Abstract
Effects of toroidal flows on ballooning mode instabilities have been studied extensively in recent years. In the published works, toroidal flow effects are taken into account only in the perturbation equation while the tokamak equilibrium is assumed to be unchanged. In this work, the influence of a toroidal flow on ballooning mode instabilities is numerically investigated by using the BOUT++ code while the modification of the tokamak equilibrium due to the flow has been taken into account in fixing the profiles of the quasi-toroidal magnetic field, quasi-density, and quasi-pressure and only changing the toroidal Mach number. A toroidal flow can significantly modify the safety factor q profile and the pressure gradient ∇P, which then affects the ballooning instability. The simulation results show that in the presence of shear flows, the growth rate of the ballooning mode will be affected if the modified equilibrium is considered. For a shear flow, the growth rates of high-n modes are significantly reduced.
Highlights
Edge localized modes (ELMs) are an important macroscopic instability in tokamaks
We investigate the effect of a toroidal flow on an equilibrium configuration, choosing the plasma boundary similar to that of Experimental Advanced Superconducting Tokamak (EAST)
In order to show the effects of the flow on the growth rate intuitively, we present the local dispersion relation of the ideal ballooning mode as follows
Summary
Edge localized modes (ELMs) are an important macroscopic instability in tokamaks. The ELM crash would release a large amount of heat in the tokamak boundary, which will damage the divertor and the first wall. At present, it is widely accepted that peeling– ballooning modes, which are driven by the edge current gradient and the pressure gradient, respectively, may trigger ELMs.. A large number of experimental results show that the plasma rotation, in either the rigid flow or the shear flow, can significantly affect ELM dynamics.. Some analytical work was done to investigate the influence of the toroidal shear flow and poloidal shear flow on the ideal MHD ballooning modes. It is found that the ideal ballooning modes with high-n are stabilized by the shear flow in a circular tokamak equilibrium.. The same work on the influence of the shear flow on the ideal ballooning modes was done numerically.. The poloidal or toroidal plasma rotations will significantly affect the energy transport and the macroscopic stability (e.g., the internal and external kinks, ballooning modes, and resistive wall modes).
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