Bulletin of the American Physical Society
71st Annual Gaseous Electronics Conference
Volume 63, Number 10
Monday–Friday, November 5–9, 2018; Portland, Oregon
Session HW3: Thermal Plasmas: Arcs, Jets, Switches, others |
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Chair: Laxminarayan Raja, The University of Texas at Austin Room: Oregon Convention Center A106 |
Wednesday, November 7, 2018 9:30AM - 9:45AM |
HW3.00001: Investigating the sealing performance of helium gas arc discharges Jian Gao, Andrew Lajoie, Felix Marti \\ Helium gas has been proved to be a good candidate for a charge stripper applicable to the acceleration of high intensity uranium beams.\footnote{ H. Imao et al., Phys. Rev. ST Accel. Beams{\bf 15}, 123501 (2012).} In order to achieve an equilibrium charge state of ions, a high pressure (around 300 $torr$) helium gas cell is desired. However, it is very challenging to maintain such a high pressure in the beam line which is under high vacuum. We are developing a recirculating helium gas charge stripper by using plasma window (PW), \footnote{A. Hershcovitch, Phys. Plasma {\bf 5}, 2130 (1998).} essentially high DC arc discharges, to reduce the leakage rate to the rest of the accelerator. In this study, the pressure, velocity, and voltage field are presented to show the sealing performance of helium gas PW. In a certain current range, it shows that both the maximum gas cell pressure and the corresponding electrical conductivity increase as we increase the current for the cathodes. Our spectral diagnostics allow to study the properties of the plasma in three different directions. The size dependent sealing performance of PW has also been investigated. [Preview Abstract] |
Wednesday, November 7, 2018 9:45AM - 10:00AM |
HW3.00002: Experimental investigation of plasma torch dynamics using magnetic diagnostics Ganesh Ravi, Vidhi Goyal, Subroto Mukherjee In a plasma torch, fluid and electromagnetic forces compete with each other and determine the movement of plasma arc root and the plasma column, which leads to fluctuations in the plasma column and associated quantities. In the present work, plasma dynamics inside a low power dc non-transferred arc plasma torch has been investigated using novel magnetic diagnostics that consists of garlands of magnetic (B-dot) probes incorporated inside the anode water cooling channels. Results show that the probes are able to capture fast rotation of the arc root under the influence of external magnetic field, not captured even by fast imaging. The phenomenon of arc root shunting is also captured by the probes. Thus, the complete spatiotemporal evolution of the plasma column is unraveled using these diagnostics. Results also show that volume return currents give way to constricted line currents in the anode return path when J x B force exceeds a threshold value due to formation of space varying eddy currents. A physical model explaining the processes is presented. The results have thus paved way for exploring magnetic tomography of plasma torch for better control and predictability of processes in a thermal plasma system. [Preview Abstract] |
Wednesday, November 7, 2018 10:00AM - 10:15AM |
HW3.00003: Student Excellence Award Finalist: Evidence of Stabilization in Current-Driven Plasma Jets Thomas Underwood, Keith Loebner, Victor Miller, Mark Cappelli We report on the first direct visualization detailing the dynamic stabilization of current-driven dense plasma jets. Videography of backlit refractometry (10 MHz, 256 frames) indicates the presence of long wavelength magnetohydrodynamic kink instabilities that stabilize over time as a quasi-steady axial-directed flow surrounding a central pinch is formed. A linear stability analysis confirms that in the presence of the surrounding flow, the pinch is most prone to the m = 1 kink mode, but that even this mode is damped at high current regimes due to the increased plasma jet velocity. The results point to the possibility for an arbitrarily stable plasma column over timescales for which a surrounding flow can be maintained. [Preview Abstract] |
Wednesday, November 7, 2018 10:15AM - 10:30AM |
HW3.00004: A "resonance" method to decrease the electrode erosion in magnetically rotated arcs Valerian Nemchinsky In many industrial application of high-current arcs with tubular or ring electrodes, the arc electrode attachments are forced to rotate in order to reduce the electrode erosion. A method aimed to further reduce electrode is suggested. This goal is achieved by forcing the attachment to drift in the axial direction. The axial arc motion results from the Lorentz force experienced by the radial arc under influence of an azimuthal magnetic field. This magnetic field could be created by a cable located outside the electrode. It is shown that if the current in the outside cable oscillates with a frequency close to the frequency of the arc rotation, it leads to a continuous arc axial drift. The effect has a resonance character: even a low AC current in the cable causes the arc drift. As a result of the combination of the fast arc rotation with a relatively slow axial drift (reversed from time to time), the arc attachment moves within a band of a controllable width. The spread of the electrode heat load over a wider electrode area reduces the electrode erosion. Sources of the azimuthal magnetic field other than a cable are suggested. [Preview Abstract] |
Wednesday, November 7, 2018 10:30AM - 10:45AM |
HW3.00005: Abstract Withdrawn
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Wednesday, November 7, 2018 10:45AM - 11:00AM |
