Experimental observations in compact capillary discharges

We present experimental results on the characterization of a non-ablating fast pulsed capillary discharge, with a hollow cathode (HC) geometry, operating in argon below 1 Torr. Both the pre-breakdown and breakdown phase of the discharge are investigated with several diagnostics, which include electron beam monitoring, capacitive probe array and extreme ultraviolet (EUV) detector array. The pre-breakdown phase is found to be characterized by the emission of HC electron beams, which assist the propagation of a high speed ionization wave, with typical velocity in the 106-107 m s-1. Coinciding with electric breakdown a fast EUV radiation pulse is emitted. The leading edge of the radiation pulse is due to beam target emission by the HC electron beams. At the breakdown the radiation emission is mainly centered in the 5-15 nm spectral window, and is emitted from a capillary plasma which is being heated by a kiloampere level, 10 ns half-width current pulse.