Electromagnetic analysis of beams for the ITER ECH Upper Launcher

Abstract

Four Electron Cyclotron Upper Launchers (UL) will be used in ITER to inject power at 170 GHz, mainly for suppression of MHD instabilities, especially Neoclassical Tearing Modes. For each UL, the quasi-optical section injecting millimetre waves into the plasma consists of eight beams divided in two rows (upper and lower) reflecting on three fixed mirrors and a steering one. In this work a simplified model of the launcher was simulated with GRASP, a commercial antenna package, in order to follow the evolution of the nominal HE11 beams through the launcher, map them on all the mirrors and calculate the spillover loss. The impact of the addition of spurious LP11 mode up to 15% of total power has also been assessed, resulting in the worst case in a total spillover loss of 2.1%, compliant with the 97% requirement of transmission efficiency of each upper launcher's beam. The first-pass distribution of the stray radiation has been mapped on about 1/3 of the simplified model of the UL, evaluating also the peak (maximum 1.9 MW/m 2 per MW input power besides mirror M2) and average incident and absorbed power (maximum 5.8 kW/m 2 per MW input power for copper coated walls, behind mirror M4).