53rd Annual Meeting of the APS Division of Plasma Physics
Volume 56, Number 16
Monday–Friday, November 14–18, 2011;
Salt Lake City, Utah
Session JI2: 3D Equilibrium, Stability and Control
2:00 PM–5:00 PM,
Tuesday, November 15, 2011
Room: Ballroom BD
Chair: Mike Mauel, Columbia University
Abstract ID: BAPS.2011.DPP.JI2.4
Abstract: JI2.00004 : First-order FLR effects on magnetic tearing and relaxation in pinch configurations*
3:30 PM–4:00 PM
Preview Abstract
Abstract
Author:
Jacob King
(University of Wisconsin - Madison)
Drift and Hall effects on magnetic tearing, island evolution, and
relaxation in pinch configurations are investigated using a non-
reduced fluid model with first-order FLR effects. When the
tearing-layer width is smaller than the ion sound gyroradius
($\rho_{s}$), cylindrical computations show that kinetic-Alfven-
wave (KAW) physics increases linear growth rates relative to
resistive MHD. An unexpected result with a uniform pressure
profile is a drift effect that reduces the growth rate at
intermediate-$\rho_{s}$ values. This drift is present only with
warm-ions FLR modeling, and analytics show that it arises from
$\nabla B$ and poloidal curvature represented in the Braginskii
gyroviscous stress. While the flux-surface average contribution
from these drifts are small relative to diamagnetic drifts in
tokamaks, they are dominant in pinch profiles. Growth rates and
rotation frequencies are derived for a heuristic dispersion
relation using the ion-drift effects and a resistive-MHD Ohm's
law. This dispersion relation is in agreement with numerical
results in the intermediate drift regime before KAW effects are
significant. Nonlinear single-helicity computations with
experimentally-relevant $\rho_{s}$ values show that the warm-ion
gyroviscous effects reduce saturated-island widths. In contrast
to diamagnetic drift-tearing, the $\nabla B$ and poloidal
curvature profiles are largely unaffected by magnetic islands.
The result suggests an increasing tendency to obtain quasi-single
helicity in reversed-field pinches with increasing ion
temperature. [King et al., Phys.\ Pl.\ 2011]
Multihelicity simulations show that both MHD and Hall dynamos
contribute to relaxation events. The presence of Hall dynamo
implies a fluctuation-induced Maxwell stress, and the simulation
results show net transport of parallel momentum. The magnitude of
force densities from the Maxwell stress and a competing Reynolds
stress, and changes in the parallel-flow profile are within a
factor of 1.5 of measurements [Kuritsyn et al., Phys.\ Pl.\ 2009]
during a relaxation event in the Madison Symmetric Torus.
*Work supported by US DOE OFES and the NSF Physics Frontiers program.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2011.DPP.JI2.4