Error field correction in ITER

Abstract

A new method for correcting magnetic field errors in the ITER tokamak is developed using the Ideal Perturbed Equilibrium Code (IPEC). The dominant external magnetic field for driving islands is shown to be localized to the outboard midplane for three ITER equilibria that represent the projected range of operational scenarios. The coupling matrices between the poloidal harmonics of the external magnetic perturbations and the resonant fields on the rational surfaces that drive islands are combined for different equilibria and used to determine an ordered list of the dominant errors in the external magnetic field. It is found that efficient and robust error field correction is possible with a fixed setting of the correction currents relative to the currents in the main coils across the range of ITER operating scenarios that was considered.

Importance of plasma response to nonaxisymmetric perturbations in tokamaks

“…3 and 4, consistent correlations were restored between the total resonant field and the locking density, for the cases where the external resonant field showed no correlations or even opposite results in both NSTX and DIII-D. Also, the strong correlations among the total resonant resonant field δB mn (δB 21 and δB 31 in Fig. 4) at different rational surfaces imply that the plasma response is sensitive to a particular external field [33,34]. However, the estimations of the total resonant field have been improved from [33] as explained in the following paragraphes.…”

“…The applications to locking experiments in both NSTX and DIII-D have shown the importance of plasma response to understand the observations, and an improved approach using the weighted resonant field including ideal plasma response. This method could be used to give more reliable correction of the intrinsic error field and the prediction of error field threshold in International Thermonuclear Energy Reactor (ITER) [34].…”

Theory of tokamak disruptions

“…The two effects are interrelated because the most important error fields are amplified by the response of the plasma 35 and the error field response of a plasma can become sufficiently strong to be an instability, the resistive wall mode.…”

Theory and observations of magnetic islands

“…[20] Among other applications, IPEC enables the optimization of the design of error-field correction coils. [21] In stellarators, by contrast, the reference-state itself contains current singularities but their amplitude is minimized by design. Stellarator equilibrium codes separate into those that assume simply nested magnetic surfaces, such as VMEC, [22] and those that allow for magnetic islands, such as HINT and PIES.…”