HW3.00006: Modeling of vacuum arcs with liquid-metal cathodes Dmitry Levko, Robert Arslanbekov, Vladimir Kolobov Vacuum arcs are multi-phase phenomena associated with melting, evaporation and ionization of electrode materials. In this paper, we will present simulations of vacuum arc ignition from the tip of a Taylor cone on the liquid cathode surface. The formation of Taylor cone on liquid InGa surface is simulated using the volume-of-fluid approach with adaptive Cartesian mesh. We analyze the conditions of the Taylor cone formation and the ejection of liquid droplets from the Taylor cone tip in electric fields. The ignition of an arc discharge is due to the field emission of electrons from the Taylor cone tip and electron-induced ionization of InGa vapors near cathode surface. This stage is considered as a precursor for explosive electron emission from the tip of the cone. We investigate the transition from the field emission to the explosive electron emission. We analyze how the plasma generation and ejection of droplets influence the dynamics of the liquid electrode. The results of our simulations are compared with the available experimental data [1]. [1] D. I. Proskurovsky, Explosive Electron Emission from Liquid-Metal Cathodes, IEEE Trans. Plasma Science 37, 1348 (2009). -/abstract- Supported by DoE SBIR Phase II Contract: DE-SC0015746 Sorting category 2.14 Thermal plasmas: arcs, jets, switc [Preview Abstract] |
Wednesday, November 7, 2018 11:00AM - 11:15AM |
HW3.00007: Global model of an arc discharge plasma for nanoparticle synthesis Sergey Averkin, Thomas Jenkins, Madhusudhan Kundrapu Global models have become an invaluable tool for quick estimates of plasma parameters such as volume-averaged number densities of plasma components or electron temperature in gas discharge plasmas. However, these estimates are a crude approximation of the plasma properties and do not contain any information regarding spatial distributions. We present a novel formulation of global model equations that allows the prediction of plasma parameters not only qualitatively (as is the case in conventional global models) but also quantitatively. In this model we choose a general functional representation of plasma properties and substitute it into fluid equations. Then we minimize the L$^{\mathrm{2}}$ norm of the resulting equations and solve a system of algebraic equations for unknown parameters in the general functional representation. The model is applied to a 1D arc discharge that is used in nanoparticle synthesis, and which was recently analyzed numerically and analytically by Khrabry et al. (2018). [Preview Abstract] |
Wednesday, November 7, 2018 11:15AM - 11:30AM |
HW3.00008: Abstract Withdrawn
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Wednesday, November 7, 2018 11:30AM - 11:45AM |
HW3.00009: Simulation of pre-breakdown discharges in air Mikhail Benilov, Nuno G. C. Ferreira, Diego Santos, Pedro G. C. Almeida, George Naidis A unified method of numerical modelling of low-current discharges in high-pressure gases is developed. The method employs, in the framework of a single code, stationary or time-dependent solvers, depending on the discharge being modelled being stationary (e.g., corona or Townsend discharge) or non-stationary (e.g., streamers). Two examples are given. In the first example, the inception voltage of positive corona in air in a wide pressure range was computed and compared with standard experimental data. At high pressures, the inception voltage is appreciably affected by the detachment. The agreement between the modelling and the experiment is very good. In the second example, a discharge in weakly non-uniform electric fields was computed and the inception electric field was compared with experimental data. It is found that field emission from microscopic non-uniformities on the negative electrode comes into play at values of pressure lower than those at which the effect of comparable non-uniformities on the positive electrode comes into play. The dependence of the inception voltage on the air pressure, computed with the account of field emission, reveals saturation with increasing pressure and conforms to the measured dependence of the breakdown voltage on pressure. [Preview Abstract] |
Wednesday, November 7, 2018 11:45AM - 12:00PM |
HW3.00010: Dynamics of Contraction of Surface Barrier Discharge in Atmospheric Air. Sergey Leonov This study examines the morphology and charge transfer dynamics of surface dielectric barrier discharge depending on the supplied voltage waveform: single polarity vs alternating polarity. Diagnostics included electric measurements, camera imaging, optical emission spectroscopy, and a set of original charge sensors [S. Leonov et al J. Phys. D: Appl. Phys., vol. 47, p. 465201, 2014]. Two basic modes were analyzed: diffusive and filamentary. The key factor of the discharge dynamics is the development of ionization instability causing the contraction of the discharge current and formation of the filamentary, highly conductive plasma during both positive and negative polarities. A main criterion of the discharge contraction is the generation of a zone with a high level of longitudinal electric field, not less than 15 kV/cm, realized during the alternating of the sign of surface charge. It is shown that the alternating polarity of the supplied voltage accompanied with the process of discharge contraction gives a significant benefit in the surface area covered by the discharge and in the power deposition, increasing it 2-4 times. [Preview Abstract] |
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