Optimization of Magnetic Confinement for Quasi-Snowflake Divertor Configuration

To realize the commercialized operation, it is preferable that tokamak devices achieve the operating scenarios with steady-state, long-pulse, H-mode and high magnetic confinement plasma current. For enhancing the magnetic confinement capability and improving the poloidal beta βp in quasi-snowflake configuration, under the consideration of the effect on other performance parameters, the method of shifting magnetic axis is employed. According to the calculated method proposed in this paper, the plasma current density distribution is modified to realize the supposed radial movement of the magnetic axis. Then the value of βp, the coordinates of X2 point, the flux expansion of outside and inside strike points (fmout and fmin), poloidal field currents and safety factor q profile are formulated, the relations between these parameters and the horizontal displacement of the magnetic axis are analyzed. Finally, in lower single-null quasi-snowflake configuration, by shifting the magnetic axis from 1.9242 to 1.9412m, βp has an increase of 86.96 %, the confinement capability of the plasma is significantly enhanced, Meanwhile, the position of X2 point is varied from (2.6789 m, −1.6439 m) to (2.2955 m, −1.6039 m), which is closer to X1 point and the plasma. Therefore, fmout is enlarged from 6.646 to 7.706, which has an increase of 15.9%. And fmin has a decrease of 0.62%, which can be neglected. The safety factor at magnetic axis q0 is decreased by 1.75%, from 1.0897 to 1.0701, which is larger than 1 and satisfies the requirement of magnetohydrodynamic stability. In addition, EFIT code is used to verify the feasibility and the accuracy of the optimized results.