Analysis and Optimization of the Impact of Ferromagnetic Inserts on the Toroidal Field Ripple in ITER

The discreteness of the toroidal field (TF) coils causes toroidally asymmetric perturbations of magnetic field (TF ripple). Maximum value of the TF ripple produced in the plasma by ITER TF coils is 1.16%. The ripple requirements are determined by loss of fast particles and by potential changes in H-mode characteristics. The fast particle behavior is well known and a maximum TF ripple at the plasma separatrix of <;1% is enough to avoid excessive fast particle losses in all ITER scenarios. The quantitative influence of TF ripple on plasma performance in the H-mode remains the subject of continuing R&D and at this time the prudent approach is to make ripple as small as reasonably achievable. It is shown that optimum distribution of ferromagnetic inserts (FI) allows reduction of the TF ripple to about 0.3% in regular sectors of the ITER vacuum vessel (VV) and to about 0.55% in irregular VV sectors. Error fields produced by irregularity of the FI and currents in correction coils required for their reduction were also calculated.