Numerical Simulation Of Edge Localized Modes Instability In Presence Of Plasma Rotation In Tokamaks

Edge localized mode is a periodicity edge perturbation during H mode discharge,which will deposit big amount of energy and particles on the wall,big ELMs will cause unbearable damage on the wall materials.In the future large fusion devices such as ITER and CFETR,ELM should be suppressed or at least controlled within an acceptable domain.Neutral Beam Injection(NBI)is a common way to control ELM in experiments,which will not only bring in particle sources but also large plasma toroidal rotation.One of the topics in this paper is to find out what those two effects caused by NBI will act on ELM instabilities.Firstly,the effects of plasma rotation and plasma density on edge localized mode instability has been verified numerically by non-ideal full MHD initial value code NIM-ROD.Linear simulation have studied the effects of toroidal flow amplitude,flow shear and the flow direction,all these three factors are effective to ELM stabilization,and the stabilization effects can be enhanced by increasing plasma density hence collisionality.Nonetheless,ELM can not be fully controlled whatever toroidal flow and plasma den-sity are used.However,with the help of poloidal rotation,the growth rates of high-n modes can reduce to 0 even with small amplitude poloidal flow.The next work in this paper is numerically analysing the nonlinear evolution of ELMs.The temperature profiles at different time indicate that the pedestal collapse and the perturbation extends outside of the plasma boundary,eventually reaches to the wall.The poincare plots of magnetic surface clearly show the existence of "filaments"structure,which act as conduits for energy and particles transport during ELMs erupt.The present design of China Fusion Engineering Test Reactor(CFETR)aims to find proper equilibrium parameters.One of the most important task is to verify the stability of these equilibria.Linear simulation using NIMROD code have found that the Upgrade phase-I equilibrium for CFETR are unstable for all-n edge localized modes.For low-n modes,on the one hand,their growth rates increase with the wall location goes away from the plasma boundary,finally reach to the ideal wall limit value.On the other hand,these modes are stable with wall location close to plasma boundary.For high-n modes,toroidal flow can slightly stabilize them,which could be a promising way to control ELMs in CFETR discharge since NBI heating will introduce large toroidal rotation.