Bulletin of the American Physical Society
73rd Annual Gaseous Electronics Virtual Conference
Volume 65, Number 10
Monday–Friday, October 5–9, 2020; Time Zone: Central Daylight Time, USA.
Session GT1: Arc Plasma and Electrical SwitchingLive
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Chair: Sabine Portal, George Washington University |
Tuesday, October 6, 2020 10:00AM - 10:15AM Live |
GT1.00001: Control Grid Testing For Optimized Lifetime In MHVDC Breaker Darryl Michael, David Smith, Jason Trotter In a related paper in this conference, work is reported describing the interruption phase of a Medium High Voltage (MHV) DC Breaker driven by a thermionic hollow cathode. When a fault in the DC grid is detected, circuit interruption occurs by driving the third electrode (Control Grid) of the plasma switch rapidly (less than 1$\mu$s) to a negative potential. The rapidly formed Child-Langmuir sheath near the grid surface and in the apertures repels the energetic electrons and absorbs the ions. The incident ions, which have the same potential energy as the negative bias, could cause damage to the grid by sputtering. In prior work, we achieved maximum interruption current density of 5 A/cm2 but through use of thermionic cathode and control grid design we expect to achieve significantly higher current densities. We describe the design and operation of a test apparatus that facilitates the use of specially fabricated demountable grids with varying geometries (grid thickness, aperture diameter and separation) that will be exposed to interruption current densities as high as 10A/cm2 for 30,000 cycles. The grids are analyzed for sputtering loses. The data is used to design the optimum grid geometry that meets the program lifetime goal for breaker operation of 30 years. [Preview Abstract] |
Tuesday, October 6, 2020 10:15AM - 10:30AM Live |
GT1.00002: Plasma behavior for LaB$_{\mathrm{6}}$ thermionic hollow cathode in low-pressure deuterium Andrey Meshkov, Jason Trotter, David Smith, Aharon Yakimov We are developing a fast inline medium-voltage direct current (MVDC) circuit breaker based on a gas discharge tube (GDT). The guiding market for the GDT breaker is the uprating of existing medium-voltage alternating current (MVAC) distribution corridors into a meshed MVDC grid to meet growing power demands in congested urban areas without the need to clear new rights-of-way. A long-life, low forward-voltage drop thermionic hollow cathode is an enabling technology for the GDT as an inline circuit breaker. We will give an overview of the hollow cathode design considerations for the performance and life requirements and present experimental results of cathode-plasma performance in low-pressure deuterium, showing plasma voltage below 25V for cathode current densities \textgreater 4 A/cm$^{\mathrm{2}}$. [Preview Abstract] |
Tuesday, October 6, 2020 10:30AM - 10:45AM Live |
GT1.00003: Investigation of pressure increase in HVDC relays during plasma arcing in short circuit situations Crispin Ewuntomah, Jens Oberrath Short circuit situations in high voltage direct current (HVDC) relays often lead to the formation of plasma arcs, which excessively heat and vaporize the contacts of the relays. Consequently, significant pressure is built up in the enclosed chambers of the relays. To quantify the pressure in such situations, a Panasonic AEV14012 relay is investigated both experimentally and numerically using two short circuits currents. Thermal plasma parameters obtained from the numerical model are used to simulate the time dependent increase of pressure within the enclosed chamber of the relay. The results are compared to show the plasma arc formation, time dependent arc evolution and pressure increase. It is established from the results that; the magnitude of the short circuit current influences the rate of vaporization of the contacts and the pressure increase in the enclosed chamber. [Preview Abstract] |
Tuesday, October 6, 2020 10:45AM - 11:00AM Live |
GT1.00004: Simulation of ultrahigh-pressure short-arc xenon discharge plasma and effect of evaporation of cathode material on plasma properties Indjira Mukharaeva, Vladimir Sukhomlinov, Georges Zissis, Nikolai Timofeev, Dmitriy Mikhaylov, Alexander Mustafaev, Pascal Dupuis High-pressure discharges in rare gases (Ar, Kr, and Xe) are widely used for developing sources of intensive optical radiation. However, one can argue that a number of problems remain unexplored and primarily the possible presence of electrode material atoms in the discharge due to the high discharge current density and a considerable heating of electrodes. These atoms usually have a lower ionization potential in comparison with rare gas atoms and hence can affect the plasma processes. Earlier experimental data led to results that could not be interpreted disregarding the emission of thorium (e.g. from a cathode) in the discharge gap. Modeling of the plasma in question in a simplified geometry also showed a strong influence of thorium atoms on the electrokinetic plasma. The present study is aimed at the development of the model of the short-arc xenon discharge plasma at a high pressure including the influence of thorium atoms on the plasma properties. The spatial distributions of the plasma temperature, electric field strength, densities of thorium atoms, and densities of thorium and xenon ions were obtained. [Preview Abstract] |
