54th Annual Meeting of the APS Division of Plasma Physics
Volume 57, Number 12
Monday–Friday, October 29–November 2 2012;
Providence, Rhode Island
Session JI2: Fast Ion Physics, RF Theory
2:00 PM–5:00 PM,
Tuesday, October 30, 2012
Room: Ballroom DE
Chair: Tobin Munsat, University of Colorado
Abstract ID: BAPS.2012.DPP.JI2.1
Abstract: JI2.00001 : Simulation and Theory of Long Range Frequency Sweeping of TAE Modes*
2:00 PM–2:30 PM
Preview Abstract
Abstract
Author:
Ge Wang
(Institute for Fusion Studies, University of Texas at Austin)
Toroidal Alfven eigenmode (TAE) excited by energetic particles is
extensively observed in magnetic fusion. Frequently, the wave frequency is
found to sweep in the TAE gap and even penetrate into the continuum. To
achieve more realism than a chirping model based on the bump-on-tail
instability, TAE wave equation reduces to a Volterra integral equation which
couples to currents from energetic particles. The code enables tracking of
the chirping signals arising from the resonant interaction in phase space. A
down-chirping signal produced by clumps eventually enters the Alfven
continuum, whereupon the mode amplitude and chirping rate both increase more
rapidly. In contrast, the up-chirping signal never penetrates the continuum.
An adiabatic theory (ADT) quantitatively produces the simulation's
down-chirping dynamics including an explosive response in the continuum. ADT
for the up-chirping signal reproduces the simulation until its frequency
approaches the upper continuum. Two extrinsic dissipation models are
employed that generally give similar results, though for frequencies near
the upper gap/continuum boundary, there is a dependence on the dissipation
models. The hole smoothly vanishes as it goes into the continuum in ADT for
both models. However, simulations show that the hole suddenly disintegrates
before reaching the upper continuum for one case and smoothly decays for the
other. The discrepancy for the hole's decay is apparently explained from the
calculation of an adiabatic validity parameter that implies that the hole's
disintegration takes place when the adiabatic condition breaks down as the
upper continuum is approached. Ongoing improvements to TAE modeling takes
into account the spatial profile variation of mode structure. The most
significant disparity between newest Hamiltonian and an older simpler one
occurs near continuum tips where there is the possibility that topological
change in the phase space may emerge. Two major qualitative results of this
theory: chirp penetration into the lower continuum with enhancement of the
field amplitude but with no chirp penetration into the upper continuum, has
been observed in the MAST experiment.
*In collaboration with H.L. Berk. Supported by US DOE contract DE-FC02-08ER54988.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2012.DPP.JI2.1