Infrared Measurements of the RF Output of 170-GHz/2-MW Coaxial Cavity Gyrotron and Its Phase Retrieval Analysis

We report the experimental results of the infrared measurements of output RF beam of the European 2-MW 170-GHz coaxial cavity gyrotron for ITER. The output beam profile is measured by the infrared thermographic technique using an infrared camera and a target material which is being irradiated by the RF output. The beam intensity was measured at several locations along the propagation direction. The data were processed for noise reduction and perspective correction and then used with the phase retrieval algorithm to yield an accurate estimate of the phase profile. The moments of the measured intensity arrays are calculated to improve the reliability of the measured infrared image data and data processing. The beam profile is also measured at specific locations in order to compare the phase calculated with the Huygens–Fresnel propagation method for fixed distance and Rayleigh–Sommerfeld diffraction integral method used for field propagation in the phase retrieval algorithm.