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Title: Nonlinear fishbone dynamics in spherical tokamaks

Linear and nonlinear kinetic-MHD hybrid simulations have been carried out to investigate linear stability and nonlinear dynamics of beam-driven fishbone instability in spherical tokamak plasmas. Realistic NSTX parameters with finite toroidal rotation were used. Our results show that the fishbone is driven by both trapped and passing particles. The instability drive of passing particles is comparable to that of trapped particles in the linear regime. The effects of rotation are destabilizing and a new region of instability appears at higher q min (>1.5) values, q min being the minimum of safety factor profile. In the nonlinear regime, the mode saturates due to flattening of beam ion distribution, and this persists after initial saturation while mode frequency chirps down in such a way that the resonant trapped particles move out radially and keep in resonance with the mode. Correspondingly, the flattening region of beam ion distribution expands radially outward. Furthermore, a substantial fraction of initially non-resonant trapped particles become resonant around the time of mode saturation and keep in resonance with the mode as frequency chirps down. On the other hand, the fraction of resonant passing particles is significantly smaller than that of trapped particles. Finally, our analysis shows that trappedmore » particles provide the main drive to the mode in the nonlinear regime.« less
 [1] ;  [2] ;  [3]
  1. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Dalian Univ. of Technology (People's Republic of China). School of Physics and Optoelectronic Technology
  2. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Zhejiang Univ., Hangzhou (China). Inst. for Fusion Theory and Simulation and Dept. of Physics
  3. Chinese Academy of Sciences (CAS), Beijing (China). Inst. of Plasma Physics
Publication Date:
OSTI Identifier:
Report Number(s):
Journal ID: ISSN 0029-5515; TRN: US1701224
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 57; Journal Issue: 1; Journal ID: ISSN 0029-5515
IOP Science
Research Org:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Sponsoring Org:
Country of Publication:
United States
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; NSTX; fishbone; frequency chirping; nonlinear dynamics; wave-particle interaction