Monitoring the Impurity Influx into Plasma Using HA&VS Diagnostic in the New ITER Baseline with a Tungsten Wall

Abstract

The problem of monitoring the impurity influx into the plasma is examined within the framework of a new baseline of ITER operation with a tungsten first wall. Replacing beryllium with tungsten increases a resistance of the wall to thermal loads and erosion but creates a risk of plasma contamination by a heavy impurity (tungsten) and complicates the pumping-out of light impurities. To solve these problems in ITER, the periodic wall boronization is proposed. A special attention is paid to the analysis of capabilities of H-alpha and Visible Spectroscopy (HA&VS) diagnostic to perform monitoring the impurities, primarily boron and tungsten, in the edge plasma layer (SOL) under the new ITER operational baseline. A list of spectral lines for recording the radiation from boron atoms and ions, as well as tungsten, is proposed. Furthermore, potential issues, such as the divertor stray light and the overlapping of spectral lines from different elements, are discussed. Using the numerical modeling (BM1D2V, SDTrimSP, SOLPS, and WallDYN3D codes), flux densities of the boron and tungsten atoms from the first wall due to sputtering by the deuterium atoms and ions were estimated for two characteristic divertor operating regimes. It is shown that the protective boron layer effectively shields the tungsten wall from an erosion but leads to the significant boron influx into the plasma. For radiation intensity calculation on HA&VS diagnostic cameras the Raysect and Cherab libraries were used. The calculations of radiation intensity on the selected spectral lines of boron demonstrate the feasibility of their recording by the HA&VS system and emphasize the importance of taking into account the wall reflectivity for the accurate signal interpretation.