Designing the X-divertor configurations for the China Fusion Engineering Test Reactor

It has been found that the X-divertor (XD) configuration can flare magnetic field lines near the divertor targets and reduce heat flux on the divertor plate (Kotschenreuther 2007 Phys. Plasmas 14 072502). To solve severe heat exhaust problems in the China Fusion Engineering Test Reactor, the XD configuration is proposed. Equilibria calculations indicate that the XD can be realized and is compatible with the long-leg divertor. The position of the extra X-point was optimized to reduce the currents in the central solenoid (CS) coils, which dominates the flattop length. Two internal coils were considered to assist in the optimization of the XD. Different plasma currents were also used to further reduce the CS coil currents. The results indicate that the aforementioned approaches can effectively extend the flattop. (paper)