Quasi-Optical Beam Analysis Based on Direct Phase Measurement at Low Power Level

Abstract

Alignments of the beam size and position, and the tilt of the propagation axis, have been pointed out to be important in transmission lines for Electron Cyclotron Heating in order to achieve high transmission efficiency. Beam size evolution along the propagation of a Gaussian-like beam, and its beam tilt are analyzed with a quasi-optical moment theory by using measured intensity and phase patterns at a low power level. The Gaussian-like beam is coupled into a corrugated waveguide in the tilted injection. The desired Gaussian content after the coupling is also evaluated in terms of the measured phase as well as the intensity. It is indicated that the direct phase measurements are essential to evaluate the beam size evolution along the propagation, the tilt angle, and the Gaussian content of the beam, which are key issues in the alignment problem.