Investigation of collisional effects in the plasma erosion opening switch

Abstract

During the conduction phase of the plasma erosion opening switch (PEOS), magnetic field has been observed experimentally to penetrate completely through plasmas up to 30 em long. Current channels in the main body of the plasma have been observed that are more than 10 em (or more than about 60 coHisionless skin depths) wide. In addition, the maximum current c<~rried by the swi.tch before opening (the conduction current) seems to scale roughly linearly wl~h plasma densIty n and switch length I. CoUisionless PIC code simulations of the plasma SWItch show current conducted in skin-depth-like channels, with the conduction current sealing close to I /IS and n 1/4. In this paper, the effect of collisions on the behavior of the PEOS is investigated and is shown to bring the PIC simulations ancl experimental results in closer agreement. In collisional simulations, current channels as wide as those in experiments are observed, and the conduction current scales linearly with I and as n 1/2 in the anode-dominated ease. In the cathode-dominated case, linear scaling with both length and density can be inferred from lhe cathode penetration distance versus time.-

Energetic electron and ion beam generation in plasma opening switches

“…These widths are much larger than the shock-front thickness predicted by EMHD or MHD theories, but are in agreement with previous results that have shown broad current channels both in the NPOS and MPOS [3]. The larger thickness of the current layer than predicted by the EMHD model may be related to development of plasma instabilities as suggested in a fluid code simulation [20] and indirectly proved by observation of high frequency electric fields during MPOS [25] and NPOS [26] conduction.…”

“…Ions can be emitted toward the POS electrodes due to the Hall field inside the current layer if the electron flow has two-dimensional structure, as predicted by EMHD theory. However, similar ion emission toward the POS electrodes may also occur due to positive potential plasma regions, formed behind the current layer, as predicted by PIC code simulations [20].…”

“…In the case of weakly collisional plasma, the thickness of the shock front is , where is the electron frequency. Fast magnetic field penetration was also predicted by fluid code [19] and particle-in-cell (PIC) code [20], [21] simulations of the POS, which also show a positive floating-potential plasma with respect to both POS electrodes behind the current channel.…”