={High frequency magnetic fluctuations correlated with the inter-ELM pedestal evolution in ASDEX Upgrade}, volume={58}, url={http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000376275600010&KeyUID=WOS:000376275600010}, DOI={10.1088/0741-3335/58/6/065005}, abstractNote={In order to understand the mechanisms that determine the structure of the high confinement mode (H-mode) pedestal, the evolution of the plasma edge electron density and temperature profiles between edge localised modes (ELMs) is investigated. The onset of radial magnetic fluctuations with frequencies above 200 kHz is found to correlate with the stagnation of the electron temperature pedestal gradient. During the presence of these magnetic fluctuations the gradients of the edge electron density and temperature are clamped and stable against the ELM onset. The detected magnetic fluctuation frequency is analysed for a variety of plasma discharges with different electron pressure pedestals. It is shown that the magnetic fluctuation frequency scales with the neoclassically estimated E ×B velocity at the plasma edge. This points to a location of the underlying instability in the gradient region. Furthermore, the magnetic signature of these fluctuations indicates a global mode structure with toroidal mode numbers of approximately 10. The fluctuations are also observed on the high field side with significant amplitude, indicating a mode structure that is symmetric on the low field side and high field side. The associated fluctuations in the current on the high field side might be attributed to either a strong peeling part or the presence of non-adiabatic electron response.}, number={6}, journal={Plasma Physics and Controlled Fusion}, author={Laggner, F. M. and Wolfrum, E. and Cavedon, M. and Mink, F. and Viezzer, E. and Dunne, M. G. and Manz, P. and Doerk, H. and Birkenmeier, G. and Fischer, R. and et al.}, year={2016} }
@article{birkenmeier_cavedon_conway_manz_stroth_fischer_fuchert_happel_laggner_maraschek_et al._2016, title={Magnetic structure and frequency scaling of limit-cycle oscillations close to L- to H-mode transitions}, volume={56}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84979747838&partnerID=MN8TOARS}, DOI={10.1088/0029-5515/56/8/086009}, abstractNote={Abstract}, number={8}, journal={Nuclear Fusion}, author={Birkenmeier, G. and Cavedon, M. and Conway, G.D. and Manz, P. and Stroth, U. and Fischer, R. and Fuchert, G. and Happel, T. and Laggner, F.M. and Maraschek, M. and et al.}, year={2016} }
@article{shao_wolfrum_ryter_birkenmeier_laggner_viezzer_fischer_willensdorfer_kurzan_lunt_et al._2016, title={On the role of the edge density profile for the L-H transition power threshold in ASDEX Upgrade}, volume={58}, url={http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000371570900005&KeyUID=WOS:000371570900005}, DOI={10.1088/0741-3335/58/2/025004}, abstractNote={The L–H transition power threshold (PL−H ?>) in full tungsten (W) wall discharges is lower by 25% compared to those with graphite (C) mix tungsten walls in ASDEX Upgrade (Ryter et al 2013 Nucl. Fusion 53 113003). The lower power threshold in the full tungsten wall discharges has been found to correlate with higher edge density as well as steeper edge density gradient. An estimate of the minimum in the neoclassical radial electric field well inside the separatrix yields a constant value for all analyzed L–H transitions at fixed toroidal magnetic field (BT ?>). The decrease of the threshold power is explained by the steeper edge density gradient in the discharges with full tungsten wall.}, number={2}, journal={Plasma Physics and Controlled Fusion}, author={Shao, L. M. and Wolfrum, E. and Ryter, F. and Birkenmeier, G. and Laggner, F. M. and Viezzer, E. and Fischer, R. and Willensdorfer, M. and Kurzan, B. and Lunt, T. and et al.}, year={2016} }
@article{willensdorfer_denk_strumberger_suttrop_vanovac_brida_cavedon_classen_dunne_fietz_et al._2016, title={Plasma response measurements of external magnetic perturbations using electron cyclotron emission and comparisons to 3D ideal MHD equilibrium}, volume={58}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84993965398&partnerID=MN8TOARS}, DOI={10.1088/0741-3335/58/11/114004}, abstractNote={The plasma response from an external n = 2 magnetic perturbation field in ASDEX Upgrade has been measured using mainly electron cyclotron emission (ECE) diagnostics and a rigid rotating field. To interpret ECE and ECE-imaging (ECE-I) measurements accurately, forward modeling of the radiation transport has been combined with ray tracing. The measured data is compared to synthetic ECE data generated from a 3D ideal magnetohydrodynamics (MHD) equilibrium calculated by VMEC. The measured amplitudes of the helical displacement around the outboard midplane are in reasonable agreement with the one from the synthetic VMEC diagnostics. Both exceed the predictions from the vacuum field calculations and indicate the presence of a kink response at the edge, which amplifies the perturbation. VMEC and MARS-F have been used to calculate the properties of this kink mode. The poloidal mode structure of the magnetic perturbation of this kink mode at the edge peaks at poloidal mode numbers larger than the resonant components |nq|$ ?