The Research Of Local Driving Helical Current On Tearing Mode Instability

Tearing mode is a macroscopic magnetohydrodynamic instability with current driving in the presence of a finite resistance or viscous effect in the plasma.It is a common physical phenomenon in magnetic confinement fusion plasma.In Tokamak magnetic confinement fusion device,tearing mode instability developed on the rational surface can reduce the temperature and plasma density in the axis,and affect the conferment performance of Tokamak-type magnetic confinement device.When magnetic islands produced by tearing instability grows big enough,and plasma disruption occurs.Therefore,the control of the tearing mode instability in the magnetic confinement device is a key issue in the research of magnetic confinement fusion.The m=2/n=1 tearing mode instability with external driving helical current are studied using the reduced MHD(RMHD)simulation method in the large-aspect-ratio tokomaks.The effect of different characteristics of driven current,such as its radial deposition width,intensity and starting deposition time are analyzed.The results indicate that local driving helical current with more focused deposition width and larger intensity have a better suppression effect on tearing modes.But destabilizing effect,called flip instability,is also observed when the driven currents over certain intensity or with too narrow deposition width.Furthermore,with the delay of starting deposition time of driven current,it will weak the control effect of driven current on magnetic islands.The influence of feedback driven helical current on tearing mode instability with the width of magnetic island width as feedback information is investigated.The results show that the feedback driven helical current can not only effectively be suppressed the development of tearing mode instability,but also flip instability can be avoided.