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

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Abstract

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.

Original languageEnglish
Article number072503
JournalPhysics of Plasmas
Volume21
Issue number7
DOIs
StatePublished - Jul 2014
Externally publishedYes

Funding

FundersFunder number
U.S. Department of EnergyDE-FG02-04ER54761, DE-AC02-09CH11466, DE-FC02-04ER54698, DE-AC05-06OR23100

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