Megavolt-Megampere Electron Gun Study.

Abstract : The principal topic of this report is numerical analysis of electron flow in high current megavolt diodes, using a computer code developed by Varian Associates. Previous work had led to the conclusion that in high impedance megavolt diodes the cathode behaves essentially spacecharge limited and there is little if any ion neutralization of space charge in the flow. Presumably the source of electrons is a plasma which remains very near the cathode surface and which is formed by field emission heating of the surface during the early part of the pulse. Reported here are further efforts to verify the models used in the previous work. Calculations are compared with experimental results for diodes for which measured results were available. Also, electron flow calculations are presented for a number of 15 MV, 0.4 MA diode geometries, leading to some indications of how changes in the geometry affect the character of the beam. Also continued from the previous work were investigations of the feasibility of generating megavolt beams by using a cavity resonator as an rf energy storage element. (Author)