Abstract
In this work we describe the operation of a continuous-wave 330/460 GHz gyrotron oscillator operating at the second harmonic of the electron cyclotron frequency. The oscillator is intended to be used in 700 MHz 1H nuclear magnetic resonance (NMR) experiments enhanced by dynamic nuclear polarization (DNP). At 460 GHz, the gyrotron operates in the TE11,2 mode and is able to generate 16 W of power continuously and stably for a beam current of 100 mA and beam voltage of 13 kV. Power and frequency tuning measurements as a function of beam voltage and magnetic field were carried out. The results show continuous frequency tunability over a range of 700 MHz with a minimum power level of 5 W for a fixed beam current of 100 mA. Extended frequency tuning due to the interaction of the electron beam with the backward-wave component of successive high order axial modes is observed. Power and frequency tuning measurements are also reported for the TE4,3 mode at 330 GHz, a frequency suitable for 500 MHz DNP/NMR spectrometers.
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