Impact of Error Fields on Equilibrium Configurations in ITER

Error fields in ITER are considered one of the major sources of possible loss of performance in the actual device with respect to the design. As a matter of fact, small discrepancies of magnetic field from the nominal one will interact with plasma evolution leading to birth of magnetic islands and finally loss of stability. This issue is well known in present experimental Tokamaks, and it is expected to be even more relevant in larger machines such as ITER. The error field level driving plasma to loss of stability can be estimated using numerical models and/or available experimental data, giving rise to estimates of ―acceptable‖ error fields. Error fields in actual devices are then counteracted using suited correction coils, to achieve satisfacory field maps. On the other hand, the effect of the error fields on plasma equilibrium configuration is still being actively investigated. In this work, the analysis of the effect of residual error fields on the ITER axisymmetric plasma configurations wll be performed. First, a number of deformed coils configurations are considered, and the corresponding error fields are computed by means of the MISTIC code [1]. Then, the CarMa0NL code [2], able to solve nonlinear Grad-Shafranov equations in presence of 3D conductors, is used to evaluate the subsequent perturbation of the plasma axisymmetric equilibrium configuration. Various cases will be presented, in order to highlight the expected effect of specific coil deformations. Moreover, also a ―statistical‖ overview of possible consequences of specific sets of deformations will be carried out.