Frequency characteristics of TE11 mode enhanced coaxial vircator

Due to poloidal-asymmetry electron emitting, TE₁₁ mode output of high-power microwave (HPM) is unavoidable in coaxial vircator. In order to obtain a pure mode output, TE₁₁ mode enhanced design by opposed section electron emitting is applied with more advantages. As two-dimensional effect along poloidal direction is coursed, the frequency of microwave generated is shifted in TE₁₁ mode enhanced coaxial vircator compared with the thoroughly coaxial one. Frequency characteristics of TE₁₁ mode enhanced coaxial vircator are studied numerically by the 3-D particle-in-cell (PIC) code UNIPIC and experimentally on a high-power pulse modulator. Simulations results show that a stable TE₁₁ mode output is generated nearly with a point frequency in TE₁₁ mode enhanced geometry, which is a little lower than that in the thoroughly coaxial geometry. In experiments, nearly point frequency and stable TE₁₁ mode output is also obtained and the effect 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 beams width, the frequency of microwave generated is higher, especially electron beams width has the same degree effect with diode voltage and anode-cathode gap, which is well agreed with simulation results.