Current distribution and plasma velocity characteristics of parallel-plate accelerator under static pressure

Abstract

Electromagnetic plasma accelerators which can generate high-density and hypervelocity plasma jets have been widely used in plasma physics research and application fields. An experimental platform of parallel-plate accelerator electromagnetically driven plasma is established in this paper, mainly including a parallel-plate accelerator, a power supply, magnetic probes, photodiodes, a current probe, and an oscilloscope. The current distribution and plasma velocity characteristics of a parallel-plate accelerator under static pressure are studied by using magnetic probe array and photodiode array. The working gas is synthetic air. A mechanical pump is used to pump the vacuum chamber to about 1 Pa, and then synthetic air is injected into the vacuum chamber to a target pressure. The power supply of the parallel-plate accelerator has a sinusoidal oscillation attenuation waveform with a total capacitance of 120 μF and a total inductance of about 400 nH. When the charging voltage is 13 kV, the discharge current is 170 kA and the pulse width is 23.5 μs. The discharge currents are 38, 100, 135 kA, and 170 kA when the pressures are 100, 200, 400 and 1000 Pa, respectively. The current distribution of the parallel-plate accelerator is concentrated, and the discharge mode is consistent with the snowplow mode, when the discharge current is small and the working pressure is high. As the discharge current increases or the working pressure decreases, a diffuse current distribution gradually appears in the parallel-plate accelerator. Two regions are formed, i.e. the plasma front region and the plasma tail region. The diffuse current distribution phenomenon is more remarkable when the discharge current is higher or the working pressure is lower. The plasma front current distribution proportion decreases and the plasma front velocity increases with the increase of discharge current and the decrease of working pressure. However, the plasma velocity proportion increased is much lower than the discharge current proportion increased or working pressure proportion decreased. When the discharge current increases from 38–170 kA, the plasma velocity increases from 25.0 km/s to 33.6 km/s, with the velocity increment being only 34.4%. The plasma front region is subjected to both the Lorentz force and the thermal pressure of the plasma tail region.