Title: Ion temperature and rotation fluctuation measurements with ultra-fast charge exchange recombination spectroscopy (UF-CHERS) in the DIII-D tokamak

Abstract

An upgraded detector and several optimizations have significantly improved the Ultra-Fast Charge Exchange Recombination Spectroscopy (UF-CHERS) diagnostic sensitivity to ion temperature and parallel velocity fluctuations at turbulence relevant spatio-temporal scales. Normalized broadband ion temperature and parallel velocity fluctuations down to x̃x∼1% (x = Ti, v∥) and up to ∼450 kHz have been measured in a variety of plasmas. The multi-field nature of the CHERS technique also allows measurements of the cross-phase angles of the fluctuating fields. UF-CHERS is optimized to observe emissions from the electron exchange reaction between intrinsic C6+ and hydrogenic neutral beam injected particles near 529 nm. UF-CHERS consists of two chords separated by ∼1 cm radially, less than the turbulence correlation length in DIII-D plasmas, which enables correlated measurements to suppress incoherent electronic and photon noise. The optical components of the spectrometer include a volume-phase-holographic grating with >90% transmission between 528 and 530 nm and f/2 200-mm lenses, selected to maximize the optical efficiency and photon flux. Diffracted light from each chord is collected in eight spectral bins, each with a bandwidth of ∼0.25 nm, and detected and amplified by chilled avalanche photodiodes and custom high-gain, wide bandwidth low-noise preamplifiers to achieve the optimal signal-to-noise ratio. The resulting signals are digitizedmore » at 1 MHz, 103–104× faster than the conventional CHERS diagnostics. Spatial coverage is achieved by repositioning a motorized fiber tray between plasmas. UF-CHERS measurements will advance the understanding of turbulent ion transport and contribute to the validation of transport models and simulations.« less

Authors:

Truong, D. D. ;

• Search DOE PAGES for author "Truong, D. D."
• Search DOE PAGES for ORCID "0000-0002-8573-2539"

McKee, G. R. ;

• Search DOE PAGES for author "McKee, G. R."
• Search DOE PAGES for ORCID "0000-0002-2754-9816"

Yan, Z.; Jaehnig, K.; Winz, G. R. ;

• Search DOE PAGES for author "Winz, G. R."
• Search DOE PAGES for ORCID "0000-0001-7762-7184"

Fonck, R. J. ;

• Search DOE PAGES for author "Fonck, R. J."
• Search DOE PAGES for ORCID "0000-0002-9438-6762"

Geiger, B.

Publication Date:

Wed May 05 00:00:00 EDT 2021

Sponsoring Org.:

USDOE

OSTI Identifier:

1781877

Grant/Contract Number:  

FC02-04ER54698; FG02-08ER54999; FG02-89ER53296

Resource Type:

Publisher's Accepted Manuscript

Journal Name:

Review of Scientific Instruments

Additional Journal Information:

Journal Name: Review of Scientific Instruments Journal Volume: 92 Journal Issue: 5; Journal ID: ISSN 0034-6748

Publisher:

American Institute of Physics

Country of Publication:

United States

Language:

English