>|m|>|nq|, whereas the poloidal mode structure of its displacement is almost resonant |m|≈|nq|. This is expected from ideal MHD in the proximity of rational surfaces. The displacement measured by ECE-I confirms this resonant response.}, number={11}, journal={Plasma Physics and Controlled Fusion}, author={Willensdorfer, M. and Denk, S.S. and Strumberger, E. and Suttrop, W. and Vanovac, B. and Brida, D. and Cavedon, M. and Classen, I. and Dunne, M. and Fietz, S. and et al.}, year={2016} }
@article{beurskens_dunne_frassinetti_bernert_cavedon_fischer_jarvinen_kallenbach_laggner_mcdermott_et al._2016, title={The role of carbon and nitrogen on the H-mode confinement in ASDEX Upgrade with a metal wall}, volume={56}, url={http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000375229300017&KeyUID=WOS:000375229300017}, DOI={10.1088/0029-5515/56/5/056014}, abstractNote={Abstract}, number={5}, journal={Nuclear Fusion}, author={Beurskens, M. N. A. and Dunne, M. G. and Frassinetti, L. and Bernert, M. and Cavedon, M. and Fischer, R. and Jarvinen, A. and Kallenbach, A. and Laggner, F. M. and McDermott, R. M. and et al.}, year={2016} }
@article{toroidal mode number determination of elm associated phenomena on asdex upgrade_2016, volume={58}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84997610947&partnerID=MN8TOARS}, DOI={10.1088/0741-3335/58/12/125013}, abstractNote={In highly confined tokamak plasmas periodically appearing edge localized modes (ELMs) are accompanied by mode-like magnetohydrodynamic (MHD) activities with defined toroidal mode numbers. Here the method of determining toroidal mode numbers n on the ASDEX Upgrade tokamak with a toroidally spread magnetic pick-up coil array is reviewed and improved by taking into account intrinsic coil phases. ELM synchronization is used to characterize inter-ELM MHD activity and their development during the ELM cycle in terms of their mode numbers. The mode number development is correlated with the development of the pedestal parameters which shows that the inter-ELM modes cause transport across the pedestal. An estimation of the position of the modes is done via a comparison between the mode velocities and the plasma rotation profile at the edge. Results show that during the ELM cycle MHD modes appear at several positions in the strong gradient region with clearly defined toroidal structures in the range of n = 1–10. These structures of inter-ELM modes are preserved during the ELM crash where also a strong n = 0 phenomenon occurs.}, number={12}, journal={Plasma Physics and Controlled Fusion}, year={2016} }
@article{viezzer_fable_puetterich_bergmann_cavedon_dux_mcdermott_angioni_churchill_dunne_et al._2015, title={Collisionality dependence of edge rotation and in-out impurity asymmetries in ASDEX Upgrade H-mode plasmas}, volume={55}, url={http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000366534500004&KeyUID=WOS:000366534500004}, DOI={10.1088/0029-5515/55/12/123002}, abstractNote={The poloidal and toroidal impurity flows in the edge transport barrier of H-mode plasmas have been studied over a wide range of pedestal top ion collisionalities. A comparison of the edge poloidal rotation measurements to neoclassical predictions shows good agreement in all cases. The measured edge impurity toroidal rotation is observed to change sign from co-current to counter-current with decreasing collisionality. The switch occurs at the same collisionality at which neoclassical theory predicts the main ion poloidal rotation to change from the electron to the ion diamagnetic direction. The behaviour of these two species, when used to calculate the main ion toroidal rotation via the radial force balance equation, leads to fairly constant co-current main ion toroidal rotation. Hence, at low collisionality, due to a reduced frictional coupling, the main ion-impurity differential rotation can be quite large. The behaviour of impurity ion flows on a flux surface has also been investigated in detail and it was found that the measurements are consistent with the continuity equation only if the poloidally asymmetric impurity density distribution is taken into account. The asymmetry is found to be the result of the interplay of all forces in the parallel momentum balance, with the friction force providing the dominant drive. Close to the separatrix the poloidal centrifugal force, which is usually neglected, also gives an additional contribution to the impurity density asymmetry. Within the experimental uncertainties the ion temperature and the electrostatic potential are simultaneous flux functions, despite the presence of a poloidally asymmetric impurity density profile.}, number={12}, journal={Nuclear Fusion}, author={Viezzer, E. and Fable, E. and Puetterich, T. and Bergmann, A. and Cavedon, M. and Dux, R. and McDermott, R. M. and Angioni, C. and Churchill, R. M. and Dunne, M. G. and et al.}, year={2015} }
