Optimization of magnetron injection gun and multi-coil collector design for 170 GHz gyrotron

As gyrotrons progress into the millimeter wave range, electron energy reaches the MW level, requiring advanced electron optical systems (EOS) to address electron velocity spread and collector thermal load challenges. This study introduces a continuously curved anode structure that smooths the spatial variation of the electric field magnitude, reduces transverse velocity spread, and enhances beam quality through improved electric-magnetic field matching. To reduce the thermal load on the collector, compensation coils carrying direct current are wound around its outer wall. Simulations of configurations with 1, 5, and 9 coils show that the 9-coil setup, combined with the residual superconducting field, forms an extended uniform magnetic region, adjusting the electron orbit radius to match the collector's inner radius. This alignment reduces the collision angle between electron trajectories and the collector wall, effectively expands the electron landing range, and reduces local power density. At a spent beam power of 2.925 MW-equal to the electron beam input power in the absence of RF interaction-the electron impact length extends from 46 to 1001.3 mm, and the peak collision power density drops by 93.7%, from 7869.6 to 494.6 W/cm2. These results demonstrate that the proposed multi-coil magnetic topology effectively overcomes heat dissipation limitations, ensuring stable operation of high-power gyrotrons and providing a promising solution for EOS design in millimeter-wave radiation sources.