Measurements of a Quasi-Optical Launcher Antenna for the 2 MW W7-X Gyrotron

The experimental verification of a quasi-optical TE28,12-mode launcher antenna for the Wendelstein 7-X (W7-X) gyrotron is presented. A step-type mode converter was used to convert the TE28,10 mode, excited in an existing mode generator to the targeted TE28,12 mode. The TE28,12 field pattern was measured with high spatial resolution, achieving a scalar mode purity of 84.6 % and a counter-rotating component below 0.2 %. The measured mode purity fits well to the theoretical design values. The launcher radiation pattern is in excellent agreement with simulation and has a scalar correlation factor of 96.4 %. These results demonstrate the reliability of the step-type mode converter. It provides a reliable and efficient method for mode conversion and preliminary launcher verification with already at KIT existing mode generators.