An intense-current electron beam source with low-level plasma formation

Abstract

The generation of high-current electron beams is accompanied by strong plasma formation on the cathode surface. The cathode plasma sheath expands towards the anode, which limits the pulse length. In this paper the experiments were performed using a high-voltage pulse generator with 400 kV output voltage and 300 ns pulse duration. We used electrical and optical diagnostics to study the process of plasma formation. This paper presents data on a caesium–iodide (CsI) coated carbon fibre cathode capable of operating with the lack of strong plasma formation. The addition of CsI caused an increase in the voltage pulse duration and reduced the turn-on electric field for electron emission, thus resulting in the fast-rise current. In particular, the CsI coating effectively inhibited the plasma expansion and, as a result, the diode gap remained almost unchanged within approximately 200 ns. These results show that CsI-coated carbon fibre cathodes are promising electron emitters for generating long pulse high-current electron beams.