@article{gray_may_bourham_2005, title={Quasi-steady state, low current behaviour of a magnetized coaxial plasma source}, volume={14}, ISSN={["0963-0252"]}, DOI={10.1088/0963-0252/14/4/010}, abstractNote={The Coaxial Plasma Source-1 facility (Mayo R M et al 1995 Plasma Sources Sci. Technol. 4 47) was modified from a short pulse, high current (SPHC) pulse forming network (PFN) with very low inductance (∼200 nH) to a large inductance ladder circuit. This modification allows for a longer, flat top gun current pulse that eliminates the under-damped, sinusoidal behaviour of the gun current with consequent interruptions in plasma parameters. The new PFN was designed to produce a current waveform for a much longer period (∼1 ms). As a consequence of increasing the pulse length, the magnitude of the gun current was reduced as no additional energy storage was added to the PFN. The characterization of the electrical and plasma behaviour of the experiment operated with the long pulse, low current (LPLC) PFN is presented. The gun currents produced by the LPLC PFN are approximately one-fifth in magnitude of the gun currents produced by the SPHC PFN. Axial plasma parameters were measured near the muzzle of the plasma source, and electron densities were found to range from 1 × 1019 m−3 to 7 × 1019 m−3 depending upon the axial location. These values are approximately 1–2 orders of magnitude less than the electron densities produced by the SPHC PFN at the same locations. Electron temperatures range from 30 to 60 eV at these locations and are very similar to those produced by the SPHC PFN. A resistive MHD model was applied as an order estimate of the plasma resistivity and demonstrates reasonable agreement with measured values of the magnetized coaxial gun resistance.}, number={4}, journal={PLASMA SOURCES SCIENCE & TECHNOLOGY}, author={Gray, TK and May, RM and Bourham, MA}, year={2005}, month={Nov}, pages={712–721} }
 @article{haverkamp_mayo_bourham_narayan_jin_duscher_2003, title={Plasma plume characteristics and properties of pulsed laser deposited diamond-like carbon films}, volume={93}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.1555695}, DOI={10.1063/1.1555695}, abstractNote={Pulsed laser deposition is a unique technique for the deposition of hydrogen-free diamond-like carbon films. During deposition, amorphous carbon is evaporated from a solid target by a high-energy KrF laser, ionized, and ejected as a plasma plume. The plume expands outwards and deposits the target material on a substrate. The plasma properties of the plume determine the quality of the thin films deposited on the substrate. These plume properties include ion density, ion flow speed, electron temperature, and plume peaking parameter. In this research, a triple Langmuir probe is used to determine various plasma properties of the plume created from the pulsed laser ablation of amorphous graphite as a function of laser energy density and laser spot size on the target. A thin diamond-like carbon film is deposited and analyzed with electron energy-loss spectroscopy to determine the sp3/sp2 fraction. A special preparation technique was used to prepare the thin film for analysis to prevent the damage that may be caused by conventional ion milling techniques.}, number={6}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Haverkamp, J. and Mayo, R. M. and Bourham, M. A. and Narayan, J. and Jin, C. and Duscher, G.}, year={2003}, month={Mar}, pages={3627–3634} }
 @article{yamagata_sharma_narayan_mayo_newman_ebihara_2000, title={Comparative study of pulsed laser ablated plasma plumes from single crystal graphite and amorphous carbon targets. Part I. Optical emission spectroscopy}, volume={88}, ISSN={["0021-8979"]}, DOI={10.1063/1.1321783}, abstractNote={A comparative study of ablation plasma plumes originated from single crystal graphite (SCG) and amorphous carbon (a-C) targets during the preparation of diamond-like carbon (DLC) films by KrF excimer pulsed laser deposition (PLD) has been carried out by means of a monochromator equipped with an intensified optical multichannel analyzer. In high vacuum, the emission lines of carbon neutral C and ions of C+, C2+, and C3+ can be observed from both the SCG and a-C plasma plumes. The emission intensity from C atoms increases with laser energy density (EL) increase for both cases. The C2 emission intensity from the SCG