Design and measuring performance of the ITER plasma position reflectometer in-port-plug antennas

Abstract

Design parameters of the ITER Plasma Position Reflectometer (PPR) in-port-plug antennas are determined and their measurement performance is assessed using 2D full wave analysis. Two ITER scenarios were selected in order to determine the optimum antenna position and orientation, namely the ITER QDT = 10 baseline scenario (15 MA) and the low density one planned for the initial non-active phase at 7.5 MA. Using them to feed a 3D ray tracing code, the spatial position and optimum orientation angles of each set of emission and detection antennas were determined. Additionally, a far field analysis of the launching radiation patterns led to the definition of the antenna dimensions in terms of optimal power coupling. After this preliminary work, 2D full wave simulations using a finite difference time domain (FDTD) code were carried out to assess the measurement performance of the system. To this end, the detected wave amplitudes and phases were evaluated for each scenario and two models of the scrape-off layer (SOL) density profiles. By calculating the spectrogram of the complex amplitude of the detected wave, the reconstruction of the plasma density profile can be made and be directly compared with the input profiles. As a result from this synthetic diagnostic analysis, an estimation of the error in the determination of the last closed flux surface position was possible.