HIGH-POWER CARM AND HARMONIC GYRO-AMPLIFIER EXPERIMENTS

Cyclotron resonance maser oscillators and amplifiers are attractive sources for applications such as electron cyclotron resonance heating (ECRH) of fusion plasmas and driving high gradient RF accelerators. For ECRH applications oscillators in the 140-280 GHz range with high average power (> 1 MW) are required. A 27.8 GHz long-pulse (1 mus) CARM oscillator experiment has been carried out at the MIT Plasma Fusion Center. A 450 keV, 80 A electron beam is generated by a diode Pierce gun. The interaction takes place inside a Bragg resonator. Output power of 1.9 MW (efficiency of 5.2%) has been measured in the TE11 mode. A significant mode competition between the modes TE11 and TM01 is present. For applications such as accelerator drivers, amplifiers or phase-locked oscillators at frequencies in the 11-33 GHz range with high peak power (> 100 MW) are required. A 17 GHz CARM amplifier experiment and a 17 GHz third harmonic gyro-amplifier experiment are presently under way. These devices utilize the SRL/MIT SNOMAD II linear induction accelerator injector for production of a 30 ns flat top electron beam up to 400 keV and 400 A. The third harmonic gyro-amplifier operating in the TE31 cylindrical wave guide mode has produced 5 MW of RF power with over 50 dB of gain at 17 GHz. Because of its high power output the gyro-amplifier will be used as the RF source for a photocatode RF electron gun. A CARM experiment designed to operate in the TE11 mode is also discussed.