Optimal error field correction (EFC) is thought to be achieved when coupling to the least-stable “dominant” mode of the plasma is nulled at each toroidal mode number (n). The limit of this picture is tested in the DIII-D tokamak by applying superpositions of in- and ex-vessel coil set n = 1 fields calculated to be fully orthogonal to the n = 1 dominant mode. In co-rotating H-mode and low-density Ohmic scenarios, the plasma is found to be, respectively, 7× and 20× less sensitive to the orthogonal field as compared to the in-vessel coil set field. For the scenarios investigated, any geometry of EFC coil can thus recover a strong majority of the detrimental effect introduced by the n = 1 error field. Despite low sensitivity to the orthogonal field, its optimization in H-mode is shown to be consistent with minimizing the neoclassical toroidal viscosity torque and not the higher-order n = 1 mode coupling.
The importance of matched poloidal spectra to error field correction in DIII-D
C. Paz-Soldan, M. J. Lanctot, N. C. Logan, D. Shiraki, R. J. Buttery, J. M. Hanson, R. J. La Haye, J.-K. Park, W. M. Solomon, E. J. Strait; The importance of matched poloidal spectra to error field correction in DIII-D. Phys. Plasmas 1 July 2014; 21 (7): 072503. https://doi.org/10.1063/1.4886795
Download citation file: