Design and Investigations of Millimeter-Wave Gyrotron With Multisection Slightly Tapered RF Cavity for DNP/NMR Spectrometer Application

Abstract

A multisection slightly tapered RF cavity for millimeter-wave gyrotron is designed and investigated to enhance the tunable bandwidth for dynamic nuclear polarization (DNP)/nuclear magnetic resonance (NMR) application. The present cavity is operated in TE $_{7.2,q}$ mode at ~260 GHz, in which $q$ is varied from 1 to 9 to achieve the desired tuning range. The effect of the multisection gyrotron cavity on the diffractive quality factor and effective cavity length are analyzed. The proposed multisection RF cavity enhances the tunable bandwidth of gyrotron to ~1.85 GHz through a magnetic tuning scheme. Besides, the effect of temperature and the corresponding deformation in the RF cavity is also studied. The tunable bandwidth of the gyrotron is further enhanced from ~1.85 to ~2.32 GHz by varying the coolant temperature, i.e., the tuneable bandwidth is increased by ~25% using a thermal tuning scheme.