Linear stability and nonlinear dynamics of the fishbone mode in spherical tokamaks
- School of Physics and Optoelectronic Engineering, Dalian University of Technology, Dalian 116024 (China)
- Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States)
Extensive linear and nonlinear simulations have been carried out to investigate the energetic particle-driven fishbone instability in spherical tokamak plasmas with weakly reversed q profile and the q{sub min} slightly above unity. The global kinetic-MHD hybrid code M3D-K is used. Numerical results show that a fishbone instability is excited by energetic beam ions preferentially at higher q{sub min} values, consistent with the observed appearance of the fishbone before the “long-lived mode” in MAST and NSTX experiments. In contrast, at lower q{sub min} values, the fishbone tends to be stable. In this case, the beam ion effects are strongly stabilizing for the non-resonant kink mode. Nonlinear simulations show that the fishbone saturates with strong downward frequency chirping as well as radial flattening of the beam ion distribution. An (m, n) = (2, 1) magnetic island is found to be driven nonlinearly by the fishbone instability, which could provide a trigger for the (2, 1) neoclassical tearing mode sometimes observed after the fishbone instability in NSTX.
- OSTI ID:
- 22218531
- Journal Information:
- Physics of Plasmas, Vol. 20, Issue 10; Other Information: (c) 2013 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); ISSN 1070-664X
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
BEAM-PLASMA SYSTEMS
FISHBONE INSTABILITY
IONS
KINK INSTABILITY
MAGNETIC ISLANDS
MAGNETOHYDRODYNAMICS
MAST TOKAMAK
NEOCLASSICAL TRANSPORT THEORY
NONLINEAR PROBLEMS
NSTX DEVICE
PLASMA
PLASMA CONFINEMENT
PLASMA SIMULATION
SPHERICAL CONFIGURATION
TEARING INSTABILITY