Numerical simulation of high-power virtual-cathode reflex triode driven by repetitive short pulse electron gun

A virtual-cathode reflex triode is investigated by numerical simulations. A trapezoidal in shape voltage pulse with an amplitude of 300 kV is applied to the solid cathode of the device to drive the cathode negative. The electron beam-to-microwave power conversion efficiency ε, calculated for the pulse flat top with a duration τ_ft=1.2 ns is approximately the same (about 1.5-2%) as well as for a long flat top (τ_ft=4 ns). The simulations show a 10-15% increase of ε at τ_ft shortening to 0.6 ns. However, this occurs when the anode mesh transparency is high (80-90%). Considerable enhancement of the efficiency (about four times) for τ_ft=0.6 ns has been calculated if the cathode side surface is brought near to the anode tube (from ≈0.5% at cathode radius R_c=1.6 cm to ≈2% at R_c=3.8 cm). The obtained results would find an application for the design of virtual-cathode reflex triode devices driven by a short pulse and high repetition rate electron gun