Triode Type Coaxial Inverse Magnetron Injection Gun for 2-MW, 240-GHz Gyrotron

Abstract

A triode type coaxial inverse magnetron injection gun (CIMIG) is designed using the 2-D and 3-D beam trajectory simulation codes for 240-GHz, 2-MW coaxial gyrotron. In IMIG, the modulating anode is adjusted at the center of the emitter ring and it provides compact size and better control on the beam instability and beam halo. As per the beam-wave interaction simulations, the CIMIG is designed to deliver the 6.5-MW (100 kV, 65 A) helical electron beam of 8.72-mm guiding center radius at the cavity center. First, the synthesis of CIMIG is performed to estimate a range of electrical and geometrical parameters based on the tradeoff equations. The Gaussian type of magnetic field profile is optimized with the peak magnetic field value of 10 T at cavity center and the beam compression ratio of 35.11. The pitch factor of 1.306 and the transverse velocity spread of 2.74% are realized in 2-D trajectory code electron GUN. The design results obtained in 2-D simulations are validated in 3-D particle trajectory simulator CST-Particle Studio. In 3-D optimization, the gun geometry and the electrical parameters are kept similar to 2-D design. The pitch factor of 1.285 and transverse velocity spread of 3.01% are obtained in 3-D design which shows good agreement with the 2-D design.