Laboratory tests of CO2 laser collective Thomson scattering for measurements of ion temperature in the divertor

Collective Thomson scattering (CTS) is a diagnostic method that measures the ion velocity distribution of a plasma. CO2 laser CTS measurements are challenging because of the inherently small Doppler broadening and scattering signals that are difficult to detect. We implemented a heterodyne detection...

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Bibliographic Details
Published in:Review of scientific instruments 2022-11, Vol.93 (11), p.113547-113547
Main Authors: Hisakado, T. H., Akiyama, T., Carlstrom, T. N.
Format: Article
Language:English
Subjects:
Carbon dioxide
Carbon dioxide lasers
Ion temperature
Ion velocity
Laboratory tests
Lenses
Scattering angle
Scientific apparatus & instruments
Thomson scattering
Velocity distribution
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Summary:Collective Thomson scattering (CTS) is a diagnostic method that measures the ion velocity distribution of a plasma. CO2 laser CTS measurements are challenging because of the inherently small Doppler broadening and scattering signals that are difficult to detect. We implemented a heterodyne detection scheme to measure spectrum changes of less than a GHz. To maximize the collected light at small scattering angles, we designed a unique light collection approach consisting of a customized conical-shaped (axicon) lens with a hole in the center. The axicon lens is used to collect the scattered light emitted within an annular cross-section from the scattering volume while the probe beam is passed through the hole at the center of the lens. The performance of the heterodyne detection scheme and annular collection approach was demonstrated using a Transverse Excited Atmospheric pressure CO2 laser with a pulse energy of 160 mJ at λ = 10.59 µm.
ISSN:0034-6748
1089-7623
DOI:10.1063/5.0101407