Study On The High Order Mode Multi-beam Klystron Electrodynamics System

In order to overcome the limit of the output power to TM010 mode multi-beam Klystron on the high frequency, the theoretical and experiment investigation of the high order mode multi-beam klystron electrodynamics system have been conducted. The research work includes how to choose the high order mode cavities and high order operating modes, the structure of double-gap output cavity of high order mode, the coupling between high order mode cavity and wave guide.Three kinds of high order mode cavities, which are rectangular cavity,cylindrical cavity and coaxial cavity, are analysed by Isfield3D which is a kind of three dimension electromagnetic field calculation software. The suitable high order mode is chosen as operating mode in the three kind cavities, field distribution and characteristic impedance of the operating mode are given. The advantage and disadvantage of different high order mode cavities and different high order operating modes is sum up. Three kinds of high order mode cavities module, which are TM220 rectangular cavity,TM310 cylindrical cavity and TM010 coaxial cavity, are made out and the experimental result accords with the calculation.A kind of C band double-gap rectangular cavity module is devised and simulated by Isfield3D.The electromagnetic field distribution and characteristic impedance of the operating mode are given. The stray modes in the module is analysed and the method to restrain stray mode oscillation with absorb cavity is put out. The module is made out and the test result accords with the analysis.Three kinds of coupling schemes between wave guide and high order mode cavity are put out. The first is through coupling iris on the narrow side of the cavity. The second is improved scheme by opening coupling iris on the narrow side of the cavity. The third is through coupling iris on the wide side of the cavity .The influence on the electromagnetic field distribution and characteristic impedance, Qext of the operating mode by the coupling iris are analysed. The module is measured, and the result accord with the analysis.