@article{birkenmeier_manz_carralero_laggner_fuchert_krieger_maier_reimold_schmid_dux_et al._2015, title={Filament transport, warm ions and erosion in ASDEX Upgrade L-modes}, volume={55}, url={http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000352020500022&KeyUID=WOS:000352020500022}, DOI={10.1088/0029-5515/55/3/033018}, abstractNote={The dynamics of blob filaments are investigated in the scrape-off layer of ASDEX Upgrade by means of lithium beam emission spectroscopy. A comparison of the measurements in L-mode with a recently developed analytical blob model based on a drift-interchange-Alfvén fluid model indicates an influence of a finite ion temperature on the blob dynamics which has typically been neglected in other blob models. The blob dynamics agree well with the sheath-connected regime at lower plasma densities, and inertial effects play only a minor role. At higher densities, a transition into another regime with large blob amplitudes and increased transport is found. This points to a prominent role of blob transport at higher Greenwald fractions. On the basis of the measured blob properties, the erosion on plasma facing components is estimated. For pure deuterium plasmas, the high ion temperatures of blobs lead to a dominant erosion induced by blobs. However, if an impurity concentration of 1% is taken into account, the blob-induced erosion plays a minor role and background plasma parameters determine the total gross erosion.}, number={3}, journal={Nuclear Fusion}, author={Birkenmeier, G. and Manz, P. and Carralero, D. and Laggner, F. M. and Fuchert, G. and Krieger, K. and Maier, H. and Reimold, F. and Schmid, K. and Dux, R. and et al.}, year={2015} }
@article{recent asdex upgrade research in support of iter and demo_2015, url={http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000363762900011&KeyUID=WOS:000363762900011}, DOI={10.1088/0029-5515/55/10/104010}, abstractNote={Recent experiments on the ASDEX Upgrade tokamak aim at improving the physics base for ITER and DEMO to aid the machine design and prepare efficient operation. Type I edge localized mode (ELM) mitigation using resonant magnetic perturbations (RMPs) has been shown at low pedestal collisionality . In contrast to the previous high ν* regime, suppression only occurs in a narrow RMP spectral window, indicating a resonant process, and a concomitant confinement drop is observed due to a reduction of pedestal top density and electron temperature. Strong evidence is found for the ion heat flux to be the decisive element for the L–H power threshold. A physics based scaling of the density at which the minimum PLH occurs indicates that ITER could take advantage of it to initiate H-mode at lower density than that of the final Q = 10 operational point. Core density fluctuation measurements resolved in radius and wave number show that an increase of R/LTe introduced by off-axis electron cyclotron resonance heating (ECRH) mainly increases the large scale fluctuations. The radial variation of the fluctuation level is in agreement with simulations using the GENE code. Fast particles are shown to undergo classical slowing down in the absence of large scale magnetohydrodynamic (MHD) events and for low heating power, but show signs of anomalous radial redistribution at large heating power, consistent with a broadened off-axis neutral beam current drive current profile under these conditions. Neoclassical tearing mode (NTM) suppression experiments using electron cyclotron current drive (ECCD) with feedback controlled deposition have allowed to test several control strategies for ITER, including automated control of (3,2) and (2,1) NTMs during a single discharge. Disruption mitigation studies using massive gas injection (MGI) can show an increased fuelling efficiency with high field side injection, but a saturation of the fuelling efficiency is observed at high injected mass as needed for runaway electron suppression. Large locked modes can significantly decrease the fuelling efficiency and increase the asymmetry of radiated power during MGI mitigation. Concerning power exhaust, the partially detached ITER divertor scenario has been demonstrated at Psep/R = 10 MW m−1 in ASDEX Upgrade, with a peak time averaged target load around 5 MW m−2, well consistent with the component limits for ITER. Developing this towards DEMO, full detachment was achieved at Psep/R = 7 MW m−1 and stationary discharges with core radiation fraction of the order of DEMO requirements (70% instead of the 30% needed for ITER) were demonstrated. Finally, it remains difficult to establish the standard ITER Q = 10 scenario at low q95 = 3 in the all-tungsten (all-W) ASDEX Upgrade due to the observed poor confinement at low βN. This is mainly due to a degraded pedestal performance and hence investigations at shifting the operational point to higher βN by lowering the current have been started. At higher q95, pedestal performance can be recovered by seeding N2 as well as CD4, which is interpreted as improved pedestal stability due to the decrease of bootstrap current with increasing Zeff. Concerning advanced scenarios, the upgrade of ECRH power has allowed experiments with central ctr-ECCD to modify the q-profile in improved H-mode scenarios, showing an increase in confinement at still good MHD stability with flat elevated q-profiles at values between 1.5 and 2.}, journal={Nuclear Fusion}, year={2015} }
