Development of an 11-channel multi wavelength imaging diagnostic for divertor plasmas in MAST Upgrade.

X Feng,J R Harrison,J S Allcock,W A J Vijvers,Y Andrebe,R T Mumgaard,A Calcines,B Lipschultz,Mast-U Team ,R M Sharples,A Perek,B P Duval,Eurofusion Mst1 Team

doi:10.1063/5.0043533

Abstract

Divertor detachment and alternative divertor magnetic geometries are predicted to be promising approaches to handle the power exhaust of future fusion devices. In order to understand the detachment process caused by volumetric losses in alternative divertor magnetic geometries, a Multi-Wavelength Imaging (MWI) diagnostic has recently been designed and built for the Mega Amp Spherical Tokamak Upgrade. The MWI diagnostic will simultaneously capture 11 spectrally filtered images of the visible light emitted from divertor plasmas and provide crucial knowledge for the interpretation of observations and modeling efforts. This paper presents the optical design, mechanical design, hardware, and test results of an 11-channel MWI system with a field of view of 40°. The optical design shows better than 5mm FWHM spatial resolution at the plasma on all 11 channels across the whole field of view. The spread of angle of incidence on the surface of each filter is also analyzed to inform the bandwidth specification of the interference filters. The results of the initial laboratory tests demonstrate that a spatial resolution of better than 5mm FWHM is achieved for all 11 channels, meeting the specifications required for accurate tomography.

Highlights

INTRODUCTIONLines and helium singlet and triplet lines. The inferred 2D map of plasma parameters, combined with localized measurements from Langmuir probes/Thomson scattering systems and 1D emission-weighted plasma profiles from spectroscopy, will provide crucial knowledge for the interpretation of observations
(Presented XXXXX; received XXXXX; accepted XXXXX; published online XXXXX) Divertor detachment and alternative divertor magnetic geometries are predicted to be promising approaches to handle the power exhaust of future fusion devices
It can be seen that the spatial resolution from Channel 4 onwards at full aperture will be larger than our requirement, but that stopping down the lens to f/2.8 could improve the image quality to make it less than 5mm FWHM over the whole field of view

Summary

INTRODUCTION

Lines and helium singlet and triplet lines. The inferred 2D map of plasma parameters, combined with localized measurements from Langmuir probes/Thomson scattering systems and 1D emission-weighted plasma profiles from spectroscopy, will provide crucial knowledge for the interpretation of observations. The bottom panel in figure 2 shows that the image quality deteriorates with channel number as expected due to the effect of additional optics for both wavelengths, and the image quality after the third channel does not meet our requirement For this analysis, the paraxial lens in front of the detector has the same aperture stop setting for all the channels and is equal to the maximum lens aperture. It can be seen that the spatial resolution from Channel 4 onwards at full aperture will be larger than our requirement, but that stopping down the lens to f/2.8 could improve the image quality to make it less than 5mm FWHM over the whole field of view. FIG. 4. 2D distribution of angle of incidence (degrees) on the filter surface in odd channels

MECHANICAL DESIGN OF THE MWI SYSTEM

HARDWARE

SYSTEM PERFORMANCE

SUMMARY