Pedestal fluctuation measurements with charge exchange imaging at the DIII-D tokamak

Journal Article · 01 November 2022 · Review of Scientific Instruments

DOI: https://doi.org/10.1063/5.0101844 · OSTI ID:1972712

Major, M. R.  ^[1]; McKee, G. R.  ^[1]; Geiger, B. ^[1]; Hartog, D. Den ^[1]; Jaehnig, K. ^[1]; Seyfert, C. ^[1]; Smith, D. R.  ^[1]; Stewart, S. D.  ^[1]; Yan, Z. ^[1]

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1. Univ. of Wisconsin, Madison, WI (United States)

A new high radial resolution 2D multichannel Charge eXchange Imaging (CXI) diagnostic is under development for deployment at DIII-D. Here, the diagnostic system will measure low-to-intermediate radial wavenumber carbon density fluctuations by observing the n = 8 – 7 (λ = 529.06 nm) C-VI emission line, resulting from charge exchange collisions between heating neutral beam atoms and the intrinsic carbon ion density. The new CXI diagnostic will provide measurements with ΔR ~ 0.4 cm to access higher k_r instabilities (k_r < 8 cm^–1) predicted to arise in the steep-gradient region of the H-mode pedestal. The CXI system will feature 60 fiber bundles in a 12 × 5 arrangement, with each bundle consisting of four 1 mm fibers. A custom optical system has been designed to filter and image incoming signals onto an 8 × 8 avalanche photodiode array. Additionally, a novel electronics suite has been designed and commissioned to amplify and digitize the relatively low-intensity carbon signal at a 2 MHz bandwidth. Forward modeling results of the active C-VI emission suggest sufficient signal to noise ratios to resolve turbulent fluctuations. Prototype measurements demonstrate the ability to perform high frequency pedestal measurements.

• Research Organization: General Atomics, San Diego, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Fusion Energy Sciences (FES)
• Grant/Contract Number: FC02-04ER54698; FG02-08ER54999
• OSTI ID: 1972712
• Alternate ID(s): OSTI ID: 1896320
• Journal Information: Review of Scientific Instruments, Vol. 93, Issue 11; ISSN 0034-6748
• Publisher: American Institute of Physics (AIP)Copyright Statement
• Country of Publication: United States
• Language: English