Cold-Cathode, High-Current Electron Source using Micro Hollow Cathode Discharge

A Micro Hollow Cathode Discharge (MHCD), a technology well known as an ion source, is adapted, using Argon, to be a cold-cathode electron beam source with high total current. Cylindrical cathodes of various internal diameters, used to confine the plasma, have been investigated. The 'pd' gas breakdown scaling rules necessitate an increase in argon pressure with decreasing tube diameter. As the tube diameter approaches micrometer regime, the operating pressure approaches 1 ATM, with the result of the current density increasing dramatically. The plasma electrons are formed into a beam using an electrostatic lens. Measured data and beam-focusing simulations indicate that using a 15mm-diameter cathode, operating at 300 mTorr, a current density of 1.5Acm-2 can be obtained. Data from 3mm and 9mm MHCDs have also been measured. To enable using the MHCD as the electron resource for a microwave tube amplifier, a focus system has been designed, incorporating an electrostatic lens with three stages, ranging up to 1 kV. The lens stages incorporate differential pumping in order to reduce the pressure to the order of 10-7 Pa for microwave tube. The apertures between stages are positioned at the minimal-diameter points of the beam, in order to enable maximum pressure isolation between stages.