Experimental study on plasma channel formation with spark discharges in high current pulsed electron beam source

The formation of plasma channel with the use of eight spark discharge sources was experimentally investigated in a high current pulsed electron beam (HCPEB) equipment. A triple Langmuir probe system was developed to diagnose the real-time plasma parameters. The spark discharges were initiated by using a high-voltage pulse of −7.0 kV and decoupling resistors of 40 Ω. Displacing the measurement positions, the plasma density distributions in a column of diameter 60 mm and length 175 mm were obtained. The duration of spark discharge is 11.0 μs and the maximum discharge current of 1.4 kA appears at 4.3 μs. Initially, the plasma concentrates in the peripheral region. With the accumulation in radial direction, the plasma density in the central region increases. After 6.6 μs, the maximum plasma density of 8.4 × 1018 m−3 appears at the center of the plane where the spark sources located. Thereafter, the plasma dissipation plays a dominant role. The plasma maintains about 20 μs. Depending on the formation features of plasma channel, the selection of timing control available was illustrated, while the transportation of HCPEB can be realized effectively within a limited distance, i.e. less than 60 mm beyond the source outlet in this case.