A correlation electron cyclotron emission diagnostic and the importance of multifield fluctuation measurements for testing nonlinear gyrokinetic turbulence simulations

Journal Article · Wed Oct 15 00:00:00 EDT 2008 · Review of Scientific Instruments

DOI:https://doi.org/10.1063/1.2981186· OSTI ID:21266451

White, A E; Schmitz, L; Peebles, W A; Carter, T A; Rhodes, T L; Doyle, E J; Gourdain, P A; Hillesheim, J C; Wang, G ^[1]; Holland, C; Tynan, G R ^[2]; Austin, M E ^[3]; McKee, G R; Shafer, M W ^[4]; Burrell, K H; Candy, J; DeBoo, J C; Prater, R; Staebler, G M; Waltz, R E ^[5]

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1. University of California-Los Angeles, Los Angeles, California 90095 (United States)
2. University of California-San Diego, 9500 Gilman Dr, La Jolla, California 92093 (United States)
3. University of Texas-Austin, Austin, Texas 78712 (United States)
4. University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States)
5. General Atomics, P.O. Box 85608, San Diego, California 92186-5608 (United States)

A correlation electron cyclotron emission (CECE) diagnostic has been used to measure local, turbulent fluctuations of the electron temperature in the core of DIII-D plasmas. This paper describes the hardware and testing of the CECE diagnostic and highlights the importance of measurements of multifield fluctuation profiles for the testing and validation of nonlinear gyrokinetic codes. The process of testing and validating such codes is critical for extrapolation to next-step fusion devices. For the first time, the radial profiles of electron temperature and density fluctuations are compared to nonlinear gyrokinetic simulations. The CECE diagnostic at DIII-D uses correlation radiometry to measure the rms amplitude and spectrum of the electron temperature fluctuations. Gaussian optics are used to produce a poloidal spot size with w{sub o}{approx}1.75 cm in the plasma. The intermediate frequency filters and the natural linewidth of the EC emission determine the radial resolution of the CECE diagnostic, which can be less than 1 cm. Wavenumbers resolved by the CECE diagnostic are k{sub {theta}}{<=}1.8 cm{sup -1} and k{sub r}{<=}4 cm{sup -1}, relevant for studies of long-wavelength turbulence associated with the trapped electron mode and the ion temperature gradient mode. In neutral beam heated L-mode plasmas, core electron temperature fluctuations in the region 0.5<r/a<0.9, increase with radius from {approx}0.5% to {approx}2%, similar to density fluctuations that are measured simultaneously with beam emission spectroscopy. After incorporating 'synthetic diagnostics' to effectively filter the code output, the simulations reproduce the characteristics of the turbulence and transport at one radial location r/a=0.5, but not at a second location, r/a=0.75. These results illustrate that measurements of the profiles of multiple fluctuating fields can provide a significant constraint on the turbulence models employed by the code.

• OSTI ID: 21266451
• Journal Information: Review of Scientific Instruments, Vol. 79, Issue 10; Other Information: DOI: 10.1063/1.2981186; (c) 2008 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
CORRELATIONS
CYCLOTRONS
DOUBLET-3 DEVICE
ELECTRON TEMPERATURE
EMISSION
EMISSION SPECTROSCOPY
EXTRAPOLATION
FLUCTUATIONS
ION TEMPERATURE
L-MODE PLASMA CONFINEMENT
NONLINEAR PROBLEMS
PLASMA
PLASMA DENSITY
PLASMA SIMULATION
TRAPPED ELECTRONS
TURBULENCE
VALIDATION