THEORY AND DESIGN OF A HIGH-HARMONIC GYROFREQUENCY MULTIPLIER

In a gyrofrequency multiplier, the entire electron beam enters the out put cavity optimally phased to lose energy in a first-order interactio n (in contrast to the second-order standard gyrotron process) resultin g in a high conversion efficiency. Because the electrons radiate at a high harmonic of the cyclotron frequency, a gyrofrequency multiplier i s capable of efficiently generating power in the millimeter to submill imeter wave region. The operational principles of the gyrofrequency mu ltiplier are described in this paper. Results from nonlinear simulatio n show that radial guiding-center spread of the beam can dramatically affect the device's efficiency while velocity spread effects are negli gible. The design is presented for a 150 kW, 17.4 GHz, sixth-harmonic gyrofrequency multiplier-which is under construction and is predicted to yield 3l% conversion efficiency of the electon 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.