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 YI3: Edge Turbulence
9:30 AM–12:30 PM,
Friday, November 2, 2012
Room: Ballroom BC
Chair: Walter Guttenfelder, Princeton Plasma Physics Laboratory
Abstract ID: BAPS.2012.DPP.YI3.6
Abstract: YI3.00006 : Global Gyrokinetic Simulations of the Dominant High-n and Intermediate-n Instabilities in the H-Mode Tokamak Edge Pedestal*
12:00 PM–12:30 PM
Preview Abstract
Abstract
Author:
Scott Parker
(Deptartment of Physics, University of Colorado, Boulder)
Global electromagnetic gyrokinetic simulations
show the existence of near threshold conditions, for both a high-n Kinetic
Ballooning Mode (KBM) and an intermediate-n kinetic version of
Peeling-Ballooning Mode (PBM). The KBM and the PBM have been used to
constrain the EPED model [1]. Global gyrokinetic simulations show that the
H-mode pedestal, just prior to the onset of the Edge Localized Mode (ELM),
is very near the KBM threshold. Two DIII-D experimental discharges are
studied, one reporting KBM features in fluctuation measurements [2].
Simulations find that in addition to the high-n KBM, an intermediate-n
electromagnetic mode is unstable. This kinetic version of the PBM has phase
velocity in the electron diamagnetic direction, but otherwise has features
similar to the MHD PBM. When the magnetic shear is reduced in a narrow
region near the steep pressure gradient, the intermediate-n ``kinetic PBM'' is
stabilized, while the high-n KBM becomes the most unstable mode. Global
simulation results of the KBM compare favorably with flux tube simulations.
The KBM transitions to an unstable electrostatic ion mode as the plasma beta
is reduced. The intermediate-n ``kinetic peeling ballooning mode'' is
sensitive to the q-profile and only seen in global electromagnetic
simulations. Collisions increase the KBM critical beta and growth rate.
These results indicate that an improved pedestal model should include, in
detail, any corrections to the bootstrap current, and any other equilibrium
effects that might reduce the local magnetic shear. It is known that the bootstrap current may flatten the q-profile in the steep gradient region [3]. Simulations are
carried out using the global electromagnetic GEM code, including kinetic
electrons, electron-ion collisions and the effects of realistic magnetic
geometry. In addition to global linear
analysis, nonlinear simulations will be reported showing that, while the
equilibrium radial electric field has a weak effect on the linear growth
rate, it has a larger stabilizing effect nonlinearly.\\[4pt]
[1] P. Snyder, et al., Phys. Plasmas 16 056118 (2009).\\[0pt]
[2] Z. Yan, et al., Phys. Plasmas 18 056117 (2011).\\[0pt]
[3] J. Callen, et al. Nucl. Fusion 50 064004 (2010).
*Collaborators: W. Wan, Y. Chen, Univ. of Colorado; Z. Yan, Univ. of Wisconsin; R. Groebner, P. Snyder, GA; C. Chang, PPPL. Work supported by DOE SciDAC Edge Physics Simulation (EPSI) Project.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2012.DPP.YI3.6