High Order TM Mode In Cylindrical Coaxial Coupling Cavities And Its Output Circuit

The characteristic of high order TM mode in cylindrical coaxial cavities of klystron is studied.By adjusting the drift tubes number, location and size etc in cavity, fields’ rotation is restrainedeffectively and its annular symmetry improved.The output circuit of klystron single gap cylindrical coaxial resonator loaded with waveguidefilters is analyzed theoretically. By using the HF Software CST powerful post-processing function,the resonance frequency, port impedance, external quality factor Qextand gap impedance frequencycharacteristic curve of output cavity are obtained and calculated. By introducing metal short line incavity nearby coupling hole the electromagnetic field in this position is increased, the Qextvaluedecreased from186.6to88.7,3dB bandwidth increases from44MHz to110MHz.For higher order TM mode in double gap cylindrical coaxial cavities of klystron，couplingslots between two cavities are designed, influences of its position, shape and size are analyzed on theTM310mode stability, characteristic impedance at the drift tubes gaps centre.To increase the gap impedance and bandwidth, the output circuit of double gap cylindricalcoaxial resonator cavity loaded with rectangular waveguide is designed. The frequencycharacteristics of the double gaps’ impedance is analyzed, simulated and calculated with equivalentcircuit theory. Similar to the case of the single gap cavity, the introduction of metal short lineobviously make the Qextfrom130to60,3dB bandwidth from110MHz to180MHz. We alsodesign preliminary waveguide filters with the equivalent circuit theory.Ours research have certain reference significance on the double gap closed coaxial cavity andits output circuit design. We will explore in the future the mode overlapping of the double gapoutput circuit.