Simulations of Explosive Electron Emission in Cathodic Arcs. Final Report for Phase I Project
The objective of this SBIR Project was to develop a computational tool for industrial engineering of electric discharges controlled by explosive electron emission (EEE). The physics of multi-phase phenomena associated with self-sustained formation of explosive emission centers (ectons) is not fully understood [1]. Ectons have been extensively studied for vacuum arcs where the gaseous plasma is produced from evaporated electrode material injected into a vacuum [2]. Our research aimed to understand effects of gas pressure on ecton dynamics, formation of plasma jets, gas-phase ionization, electrical breakdown mechanisms, and electrode erosion by cathodic arcs under different operating regimes. During this Project, CFD Research Corporation (CFDRC) has advanced its Adaptive Mesh and Algorithm Refinement (AMAR) framework to model explosive electron emission from liquid-metal cathodes and multi-phase processes associated with plasma-surface interactions [3]. The Volume-of-Fluid method has been used to simulate Taylor cone formation, emission of droplets from liquid cathodes, heating, melting and vaporization of micro-protrusions on solid electrode surfaces. The plasma solver capabilities in the AMAR framework have been enhanced for modeling plasma expansion into vacuum and its transition from non-ideal to ideal state. We have demonstrated that a combination of Adaptive Mesh Refinement (AMR) with high-order numerical schemes is very suitable for efficient and accurate modeling of plasma expansion in vacuum [4 ,5]. A multi-scale model of gas discharges ignited over liquid electrodes has been developed. This model takes into account both the liquid electrode motion under the influence of the applied electric field and the plasma generation in the gas phase during gas breakdown. We have obtained that gas breakdown occurs at ns time scale and develops in two stages. During the first stage, a fast ionization wave propagates from the liquid hump to the anode. The second stage was initiated by the secondary electrons emitted from the liquid cathode due to ion impact. We have demonstrated that the second stage develops much faster than the first one, as was previously predicted by the theory. During the gas breakdown, which occurs at the electron time scale, the ion motion can be neglected, while the liquid can be considered motionless. We have demonstrated that the dynamics of multi-phase plasmas containing gas, plasma, and liquid states is characterized by three disparate time scales: the fast electron scale, the slow ion time scale, and the slowest time scale of liquid dynamics. These scales differ by orders of magnitude, and the disparity of the time scales can be used to simplify the description of the system [6]. We have developed a hybrid model of fast gas breakdown. In this model, electrons were described using the Boltzmann kinetic equation, while ions were modeled as a fluid. We used this model to explain the influence of the voltage rise time τ on the Paschen’s curves for planar gaps [7]. We have developed, tested and demonstrated a new compressible, multi-species LTE plasma solver for modeling non-ideal plasma expansion with the ionization energy correction due to the electron-ion Coulomb coupling. The expansion of weakly non-ideal plasma into vacuum was analyzed for the conditions typical to explosive electron emission. Our simulation results have shown that the plasma remains in the Local Thermodynamic Equilibrium (LTE) at distances about 1 mm from the explosive emission center. However, the plasma expansion at this distance is accompanied by the transition from the pressure-ionization-dominant regime to the thermal-ionization-dominant regime, which leads to drastic changes of the ion composition within the LTE region. Our results make questionable the validity of the “frozen” state theory often used in vacuum arcs plasma diagnostics [8].
- Research Organization:
- CFD Research Corp., Huntsville, AL (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- SC0015746
- OSTI ID:
- 1596291
- Type / Phase:
- SBIR (Phase II)
- Report Number(s):
- DOE-CFDRESEARCH-15746
- Resource Relation:
- Related Information: G. A. Mesyats, Explosive Electron Emission, Fizmatlit, Moscow (2011) [in Russian].G. A. Mesyats, Cathode Phenomena in a Vacuum Discharge: The Breakdown, the Spark and the Arc, Moscow Nauka Publishers (2000).D.I. Proskurovsky, Explosive Electron Emission from Liquid-Metal Cathodes, IEEE Trans. Plasma Science 37, 1348 (2009).R Arslanbekov and V Kolobov, Adaptive Kinetic-Fluid Models for Expanding Plasmas, Journal of Physics: Conf. Series 1031 (2018) 012018; doi:10.1088/1742-6596/1031/1/012018V Kolobov, R Arslanbekov and D Levko, Kinetic Solvers with Adaptive Mesh in Phase Space for Low-Temperature Plasmas 2019 J. Phys.: Conf. Ser. 1225 012016 https://arxiv.org/abs/1809.05061D. Levko, R. R. Arslanbekov, V. I. Kolobov, Multi-scale dynamics of atmospheric-pressure discharges ignited over liquid electrodes, Journal of Applied Physics 127, 043301 (2020); https://doi.org/10.1063/1.5132319D. Levko, R. R. Arslanbekov, and V. I. Kolobov, Modified Paschen curves for pulsed breakdown, Phys. Plasmas 26, 064502 (2019); https://doi.org/10.1063/1.5108732D. Levko, R. R. Arslanbekov and V. I. Kolobov, On the expansion of non-ideal copper plasma into vacuum, submitted to Physics of Plasmas (2020)
- Country of Publication:
- United States
- Language:
- English
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