Design modification of millimeter wave transmission on ITER equatorial launcher

An injection antenna, so-called launcher, of millimeter wave power to plasma for the ITER (International Thermonuclear Experimental Reactor) has been designed. Two kinds of the ITER launcher, "Equatorial" and "Upper" are required and JAEA has been designing the former and developing its components. The mm-wave transmission section of the equatorial launcher originally consists of a steering mirror injecting the wave power and the waveguide transmission line. In order to increase the structure reliability and the cost reduction, the modification to a free space transmission line has been considered. Approximately half of the waveguide components are removed and a large focusing mirror is introduced instead. The mm-wave analysis for the modification shows almost no degradation of the transmission efficiency compared to the reference design. It was also verified that the heat load on the steering mirror, which was one of the critical launcher components, reduced from 3.2 MW/m² to 1.3 MW/m². The thermomechanical analysis for the mirror was also carried out and the results showed that thermal stress was reduced by ~frac12. This means that the mirror design has a large design margin and promises the possible power handling of more than 1 MW/line. In order to verify the design qualification of the launcher, th e high power RF transmission experiment of the components of the launcher, such as the mirrors and the waveguides components, based on the design modification described above will be carried out and the results will be reported at the conference.