Estimation of RF power absorption and stray distribution at plasma breakdown based on the design of ITER ECH&CD equatorial launcher

Abstract

Based on the latest optical design of ITER ECH&CD equatorial launcher, the power absorption at the plasma breakdown is evaluated with considering reflections by the 3-dimensional first wall structure. The beam diffusion is simulated by a bunch of spreading rays and the reflections on the first wall are analyzed for each ray. The power absorption is evaluated by the optical thickness when the rays pass across the resonant surface. The frequency of EC wave is 170 GHz and the density of concern is from 2.5 × 1015 m−3. As a result, at least 2 MW is absorbed out of 6.7 MW injection from the Top row in the case of fundamental O-mode injection even at the breakdown. In the case of 2nd harmonic X-mode injection, the total absorbing power is 200 kW at the electron density of 1018 m−3 and the electron temperature of 5 eV, which is proportional to the electron density and the electron temperature. It is found that a certain injection angle should be excluded in order to prevent intense stray RF injection up to 4 MW propagating toward specific ports within a few reflections.