Tuesday, October 6, 2020 11:00AM - 11:15AM Live |
GT1.00005: Analysis of Driven Factor of Cathode Spot Initial Movement in Parallel Electrodes by Numerical Simulation Zhenwei Ren, Yusuke Nemoto, Yoshifumi Maeda, Toru Iwao The arc mobility increases along with the arc current increment in the case of an arc generated between a pair of parallel electrodes, which is different from the arc welding or the direct current interruption. It is assumed that the electromagnetic force derived from the electrodes become stronger with the arc current increasing, which benefits to the charged particles advance forward on the cathode surface and lead to the velocity of cathode spot increase. In order to find out the effect of self-magnetic field derived from the electrodes to the mobility of cathode spot, a rail-gun current path model and a straight current path model are simulated by a 3-dimensional electromagnetic thermal fluid simulation. External magnetic field is applied to the straight current path model for achieving the same mobility of cathode spot with the rail-gun current path model. It found out that the cathode spot advances because the balance of electromagnetic force on the cathode spot area is collapsed by the electromagnetic force derived from the electrodes. Therefore, the arc mobility increases with increasing the arc current in a pair of parallel electrodes. [Preview Abstract] |
Tuesday, October 6, 2020 11:15AM - 11:30AM Live |
GT1.00006: Student Excellence Award Finalist: Validated two-dimensional modeling of ablated carbon arc Jian Chen, Alexander Khrabry, Igor Kaganovich, Andrei Khodak, Vladislav Vekselman, Heping Li An atmospheric pressure arc discharge is a convenient method for the synthesis of carbon nanoparticles. To describe the rate of production of nanoparticles we developed two-dimensional self-consistent modeling of the entire carbon arc device. The developed fluid model takes into account the transport of heat and current in both plasma and electrodes in a coupled manner as well as multiple surface processes at the electrodes including the formation of the sheath, carbon ablation and deposition, thermionic emission, and radiation. Sheath is included in the model as a nonlinear boundary condition for particle and heat fluxes. This model is used to obtain a self-consistent solution that determines the arc and sheath voltage drops, current density, and heat flux without any prior assumption. The simulated ablation rate and plasma density are validated using our experimental data. Spot formation is observed at the anode. Simulations show that the spot radius increases with the arc current in accordance with our experimental data and our analytical model. Due to the anode spot formation, some of the ablated carbon from the spot region returns to anode periphery, thereby reducing the total ablation rate. [Preview Abstract] |
Tuesday, October 6, 2020 11:30AM - 11:45AM Live |
GT1.00007: Calculation of Ablation Amount from Nozzle Caused by Radiation Using Three-Dimensional Electromagnetic Thermal Fluid Simulation Yuki Suzuki, Shoya Nishizawa, Yusuke Nemoto, Zhenewei Ren, Yoshifumi Maeda, Toru Iwao The nozzle ablation of circuit breakers is the physical phenomenon caused by the heat and radiation of arc. In recent years, the air circuit breakers (ACB) that replaces the gas circuit breakers (GCB) for high voltage is required in order to reduce the environmental load. Thus, the cooling method using the ablation from nozzle has been proposed in order to improve the arc interruption performance of the ACB. The amount of ablation gas which generated from nozzle is important for efficient cooling of the arc. It is necessary to consider the ablation by heat transfer and radiation in order to clarify the amount of ablation gas. However, the time scales of heat input to nozzle are different for heat conduction and radiation. In addition, the amount of heat input to the nozzle and the amount of ablation gas generated by the radiation is not elucidated. In this paper, the ablation amount from nozzle caused by radiation using the three-dimensional electromagnetic thermal fluid simulation was calculated. As a result, the amount of ablation from nozzle caused by radiation increased with time. In addition, it was confirmed that the ablation gas caused by radiation was generated on the small time scale as compared with the heat conduction. [Preview Abstract] |
