@article{unterberg_abrams_bykov_donovan_duran_elder_guo_hollmann_lasnier_leonard_et al._2020, title={Localized divertor leakage measurements using isotopic tungsten sources during edge-localized mode-y H-mode discharges on DIII-D}, volume={60}, ISSN={["1741-4326"]}, DOI={10.1088/1741-4326/ab537b}, abstractNote={Experiments carried out on DIII-D using a novel setup of isotopic tungsten (W) sources in the outer divertor have characterized how the W leakage from this region depends on both the exact source location and edge-localized mode (ELM) behavior. The sources are toroidally-symmetric and poloidally-localized to two regions: (1) the outer strike point (OSP) with natural abundance of W isotopes; and (2) the far-target with highly-enriched 182W isotopes. With the use of a dual-faced collector probe (CP) in the main scrape-off layer (SOL) near the outside midplane and source-rate spectroscopy, a proxy for divertor impurity leakage is developed. Using this proxy, it is found that for the OSP W location, there is a nearly linear increase of leakage with the power across the separatrix (), which is consistent with the effect of an increased upstream ion temperature parallel gradient force in the near-SOL; trends in the pedestal density and collisionality are also seen. Conversely, it is found that for the far-target W location leakage falls off rapidly as increases and ELM size decreases, which is suggestive that ELM size plays a role in the leakage from this location. Indications for main SOL W contamination is evidenced by the measurement of large deposition asymmetries on the two opposite CP faces. These measurements are coupled with interpretive modeling showing SOL W accumulation near the separatrix furthest from both targets driven by forces parallel to the magnetic field. This experimental setup, together with the target and upstream W measurements, provides information on the transport from different divertor W source locations and leakage. These studies help to elucidate the physics driving divertor impurity source rates and leakage, with and without ELMs, and provide better insight on the link in the chain connecting wall impurity sources to core impurity levels in magnetic fusion devices.}, number={1}, journal={NUCLEAR FUSION}, author={Unterberg, E. A. and Abrams, T. and Bykov, I and Donovan, D. C. and Duran, J. D. and Elder, J. D. and Guo, H. Y. and Hollmann, E. M. and Lasnier, C. J. and Leonard, A. W. and et al.}, year={2020}, month={Jan} }
 @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{coburn_gebhart_parish_unterberg_canik_barsoum_bourham_2019, title={Surface Erosion of Plasma-Facing Materials Using an Electrothermal Plasma Source and Ion Beam Micro-Trenches}, volume={75}, ISSN={1536-1055 1943-7641}, url={http://dx.doi.org/10.1080/15361055.2019.1623570}, DOI={10.1080/15361055.2019.1623570}, abstractNote={Abstract Erosion characteristics of tungsten-alternative plasma-facing materials (PFMs) were tested under high heat flux conditions in the electrothermal plasma source facility at Oak Ridge National Laboratory. The PFMs of interest are high-purity β-3C chemical vapor deposition silicon carbide (SiC) and the MAX phases Ti3SiC2 and Ti2AlC [MAX = chemical formula Mn+1AXn, where M is an early transition metal (such as Ti or Ta), A is an A-group element (such as Si or Al), and X is carbon or nitrogen]. An erosion analysis method was developed using a combination of focused ion beam microscopy and scanning electron microscopy, carving micro-trench geometries into polished sample surfaces. Samples of SiC, Ti3SiC2, and Ti2AlC were exposed to the electrothermal plasma source alongside tungsten and monocrystalline silicon. Samples were exposed to a Lexan polycarbonate (C16H14O3) electrothermal plasma stream in a He environment, at a specified impact angle, with infrared camera diagnostics. Edge localized mode–relevant heat fluxes of 0.9 to 1 GW/m2 over 1-ms discharges were generated on the target surfaces. Tungsten samples exhibited pronounced melt-layer formation and deformation, with measured molten pits 2 to 10 μm in diameter and melt-layer depths of up to 7 μm deep. Surface erosion rates for Ti3SiC2 and Ti2AlC ranged from 80 to 775 μm/s and 85 to 470 μm/s, respectively. Both MAX phases exhibited extreme surface fracture and material ejection, with damage depths past 4 μm for Ti2AlC and 11 μm for Ti3SiC2. SiC displayed the best performance, in one case surviving 15 consecutive electrothermal plasma exposures with an average erosion rate of about 29 μm/s and no surface fracturing. SiC erosion rates ranged from 23 to 128 μm/s.}, number={7}, journal={Fusion Science and Technology}, publisher={Informa UK Limited}, author={Coburn, J. D. and Gebhart, T. E. and Parish, C. M. and Unterberg, E. and Canik, J. and Barsoum, M. W. and Bourham, M.}, year={2019}, month={Jun}, pages={621–635} }