plasma plume changes drastically with EL, while that from the a-C plasma plume is almost constant. The C2/C emission intensity ratio for the a-C case decreases with EL increase. As for the SCG case, the C2/C ratio decreases with EL increase up to 3.0 J/cm2, and increases slightly with further EL increase. Nanohardness of the deposited films decreases with the increase of the C2/C emission intensity ratio. It is suggested that for both the SCG and a-C target cases, the C2 molecule in the ablated plasma plume may not play an important role in producing high quality DLC films. It is further proposed that the threshold of laser fluence for the formation of diamond-like character film using KrF excimer PLD is 2.1 J/cm2(0.84×108 W/cm2) for the a-C target and 3.0 J/cm2(1.2×108 W/cm2) for the SCG target. The C2 vibrational temperature of the SCG and the a-C plasma plumes show different features on both the laser energy density and nitrogen pressure dependencies. Through optical emission spectroscopy and Langmuir probe measurements in vacuum and nitrogen background, it is concluded that there are many particles with higher mass in the SCG plasma plume, especially at relatively lower laser energy density below 3.0 J/cm2.}, number={11}, journal={JOURNAL OF APPLIED PHYSICS}, author={Yamagata, Y and Sharma, A and Narayan, J and Mayo, RM and Newman, JW and Ebihara, K}, year={2000}, month={Dec}, pages={6861–6867} }
 @article{mayo_newman_yamagata_sharma_narayan_2000, title={Comparative study of pulsed laser ablated plasma plumes from single crystal graphite and amorphous carbon targets. Part II. Electrostatic probe measurements}, volume={88}, ISSN={["0021-8979"]}, DOI={10.1063/1.1321784}, abstractNote={In an ongoing effort to investigate plasma plume features yielding high quality diamond-like carbon films, we have applied plasma plume diagnosis and film characterization to examine plume character distinction from KrF laser ablation of both amorphous carbon (a-C) and single crystal graphite (SCG) targets. The advancing plasma plume produced by these structurally different targets are observed to possess quantitatively similar total heavy particle inventory, ionized fraction, and electron thermal content, yet quite different ion kinetic energy, plume profile, C2 formation mechanism, and concentration of complex molecules. Plume electron temperatures are observed to reside in the range 1–3 eV, with those in SCG plumes ∼10%–30% greater than a-C at all spatial positions downstream of the target. For both target cases, we find Te drop off with position away from the target with radiation as the most likely loss mechanism for these noninteracting plumes propagating in vacuum. Electron density is found to be ∼10%–12% lower near the target in SCG than a-C plumes consistent with mass loss inventory measurements, whereas ion fractions are estimated in the range ∼10%–15% for both target cases. All recorded data support the conclusion that the SCG target plasma plume is populated with heavier, more complex molecules than those in a-C which have been shown to be predominantly comprised of C and C+ under vacuum conditions with the addition of C2 at high fill pressure. A significantly smaller profile peaking factor for SCG plumes supports this conclusion. Less energetic and slightly lower temperature SCG plume conditions are consistent with reduced peaking and more massive plume species. Plasma plumes from SCG targets exhibit laser energy (El) dependent peaking, again consistent with more complex molecules increasingly disassociated with El increase. The El dependence further suggests the potential for control of particle size distribution and plume profile peaking, though not independently. Consistent with this scenario is the observation of harder films produced from SCG targets at lower El. Micro-Raman results indicate strongly heterogeneous films deposited by SCG target ablation even under vacuum conditions further supporting the case for more complex structures with greater hardness. Energy balance estimates indicate that ion kinetic energy dominates the balance and that SCG ablation liberates about twice the number of C12 atoms from the target per unit El. As well, high pressure background fill indicates lesser plume energy attenuation for SCG plumes, again suggesting the presence of higher mass particles.}, number={11}, journal={JOURNAL OF APPLIED PHYSICS}, author={Mayo, RM and Newman, JW and Yamagata, Y and Sharma, A and Narayan, J}, year={2000}, month={Dec}, pages={6868–6874} }
