Transition from snowplow to deflagration mode in a gas-prefilled parallel-plate plasma accelerator

Abstract

The transition from snowplow mode to deflagration mode of a parallel-plate plasma accelerator under gas-prefilled conditions is studied. The accelerator is powered by a sinusoidal-wave power supply with a first half-period current of 24.3 μs. The current distribution of the current conduction channel is measured by magnetic probes, the optical emission spectrum by a spectroscopic system, and the plasma optical intensity by photodiodes. The parallel-plate plasma accelerator does not form a thin current sheet, but a wide and diffuse current conduction region when the capacitors are charged to 8 kV and 13 kV. The discharge mode is a transition from snowplow mode to deflagration mode, from the current leading edge to the trailing edge. The plasma front region continuously sweeps and ionizes the neutral gas within a certain thickness, which is characteristic of snowplow mode, whereas the plasma tail region is a stationary current conducting channel maintained by ablating the copper electrodes, which is characteristic of deflagration mode. The transition mechanism from snowplow mode to deflagration mode might be breakdown caused by rail electrode overvoltage.

Effects of bias magnetic field on plasma ejection and dynamic characteristics of a coaxial gun operated in gas-puffed mode

“…For the formation of spheromak, the accelerated plasma needs to compress, stretch the bias magnetic field and complete the magnetic reconnection to finally relax into the spheromak state. Some previous experimental works [21][22][23] have indicated that the evolution of plasma current path in a puffed gas mode is a strong function of the time delay between gas injection and the firing of the capacitor bank to initiate gas breakdown. Snowplow occurs for a long time delay while deflagration occurs for a short time delay.…”