Six-Beam Gun Design for a High Power Multiple-Beam Klystron

This paper presents the detailed design of a six-beam gun for use in an L-band 10-MW multiple-beam klystron. To facilitate the gun simulation, we developed a joint design methodology with 2-D and 3-D simulation codes. The six-beam gun is designed to produce a total current of 132 A divided equally among the six beams at an accelerating potential of 115 kV. For the design of the gun, special emphasis is placed on the geometric layout of the electrodes to ensure moderate voltage gradient, accurate beam perveance and reasonable cathode loading. The magnetic circuit consists of solenoid magnet structures. Special coils and iron shells are set to ensure a uniform parallel magnetic field in the region between the cathode and the anode. Two set of amendatory coils and shield irons are set in the transition region to optimize the beam radius. Special coils are set in the both ends of the interaction region to trim the radial magnetic fields. The gun design is accomplished with EGUN and CST codes. Simulation results show that the joint design methodology is effective and the magnetic circuit has an excellent flexibility. The final gun has a cathode loading lower than 2.1 A/cm² and excellent beam transport characteristics. The dependency relationship between the beam off-centering and the asymmetry radial magnetic fields is analyzed.