56th Annual Meeting of the APS Division of Plasma Physics
Volume 59, Number 15
Monday–Friday, October 27–31, 2014;
New Orleans, Louisiana
Session NI2: Basic Plasma Physics
9:30 AM–12:30 PM,
Wednesday, October 29, 2014
Room: Bissonet
Chair: Troy Carter, University of California, Los Angeles
Abstract ID: BAPS.2014.DPP.NI2.4
Abstract: NI2.00004 : Effect of q-profile structure on intrinsic torque reversals*
11:00 AM–11:30 AM
Preview Abstract
Abstract
Author:
Zhixin Lu
(UCSD)
Intrinsic toroidal rotation plays an important role in mitigating macroinstability and regulating turbulent transport in ITER, where neutral beams are not sufficient to provide the requisite torque. Recent experiments on C-Mod with LHCD observed rotation reversal related to a change in the q profile [1]. In this work, we focus on understanding the physics of intrinsic rotation reversals in LHCD plasmas, using nonlinear, global gyro-kinetic simulations [2] and analysis of mode structure and spectrum symmetry breaking [3]. The sensitive dependence of turbulent residual stress on magnetic shear is identified and characterized. The basic residual stress is non-vanishing when the k-parallel spectrum symmetry is broken, e.g., by E x B shear induced radial shift, non-uniformity in turbulence intensity, etc. [3]. It is found that at low magnetic shear, the poloidal harmonics can shift strongly in the radial direction, as a feature of non-local effects, due to radial propagation and amplitude variation of the mode. This new symmetry breaking mechanism leads to a change in the sign of spectrum averaged parallel wave vector and thus the direction of intrinsic torque. Theoretical study [4] shows that the competition between magnetic drift and ion kinetic effects determines the non-local effects and the structure of the asymmetry. Specifically, it is found that the direction of the intrinsic torque changes from counter- to co-current in the core, when magnetic shear decreases through a critical value. A critical shear $\hat s_R=0.2\sim0.5$ for reversal of CTEM-induced intrinsic torque found by simulation is consistent with that from the LHCD C-Mod reversal experiments. In addition, simulations indicate $\hat s_R=1\sim2$ for the reversal of ITG-induced torque, a prediction which can be tested by experiments.\\[4pt]
[1] Rice, J.E. et al. 2011 Phys. Rev. Lett. 107, 265002\\[0pt]
[2] Wang W.X. et al 2006 Phys. Plasmas 13, 092505\\[0pt]
[3] Diamond, P.H. et al. 2013 Nucl. Fusion 53 104019\\[0pt]
[4] Lu, Z.X. et al. 2012 Phys. Plasmas 19, 042104
*This work is supported by CER and CMTFO, UCSD and U.S. DOE-PPPL Contract DE-AC02-09CH11466.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2014.DPP.NI2.4