Millimeter Wave Gyrotron Development - Phase 1

Abstract : This report describes Phase I of a program to develop a high-power 94 GHz amplifier based on the gyrotron or cyclotron resonance interaction. Ultimate goals are 100 kw peak power, 5 to 10 kW average power, 1 to 10% bandwidth, 30% beam efficiency, and 30 dB gain. The experimental work in Phase I has been performed at X-band to demonstrate feasibility of this approach. The first section of this report contains a review of previous work on cyclotron resonance devices. This is followed by the analysis of a number of cyclotron harmonic interactions with TE01 and TEn1 cylindrical fields. The next section describes the design of an X-band gyroklystron amplifier. A calculation of a large-signal power output is included which predicts an efficiency from beam power to microwave output of 36%. A computer simulation of the gun and beam performance is presented. Initial measured results for the experimental amplifier are presented. The maximum measured gain was 9 - 10 dB. The gain was limited by an interfering oscillation which prevented full optimization of the beam parameters. One oscillation produced an output power of 19.5 kw peak with an efficiency of 9.8%. An analysis is included to predict the bandwidth of gyroklystrons at 94 GHz. Bandwidths of 1 t0 4% are predicted with the fundamental interaction which requires a superconducting magnet.