Experimental Study Of The MHD Instabilities Controlling By External Magnetic Field System On SUNIST Spherical Tokamak

An external n=1 magnetic field system is set up on the Spherical Tokamak SUNIST for the study of the MHD instabilities. The power system has 1 ms rising time and 3 ms current platform, and the output current can be terminated instantly. Testing results demonstrate that this system can generated magnetic field with n=1 main mode in toroidal direction at the centre of vacuum chamber. Consideration the eddy current induced by the penetration of this external magnetic field in chamber wall, and the mode measured from the pick up coil, it is indicated that the major mode of the setup external field is m/n=4/1, which is agreed with the design. Experimental results demonstrate that with addition of the external n=1 magnetic field, the MHD instabilities mode structure was changed, and certain main instabilities modes has been suppressed. Meanwhile the external field can change the plasma current shape and improved the plasma density.