Investigation of Different Filament Heater Configurations for Magnetron Injection Guns of High-Power Gyrotrons

Gyrotrons are high-power vacuum tubes relevant for Electron Cyclotron Resonance Heating of magnetically confined nuclear fusion devices. One of the most critical elements that determines the performance of a gyrotron is the electron emission of the cathode. Two different configurations of cathode heaters for electron emission, are compared with regard to the influence of the stray magnetic fields, induced by the heating current, on the electron beam parameters. The investigation uses electron beam optics simulations. The results confirm the expected relationship between heater current and beam parameters. While the bifilar-coil configuration shows negligible influence on beam quality, the simpler single-coil variant exhibits a significant impact, potentially affecting the overall efficiency.