 @article{mayo_newman_sharma_yamagata_narayan_1999, title={Electrostatic measurement of plasma plume characteristics in pulsed laser evaporated carbon}, volume={86}, ISSN={["0021-8979"]}, DOI={10.1063/1.371135}, abstractNote={A triple Langmuir probe measurement has been implemented to investigate plasma plume character in low fluence (∼3.0 J/cm2) pulsed laser evaporation (PLE) discharges and has been found to be an extremely valuable tool. Absolute plasma plume density estimates are found to reside in the range 1.0×1013–2.0×1014 cm−3 for vacuum pulses. A simple heavy particle streaming model for vacuum pulses allows estimates of the plume ionization fraction of ∼10%. This is consistent with typical deposition inventory suggesting that high kinetic energy ions may play an important role in diamond-like carbon (DLC) film deposition. Electron temperature inferred from the electrostatic probe is found to consistently reside in the range 0.5–3.0 eV, and appears to be uninfluenced by operating conditions and large variations in Ar and N2 fill gas pressure. Consistent with strong plume ion and neutral particle coupling to the background fill, constancy of Te suggests expulsion of background gas by the energetic plume. The leading edge ion plume speed is measured via temporal displacement of spatially separated probe signals on consecutive PLE pulses. Flow speeds as high as 5.0×104 m/s are observed, corresponding to ∼156 eV in C+. The ion flow speed is found to be a strongly decreasing function of fill pressure from an average high of ∼126 eV in vacuum to ∼0.24 eV at 600 mTorr N2. Raman scattering spectroscopy indicates DLC film quality also degrades with fill pressure suggesting the importance of high ion kinetic energy in producing good quality films, consistent with earlier work demonstrating the importance of energetic particles. Optical emission indicates an increase in C2 molecular light intensity with fill gas pressure implying a reduced, if any, role of these species in DLC production. Ion current signal anomalies are often seen during high pressure pulses. It is suggested that this may indicate the formation of high mass carbon clusters during plume evolution in the presence of background gas. Mass diffusivity estimates, based on density decay, suggest the presence of C2+ under these conditions. Demonstration and control of such cluster formation may provide method(s) for controlling novel advanced materials properties.}, number={5}, journal={JOURNAL OF APPLIED PHYSICS}, author={Mayo, RM and Newman, JW and Sharma, A and Yamagata, Y and Narayan, J}, year={1999}, month={Sep}, pages={2865–2871} }
 @article{yamagata_sharma_narayan_mayo_newman_ebihara_1999, title={Optical emission study of ablation plasma plume in the preparation of diamond-like carbon films by KrF excimer laser}, volume={86}, ISSN={["0021-8979"]}, DOI={10.1063/1.371340}, abstractNote={Optical emission study of the laser ablation plasma plume during the preparation of diamond-like carbon (DLC) films using KrF excimer (248 nm) pulsed laser deposition (PLD) has been carried out by means of a monochromator equipped with an intensified optical multichannel analyzer. In high vacuum (1×10−7 Torr), the emission lines from carbon ions of C+, C2+, and C3+ are observed in addition to atomic carbon emission lines, while no emission from the diatomic carbon molecule (C2) is observed. With increasing background nitrogen pressure up to 500 mTorr, the emission intensities of the C2 Swan band and the carbon nitride (CN) violet band increase. The diamond-like character of deposited DLC film degrades with background nitrogen pressure. The vibrational temperature of C2 and CN molecules decreases with the increasing of nitrogen pressure. The CN vibrational temperature for the first 2 μs after the laser pulse is very high and in agreement with the kinetic energy of monatomic carbon ions. The C2 vibrational temperature is as low as 0.6 eV and is consistent with the electron temperature of about 0.8–3.0 eV. It is conjectured that CN molecules are formed directly in reactions involving energetic ionic monatomic carbon, and that the formation of excited C2 molecules is the result of molecular recombinations of C atoms and ions. From the emission intensity measurements and the estimation of the vibrational temperature, it is suggested that the C2 molecule in the ablated plasma plume is not important, but energetic species, such as C+, are very important for producing high quality DLC films using PLD.}, number={8}, journal={JOURNAL OF APPLIED PHYSICS}, author={Yamagata, Y and Sharma, A and Narayan, J and Mayo, RM and Newman, JW and Ebihara, K}, year={1999}, month={Oct}, pages={4154–4159} }