Tuesday, October 6, 2020 11:45AM - 12:00PM Live |
GT1.00008: Convective Force Derived from Arc Jet Affected by Convective Force of Lateral Gas Flow for Elucidation of Arc Deflection Phenomenon Yoshifumi Maeda, Yuki Sugiyama, Zhenwei Ren, Yusuke Nemoto, Toru Iwao The arc welding has a problem that the heat transfer to the base metal decreases when the arc is deflected by lateral gas flow because the energy loss occurs in the leeward direction. For this reason, it is necessary to elucidate the factors that cause the arc deflection in order to obtain an appropriate heat transfer. It has been reported that it is difficult to deflect when the flow velocity in axial direction is large. Hence, it is necessary to clarify the relation between the arc deflection length and flow velocity considering not only the force to leeward direction but also the force to axial direction. However, the flow velocity and mass density have a three-dimensional distribution, which is difficult to clarify experimentally. Therefore, it is important to visualize the force generated by the convection of lateral gas flow and arc jet using a three-dimensional electromagnetic thermal fluid simulation. In this paper, the convective force derived from the arc jet affected by the convective force of lateral gas flow for the elucidation of arc deflection phenomenon is analyzed. As a result, the convective force generated by the arc jet tended to increase and then decrease with the increase in the convective force generated by the lateral gas flow. [Preview Abstract] |
Tuesday, October 6, 2020 12:00PM - 12:15PM Live |
GT1.00009: Conditions for Retrograde Motion of Vacuum Arc Cathode Spot Affected by Initial Pressure Yusuke Nemoto, Masahiro Takagi, Yuki Suzuki, Zhenwei Ren, Yoshifumi Maeda, Toru Iwao The vacuum arc is maintained by the metal vapor from the cathode and moves at high speed. It has been reported that the vacuum arc cathode spot has the retrograde motion when the external magnetic flux is applied. Also, the retrograde movement of the vacuum arc cathode spot is reduced in the case of high initial pressure. From these reports, it was hypothesized that retrograde motion occurs when electrons and ions have different motions and energies in the low pressure. However, the conditions for retrograde motion of vacuum arc cathode spot have not been clarified because the vacuum arc is fast phenomenon and difficult to measure experimentally. Thus, it is important to analyze the sheath length, the mean free path, and the Debye length of the vacuum arc. In this paper, the conditions for retrograde motion of vacuum arc cathode spot affected by the initial pressure was elucidated. Specifically, the vacuum arc was analyzed by simulating the heat input to cathode and the evaporation of metal using the three-dimensional electromagnetic thermal fluid simulation with changing the initial pressure. As a result, it is possible to calculate the sheath length, the mean free path, and the Debye length of the vacuum arc when the vacuum arc cathode spot has the retrograde movement. [Preview Abstract] |
Tuesday, October 6, 2020 12:15PM - 12:30PM |
GT1.00010: A model explaining low and high ablation regimes in a carbon arc Alexander Khrabry, Igor Kaganovich, Andrei Khodak, Vladislav Vekselman, Tianyuan Huang Graphite ablation in a presence of inert background gas is widely used in different methods for the synthesis of carbon nanotubes, including electric arcs and laser/solar ablation systems. The ablation rate is an important characteristic of the synthesis process. It is known from multiple arc experiments that there are two distinguishable ablation regimes, so-called ``low ablation'' and ``high ablation'' regimes in which the ablation rate behaves qualitatively differently with variation of the arc parameters [1], [2]. We developed a theoretical model that explains low and high ablation regimes by taking into account the presence of a background gas and its effects on the ablation rate. We derive analytical relations for these regimes and verify them by comparing them with full numerical solutions in a wide range of arc parameters. We comprehensively validate the model by comparing to multiple experimental data on the ablation rate in carbon arcs, where various arc parameters were varied. Good qualitative and quantitative agreement between full numerical solutions, analytical solutions, and experimental data was obtained. [1] V. Vekselman et. al., Plasma Sources Sci. T. 26, 065019 (2017). [2] J. Ng and Y. Raitses, J. Appl. Phys. 117, 063303 (2015) [Preview Abstract] |
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