Measurement of local, internal magnetic fluctuations via cross-polarization scattering in the DIII-D tokamak (invited)

Journal Article · Tue Nov 15 00:00:00 EST 2016 · Review of Scientific Instruments

DOI:https://doi.org/10.1063/1.4960154· OSTI ID:22596471

Rhodes, T. L.; Crocker, N. A.; Peebles, W. A. ^[1]

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1. University of California-Los Angeles, P.O. Box 957099, Los Angeles, California 90095 (United States)

We present new measurements of internal magnetic fluctuations obtained with a novel eight channel cross polarization scattering (CPS) system installed on the DIII-D tokamak. Measurements of internal, localized magnetic fluctuations provide a window on an important physics quantity that we heretofore have had little information on. Importantly, these measurements provide a new ability to challenge and test linear and nonlinear simulations and basic theory. The CPS method, based upon the scattering of an incident microwave beam into the opposite polarization by magnetic fluctuations, has been significantly extended and improved over the method as originally developed on the Tore Supra tokamak. A new scattering geometry, provided by a unique probe beam, is utilized to improve the spatial localization and wavenumber range. Remotely controllable polarizer and mirror angles allow polarization matching and wavenumber selection for a range of plasma conditions. The quasi-optical system design, its advantages and challenges, as well as important physics validation tests are presented and discussed. Effect of plasma beta (ratio of kinetic to magnetic pressure) on both density and magnetic fluctuations is studied and it is observed that internal magnetic fluctuations increase with beta. During certain quiescent high confinement operational regimes, coherent low frequency modes not detected by magnetic probes are detected locally by CPS diagnostics.

• OSTI ID: 22596471
• Journal Information: Review of Scientific Instruments, Vol. 87, Issue 11; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA); ISSN 0034-6748
• Country of Publication: United States
• Language: English

Related Subjects

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
BEAMS
DENSITY
DOUBLET-3 DEVICE
FLUCTUATIONS
GEOMETRY
MAGNETIC PROBES
MICROWAVE RADIATION
MIRRORS
NONLINEAR PROBLEMS
OPTICAL SYSTEMS
PLASMA
POLARIZATION
SCATTERING
TORE SUPRA TOKAMAK
VALIDATION
WINDOWS