Doppler-shift compensated spatial heterodyne spectroscopy for rapidly moving sources

High resolution luminosity product measurements of neutral beam emission in magnetized plasmas are severely limited by the artificial Doppler broadening inherent to the use of large diameter collection optics. In this paper, a broadening compensation method is developed for the spatial heterodyne spectroscopy interferometric technique. The compensation technique greatly reduces the artificial broadening, thereby enabling high resolution measurements at a significantly higher photon flux than previously available. Compensated and uncompensated measurements of emission generated by impact excitation of 61 keV deuterium neutrals in a tokamak plasma at the DIII-D National Fusion Facility are presented. The spectral width of the compensated measurement is similar to 0.13 nm, which is comparable to the instrument resolution. This width is similar to 4x smaller than the uncompensated width, which for the 20 cm diameter collection lens system utilized in this study is similar to 0.5 nm. (C) 2021 Optical Society of America

Automated summary

A broadening compensation method was developed for spatial heterodyne spectroscopy interferometric technique to reduce artificial broadening and enable high resolution measurements at a significantly higher photon flux. The compensated measurement of emission from deuterium neutrals in a tokamak plasma showed a spectral width of about 0.13 nm, 4 times smaller than the uncompensated width of 0.5 nm.