Numerical Study On Suppression Of Tearing Modes Instability By Local Driven Current

Tearing modes is one of the forms transforming the magnetic energy into plasma kinetic energy and heat energy.This instability may cause dramatic change of tokamak plasma,and even trigger break of device.Therefore,it is important attempt to avoid the generation of tearing mode instability in the experiment and controlling methods after the appearance of tearing modes.In order to improve the current distribution,join the drive current near the rational magnetic surface.Experiment found that radio frequency wave current drive can effectively restrain the tearing modes instability.There are many problems to be further discussed and explained of radio frequency wave current drive restrain tearing mode instability.Firstly,simulating the tokamak plasma under the straight cylindrical configuration is based on the basic equations,adopting the incompressible MHD model.Then external driven current is introduced as Gaussian distribution form.The distribution features of the driven current is studied,including the current distribution of peak and half high width.Test the change of motion state of the plasma under different external current environment.Study the influence of external driven current in the straight cylinder configuration on 2/1 and 3/1 tearing modes.Simulating the external driven current with different distribution characteristics,or a fixed constant current characteristics with different injection times,observethe different magnetic island width of tearing modes.It has been found that,along the radial deposition has a Gaussian external driven current distribution on the rational surface,can effectively slow down the 2/1 single tearing mode and 3/1 double tearing mode in tokamak device.After the 2/1 single tearing modes developing,add the local driven current,observe magnetic island wide and find out the growth slowed significantly.The results show that when the local current amplitude accounted for about 12% of the background plasma current,current deposition width is about 25% of the small ring radius,the inhibition effect is better.In addition,it has been observed that as soon as possible to join the external driven current,can effectively inhibit the tearing mode.When 3/1 double tearing mode initial magnetic island width is medium,the modes experience linear drive,nonlinear drive,fast magnetic reconnection and reconnection attenuation stages.In rational surface,two of the fastest growing pattern coupling drive nonlinear development of the plasma system.The research results show that deposition in the tokamak device along the right direction of the driven current on the rational surface can effectively slow down the progress of the double tearing modes.When current amplitude accounted for about 4% of the background plasma current,the driven current deposition width is about 7% of the small ring radius,inhibition effect is better.Before double tearing modes falling into the third stage namely fast magnetic reconnection,external driven current can effectively inhibit the tearing mode magnetic eruption.