Effect Of Toroidal Plasma Rotation On Double Tearing Modes

Double tearing mode is an important magnetohydrodynamic instability in reversed magnetic shear(RMS)configuration,who can break the equilibrium of plasma.Moreover,poloidal shear flow appears in the evolution of DTM,who is thought to be the reason of triggering Internal transport barrier.Other wise,toroidal plasma rotation usually exists in Tokamak.That is why studying the effect of toroidal plasma rotation on double tearing modes is important.In this paper,reduced magnetohydrodynamic equations are deduced in cylindrical geometry.And the effect of toroidal plasma rotation on double tearing modes is numerical simulated.The main results are as follows:Toroidal plasma rotation,with or without shear,can delay the evolution of DTMs.In the case of toroidal rotation without shear,the growth rate of DTM decreases slightly as the magnitude of the velocity increases.In the case of sheared toroidal rotation,the growth rate of DTM decreases as the magnitude of velocity increases too,and the suppression effect is much higher than that without shear.With the shear on the two rational surfaces increasing,the suppression effect is more obvious.Sheared toroidal flow,no matter its shear is on the rational surface or between the two rational surfaces,can delay the evolution of q=3double tearing mode.And the suppression effect gets better while the shear rate increases.When the shear is large,the suppressing effect of the flow whose shear exists both on and between two rational surfaces is much better.The suppression effect of toroidal plasma flow located between the two rational surfaces is the best.And the flow located in inner rational surface is in the second place.Moreover,the flow located in the core,between the core and the inner rational surface,and outside the outer rational surface have no effect on the evolution of DTM.Besides,the suppression effect of the flow located in the outer rational surface has a slightly destabilizing effect on the evolution of DTM.And when the width of toroidal flow between the two rational surfaces is equal or greater than the interval of two rational surfaces,the evlotion of DTM will remain in the transition stage and won't turn into fast growth stage.Furthermore,the toroidal rotation can suppress the poloidal stream induced by DTMs.In the early growth stage and transition stage,when the velocity shear exists on rational surfaces,the poloidal stream on the outer rational surface is suppressed,and decreases as the shear of toroidal velocity increases.In the fast growth stage,the poloidal stream turns into strongly and inversely sheared on the two rational surfaces in transition stage and fast growth stage due to the toroidal sheared plasma rotation.