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.