High-resolution spectroscopic diagnostic for divertor and scrape-off layer neutral and impurity emission measurements in the National Spherical Torus Experiment

Abstract

The National Spherical Torus Experiment boundary physics program presently focuses on edge power and particle flow optimization and control in β⩾25% long pulse L- and H-mode plasmas with high harmonic fast wave heating power up to 6 MW and neutral beam injection power up to 5 MW, with the emphasis on the edge physics implications resulting from the low aspect ratio geometry. To address the particle flux measurements in the divertor and plasma scrape-off layer (SOL), two spectrally filtered one-dimensional charge coupled device cameras have been fielded. The cameras utilize 2048 pixel 12-bit Dalsa CL-C6 arrays, f=85 mm lenses, and Δλ=1.5 nm bandpass interference filters. Both cameras provide mm spatial resolution, sub-ms temporal resolution and are spatially and photometrically calibrated. Midplane SOL and divertor brightness profiles of C III and deuterium species have been obtained in the L- and H-mode phases of center stack limited and diverted plasmas. The equilibria reconstructed by the EFIT code are found in agreement with the optical and infra-red measurements. In–out asymmetries in divertor recycling and carbon fluxes have been observed in L- and H-mode plasmas. The analysis of neutral recycling and impurity fluxes using the two-dimensional multifluid code UEDGE is in progress.