49th Annual Meeting of the Division of Plasma Physics
Volume 52, Number 11
Monday–Friday, November 12–16, 2007;
Orlando, Florida
Session NI1: Electron Confinement and Zonal Flows
9:30 AM–12:30 PM,
Wednesday, November 14, 2007
Rosen Centre Hotel
Room: Junior Ballroom
Chair: Stanley Kaye, Princeton Plasma Physics Laboratory
Abstract ID: BAPS.2007.DPP.NI1.6
Abstract: NI1.00006 : Spectral Features of the Geodesic Acoustic Mode and its Interaction with Turbulence in a Tokamak Plasma
12:00 PM–12:30 PM
Preview Abstract
Abstract
Author:
Chang-Xuan Yu
(USTC, China)
The measurements of the geodesic acoustic mode (GAM) by a set of
probe
arrays with large poloidal and toroidal separations in the edge
region of
the HL-2A tokamak have been performed. By the two-point
cross-correlation
technique, the three-dimensional wavenumber and frequency
spectrum for the
GAM is measured for the first time. The spectrum for the GAM
exhibits a
anisotropic feature: the poloidal and toroidal wavenumber spectra
are peaked
at $k_\theta =k_\phi =0$ with a width given by the spectral
variance, while
the radial spectrum shows a peak in the range of $q_r \rho _i \simeq
0.05\sim 0.09$ with the FWHM of$\Delta q_r \rho _i \simeq
0.04\sim 0.07$.
The spectrum also shows the GAM propagates in the radially outward
direction. Using a newly developed method based on the poloidal
momentum
equation, the generation of the GAM by the triad interaction of
turbulence
via the Reynolds stress has been directly measured. The result
manifests
that the energy is transferred from small scale turbulence into
the GAM by
the gradient of the Reynolds stress and the GAM saturation
amplitude is
determined by balancing between the generation and damping rates
of the GAM.
In addition, it is found that the envelope of the radial electric
field
fluctuations $\tilde {E}_r $ is modulated by the GAM and the
cross-phase
between the envelope and GAM oscillation is about$\pi $. The
numerical
investigation shows that the modulation of the $\tilde {E}_r $
envelope is
dominantly induced by the amplitude modulation. This fact
together with the
anti-phase relation between the $\tilde {E}_r $ envelope and GAM
oscillation
imply that the modulation of the $\tilde {E}_r $envelope is
accompanied with
the GAM generation in the energy-conserving triad interaction.
These results
suggest that the GAM is generated dominantly by the parametric
instability
driven by the turbulent Reynolds stress.
In collaboration with T. Lan, A.D. Liu (USTC, China); L.W. Yan,
W.Y. Hong,
K.J. Zhao, J. Q. Dong, Q.W. Yang (SWIP, China).
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2007.DPP.NI1.6