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

Allcock, J.S.; Silburn, S.A.; Sharples, R.M.; Harrison, J.R.; Conway, N.J.; Vernimmen, J.W.M.

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.

Citation

Allcock, J., Silburn, S., Sharples, R., Harrison, J., Conway, N., & Vernimmen, J. (2021). 2D measurements of plasma electron density using coherence imaging with a pixelated phase mask. Review of Scientific Instruments, 92(7), Article 073506. https://doi.org/10.1063/5.0050704

• Journal Article Type: Article
• Acceptance Date: Jun 30, 2021
• Online Publication Date: Jul 16, 2021
• Publication Date: 2021-07
• Deposit Date: Oct 26, 2021
• Publicly Available Date: Oct 27, 2021
• Journal: Review of Scientific Instruments
• Print ISSN: 0034-6748
• Electronic ISSN: 1089-7623
• Publisher: American Institute of Physics
• Peer Reviewed: Peer Reviewed
• Volume: 92
• Issue: 7
• Article Number: 073506
• DOI: https://doi.org/10.1063/5.0050704
• Public URL: https://durham-repository.worktribe.com/output/1228275