High sensitivity far infrared laser diagnostics for the C-2U advanced beam-driven field-reversed configuration plasmas

• Published in: Review of scientific instruments Vol. 87; no. 11; p. 11E125
• Main Authors: Deng, B H, Beall, M, Schroeder, J, Settles, G, Feng, P, Kinley, J S, Gota, H, Thompson, M C
• Format: Journal Article
• Language: English
• Published: United States 01.11.2016
• ISSN: 1089-7623
• DOI: 10.1063/1.4959575

A high sensitivity multi-channel far infrared laser diagnostics with switchable interferometry and polarimetry operation modes for the advanced neutral beam-driven C-2U field-reversed configuration (FRC) plasmas is described. The interferometer achieved superior resolution of 1 × 10 m at >1.5 MHz bandwidth, illustrated by measurement of small amplitude high frequency fluctuations. The polarimetry achieved 0.04° instrument resolution and 0.1° actual resolution in the challenging high density gradient environment with >0.5 MHz bandwidth, making it suitable for weak internal magnetic field measurements in the C-2U plasmas, where the maximum Faraday rotation angle is less than 1°. The polarimetry resolution data is analyzed, and high resolution Faraday rotation data in C-2U is presented together with direct evidences of field reversal in FRC magnetic structure obtained for the first time by a non-perturbative method.