Time variation of error field correction in ITER

The time variation of required error field correction (EFC) in ITER is evaluated in a feedforward way based on the estimation of total n=1 error fields (EFs, n is the toroidal mode number) for two typical ITER scenarios, steady state scenario 10MA/5.3T with Q=5 and baseline scenario 15MA/5.3T with Q=10. The total n=1 EFs are evaluated in two parts: the first part is EFs that can be calculated before ITER assembly, i.e., those due to non-axisymmetric coil winding and intrinsic non-axisymmetric components such as Ferromagnetic Inserts (FIs) and Test Blanket Modules (TBMs) in ITER. The second part of n=1 EFs is due to misalignment of coils during assembly which remains yet unknown; these EFs are estimated by the Monte-Carlo simulation while assuming certain misalignment tolerances planned to be used as target for assembly. By taking into account the ideal plasma response to EFs using the General Perturbed Equilibrium Code (GPEC), it is found that n=1 overlap EFs due to FIs and TBMs are comparable to those due to the expected ones from misalignment of coils, while those due to non-axisymmetric coil winding is an order of magnitude lower. Their expected sum, i.e., total n=1 EFs, remain below the corresponding n=1 locking threshold predicted for ITER. These n=1 EFs will then be corrected by the side correction coils in ITER along the plasma pulses. The required EFC current is evaluated at multiple time slices, and it does not show monotonic variation during the increase of β_N after L-H transition. Instead it will first increase and then decrease, and the maximum value will not more than 40kAt if the tolerances for misalignment are achieved. Besides n=1 EFs, the possible sources and correction of n=2 EFs in ITER are also discussed.