Ultra-fast charge exchange spectroscopy for turbulent ion temperature fluctuation measurements on the DIII-D tokamak (invited)

Journal Article · Mon Oct 15 00:00:00 EDT 2012 · Review of Scientific Instruments

DOI:https://doi.org/10.1063/1.4733548· OSTI ID:22093836

Uzun-Kaymak, I. U.; Fonck, R. J.; McKee, G. R. ^[1]

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1. Department of Engineering Physics, University of Wisconsin, Madison, Wisconsin 53706 (United States)

A novel two-channel, high throughput, high efficiency spectrometer system has been developed to measure impurity ion temperature and toroidal velocity fluctuations associated with long-wavelength turbulence and other plasma instabilities. The spectrometer observes the emission of the n= 8-7 hydrogenic transition of C{sup +5} ions ({lambda}{sub air}= 529.06 nm) resulting from charge exchange reactions between deuterium heating beams and intrinsic carbon. Novel features include a large, prism-coupled high-dispersion, volume-phase-holographic transmission grating and high-quantum efficiency, high-gain, low-noise avalanche photodiode detectors that sample emission at 1 MHz. This new diagnostic offers an order-of-magnitude increase in sensitivity compared to earlier ion thermal turbulence measurements. Increased sensitivity is crucial for obtaining enough photon statistics from plasmas with much less impurity content. The irreducible noise floor set by photon statistics sets the ultimate sensitivity to plasma fluctuations. Based on the measured photon flux levels for the entire spectral line, photon noise levels for T(tilde sign){sub i}/T{sub i} and V(tilde sign){sub i}/V{sub i} of {approx}1% are expected, while statistical averaging over long data records enables reduction in the detectable plasma fluctuation levels to values less than that. Broadband ion temperature fluctuations are observed to near 200 kHz in an L-mode discharge. Cross-correlation with the local beam emission spectroscopy measurements demonstrates a strong coupling of the density and temperature fields, and enables the cross-phase measurements between density and ion temperature fluctuations.

• OSTI ID: 22093836
• Journal Information: Review of Scientific Instruments, Vol. 83, Issue 10; Other Information: (c) 2012 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0034-6748
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
CARBON IONS
CHARGE EXCHANGE
CHARGE-EXCHANGE REACTIONS
DOUBLET-3 DEVICE
ELECTRON TEMPERATURE
ION TEMPERATURE
L-MODE PLASMA CONFINEMENT
PLASMA DIAGNOSTICS
PLASMA IMPURITIES
PLASMA INSTABILITY
QUANTUM EFFICIENCY
SENSITIVITY
SPECTROMETERS
SPECTROSCOPY
STRONG-COUPLING MODEL
TEMPERATURE MEASUREMENT
WAVELENGTHS