Experimental study of the compression effect of a gradient magnetic field on compact torus plasma

The compression effect of compact torus (CT) plasma in gradient magnetic field is investigated in this work. A magnetic compression platform is built which can generate a variable axial magnetic field (1.0, 0.8, 0.6, 0.4, 0.2, 0.1 T) with different coil currents (146.0, 116.8, 87.6, 58.4, 29.2, 14.6 A). Five magnetic pickup coils are arranged which are used to display the time-spatial revolution of CT plasma during the penetration process, and they are located at the positions of 0, 200, 400, 600, and 800 mm in the axial direction, respectively. These experiments are carried out on the Experimental Advanced Superconducting Tokamak (EAST)-Compact Torus Injector (CTI) system, and the results show that the velocity of CT plasma was reduced significantly in places with large magnetic field gradients, as well as the full width at half maximum of the CT plasma. In addition, the magnetic field strength increases initially and then rapidly decreases during the compression process, or even reverses at the end, which may be related to the squeezing of the magnetic field lines and reconnection of the magnetic platform.