Preliminary assessment of ex-vessel waveguides for the ITER Plasma Position Reflectometer

Abstract

This work describes the preliminary assessment of the different waveguide technologies for the ex-vessel transmission lines of the Plasma Position Reflectometer (PPR) in ITER. Using the available layout information at the initial stage of the PPR design, several waveguide dimensions of both rectangular waveguide and circular corrugated waveguides were evaluated; namely WR137, WR187, WR284, WR340 and WR430 in case of rectangular waveguides and 31.75mm, 63.5mm, 76.2mm and 88.9mm diameters for circular corrugated waveguides. In order to narrow the selection, an initial study was performed using available results from literature to obtain ohmic losses and mode conversion in mitre bends. Once the possibilities were trimmed, a final estimation was made using rigorous codes for the ohmic and mitre bend losses, also adding losses in waveguide gaps, on the selected candidates. This process led to the final estimation of performance for the preliminary routing of the PPR ex-vessel transmission lines. The chosen solution was 88.9mm internal diameter circular corrugated waveguide, as the best compromise between in-band performance and space constraints.