The Study Of Fishbone Instability On EAST-NBI

In this thesis, the main content is carried out on the EAST (Experimental Advanced Superconducting Tokamak) campaign experiment. In order to achieve the scientific mission of high performance, the effective and flexible auxiliary heating system is equipped. Neutral beam injection (NBI) has been recognized as one of the most effective means for plasma heating and the physical mechanism of neutral beam injection is relatively clear. Neutral beam injection will generate many energetic ions, for more energy of these energetic ions they can drive MHD instabilities. This paper mainly describes the fishbone mode phenomena during the injection of high-power neutral beams in EAST.In present, there are two main theoretical interpretations of ion fishbone mode instability. One considers that the fishbone oscillations are excited through the resonant interaction between the fast-ion population in the tokamak plasma and the internal kink mode, and the measured fishbone perturbation frequency is comparable to the precession frequency of the deeply trapped energetic ions. When the fast ion beta is high, the fishbone mode instabilities occur. The other theory is included the effect of finite diamagnetic frequency. When the value of hot ion pressure is lower, the fishbone instability is also excited. This theory considers that the fishbone perturbation frequency is comparable to diamagnetic frequency, and the destructive mechanisms of the fishbone include the effect of ion viscosity and momentum transfer. To some degree these two distinct branches can exist or merge.This paper emphasizes the ion fishbone excited by energetic beam ions. Firstly, from the soft x-ray signals (SXR) and Mirnov coil signals in EAST experiment, we can get the period, amplitude, mode numbers and frequency. The mode perturbation frequency ranges from 1 to 6 kHz. The periodic frequency chirping has also been detected. In the simulation, the transport analysis code TRANSP is introduced to calculate plasma current, neutron emission, beam power deposition and beam power loss. The results of the numerical simulation show that the ohmic current is a major part of the plasma current, and the neutron emission is up to 1.2×1014 n/s. The numerical simulation results show that 70% of the beam power is absorbed by the target-plasma, while 30% of it is lost. This paper introduces four energy-loss mechanisms, and the shine-through power loss is the main loss. In addition, the TRANSP is introduced to calculate fast ion distribution, the results show that the fishbone mode is excited by the deeply trapped energetic ions. The mode frequency is comparable to the toroidal precessional frequency of the deeply trapped energetic ions, and the frequency ranges from 14 to 19 kHz. Lastly, The nonlinear behavior of the fishbone mode is analyzed by using a prey-predator model, which is consistent with the experimental results. The period of the fishbone ranges from 2 to 3 ms. This model indicates that the periodic oscillations of the fishbone mode always occur near the critical value of fast ion beta, and the amplitude of the fishbone mode depends on the deposition rate of trapped particles.