Quasi-optical mode converter for high power gyrotron

Abstract

Gyrotrons are microwave / millimeter wave devices capable to deliver megawatt level continuous power at a frequency range up to 170GHz. The critical design issues for a high power gyrotrons are: (1) Magnetron injection Gun (2) Cavity with proper mode (3) quasi-optical launcher (4) depressed collector system and (5) RF-window. The higher order cavity modes like TE mp (m, p >>2) are normally selected for high power, high frequency, long pulse Gyrotrons. These higher order modes are converted into a Gaussian beam output (TEM 00 mode) to transmit power from gyrotron with minimized diffraction losses. The quasi-optical launchers are used to convert higher order modes to a Gaussian beam. The basic quasi-optical launcher consists of a Vlasov type launcher with a helical cut in a cylindrical cavity output waveguide section and a combination of profiled mirrors. The profiled mirrors are basically phase correcting mirrors, which give desired output as Gaussian beam. Fast Fourier Transform (FFT) analysis can be performed to design phase correcting mirrors for quasi-optical launcher of gyrotron. The FFT analysis is being carried to study and design of quasi-optical mirrors for matching optic unit. The simulation is done for a Gaussian beam propagating in free space. The paper discusses about the design of quasi-optical mode converter for the Gyrotron. The FFT analysis on the propagation of a gaussian beam in free space will be presented.