Concepts and Requirements for ITER X-Ray Diagnostics

Abstract

X-ray diagnostics are used on present-day tokamaks to measure a variety of plasma parameters. 1,2 Some x-ray diagnostics are not directly adaptable to ITER because of the high sensitivity of the detectors to noise and damage induced by the radiation background from fusion neutrons.3,4 Those diagnostics which use compact, highly efficient solid-state detectors are particularly vulnerable. This work addresses mainly the issues involved in adapting a subset of the existing x-ray instrumentation to ITER, mainly by use of additional x-ray optics to deflect the x-ray beam out of the path of the neutron beam. 5,6,7 The topics discussed will be the required x-ray intensities and energy ranges, the necessary reduction in radiation background, and the x-ray optics and geometries best suited to accomplishing these requirements. Preliminary work on this subject appears in Refs. 5–7. We will be focusing on the x-ray energy range around 5 – 40 keV, and somewhat higher in some cases. The main diagnostics discussed are the XIS (X-Ray Imaging System) or SX arrays, the broad-band PHA (Pulse-Height-Analyzer) continuum and line measurement spectrometer, and the high energy resolution XCS (X-ray Crystal Spectrometer). 2 Other diagnostics suitable for ITER have been discussed by Barnsley. 8,9