Zonal flow generation and toroidal Alfven eigenmode excitation due to tearing mode induced energetic particle redistribution

Generation of the n = 0 zonal flow and excitation of the n = 1 toroidal Alfven eigenmode (TAE) due to the redistribution of energetic particles (EPs) by the m/n = 2/1 tearing mode (TM) are systematically studied with the hybrid drift-kinetic magnetohydrodynamic (MHD) simulations (m and n represent the poloidal and toroidal mode number, respectively). In the presence of the m/n = 2/1 TM, the amplitude of the n = 1 TAE shows a slower decay after its first saturation due to the wave-particle nonlinearity and the nonlinear generation of the n = 0 & higher-n (n > 2) sidebands. Meanwhile, a strong n = 0 zonal flow component is nonlinearly generated when both TAE and TM grow to large amplitudes. The redistribution of EPs by the m/n = 2/1 magnetic island results in a continuous drive on the background plasma, and finally produces the zonal flow through the MHD nonlinearity. In addition, the large m/n = 2/1 magnetic island is found to be responsible for the formation of the strong spatial gradient of the EP distribution through the resonance between EPs and TM, which can lead to burst of unstable TAE and destabilization of originally stable TAE.

Automated summary

The generation of the n = 0 zonal flow and the excitation of the n = 1 toroidal Alfven eigenmode (TAE) due to the redistribution of energetic particles (EPs) by the m/n = 2/1 tearing mode (TM) were systematically studied using hybrid drift-kinetic magnetohydrodynamic (MHD) simulations. The study showed that the amplitude of the n = 1 TAE decays slower after saturation due to wave-particle nonlinearity and the nonlinear generation of sidebands. Additionally, a strong n = 0 zonal flow component is generated when both TAE and TM reach high amplitudes. The redistribution of EPs by the m/n = 2/1 magnetic island drives the background plasma and leads to the generation of the zonal flow through MHD nonlinearity. Furthermore, the large m/n = 2/1 magnetic island is responsible for the formation of a strong spatial gradient of the EP distribution, which can result in the burst of unstable TAE and destabilization of originally stable TAE.