Experiments on a 28 GHz, 200 kW gyroklystron amplifier for plasma heating

Summary form only given. Experiments are underway to demonstrate an amplified radiation power of 200 kW operating at 28 GHz. A long pulse operation of up to 500 msec is required for plasma heating experiments of Hanbit. A five-cavity interaction circuit is designed by the use of small signal and large signal non-linear simulation codes. Simulations predict a saturated gain of 54 dB and an electronic efficiency of 35%. An input drive cavity designed by the use of HFSS consists of a WR-28 waveguide, a TE311 single-ridged coaxial cavity, and a circular TE011 central cavity. In this high gain amplifier, an input power of less than 1 W is enough to saturate the amplifier, which is the power level available from a high power solid state power amplifier. Three penultimate cavities are loaded by lossy ceramic rings. A water cooled beam collector is designed to spread the beam over a wide surface by carefully tapering an external magnetic field. An input window which is a typical pillbox configuration is designed. Simulations predicts a bandwidth of more than 7% with a center frequency of 28 GHz at -20 dB return loss. An half wavelength thick BeO window is designed for extracting the amplified radiation power of 200 kW with a pulse length of 500 msec. Thermal analyses on ceramic loaded cavities, RF vacuum windows, beam collector performed by ANSYS are currently underway to design the tube to be operated at a duty of 50%. Cold tests of the interaction circuits are presented.