Recent tests on a multi-megawatt 95 GHz GYROTRON

A 95 GHz gyrotron capable of generating CW power levels in excess of 2 MW is currently under development at CPI. The gyrotron employs a single-anode electron gun that produces a 90-kV, 75-A electron beam for interaction with the TE22,6,1 cavity mode. Output power from the cavity is transformed into a fundamental Gaussian beam using an internal converter that consists of a waveguide launcher and three focusing and phase-correcting mirrors. The Gaussian beam exits the tube through a chemical-vapor-deposition (CVD) diamond window. The spent electron beam is dissipated in a 40.6-cm diameter collector fabricated from a strengthened copper alloy. The collector nominally operates at a voltage of 61 kV relative to the cathode potential to minimize the amount of power absorbed in the collector and to improve efficiency. In recent tests on the gyrotron an output power of 1.92 MW was achieved with 40% efficiency at the nominal beam current of 75 A. During the tests, we noted a significant reduction in the amount of power absorbed in the beam tunnel compared with earlier versions of the tube. The reduction in beam tunnel power is attributed to the use of a modified beam tunnel design to reduce the possibility of parasitic oscillations.1 Results of recent tests and future plans will be presented.