Perveance characteristics of intense electron beams in high power cylindrical diodes

When an electron beam is generated from a cathode, an electron sheath plasma is also generated so that perveance of the diode is varied and changes the diode output characteristics. In our pulse power system "Chundoong" (Max 600 kV, 88 kA, 60 ns), the perveance value have been experimentally investigated and estimated from diode voltage and diode current. In this experiment, the anode- cathode (A-K) gap distance d has been varied from 4 mm to 10 mm. It is noted in this experiment that the diode perveance characteristics could be described as 7.0/spl times/10/sup -9//d/sup 1.82/. The sheath plasma expansion speed has also been estimated from the experiment, which is to be about 7 cm/us under A-K gap distance 4 mm.