Numerical and Experimental Studies on Frequency Characteristics of $hbox{TE}_{11}$-Mode Enhanced Coaxial Vircator

摘要

Due to azimuthal-asymmetric electron emitting, $hbox{TE}_{11}$ -mode output of high-power microwave is unavoidable in coaxial vircator. In order to obtain a pure mode output, $hbox{TE}_{11}$-mode enhanced design by opposed section electron emitting is applied. As 2-D effect along azimuthal direction is introduced, the frequency of microwave generated is shifted in $hbox{TE}_{11}$-mode enhanced coaxial vircator, compared with the thoroughly coaxial one. Frequency characteristics of $hbox{TE}_{11}$-mode enhanced coaxial vircator are numerically and experimentally studied by the 3-D particle-in-cell code UNIPIC. Simulation results show that a stable $ hbox{TE}_{11}$-mode output is generated nearly with a point frequency in the S-band by $hbox{TE}_{11}$-mode-enhanced geometry, which is a little lower than that in the thoroughly coaxial geometry. In experiments, nearly point frequency and stable $hbox{TE}_{11}$-mode output is also obtained, and the effects of diode voltage, anode–cathode gap, and electron beams width are investigated. The results show that with higher diode voltage, smaller anode–cathode gap, and larger electron beam width, the microwave frequency is higher, particularly that the electron beam width has an equal effect with the diode voltage and the anode–cathode gap, which agree well with the simulation results. Meanwhile, microwave generation was obtained with steady power above 800 MW at about 5% efficiency in the experiments.