Effects of Shear-Flow Instabilities on Plasma Formation and Expansion in Crossed-Field Diodes
Andres Castillo, Stanford University
Magnetically insulated transmission lines (MITLs) are a critical component in several pulsed power systems, including the Z machine in Sandia National Laboratories. Effectively functioning as a crossed-field diode, MITLs maintain an insulated electron layer that flows along the cathode surface. In addition, the pulsed power systems can form plasmas near the electrodes due to ionization of outgassed particles, leading to plasma expansion and eventually gap closure. The velocity gradient in the electron layer makes it susceptible to shear-flow instabilities that may affect the plasma transport mechanisms, which reduce the efficacy of the pulsed power systems [1,2]. First, we explore the shear-flow instabilities relevant to MITLs in the electrostatic limit, where induced fields from the electron layer current are neglected, theoretically and computationally. Without the consideration of the electron gyromotion, this setup becomes the plasma equivalent of the Kelvin-Helmholtz instability [3]. Future studies explore how the instabilities (particularly, the diocotron and magnetron instabilities) are modified in the full electromagnetic configuration. Another important consideration is an additional layer of contaminant plasma from the electrode surface. These studies aim to characterize the shear-flow instability relevant to MITLs, how it is affected by the global parameters, and how it contributes towards plasma expansion to the anode.
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[2]Gomez, M. R., Gilgenbach, R. M., Cuneo, M. E., Jennings, et al. (2017). Experimental study of current loss and plasma formation in the Z machine post-hole convolute. Physical Review Accelerators and Beams, 20(1), 010401.
[3]Buneman, O., Levy, R. H., & Linson, L. M. (1966). Stability of crossedâfield electron beams. Journal of Applied Physics, 37(8), 3203-3222.