Plasma sources for pulsed high-current relativistic electron beam generation

Results of an experimental study of pulsed electron beams generation by a plasma electron sources operating in the moderate pressure range (10^-4-10^-5 Torr) are presented. Current research offers views on two types of plasma cathodes - passive and active, which are extensively used in various applications, for instance, generation of strong shock waves, high power pulses of microwave radiation, powerful X-ray radiation, pumping of gaseous lasers, electron beam welding, surface modification of materials, etc. They are distinguished by the inception of the plasma formation – before or simultaneously with application of the accelerating pulse.

As a passive electron source the carbon-fiber cathodes based on VEL-BLACK carbon-fiber material or a composite of Al−carbon-fiber material with and without CsI coating have been investigated. Both cathodes showed nanosecond timescale turn-on, long lifetime, reliable and reproducible generation of electron beam in a planar diode under accelerating pulse of 200 kV and duration ~250 ns. All investigated carbon-fiber cathodes form the dense surface plasma (flashover mechanism) from which the electron beam is extracted. The plasma parameters were obtained by space- and time- resolved spectroscopic diagnostics. The plasma expansion velocity of 1.5 cm/µs was estimated using time of flight technique.

The active plasma electron source – FPS-assisted HA discharge allows reliable and reproducible generation of electron beams with total current up to 3 kA, and current density ≤30 A/cm², electron energy ≤400 keV, pulse duration ≤350 ns and cross-sectional area up to 130 cm². Laser induced fluorescence (LIF) technique was applied to obtain data on plasma generation and evolution and develop corresponding models of physical processes.