A 5 MV Radial Insulator Electron Gun for an Electron Ring Accelerator

Abstract : A massive radial insulator is considered as an approach for a stable mounting of a vacuum diode electron gun and connection to a 5-MV, 70-ohms, oil dielectric pulse generator. A rationale for determining the electric field permitted without breakdown along the insulator-vacuum interface is presented. The electric field along this interface and on the center conductor is determined by numerical solutions of Laplace's equation for specific models. A dished head and field shaping collar make it possible to operate a 4.5 ft. diameter insulator at 5 MV. The rise-time due to the shunt capacitance of the electron gun is calculated to be 13 ns. A proposal is made to design and construct such a radial insulator from cast nylon. An external magnetic field must be used to prevent vacuum breakdown and limit the current from the cathode stalk. The electron gun impedance cannot be calculated at this time.