Evaluation on the method of reducing CFETR TF ripple generated by WCCB blanket

摘要

Reduced Activation Ferritic/Martensitic (RAFM) steel is selected as structural material for the water cooled ceramic breeder (WCCB) blanket for China Fusion Engineering Test Reactor (CFETR). Due to the magnetization of RAFM steel, the toroidal field (TF) ripple is generated by the WCCB blanket. The TF ripple induces significant losses of high-energy particles, and then causes issues of heat load on plasma-facing components (PFCs) and energy balance of plasma. Hence, TF ripple generated by WCCB blanket is calculated, and several effective optimization methods are explored in this paper. The simulation results indicate that TF ripple in plasma target separatrix is greater than design limits (delta(TF) 0.5%) in present design. Four methods are employed to study and evaluate the effect of decreasing TF ripple including installing ferromagnetic inserts, using correction coils, changing the related parameter of diagnostic system and moving the WCCB blanket, respectively. Based on the analysis results, it is found that these four methods can reduce TF ripple to some extend through different optimizing methods. The location of five TF ripple peaks of a 22.5 degrees sector are at 0 degrees, +/- 3.07 degrees and +/- 7.67 degrees respectively. The TF ripple can only reduce from 0.25% to 0.21% at +/- 3.07 degrees plane using optimization method of installing ferromagnetic inserts. The rest of the location has almost little impact. The TF ripple can only reduce from 0.31% to 0.20% at 0 degrees plane using correction coils, but the peak value will increase to 0.33% at +/- 3.07 degrees plane. Moving diagnostic system 40 mm outward in radial direction will effectively decrease the TF ripple from 3.54% to 0.37% at -3.07 degrees plane. Moving WCCB blankets 20 mm outward in radial direction makes the maximum TF ripple from 0.56% to 0.09%. Discussions are made about the effect of the optimization methods for reducing TF ripple.