Assessment of neutral particle analysis abilities to measure the plasma hydrogen isotope composition in ITER burning scenarios

Abstract

The main object of the neutral particle analysis (NPA) on ITER is to measure the hydrogen isotope composition of the plasma using measurements of the neutralized fluxes of the corresponding hydrogen ions. In burning scenarios the reliable on-line measurements of the tritium/deuterium (T/D) density ratio stands out as the most important application of the diagnostics. This paper presents the results of the error analysis of the NPA signals for ‘official’ ITER burning scenarios—inductive and steady state. The goal of the study is to find the range of values of T/D density ratio, where NPA measurements meet the ITER requirements specified for this parameter, i.e. 10% of accuracy and time resolution equal to 0.1 s. This analysis takes into account both the statistics of the particle counts detected by NPA and of the noise counts induced in NPA detectors by neutrons and gammas. The calibration errors and errors of the external plasma parameters, used in the interpretation of NPA data, are also accounted. The results of the study for low (20–200 keV) and high (200 keV–2 MeV) energy ranges of the D and T neutral fluxes are discussed. It was shown that in the inductive scenario NPA can provide the required accuracy of the T/D density ratio measurement if the plasma composition varies within 0.2–10 (edge measurements) and 0.15–10 (core measurements). In the steady-state scenario these ranges are 0.01–10 (edge measurements) and 0.07–7 (core measurements).