Design status of the in-vessel subsystem of the ITER Plasma Position Reflectometry system

Abstract

The aim of the Plasma Position Reflectometry (PPR) diagnostic is to provide the ITER Plasma Control System with real-time measurements of the edge density profile at four locations, known as gaps 3, 4, 5 and 6, which can be used to supplement the magnetic measurements of the plasma-wall gaps as well as to correct potential drifts of the magnetics during long pulses. The systems of gaps 4 and 6 will have some components inside the vacuum vessel. These components make up the PPR in-vessel subsystem and consist of: (i) the antennas, installed in small apertures between blanket modules; and (ii) waveguide components connecting the antennas to the primary confinement barriers, which form the boundary between the in-vessel and ex-vessel part of the systems. Herein, we describe the design status of the in-vessel subsystem, namely of the components already prototyped, including the most relevant results of the tests conducted to assess the EM performance of the components as well as the feasibility and quality of the manufacturing techniques. With the exception of one of the waveguide bends of gap 4, the tests show that the waveguide prototypes exhibit adequate performance, which indicates that it is possible to manufacture these components according to their technical specifications. Concerning the antennas, the tests show that both gaps should be able to achieve the target error margin of ±1 cm except in the K band, where they might face some difficulties.