Speaker:
C.P. Hung
Institution:
Univ. of Maryland
Date:
Tuesday, August 6, 2013
Time:
11:00 am
Location:
FRH 2111
ABSTRACT:
Phase mixing and nonlinear resonance detuning of geodesic acoustic modes in a tokamak plasma are examined. Geodesic acoustic modes (GAMs) are tokamak normal modes with oscillations in poloidal flow constrained to lie within flux surfaces. The mode frequency is sonic, dependent on the local flux surface temperature. Consequently, mode oscillations between flux surfaces get rapidly out of phase, resulting in enhanced damping from the phase mixing. Damping rates are shown to scale as the negative 1/3 power of the large viscous Reynolds number.
The effect of convective nonlinearities on the normal modes is also studied. Resonant amplification is shown to be suppressed nonlinearly, similar to the physics of the Duffing oscillator. All analyses are verified by numerical simulation. The findings are applied to a recently proposed GAM excitation experiment on the DIII-D tokamak.
Host:
Liu Chen