Theory and design of a high-harmonic gyrofrequency multiplier

In a gyrofrequency multiplier, the entire electron beam enters the output cavity optimally phased to lose energy in a first-order interaction (in contrast to the second-order standard gyrotron process) resulting in a high conversion efficiency. Because the electrons radiate at a high harmonic of the cyclotron frequency, a gyrofrequency multiplier is capable of efficiently generating power in the millimeter to submillimeter wave region. The operational principles of the gyrofrequency multiplier are described in this paper. Results from nonlinear simulation show that radial guiding-center spread of the beam can dramatically affect the device´s efficiency while velocity spread effects are negligible. The design is presented for a 150 kW, 17.4 GHz, sixth-harmonic gyrofrequency multiplier which is under construction and is predicted to yield 31% conversion efficiency of the electron beam into the output wave. The 300 keV, 1.67 A axis-encircling beam is produced by a 1 MW, 2.9 GHz gyroresonant RF accelerator