High-power cusp gun for harmonic gyro-device applications

A cusp gun, designed to generate an axis encircling beam with low-velocity spread for high-harmonic high-power (70 kV, 3.5 A) operation in gyrotrons and peniotrons, was successfully fabricated and hot tested at reduced voltage in a beam tester designed to measure beam perveance, size, thickness, velocity ratio (beam α), and, in the near future, beam ripple and velocity spread. A relatively thin, round, hollow beam was imaged on the Cerium glass witness plate. Beam transmission through the anode was 98.5%. The beam α, as determined by capacitive probe data, agreed well with simulations over a large range of operating parameters.