 @article{coburn_bourham_2017, title={Ablation Simulation of Tungsten-Alternative Plasma-Facing Components due to Edge Localized Modes and Hard Disruptions}, volume={72}, ISSN={1536-1055 1943-7641}, url={http://dx.doi.org/10.1080/15361055.2017.1352426}, DOI={10.1080/15361055.2017.1352426}, abstractNote={Abstract Innovative materials are investigated using a simulated electrothermal (ET) plasma to characterize erosion characteristics under ITER-relevant off-normal conditions. The tungsten alternatives investigated are mono-crystalline silicon carbides and MAX Phase ceramics. Preliminary code simulations using the ETFLOW plasma code are presented to assess erosive behavior in preparation for future experiments at ORNL’s electrothermal high heat flux experiment and the DiMES experiments for induced disruption on the DIII-D tokamak. Results indicate that erosion properties for SiC and two commercially available MAX Phases, Ti3SiC2 and Ti2AlC, compare well with tungsten and other ITER relevant components. A material-specific ablation constant, measured as total mass removed per incident heat flux per second, serves as a means for directly comparing erosion properties. Tungsten possesses the highest ablation constant value when compared to carbon, beryllium and the alternative materials α-6H SiC, Ti3SiC2, and Ti2AlC. The ablation thickness, calculated from the ablation constant and the specific density of the material, provides a comparison of surface thickness lost during a given off-normal event. Carbon (4.25 cm3/MJ) and tungsten (5.98 cm3/MJ) possess the lowest values. The alternative materials Ti3SiC2 (7.32 cm3/MJ) and α-6H SiC (8.44 cm3/MJ) exhibit the next best values, with Ti2AlC being the least effective (9.35 cm3/MJ). SiC shows the best vapor shielding efficiency of the three alternative materials, with Ti3SiC2 and Ti2AlC giving similar efficiencies. Taking into account vapor shielding effects using both opacity and fractional models, SiC exhibits the best ablation characteristics of the three materials in terms of thickness loss, with Ti3SiC2 giving similar results and overall appearing the superior of the two MAX Phases.}, number={4}, journal={Fusion Science and Technology}, publisher={Informa UK Limited}, author={Coburn, Jonathan and Bourham, Mohamed}, year={2017}, month={Sep}, pages={692–698} }
 @article{coburn_luker_parma_depriest_2016, title={Modeling, Calibration, and Verification of a Fission Chamber for ACRR Experimenters}, volume={106}, ISSN={["2100-014X"]}, DOI={10.1051/epjconf/201610605001}, abstractNote={When performing research at a reactor facility, experimenters often need to determine the neutron fluence achieved during an operation. Facilities typically provide guidance in the form of neutron fluence per megajoule (MJ) or through passive dosimetry results. After experiment completion, there is sometimes a delay of several days (or weeks) before the passive dosimetry results are available. In the interim, an experimenter does not have confirmation that the desired irradiation levels were reached. Active dosimetry may provide an estimate of neutron fluxes, but few active detectors are available that have been calibrated to measure neutron fluxes obtained inside the Annular Core Research Reactor (ACRR) central cavity environment. For past experiments at the ACRR, the neutron fluence was calculated by integrating the response of a fission chamber rate detection signal and then normalizing this integral to fluence determined from passive dosimetry. An alternative method of directly measuring neutron flux is desired; the new methodology described provides a complete neutron flux profile after a reactor pulse, utilizing fission chamber physics in combination with a compensating ion chamber to extract and convert a current signal to neutron flux as a function of time.}, journal={ISRD 15 - INTERNATIONAL SYMPOSIUM ON REACTOR DOSIMETRY}, author={Coburn, Jonathan and Luker, S. Michael and Parma, Edward J. and DePriest, K. Russell}, year={2016} }