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Title: Multi-field characteristics and eigenmode spatial structure of geodesic acoustic modes in DIII-D L-mode plasmas

The geodesic acoustic mode (GAM), a coherent form of the zonal flow, plays a critical role in turbulence regulation and cross-magnetic-field transport. In the DIII-D tokamak, unique information on multi-field characteristics and radial structure of eigenmode GAMs has been measured. Two simultaneous and distinct, radially overlapping eigenmode GAMs (i.e., constant frequency vs. radius) have been observed in the poloidal E×B flow in L-mode plasmas. As the plasma transitions from an L-mode to an Ohmic regime, one of these eigenmode GAMs becomes a continuum GAM (frequency responds to local parameters), while the second decays below the noise level. The eigenmode GAMs occupy a radial range of ρ = 0.6–0.8 and 0.75–0.95, respectively. In addition, oscillations at the GAM frequency are observed for the first time in multiple plasma parameters, including n{sub e}, T{sub e}, and B{sub θ}. The magnitude of T(tilde sign){sub e}/T{sub e} at the GAM frequency (the magnitude is similar to that of ñ{sub e}/n{sub e}) and measured n{sub e}–T{sub e} cross-phase (∼140° at the GAM frequency) together indicate that the GAM pressure perturbation is not determined solely by ñ{sub e}. The magnetic GAM behavior, a feature only rarely reported, is significantly stronger (×18) on the high-field side ofmore » the tokamak, suggesting an anti-ballooning nature. Finally, the GAM is also observed to directly modify intermediate-wavenumber ñ{sub e} levels (kρ{sub s} ∼ 1.1). The simultaneous temperature, density, flow fluctuations, density-temperature cross-phase, and magnetic behavior present a new perspective on the underlying physics of the GAM.« less
Authors:
; ; ; ; ; ;  [1] ;  [2] ; ;  [3] ; ; ; ; ; ; ;  [4] ;  [5]
  1. Physics and Astronomy Department and PSTI, University of California, Los Angeles, California 90095 (United States)
  2. University of Texas, Austin, Texas 78712 (United States)
  3. Department of Engineering Physics, University of Wisconsin, Madison, Wisconsin 53706 (United States)
  4. General Atomics, P.O. Box 85608, San Diego, California 92186-5608 (United States)
  5. Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States)
Publication Date:
OSTI Identifier:
22220602
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 20; Journal Issue: 9; Other Information: (c) 2013 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; BALLOONING INSTABILITY; DOUBLET-3 DEVICE; ELECTRON TEMPERATURE; ION ACOUSTIC WAVES; ION TEMPERATURE; L-MODE PLASMA CONFINEMENT; MAGNETIC FIELDS; PERTURBATION THEORY; PLASMA DENSITY; PLASMA PRESSURE; TURBULENCE