The design of space-charge limited MIGs with control grids for gyroklystron applications

Summary form only given. At the University of Maryland we have been investigating the designs of space-charge-limited (SCL) Magnetron Injection Guns (MIGs) as potential replacements for temperature-limited (TL) MIGs, which can suffer from non-uniform azimuthal current density distributions due to thermal and work-function variations. Preliminary designs indicate that the same beam-quality can be achieved with only a slight cost in terms of required peak electric fields and cathode loading densities. One objection to these devices has been that you lose some control of the beam current which is available with TL MIGs. In this paper we address this issue, in part with parameter studies of the SCL MIG designs, and in part with the design of SCL MIGs with control grids. Two different designs with non-intercepting control grids are presented. The first design has small grids with low capacitance that can be adjusted by a few percent of the main beam voltage to adjust the current by +/-20%. The second design has larger control grids that can be biased sufficiently to actually cut off the beam flow even when the full beam voltage is applied.