A fully demountable 550 kV electron gun for low emittance beam experiments with a 17 GHz linac

The design details and fabrication features of a 550 kV electron source for operation with a 17 GHz chopper-prebuncher linac injector are described, and initial test results using the M.I.T. Plasma Fusion Center HV pulse modulator are presented. The electron gun was designed to satisfy the stringent injection specifications required for the linac to demonstrate a 20 MeV beam with a bunch current of 100 A and a normalized emittance of 5 mm-mradian. Fine mesh simulations of the electron gun optics revealed that, to minimize geometric contributions to the source emittance, a very tight tolerance (±25 μm) was required for the edge spacing between the cathode and focus electrode. Means of accurately locating the gun electrodes are discussed; and the vacuum demountable features that enable convenient field replacement of the anode, focus electrode and cathode/heater are described