PIC simulation of a millimeter wave gyrotron traveling wave amplifier

Abstract

In this paper, 3D particle-in-cell (PIC) simulation of a W-band, second harmonic gyrotron travelling wave tube (gyro-TWT) amplifier has been presented for investigating its transient behaviour. Its RF interaction circuit is loaded with the wedge shaped lossy ceramic rods arranged azimuthally symmetric in the axial direction to make the device operation stable by suppressing the parasitic modes including TE01 (2), TE02 (3) and TE03 (4) . Through PIC simulation, the transmission loss for the desired (2) 02 TE mode of the device has been found to be ~19dB /cm at 91.4GHz with saturated RF output power of ~435kW. The conversion efficiency has been obtained as ~17% for the gyrating beam of 100kV, 25A with a pitch of 1.2 and an axial spread of 5%. Further, the saturated gain of the amplifier has been calculated as ~30dB with an instantaneous bandwidth ~3%. The PIC simulation values have also been validated with the nonlinear analytical results and found in agreement within 3%. The present study should be helpful in the design and stability study of gyro- TWTs. © 2017 IAMOT.