Effect of cathode diameter on beam generation in the presence of prepulse

Summary form only given. Intense gigawatt relativistic electron beam generation studies were carried out in the presence of prepulse. Electron beams were generated using planar and annular graphite cathodes of various diameters. At 25 mm anode-cathode gap beam parameters obtained are 386 kV, 25 kA, 100 ns. A bipolar prepulse voltage has been recorded at the diode for both the cathodes. Amplitude of the negative prepulse voltage varies with the Marx generator voltage but the time duration remains same. The positive prepulse voltage varies both in amplitude and time duration with the Marx generator voltage. Some shot to shot variation in the diode voltage and current were recorded for the annular cathode due to the nonreproducibility of the prepulse generated plasma. It was found that the effect of prepulse is more pronounced in the cathode of larger diameter.