Imaging and Mode Content Analysis of the Wave Beam From a Short-Pulse High-Power Gyrotron Using the Millimeter-Wave-Induced Gas Breakdown Initiated by a Metal–Dielectric Screen

The wave beam of a sub-terahertz (THz) gyrotron with a pulsed magnetic field was imaged in a single pulse using a microwave-induced gas breakdown initiated by a metal–dielectric (MD) screen. Images of sub-THz beams, which were recorded at the output of a quasi-optical mode converter, were compared with data obtained by numerical simulation of propagation and transformation of the wave beam from the gyrotron. The analysis of the waveguide mode content in the gyrotron was done. Based on experimental and simulation data, it was shown that the distortion of the sub-THz wave beam is caused by the deformation of the Teflon window at the gyrotron output. Based on the results of the study, the gyrotron was modified, and the quality of its wave beam was improved.