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.