 @book{mayo_1998, title={Introduction to nuclear concepts for engineers}, ISBN={0894484540}, publisher={La Grange, Ill.: American Nuclear Society}, author={Mayo, R. M.}, year={1998} }
 @article{black_mayo_caress_1997, title={Determination of microturbulence enhanced electron collisionality in magnetized coaxial accelerator channels by direct magnetic field measurement}, volume={4}, ISSN={["1089-7674"]}, DOI={10.1063/1.872253}, abstractNote={A miniature magnetic probe array, consisting of 10 spatially separated coils, has been used to obtain profile information on the time varying magnetic field within the 2.54 cm wide flow channel of the coaxial plasma source experiment (CPS-1) [R. M. Mayo et al., Plasma Sources Sci. Technol. 4, 47 (1995)]. The magnetic field data have been used, together with a resistive, Hall magnetohydrodynamic (MHD) model of applied field distortion by the flowing plasma, to obtain estimates of the microturbulent enhancement to electron collisionality within the CPS-1 flow channel. These measurements provide direct experimental evidence of anomalous electron collisionality, a previously predicted effect in these devices. The anomaly parameter, a=νan/νcl, determined both from the distortion of contours of constant magnetic flux, and from local Bθ and Bz measurements scales with the classical electron magnetization parameter (Ωcl=ωce/νecl), indicating that collisionality plays a strong role in determining the level of anomalous transport in the plasma. When this anomaly parameter scaling is cast in terms of the ratio νecl/ωlh, it is found that the resistivity enhancement scales with νecl/ωlh, and becomes significant at νecl/ωlh⩽1, suggesting that a lower hybrid drift instability may be the responsible mechanism for enhanced transport.}, number={10}, journal={PHYSICS OF PLASMAS}, author={Black, DC and Mayo, RM and Caress, RW}, year={1997}, month={Oct}, pages={3581–3590} }
 @article{black_mayo_caress_1997, title={Direct magnetic field measurement of flow dynamics in magnetized coaxial accelerator channels}, volume={4}, ISSN={["1089-7674"]}, DOI={10.1063/1.872415}, abstractNote={A miniature magnetic probe array, consisting of ten spatially separated coils, has been used to obtain profile information on the time-varying magnetic field within the 2.54 cm wide flow channel of the Coaxial Plasma Source experiment (CPS-1) [R. M. Mayo et al., Plasma Sources Sci. Technol. 4, 47 (1995)] at the North Carolina State University. Two-dimensional (2-D) current profiles within the annular flow channel, which were constructed from the time-varying magnetic field data, reveal several complex features reflecting the influence of gun inductance, the Hall effect, and the applied magnetic field. When an external, electrode linking magnetic field is applied, the evolution of the 2-D current profile shows evidence of an ionizing shock front identified by a narrow current sheet propagating through the channel during the first few microseconds of the discharge. The thickness of this current sheet is on the same order as both the collisional mean-free path and the ion electromagnetic skin depth. In this applied field case, the plasma is prevented from advancing ahead of the current sheet by the applied magnetic field, which turns the ions and electrons without collisions. In the absence of an applied field, plasma is able to advance ahead of the current sheet, where it may initiate ionization downstream before the advance of the ionization front.}, number={8}, journal={PHYSICS OF PLASMAS}, author={Black, DC and Mayo, RM and Caress, RW}, year={1997}, month={Aug}, pages={2820–2836} }
 @article{boivin_koltonyuk_munson_mayo_1997, title={Time of flight neutral particle analyzer for alcator C-mod}, volume={68}, number={1 pt.2}, journal={Review of Scientific Instruments}, author={Boivin, R. I. and Koltonyuk, M. and Munson, C. P. and Mayo, R. M.}, year={1997}, pages={982–985} }