Experimental Research On Several Nonlinear Physics Problems Of Low-collisional Plasma In EAST Tokamak

Magnetically confined plasma is a highly self-organized nonlinear system.Abundant plasma structures are formed in the nonlinear Tokamak plasma system.The plasma structures and balance are self-consistent,which determines the final plasma state.The collisionlity of burning plasma in tokamak is lower,and the non-linear characteristics of the system will be more significant.Based on the deuteriumdeuterium plasma experiments on EAST with high temperature and low collision,this paper studies the dynamics among plasma structures,the dynamics between plasma structures and equilibrium.And we try to explore the nonlinear system control scheme that is conducive to the realization of magnetic fusion.The turbulence-flow system is the basic subsystem of the Tokamak nonlinear plasma system,and its evolution is directly related to the abnormal transport of plasma.(1)First,the basic mechanism of the interaction between turbulence and plasma flow is studied.Through the analysis of experimental results,this article clarified the mechanism of the interaction between turbulence and mean flow,turbulence and low frequency zonal flow.Including the effect of turbulence driving spontaneous rotation,the decorrelation effect of E×B mean flow and the non-linear coupling between turbulence and zonal flow.(2)Secondly,the influence of the turbulence-flow system on the confinement and transport is studied.The electronic-scale turbulence was adjusted by ECRH,and the experimental results show that the TEM mode driven turbulence is conducive to particle transport.Turbulence may has particle pinch effect.Besides,in high-power electron heating discharge,experimental result show that the the electron temperature decrease with the ETG model driven turbulence.This suggests that the ETG model driven turbulence will increase the heat transport in electron channel.(3)Third,the control scheme of turbulence-flow is studied with the goal of optimizing transport.Under the condition of NBI injection,the local density peaking factor of the plasma core is modulated by adjusting the electron scale turbulence.Besides,in the experiment with rapid growth of low-frequency zonal flow,the highwavenumber turbulence suppression and the electron temperature internal transport barrier(e-ITB)were found.Experimental results suggest that lower-frequency zonal flow is beneficial to formation of e-ITB.Alfven eigenmodes are important plasma structure in tokamak nonlinear plasma system,and Alfvén eigenmode physics is a branch of energetic ions physics.(1)First,the physical mechanism of the interaction between Alfven eigenmode and the turbulence-flow system is studied.Finite magnetic perturbation is applied in the hightemperature low-density plasma,and the couplings of the high-frequency electron-scale turbulence and Torodial Alfven eigenmode,torodial Alfven eigenmode and lowfrequency zonal flow are found.Alfven eigenmode can adjust the distribution of free energy in turbulence and low-frequency zonal flow.(2)Secondly,the relationship between the Alfén eigenmode and the of energetic ions confinement was studied.We found that the confinement of energetic ions is significantly improved after the amplitude of torodial Alfven eigenmode is reduced to a non-zearo level.(3)Finally,with the goal of optimizing the confinement and transport of high-energy ions,the Alfén eigenmode and turbulence control scheme are studied.With magnetic perturbation,the amplitude of the Torodial Alfven eigenmode is reduced,the heat transport in the electron channel and the ion channel is improved because of the multi-scale physics,and the confinement of energetic ions is improved.The tearing modes are important plasma structure in the Tokamak nonlinear plasma system.The tearing mode instabilities is associated with the stable operation and high parameters plasma acquisition.(1)Firstly,the interaction mechanism between stable tearing mode and turbulence,unstable tearing mode and turbulence are studied.,It is found that when the tearing mode is in a quasi-steady state,the electron-scale turbulence in the plasma core can trigger the coupling of the tearing mode(1/1 and 2/1)after turbulence reaches a certain power.Besides.during the non-linear development of the tearing mode and the disruption,it was found that unstable tearing mode can modulate the power of the turbulence.High-power turbulence and weak plasma flow can explain the thermal quenching process caused by the tearing mode.(2)After that,the modulatation of tearing mode to turbulence-flow system and confinement improvement are studied.Experimental results show that the tearing mode can adjust the distribution of free energy in turbulence and plasma flow.The coupled tearing mode with limited amplitude promotes the growth of the plasma flow and reduces the heat transfer in the electron channel.(3)Finally,the tearing mode mitigation is studied with ECRH.The plasma flow generation and the tearing mode suppression are achieved with ECRH.The plasma flow may be beneficial to the suppression of tearing mode.This paper analyzes some important physical mechanisms in the evolution of tokamak nonlinear plasma system,and proposes optimization ideas and engineering control suggestions for confinement and transport,energetic particle physics,and MHD related issues.Besides,The work of this paper is helpful to the research of ITER and CFETR devices.