Experimental Research On The Influence Of Toroidal Field Ripple On Edge Toroidal Flow Of Plasmas In J-TEXT Tokamak

In a tokamak device,the toroidal flow of plasma is helpful for stabilizing the macroscopic and microscopic instability and improving the confinement performance of plasma.However,in advanced fusion devices of the next generation,the external momentum input provided by auxiliary heating systems may not be sufficient to drive enough toroidal flow required by the high confinement mode plasma.This motivates researchers to focus on seeking mechanisms that can provide appreciable toroidal momentum.The existing theoretical and experimental results show that the ion loss effect caused by ripple of magnetic field will introduce toroidal momentum which is opposite to the direction of plasma current.The larger ripple amplitude is,the more obvious the effect will be on toroidal momentum.However,the effects of ripple loss on toroidal flow depend on the macroscopic parameters of plasmas which have not been clearly understood.Based on J-TEXT(Joint Texas Experimental Tokamak)and the ERD(Edge Rotation Diagnostic)system,the mechanisms for affecting the edge toroidal are experimentally studied under the condition of large magnetic ripple amplitude(up to 3.5% at the edge).The experimental observations and conclusions are as follows:(1)It is found that the ripple loss effect may be the dominant mechanism for driving the edge toroidal flows during density ramping.The experiment and analysis of the plasma edge toroidal flow with increasing density after the establishment of J-TEXT plasma equilibrium are carried out.It is found that the edge toroidal flow increases in the opposite direction to the plasma current during the increase of density,which is consistent with the neoclassical theory in which the toroidal flow is driven by ion loss effect caused by toroidal field ripple.This indicates that in tokamak plasmas with large magnetic ripple amplitude,ripple loss effect may be one of the dominant physical mechanisms driving the edge toroidal flow.(2)It is found that there exists a density threshold in the influence of ripple loss effect on the toroidal flows.When the density rises,the radial gradient of the plasma toroidal flow increases.When the density rises to a certain threshold,the flow velocity no longer changes with the increase of density.This shows that the density threshold is one of the key factors of the ripple loss effect on the toroidal flow.The influence of this factor on the toroidal flow on each magnetic surface is different,so the edge toroidal flow gradient can be formed.It is proved that this threshold is close to the transition threshold of J-TEXT plasma from LOC(Linear Ohmic Confinement)regime to SOC(Saturated Ohmic Confinement)regime.(3)Other mechanisms that may affect the edge toroidal flows are studied.We have studied the effects of changing core toroidal flows and MHD on the edge toroidal flows.It is found that the changing core toroidal flows can hardly affect that of the edge,while the tearing mode can flatten the profile of the edge toroidal flows.This can complementarily affect the final profile of toroidal flows.In conclusion,we find that ripple loss effect is the dominant mechanism affecting the edge toroidal flows in LOC regime.Experimental results agree well with the precdiction of toroidal flow from neoclassical theory considering ripple loss.There exists a density threshold in the influence of ripple loss effect on the toroidal flows.This threshold is close to the transition threshold of J-TEXT plasma from LOC regime to SOC regime.The results of this thesis are expected to provide a reference for understanding and predicting the edge toroidal flow in International Thermonuclear Experimental Reactor in which the toroidal field ripple amplitude is also large and the external momentum input is insufficient.