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2D measurements of plasma electron density using coherence imaging with a pixelated phase mask

Allcock, J.S. and Silburn, S.A. and Sharples, R.M. and Harrison, J.R. and Conway, N.J. and Vernimmen, J.W.M. (2021) '2D measurements of plasma electron density using coherence imaging with a pixelated phase mask.', Review of Scientific Instruments, 92 (7). 073506.

Abstract

In this paper, the pixelated phase mask (PPM) method of interferometry is applied to coherence imaging (CI)—a passive, narrowband spectral imaging technique for diagnosing the edge and divertor regions of fusion plasma experiments. Compared to previous CI designs that use a linear phase mask, the PPM method allows for a higher possible spatial resolution. The PPM method is also observed to give a higher instrument contrast (analogous to a more narrow spectrometer instrument function). A single-delay PPM instrument is introduced as well as a multi-delay system that uses a combination of both pixelated and linear phase masks to encode the coherence of the observed radiation at four different interferometer delays simultaneously. The new methods are demonstrated with measurements of electron density ne, via Stark broadening of the Hγ emission line at 434.0 nm, made on the Magnum-PSI linear plasma experiment. A comparison of the Abel-inverted multi-delay CI measurements with Thomson scattering shows agreement across the 3 × 1019 < ne < 1 × 1021 m−3 range. For the single-delay CI results, agreement is found for ne > 1 × 1020 m−3 only. Accurate and independent interpretation of single-delay CI data at lower ne was not possible due to Doppler broadening and continuum emission.

Item Type:Article
Full text:(AM) Accepted Manuscript
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Status:Peer-reviewed
Publisher Web site:https://doi.org/10.1063/5.0050704
Publisher statement:This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in (citation of published article) and may be found at https://doi.org/10.1063/5.0050704
Date accepted:30 June 2021
Date deposited:27 October 2021
Date of first online publication:16 July 2021
Date first made open access:27 October 2021

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