Stability and amplification studies of a multi-megawatt X-band gyroklystron

A TE/sub 01/ gyroklystron experiment in the 9.7-10.0 GHz range is discussed. The target microwave power of 30 MW is to be derived from the interaction of a 500 kV, 160-A beam with a two-cavity circuit. The first tube was tested in spring 1990 and was plagued by a multitude of spurious oscillations. The most damaging oscillations included ´whole tube´ modes and modes in the beam tunnel between the electron gun and the input cavity. Limited amplification studies were performed at 175 kV and produced only tens of kilowatts at nearly zero gain. The second tube featured additional beam tunnel loss and a new drift tube configuration, and was tested in summer 1990. Enhanced stability allowed amplification studies up to 350 kV, which resulted in output powers in excess of 1.5 MW with gains of 16 dB and efficiencies of approximately 5%. A spurious mode near 9.85 GHz existing in the output waveguide adjacent to the final cavity severely limited the available magnetic field range. A third tube, with a redesigned output waveguide, will undergo testing by September 1, 1990.<>