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Multi-field characteristics and eigenmode spatial structure of geodesic acoustic modes in DIII-D L-mode plasmas.
- Source :
-
Physics of Plasmas . Sep2013, Vol. 20 Issue 9, p092501. 10p. - Publication Year :
- 2013
-
Abstract
- 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 ne, Te, and Bθ. The magnitude of Te/Te at the GAM frequency (the magnitude is similar to that of ñe/ne) and measured ne-Te cross-phase (∼140° at the GAM frequency) together indicate that the GAM pressure perturbation is not determined solely by ñe. The magnetic GAM behavior, a feature only rarely reported, is significantly stronger (×18) on the high-field side of the tokamak, suggesting an anti-ballooning nature. Finally, the GAM is also observed to directly modify intermediate-wavenumber ñe levels (kρs ∼ 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. [ABSTRACT FROM AUTHOR]
Details
- Language :
- English
- ISSN :
- 1070664X
- Volume :
- 20
- Issue :
- 9
- Database :
- Academic Search Index
- Journal :
- Physics of Plasmas
- Publication Type :
- Academic Journal
- Accession number :
- 90480707
- Full Text :
- https://doi.org/10.1063/1.4819501