Bulletin of the American Physical Society
72nd Annual Gaseous Electronics Conference
Volume 64, Number 10
Monday–Friday, October 28–November 1 2019; College Station, Texas
Session NR2: Thermal Plasmas |
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Chair: Yevgeny Raitses, Princeton Plasma Physics Laboratory Room: Century II |
Thursday, October 31, 2019 8:00AM - 8:15AM |
NR2.00001: Investigation of moving structures inside a magnetized non-transferred arc plasma torch Vidhi Goyal, Ganesh Ravi In the present work, an indigenously made low power non-transferred arc plasma torch has been used to investigate the formation and dynamics of moving structures inside the arc channel in the presence of external axial magnetic field. Experiments have been carried out at atmospheric pressure with nitrogen as working gas for various currents, magnetic field values and gas flow rates. A high speed camera has been installed at the central end-on line direction from the nozzle exit (1.5 m away). Visual images have been sampled at the rate of 117000 fps to capture all known phenomena inside arc plume. Results show clear rotation of small hollow profiles inside arc column with changing shape size and rotation speed for different parameters. Changing intensity of different portion of arc column is clearly indicating change in current density and J\texttimes B force. Detailed results will be discussed and presented. [Preview Abstract] |
Thursday, October 31, 2019 8:15AM - 8:30AM |
NR2.00002: Nitrogen Concentration near Anode Affected by Convective Mass Transfer Flux of Arc in Atmospheric Pressure Yoshifumi Maeda, Yusuke Nemoto, Zhenwei Ren, Toru Iwao Gas shielded arc welding is widely used because of the simplicity and high productivity. This welding method has advantages such as the protection of the arc from monatomic gas of the atmosphere using the sheilding gas, and the high quality welding is possible. However, a shielding gas flows downwind and the arc is deflected in strong winds. Hence, the blow hole may occur because the nitrogen from the atmosphere is contaminated into the melted metal. In order to prevent this problem, it is necessary to elucidate the process of nitrogen contamination into the arc caused by the crosswind. It has been reserached that the observation of the nitrogen contamination process caused by crosswinds using the Schlieren method. However, the nitrogen contamination phenomenon in the arc has not been clarified because of the high radiation power density from the arc. Therefore, it is required to investigate numerically the nitrogen contamination process in the arc caused by the crosswind. In this study, the nitrogen concentration near anode affeced by the convective mass trasnfer flux of arc in atmospherice pressure was elucidated. As a result, the nitrogen concentration near anode increased with increasing the convective mass transfer flux of arc. [Preview Abstract] |
Thursday, October 31, 2019 8:30AM - 8:45AM |
NR2.00003: Student Excellence Award Finalist: Hydromagnetic Stability and Collisional Properties of Current-Driven Plasma Jets Thomas Underwood, Mark Cappelli In this work, the ability to extend the operational duration of a pulsed plasma accelerator in the deflagration regime is explored. This mode generates a dense plasma jet that features distinctly high exhaust velocities, $V \sim 100$ km/s, distributed current conduction, and thus low electrode degradation rates. Along with these features however, hydromagnetic plasma jets are also susceptible to rapid instability growth and shock generation that lead to inefficient acceleration efficiency and propellant utilization. Collisionality is first described in the plasma accelerator by considering the impact of the initial neutral gas distribution within the electrode volume. Measurements indicate that neutral gas governs the transition between these operating modes and indicates regimes over which the deflagration mode can be maintained. Hydromagnetic stability is investigated by describing the underlying theory, apparatus, and optical features of a novel schlieren diagnostic capable of cinematically visualizing dense plasma jets. Dynamic coherent flow features are identified and tracked over time throughout the evolutionary progression of plasma jets. The results indicate that a stable dense plasma jet can be maintained for timescales over which a steady pinch current can be sustained. [Preview Abstract] |
Thursday, October 31, 2019 8:45AM - 9:00AM |
NR2.00004: A hydrodynamic model of ablating arc discharge in atmospheric pressure Adnan Mansour, Kentaro Hara A one-dimensional fluid plasma model has been developed to investigate ablating carbon arc discharge in atmospheric pressure conditions \footnote{Mansour and Hara 2019 J Phys D: Appl Phys {\bf 52} 105204}. The multispecies model simulates the coupled chemistry and physics of the ablating arc, including plasma-material interactions, such as evaporation and deposition rates, and interspecies interactions, such as reactions and collisions. A model for predicting the size of the cathode deposit has been proposed based on the principal of energy minimization, namely, there is an optimal deposit area that minimizes the energy lost due to radiation and re-evaporation for a given electron current. The results have shown good qualitative agreement with experimental results, exhibiting transition between high and low ablation rates for different conditions. It is hypothesized, based on the numerical results, that the radiative heat transfer between the anode and the cathode plays an important role in determining the electrode temperatures, potentially explaining the enhanced ablation observed in experiment. [Preview Abstract] |
Thursday, October 31, 2019 9:00AM - 9:15AM |
NR2.00005: Analysis of Dielectric Strength of Re-strike Phenomenon in Magnetic Driven Arc with External Magnetic Field by Numerical Simulation Zhenwei Ren, Yusuke Nemoto, Yoshifumi Maeda, Toru Iwao Re-strike phenomenon occurs when the arc moves between two parallel electrodes, and its frequency increases and the re-strike stride becomes short with applying external magnetic field. It is because the distance between the arc column and anode surface becomes short which leads to the occurrence of electrical breakdown become easier. According to the experiment figures, the locations of cathode spot and anode spot during arc advancement are extracted, and a 3-dimensional electromagnetic thermal fluid simulation is used to mimic the re-strike phenomenon on the basis of those data. The distance and potential difference between re-strike point and arc column right before the re-strike phenomenon occurrence are calculated. As a result, the distance between anode surface and arc column becomes shorter because of the electromagnetic force derived from external magnetic field, which also leads to the re-strike stride decrement. According to the simulation results, the dielectric strength between anode surface and arc column is calculated prior to the new anode spot appearance, and it has a minimum value when 2 mT external magnetic field density is applied. Therefore, it implies that optimal proportion of external magnetic field density and arc current does exist. [Preview Abstract] |
Thursday, October 31, 2019 9:15AM - 9:30AM |
NR2.00006: Threshold behavior of the magnetized arc in two-stage pulsing microcathode arc thruster. Denis Zolotukhin, Keir Daniels, Michael Keidar The concept of two-stage microcathode arc thruster implies the preliminary production of almost fully-ionized metal plasma by the first stage based on pulsing vacuum arc, and acceleration of this plasma by the second stage, in order to achieve higher thrust and thrust-to-power ratio. A second stage based on applied-field magneto plasma dynamical (MPD) approach looks promising since it allows accelerating quasi-neutral plasma without using low-transparent accelerating grids, high voltages, or additional power-consumable electron sources for charge neutralization. We found that being sufficiently magnetized by a dc magnetic field having both axial and radial components, such two-stage pulsing vacuum arc discharge demonstrate a threshold behavior: such parameters as power dissipating by the second stage, charge of expelling ions, and ion-to-arc ratio rapidly grow at certain threshold dc voltage applied between the cathode of the first-stage microcathode arc thruster and the accelerated electrode. Without magnetic field, no threshold behavior was observed for the same thruster construction. Such effect can be used to controllably improve thrust and thrust-to-power ratio in such thrusters. [Preview Abstract] |
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