@article{willensdorfer_birkenmeier_fischer_laggner_wolfrum_veres_aumayr_carralero_guimarais_kurzan_et al._2014, title={Characterization of the Li-BES at ASDEX Upgrade}, volume={56}, url={http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000329852200008&KeyUID=WOS:000329852200008}, DOI={10.1088/0741-3335/56/2/025008}, abstractNote={The lithium beam emission spectroscopy (Li-BES) is a powerful diagnostic to resolve the plasma edge density with high temporal and spatial resolution. The recent upgrades of the Li-BES at ASDEX Upgrade and the resulting gain in photon flux allow the plasma edge density to be determined with an advanced level of accuracy. Furthermore, electron density fluctuations are measured using Li-BES. The Li-BES capabilities and limitations to measure electron density profiles as well as density fluctuations are presented. It is well suited to characterize electron density turbulence in the scrape off layer (SOL) with decreasing sensitivity towards the plasma core. This is demonstrated by simulations as well as by comparisons with other diagnostics. The Li-BES is an appropriate tool to study transport phenomena in the SOL over a wide range of plasma parameters due to its robustness and routine usage.}, number={2}, journal={Plasma Physics and Controlled Fusion}, author={Willensdorfer, M. and Birkenmeier, G. and Fischer, R. and Laggner, F. M. and Wolfrum, E. and Veres, G. and Aumayr, F. and Carralero, D. and Guimarais, L. and Kurzan, B. and et al.}, year={2014} }
@article{birkenmeier_laggner_willensdorfer_kobayashi_manz_wolfrum_carralero_fischer_sieglin_fuchert_et al._2014, title={Magnetic field dependence of the blob dynamics in the edge of ASDEX upgrade L-mode plasmas}, volume={56}, url={http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000338515300020&KeyUID=WOS:000338515300020}, DOI={10.1088/0741-3335/56/7/075019}, abstractNote={The magnetic field dependence of intermittently expelled density filaments (blobs) is investigated in the scrape-off layer of ASDEX Upgrade low confinement (L-mode) plasmas. It is demonstrated that lithium beam emission spectroscopy can be used to determine the frequency, radial size and velocity of the blobs. The measured radial blob sizes depend only weakly on magnetic field B. Normalizing the blob sizes to the drift parameter ρs ∝ B−1 results in a large variation beneficial for a quantitative comparison with theoretical blob scaling laws. The blob velocity scales inversely proportional to the square of the blob size in agreement with analytic models for blobs in the sheath-connected regime. The measurements point towards an influence of finite ion temperature on radial blob transport.}, number={7}, journal={Plasma Physics and Controlled Fusion}, author={Birkenmeier, G. and Laggner, F. M. and Willensdorfer, M. and Kobayashi, T. and Manz, P. and Wolfrum, E. and Carralero, D. and Fischer, R. and Sieglin, B. and Fuchert, G. and et al.}, year={2014} }
@article{kobayashi_birkenmeier_wolfrum_laggner_willensdorfer_stroth_inagaki_itoh_itoh_2014, title={Method for estimating the propagation direction of a coherent plasma structure using a one-dimensional diagnostic array}, volume={85}, url={http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000342913500031&KeyUID=WOS:000342913500031}, DOI={10.1063/1.4893482}, abstractNote={This article proposes a new method to evaluate basic characteristics of the dynamics of a coherent plasma structure (blob). With this method, one can evaluate the propagation angle of a blob in a two-dimensional plasma cross section as well as the blob velocity, size, and amplitude from one-dimensional data. The method is applied to blob measurements from the Lithium beam emission spectroscopy system in ASDEX-Upgrade. Statistical features of the observed blob velocities, angles of propagation, blob sizes, and amplitudes are discussed. The validity of the method is examined by comparing two values of the propagation angle that are evaluated in an independent manner.}, number={8}, journal={Review of Scientific Instruments}, author={Kobayashi, T. and Birkenmeier, G. and Wolfrum, E. and Laggner, F. M. and Willensdorfer, M. and Stroth, U. and Inagaki, S. and Itoh, S. -I. and Itoh, K.}, year={2014} }