Abstract
Numerically optimized launchers for the quasi-optical output coupler of high power gyrotrons have been developed to provide RF beams with high Gaussian mode content. Generally, the profiles of numerically optimized launchers are quite complicated, so the improvement of their tolerance to fabrication errors is very important. In order to reduce the stray radiation generated by launchers with quite complicated wall profile, and also to reduce their sensitivity to fabrication errors, a method for the smoothing of the numerically optimized launcher wall has been developed at KIT, which is based on the spectrum reconstruction approach. As an example, a launcher designed for the KIT TE34,19-mode, 2 MW CW coaxial-cavity gyrotron has been investigated.
Highlights
Gyrotrons are used as highest-power millimetre wave sources for Electron Cyclotron Resonance Heating (ECRH) of nuclear fusion plasmas
In order to reduce the stray radiation generated by launchers with quite complicated wall profile, and to reduce their sensitivity to fabrication errors, a method for the smoothing of the numerically optimized launcher wall has been developed at KIT, which is based on the spectrum reconstruction approach
In order to smoothen the wall surface to satisfy fabrication requirements and to improve the tolerance of the launcher to fabrication errors and frequency shifts, it is very important to develop a method for smoothing of the surface of the launcher wall in the numerical synthesis procedure
Summary
Gyrotrons are used as highest-power millimetre wave sources for Electron Cyclotron Resonance Heating (ECRH) of nuclear fusion plasmas. The mirror-line launcher developed for the KIT 170 GHz 2 MW TE34,19-mode coaxial-cavity gyrotron has been investigated with and without wall smoothing in terms of the spectrum reconstruction method. From the experimental results one can see that the Gaussian mode content of the RF beam is slightly decreased when the wall surface is smoothed based on the spectrum reconstruction method, the stray radiation can be obviously reduced. In the numerical synthesis procedure for the mirror-line launcher of the coaxial-cavity gyrotron, the wall perturbations were iteratively checked and modified by linear interpolation, so that the curvature radius at each mesh point should be larger than the minimum allowable curvature radius of 5 mm according to the tool used to machine the launcher. The high power measurement results reveal that the Gaussian mode
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