| The Relativistic Klystron Amplifier (RKA) is a kind of gigawatt-class linear microwave tube with high output microwave, high efficiency and stabilization of phase and amplitude for the generation of electron, interaction of beam-wave, extraction of microwave and collection of electron beams are completed at different zones. The theory and the numerical simulation on double-gap output cavity of S-band RKA are investigated, and the corresponding conclusions are used to design and guide the double-gap output cavity experiments. The experimental results are almost consistent with the theoretical results and simulant results.The paper includes four parts:1. A three-dimension high frequency analysis procedure is applied to study the eigenmodes of double-gap output cavity with close boundary and the high frequency characteristics of double-gap output cavity with open boundary of S-band RKA. The relation between the operating frequencies and the structure parameters is obtained. The relation between loaded quality factor and the structure parameters of coupling hole is described in detail.2. Some rules of dissertation double-gap output cavity are analyzed by applying one-dimension large signal disc mode. The electron efficiency equations for two gaps are derived. Some variable relation curves between unknown quantities and electron efficiency are obtained by plotting.3. Using a three-dimension fully electronmagnetic Particle-In-Cell (PIC) code, the simulation of microwave extraction from a modulated intense relativistic electron beams which pass through double-gap output cavity is investigated, and the beams and double-gap output cavity geometry parameters are optimized. An output microwave power of 1.48 GW, is generated by simulation, with an electron beam voltage of 760kV, a current of 7kA , 80% depth of the modulated current and 1.5T leading magnetic field density. The efficiency is 28%. In addition, the output pattern in coaxial transmission line is analyzed.4. The S-band RKA double-gap output cavity is designed according to theoretical analysis and particle simulation results. Subsequently, the experiment is performed. The experiment includes cold test and hot test. In hot experiment, an annular electron beams of 600kV, 6.2kA generates a microwave pulse power of 1GW, a frequency of 2.9GHz, pulse duration of 22 ns with efficiency of 27%.The experimental results agree well with the results of theoretical analysis andparticle simulation. |
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