Abstract
Energetic particle transport by a magnetohydrodynamic (MHD) instability driven by helically trapped energetic particles is studied for a high-performance Large Helical Device plasma with kinetic-MHD hybrid simulations. It is observed in the simulation that an MHD mode with poloidal/toroidal mode numbers m/n=2/1 driven by helically trapped energetic particles causes a significant redistribution of perpendicular energetic particle pressure profile. The frequency of the MHD mode decreases rapidly at the saturation of the instability and changes sign, which indicates a reversal of the mode propagation direction. It is found that the helically trapped energetic particles interacting strongly with the MHD mode change the precession drift direction at the same time as the reversal of the MHD mode propagation direction. The helically trapped energetic particles with the precession drift reversal are transported rapidly in the radially outward direction before the original precession drift direction is recovered. The precession drift reversal and the outward transport are caused by interaction with the electric field of the MHD mode. The vast majority of trapped energetic particles which interact strongly with the MHD mode experience precession drift reversal, leading to a significant redistribution of the perpendicular energetic particle pressure profile.
Highlights
The energetic-particle transport by a magnetohydrodynamic (MHD) instability driven by helically-trapped energetic particles is studied for a high-performance Large Helical Device plasma with kinetic-MHD hybrid simulations
It is observed in the simulation that an MHD mode with poloidal/toroidal mode numbers m/n = 2/1 driven by helically-trapped energetic particles causes a significant redistribution of perpendicular energetic-particle pressure profile
The frequency of the MHD mode decreases rapidly at the saturation of the instability and changes the sign, which indicates the reversal of the mode propagation direction
Summary
In order to maintain favorable conditions for fusion, the energetic particles need to remain confined inside the plasma core long enough to deposit most of their energy onto the thermal particle population Due to their high energy, EPs can have a strong influence on the global behavior of the plasma, by for example destabilizing magnetohydrodynamic (MHD) modes in the devices, which can lead to losses of energetic particles, reducing their ability to maintain the high plasma temperature required for fusion. This phenomenon is present in different configurations, with various different modes, for example the fishbone instability[1,2,3] in tokamaks, or toroidal. Alfvén eigenmodes destabilized by energetic particles in tokamaks[4,5,6,7,8,9,10,11] as well as in stellarators
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