Modelling of expected B, C, N and O Lyman-α line intensities emitted from W7-X plasmas and measured by means of the W7-X light impurity monitor system

Abstract

The “C/O Monitor” for Wendelstein 7-X (W7-X) is a dedicated light impurity XUV spectrometer intended to measure Lyman-α transitions of hydrogen-like ions of four low-Z impurities—boron (4.9 nm), carbon (3.4 nm), nitrogen (2.5 nm) and oxygen (1.9 nm). Since the discussed diagnostic will deliver continuous information about the line intensities, it is crucial to understand the origin of the obtained signals with respect to the experimental plasma conditions (electron temperature and density). This, however, might be difficult because of the broad acceptance angle of the spectrometer and irregular shape of the plasma edge or SOL where the radiation is expected to mostly come from, depending on the plasma temperature. For that reason, numerous analyses assuming various ranges of electron density and temperature profiles of the W7-X plasmas have been performed (assuming corona equilibrium and neglecting impurity transport processes). The aim of this work is to estimate the expected radiant flux and determine the sensitivity of the system on impurity-level changes. It will allow to improve understanding between measured signal and impurity concentration.