Quasi-optical 140 GHz ECRH system on the advanced W VII-AS stellarator

A design is presented of a 140 GHz 2nd harmonic electron cyclotron resonance heating (ECRH) system to be used on the advanced stellarator W VII‐AS at IPP Garching. The primary objectives of these ECRH experiments will be (1) to extend the density range for ECRH and for combined heating (NBI and/or ICRH), (2) to investigate the local electron heat transport in high density plasmas by the heat‐wave technique, (3) to develop new millimeter‐wave transmission line concepts and antenna systems for reactor‐compatible multi‐megawatt heating of future large‐size stellarators. The planned 140 GHz ECRH facility will use a 200 kW/100 to 200 ms TEO3‐mode gyrotron from KfK Karlsruhe combined with a quasi‐optical fundamental Gaussian‐mode transmission system employing focusing metallic mirrors as phase correcting elements. The unpolarized gyrotron output mode will be converted directly into the linearly polarized Gaussian free‐space beam with the help of a quasi‐optical coupler. A universal quasi‐optical polarizer will ...