Simulation Investigations and Optimization of a Millimeter-Wave Gyrotron for Its Tunability Using Magnetic and Thermal Tuning Schemes

The present gyrotron is designed to operate in TE
_7,2
mode at 260 GHz for studying its beam-wave interaction behavior and its tunability for dynamic nuclear polarization/nuclear magnetic resonance (DNP/NMR) application. The operating frequency of the gyrotron is very sensitive to the physical dimension of the RF interaction circuit and its shape can be deformed due to the ohmic loss led temperature. Therefore, the combined magnetic and thermal tuning schemes are used to control the deformation and enhance the tunability of millimeter-wave gyrotron. The 3-D particle-in-cell simulation technique is used to study the beam-wave interaction behavior of gyrotron and validated with a multimode nonlinear code. Further, the structural deformation and thermal studies are made in a finite-element method based ANSYS. The use of combined magnetic tuning and water coolant based thermal tuning schemes have improved the tunable bandwidth of the present gyrotron to ~1.88 GHz, which is ~44.60% higher than the one obtained by varying the magnetic field only.