A high-energy (200 keV) high-brightness (8/spl times/10/sup 10/ A/cm/sup 2/) pseudospark electron beam was generated. Its beam quality was much better than that of cold-cathode beams. A solid and layer-like beam structure was observed. The propagation range of /spl ges/25 cm was useful for compact gas-loaded FELs. Field-induced explosive electron emission is considered to be more likely the most possible mechanism for pseudosparks by solving 1-D heat conduction equation with Joule-heating source for a micropoint on a cathode surface. The mean electric field on the cathode surface up to 1-5 MV/cm prior to the conducting phase is enough to initiate the mechanism at high threshold current density (/spl ges/10/sup 8/ A/cm/sup 2/) and within very short time (>10 ns).
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