Comparative EGUN and TRAK simulation studies on the design of the magnetron injection gun of a 200kW, 42GHz gyrotron

Abstract

A triode-type magnetron injection gun (MIG) for a 42 GHz, 200 kW gyrotron was designed by two commercial codes: EGUN and TRAK. An in-house code MIGANS was used as the p ost-processor of the EGUN. Some basic equations relevant to the problem available in literature were used while using the EGUN code for the purpose. The results on the design output parameters obtained by these two codes were found to be in close agreement. The gyrotron is a device to generate high powers at high frequencies. In this device, the source of electrons is a magnetron injection gun (MIG) which forms a beam of electrons in which the electrons execute the small cyclotron orbits at a frequency required for the cyclotron resonance interaction with RF waves in the device (1,2). The MIG is placed in an axially symmetrical magnetic field at the magnetic field strength determined by the magnetic compression ratio . The initial electron motion occurs in the crossed electric and magnetic fields so that the electron s follow the helical trajectories around the magnetic field lines. The gun anode accelerates the beam to th e final beam energy. Downstream from the gun, the magnetic field increases smoothly in the magneti c compression region to the required peak value at the interaction region. The magnetic field compress ion reduces the radius of the beam and results in an increase of the velocity component perpendicular to the magnetic field. Since the total energy is constant, the drift velocity is correspondingly reduced. In India, an activity related to the design and development of 42GHz, 200kW gyrotron has been started. The operating mode has been selected as TE03 with the second maximum of the transverse-plane field pattern of the cylindrical interaction cavity as the be am launching position for the fundamental beam-mode operation. For the better performances of the gyrotron and the gyro-devices, an electron beam of good quality is required (1-6). The triode-type MIG has been designed having the beam voltage V0 = 65kV, the beam current I0 = 10A and the transverse-to-axial beam velocity ratio � = 1.26. The