Abstract Details
Abstracts
Author: GE DONG
Requested Type: Pre-Selected Invited
Submitted: 2019-02-20 14:31:24
Co-authors: J. Bao, A. Bhattacharjee, Z. lin
Contact Info:
Princeton Plasma Physics Laboratory
100 Stellarator Road
Princeton, New Jersey 08540
United States
Abstract Text:
Kinetic ballooning modes (KBM) are believed to play important roles in the eruptive events in the tokamak edge [1] and the magnetospheric substorms [2]. However, the role of kinetic effects in nonlinear KBM dynamics remains largely unexplored. Numerical studies on the nonlinear saturation of KBMs have not reached conclusive results [3, 4]. In this work, we present global gyrokinetic particle-in-cell simulation results of nonlinear KBM, for both the cyclone base case (CBC) [5], and the parameters measured at DIII-D edge. We found that instead of the detonation predicted by the ideal MHD analysis [6], the nonlinear KBM develops into a kinetic "intermediate" regime [7], followed by nonlinear saturation regulated by spontaneously generated zonal fields. The origin of the zonal fields can be attributed to three-wave coupling processes. In the intermediate nonlinear regime, we observed development of localized current sheets that can induce secondary microtearing mode (MTM) instabilities. In the simulations using DIII-D edge equilibrium, the nonlinear convective motion appears to compete with the shearing effect produced by zonal fields, which is weaker in the narrow steep gradient region compared with that in the core plasma. The effects of the zonal fields and the nonlinear convection together regulate the KBM nonlinear saturation level in the DIII-D steep gradient region. Implications of these results for ELMs in tokamaks and substorm onset in the Earth's magnetotail will be discussed. Initial benchmark results from MTM simulations will also be reported.
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[5] G. Dong et al., Phys. Plasmas, 26, 010710, 2019
[6] S. Cowley and M. Artun, Phys. Reports, 283, 185, 1997
[7] P. Zhu et al., Phys. Rev. Lett., 96, 065001, 2006
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