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

Rev Sci Instrum

General Atomics, San Diego, California 92186-5608, USA.

Published: November 2022

Collective Thomson scattering (CTS) is a diagnostic method that measures the ion velocity distribution of a plasma. CO 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 CO laser with a pulse energy of 160 mJ at λ = 10.59 µm.

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http://dx.doi.org/10.1063/5.0101407DOI Listing

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