Experimental Study Of The Effect Of 3D Magnetic Perturbations On The Alfven Eigenmodes In The EAST Tokamak

Good confinement of the fusion born Energetic Particles(EPs)is essential to the self-sustained nuclear fusion reaction and economical fusion reactor.The Alfven Eigen-modes(AEs)exist in the toroidal fusion device will damage the confinement of the energetic particles.The wave-particle resonance will produce additional transport and loss to the energetic particles.This loss plays a dominant role in future low collision-ality burning fusion plasma.Thus it is important to study the excitation and control of Alfven eigenmodes.In EAST tokamak,we have conducted extensive experiments on the control of Alfven eigenmodes with the help of the Electron Cyclotron Resonant Heating/Current Drive(ECRH/ECCD)and the 3 Dimensional Magnetic Perturbations(3D MPs)pro-duced by the Resonant Magnetic Perturbation(RMP)coils.We found for the first time in the world that the application of static magnetic perturbation could generate barely trapped energetic electrons after the magnetic reconnection/penetration.These ener-getic electrons will hence excite a 150 kHz high frequency Toroidal Alfven Eigenmode(TAE)and a low frequency 20 kHz Beta-induced Alfven Eigenmode(BAE).This BAE will split to two branches(f1 = 18 kHz,f2 = 22 kHz)when a 2 kHz Tearing Mode(TM)appears.We also found for the first time in EAST that the application of ECRH could excite TAE.And the 50 ms period heating power modulation between 200 kW and 500 kW could modulate the frequency of the 200 kHz TAE with Δf=25 kHz in a zigzag form.With careful analysis of the possibilities of the frequency modulation,we found that the modulation of local density or q profile by the ECRH may be the reason for this frequency oscillation.Besides the above experimental observation to the AEs,we also conducted experi-ments to control the AEs with the combination of 3D MPs and ECRH.We found that the application of ECRH could fully suppress the TAE while strength the BAE.However,under the ECCD mode,it has just the opposite effect.It is the TAE that is strengthened while the BAE is mitigated by the ECCD.The application of 3D MPs could strengthen the AEs in microwave heating background.The strength of the BAE even has linear proportional relation with the strength of 3D MPs.In the end,we also investigated the effect of plasma density to the stability of AEs.We found the higher density could slow down the fast electrons and stabilize the TAE.These works indicate the application of the 3D MPs and ECRH/ECCD might be used as powerful tools to control the AEs in future burning plasmas to achieve a good confinement of EPs.