Cold cathode, high current electron source for microwave tube devices using Micro Hollow Cathode Discharge (MHCD)

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 for applications such as microwave tubes amplifier, which require high total current and high current density. To enable using the MHCD as the electron resource for a microwave tube devices, a focus system has been designed, incorporating an electrostatic lens with three stages ranging up to 2 kV. The lens stages incorporate differential pumping in order to reduce the pressure to the order of 10^-7 Pa as needed for a 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. Measured data and beam-focusing simulations indicate that using a 4mm-diameter cathode, operating at 480mTorr, a current density of 10.19 A/cm² can be obtained. Data from 8mm, 11mm and 16mm diameter MHCDs have also been measured showing an increase in current density with decreasing cathode diameter.