Frequency modulation in a submillimeter-wave Gyrotron

A first demonstration has been made of frequency modulation of a gyrotron output signal. The experiment was performed on a submillimeter-wave gyrotron operating near 300 GHz. The modulation amplitude of several tens of MHz has been achieved by a 120 V modulation of the accelerating voltage; this results in variation of the relativistic electron mass and corresponding variation in the electron cyclotron frequency f(c). The observed modulation of the output frequency is 2.3 times smaller than the variation in f(c). There is reasonable agreement between the experimental results and a simulation employing the energy transfer formula in a cavity.