Electron Transportation Experiment and Analysis for a G-Band Magnetron Injection Gun

The electron beam transportation profile is important for the gyro-traveling-wave tube (Gyro-TWT), and a transportation prototype of Gyro-TWT has been developed. The symmetric-rotating calibration (SRC) method for the superconducting magnet (SCM) alignment is proposed, and the tilt angle and transverse displacement of the magnetic field are reduced from 0.05° to 0.01° and 0.15 to 0.05 mm after alignment, respectively. Then, the beam transportation experiment is done, with a transportation rate of ~85%. The beam trajectory is analyzed and indicates that the stray electron is the main reason for transportation degeneration. Then, a new magnetron injection gun (MIG) with an optimized rear electrode, isolated thermal gap, and antiemission coating is designed and fabricated to enhance the transmission rate. The stability of the new gun is also analyzed, and the stray electron is reduced. Finally, the transportation rate improves to 97.1%, and the transported beam is with a pitch factor of 1.25 and a velocity ratio of 2.5%. The beam quality is good for the interaction circuit.