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 HuygensFresnel propagation method for fixed distance and RayleighSommerfeld diffraction integral method used for field propagation in the phase retrieval algorithm

Automated Generation of High-Order Modes for Tests of Quasi-Optical Systems of Gyrotrons for W7-X Stellarator

A test system for the verification of the quasi-optical converter system is vital in the gyrotron development. For this reason, an automated measurement setup has been developed and is benchmarked with the TE$_{28,8}$ mode operating in the cavities of the gyrotrons of W7-X with a high purity of about 95 % and a counter-rotating amount of about 0.3 %. The time duration for the mode generator adjustment has been reduced to two days for this mode. After a successful mode excitation, the quasi-optical mode converter, consisting of a launcher and three mirrors, is measured having a vectorial Gaussian mode content of 97 %

Experimental Testing of the European TH1509U 170-GHz 1-MW CW Industrial Gyrotron – Long Pulse Operation

The upgraded European 1-MW, 170-GHz continuous wave (CW) industrial prototype gyrotron (TH1509U) for electron cyclotron resonance heating and current drive in ITER was tested at the Karlsruhe Institute of Technology (KIT). In this work, we report on the major achievements during the experimental campaigns that took place intermittently between October 2020 and July 2021. The upgraded gyrotron clearly surpassed the performance of the previous TH1509 tube. In particular, TH1509U delivered (i) 0.9 MW in 180 s pulses (maximum possible pulse length with the KIT test stand) and (ii) more than 1 MW at a pulse length limited to 40 s, due to an unforeseen problem with the test stand cooling circuit at that time. In addition, it was possible to also demonstrate gyrotron operation at (iii) 0.5 MW in 1600 s pulses. The experiments will be continued at the FALCON test stand at the École Polytechnique Fédérale de Lausanne (EPFL)