Time variation of error field correction in ITER

Abstract The time variation of the required error field correction (EFC) in ITER is evaluated in a feedforward way based on estimates of the total n = 1 error fields (EFs, where n is the toroidal mode number) for two typical ITER scenarios: a steady state scenario at 10 MA/5.3 T with Q = 5 and a baseline scenario at 15 MA/5.3 T with Q = 10. The total n = 1 EFs are evaluated in two parts: the first part consists of 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 the n = 1 EFs is due to misalignment of coils during assembly, which are not yet known; these EFs are estimated by Monte Carlo simulations while assuming certain misalignment tolerances that are planned to be used as assembly targets. By taking into account the ideal plasma response to EFs using a general perturbed equilibrium code, it is found that n = 1 overlap EFs due to FIs and TBMs are comparable to those due to those expected from misalignment of coils, while those due to non-axisymmetric coil winding are an order of magnitude lower. Their expected sum, i.e., the total n = 1 EFs, remains 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi>β</mml:mi> <mml:mrow> <mml:mtext>N</mml:mtext> </mml:mrow> </mml:msub> </mml:mrow> </mml:mrow> </mml:math> after L–H transition. Instead, it will first increase and then decrease, and the maximum value will not be more than 40 kAt 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.