Speaker: Zhixin Lu

Title: Study of Mode Structure Symmetry Breaking and Intrinsic Torque Reversal Based on Gyrokinetic Simulation and Mixed WKB-full-wave Approach

Abstract: Reversals in intrinsic torque have been inferred according to rotation experiments with LHCD on Alcator C-Mod. This work proposes a mechanism for intrinsic torque reversal linked to magnetic shear. Gyrokinetic simulations demonstrate that as compared to the normal magnetic shear case, the intrinsic torque reverses if the magnetic shear is lower than the critical value. Analysis based on mixed WKB-full-wave approach shows that the reversal occurs due to the dominance of the symmetry breaking mechanism in residual stress due to the synergy of toroidal coupling and the intensity gradient. This mechanism is a consequence of ballooning structure at weak magnetic shear. Gyrokinetic simulation gives 0.4 as the critical magnetic shear for trapped electron modes (TEM) and 0.9 for ion temperature gradient (ITG) modes. As an extension of this work, the intrinsic torque direction in multiple parametric space will be studied in order to predict the rotation profile in different devices and various parameter regimes.

About the speaker: Zhixin Lu obtained his B.S. and Ph.D. in Plasma Physics from Peking University. Then he worked in Princeton Plasma Physics Laboratory (PPPL) since July 2013, as a postdoctoral scholar of University of California at San Diego (UCSD). He developed the mixed WKB-full-wave approach for 2D mode structure analysis. He proposed a mechanism to explain the intrinsic torque reversal of LHCD discharges on Alcator C-Mod. As a user and developer of PPPL code GTS, he contributed to the maintenance and upgrade of GTS.

Time：9:00 a.m. March 10, 2016 (Thursday)

Address：Meeting room of second floor