A systematic theoretical and experimental study on 35 GHz 45KV third-harmonic gyrotron with a permanent magnet system is presented in this paper. A complex cavity with gradual transition, and a diode magnetron injection electron gun (MIG) are employed in the gyrotron. A self-consistent field nonlinear theoretical investigation and numerical simulation for electron beam interaction with RF fields are given. The diode MIG is simulated numerically utilizing our code in detail. The permanent magnet system provided the axial magnetic field of about 4.5KGs in the cavity region of the gyrotron. The Ka band third-harmonic complex cavity gyrotron with a permanent magnet system has been designed, constructed and tested. A peak output power of 146.3KW was obtained at a beam voltage of 45KV with beam current of 32.2A, corresponding to an efficiency of 10.2%.

从模式场匹配理论出发系统地研究了回旋管中过渡段突变这一类复合腔的高频场结构，并考虑了TM型寄生模式的影响，研究了诸多因素的变化对谐振频率、Q值以及轴向场分布的影响。

利用含电流的传输线方程,在考虑多模与电子注互作用及多模耦合的情况下,对三次谐波渐变复合腔回旋管进行了非线性模拟,计算了H51-H52模式下三次谐波注波互作用,分析了多模对注-波互作用的影响.

A self-consistent nonlinear theoretical model for a complex cavity gyrotron with abrupt transitions is presented in this paper. The model accounts for mode conversion in the transition region of the complex cavity through the general theory of modal expansion techniques. The interaction between the electron beam and TE61/TE62 RF field in the step cavity for a third-harmonic gyrotron is simulated; many calculations are carried out under different electron beam parameters.

The PaPer presents the design of the two-stage depressed collector system for 35GHz gyrotron, taking into account the effect of secondary electrons. Employed a new 2.5-D computer-aided design codes named CHAELOPS, including the auto-gridding generator, the electromagnetic solver, the accurate particle trajectory tracer and the secondary electron emitter including true secondary and backscattered seondary electron models based on Monte-Carlo method. The codes take into account either the safety and the reliability. The user interface is very friendly and fiexible. The collector electrode potentials were optimized in order to maximize the efliciency of the collector system s and minimize the effect of the secondary electrons. The primary beams come from the beam-wave interaction simulation codes. When the potentials were-20kV and -35kV, the magnetic com press ratio was 5.38, the better collector efliciency was 60.0％ with all the secondary electrons landing on the same electrode. The normalized velocity distribution of one trajectory in phase-space was shown in the paper, indicated the theory of the energy conversion of the electrons in retarding electric field and adiabatic magnetic field. The results comparison between EGUN and CHAELOPS has been made and good agreements have been obtained.