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Title: Tokamak plasma high field side response to an n = 3 magnetic perturbation: a comparison of 3D equilibrium solutions from seven different codes

Abstract

In comparing equilibrium solutions for a DIII-D shot that is amenable to analysis by both stellarator and tokamak three-dimensional (3D) equilibrium codes, a significant disagreement has been seen between solutions of the VMEC stellarator equilibrium code and solutions of tokamak perturbative 3D equilibrium codes. In this research, the source of that disagreement has been investigated, and that investigation has led to new insights into the domain of validity of the different equilibrium calculations, and to a finding that the manner in which localized screening currents at low order rational surfaces are handled can affect global properties of the equilibrium solution. The perturbative treatment has been found to break down at surprisingly small perturbation amplitudes due to overlap of the calculated perturbed flux surfaces, and that treatment is not valid in the pedestal region of the DIII-D shot studied. The perturbative treatment is valid, however, further into the interior of the plasma, and flux surface overlap does not account for the disagreement investigated here. Calculated equilibrium solutions for simple model cases and comparison of the 3D equilibrium solutions with those of other codes indicate that the disagreement arises from a difference in handling of localized currents at low order rational surfaces,more » with such currents being absent in VMEC and present in the perturbative codes. The significant differences in the global equilibrium solutions associated with the presence or absence of very localized screening currents at rational surfaces suggests that it may be possible to extract information about localized currents from appropriate measurements of global equilibrium plasma properties. Therefore, that would require improved diagnostic capability on the high field side of the tokamak plasma, a region difficult to access with diagnostics.« less

Authors:
 [1];  [2];  [2];  [1];  [3];  [2];  [2];  [4];  [5];  [6];  [1];  [7]
  1. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  2. General Atomics, San Diego, CA (United States)
  3. New York Univ. (NYU), NY (United States)
  4. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  5. Culham Science Centre, Abingdon (United Kingdom)
  6. National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States)
  7. National Institute for Fusion Science, Kyoto (Japan)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1311250
DOE Contract Number:  
AC05-00OR22725; AC02-09CH11466; FC02-04E854698; FG02-95E854309; FG02-86ER53223
Resource Type:
Journal Article
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 55; Journal Issue: 6; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; 3D equilibrium; magnetic perturbation; ELM; 3-DIMENSIONAL MAGNETOHYDRODYNAMIC EQUILIBRIA; SPECTRAL CODE

Citation Formats

Reiman, A. H., Ferraro, N. M., Turnbull, A. D., Park, J. K., Cerfon, A., Evans, T. E., Lanctot, Matthew J., Lazarus, E. A., Liu, Y. Q., McFadden, G., Monticello, D., and Suzuki, Y. Tokamak plasma high field side response to an n = 3 magnetic perturbation: a comparison of 3D equilibrium solutions from seven different codes. United States: N. p., 2015. Web. doi:10.1088/0029-5515/55/6/063026.
Reiman, A. H., Ferraro, N. M., Turnbull, A. D., Park, J. K., Cerfon, A., Evans, T. E., Lanctot, Matthew J., Lazarus, E. A., Liu, Y. Q., McFadden, G., Monticello, D., & Suzuki, Y. Tokamak plasma high field side response to an n = 3 magnetic perturbation: a comparison of 3D equilibrium solutions from seven different codes. United States. doi:10.1088/0029-5515/55/6/063026.
Reiman, A. H., Ferraro, N. M., Turnbull, A. D., Park, J. K., Cerfon, A., Evans, T. E., Lanctot, Matthew J., Lazarus, E. A., Liu, Y. Q., McFadden, G., Monticello, D., and Suzuki, Y. Fri . "Tokamak plasma high field side response to an n = 3 magnetic perturbation: a comparison of 3D equilibrium solutions from seven different codes". United States. doi:10.1088/0029-5515/55/6/063026.
@article{osti_1311250,
title = {Tokamak plasma high field side response to an n = 3 magnetic perturbation: a comparison of 3D equilibrium solutions from seven different codes},
author = {Reiman, A. H. and Ferraro, N. M. and Turnbull, A. D. and Park, J. K. and Cerfon, A. and Evans, T. E. and Lanctot, Matthew J. and Lazarus, E. A. and Liu, Y. Q. and McFadden, G. and Monticello, D. and Suzuki, Y.},
abstractNote = {In comparing equilibrium solutions for a DIII-D shot that is amenable to analysis by both stellarator and tokamak three-dimensional (3D) equilibrium codes, a significant disagreement has been seen between solutions of the VMEC stellarator equilibrium code and solutions of tokamak perturbative 3D equilibrium codes. In this research, the source of that disagreement has been investigated, and that investigation has led to new insights into the domain of validity of the different equilibrium calculations, and to a finding that the manner in which localized screening currents at low order rational surfaces are handled can affect global properties of the equilibrium solution. The perturbative treatment has been found to break down at surprisingly small perturbation amplitudes due to overlap of the calculated perturbed flux surfaces, and that treatment is not valid in the pedestal region of the DIII-D shot studied. The perturbative treatment is valid, however, further into the interior of the plasma, and flux surface overlap does not account for the disagreement investigated here. Calculated equilibrium solutions for simple model cases and comparison of the 3D equilibrium solutions with those of other codes indicate that the disagreement arises from a difference in handling of localized currents at low order rational surfaces, with such currents being absent in VMEC and present in the perturbative codes. The significant differences in the global equilibrium solutions associated with the presence or absence of very localized screening currents at rational surfaces suggests that it may be possible to extract information about localized currents from appropriate measurements of global equilibrium plasma properties. Therefore, that would require improved diagnostic capability on the high field side of the tokamak plasma, a region difficult to access with diagnostics.},
doi = {10.1088/0029-5515/55/6/063026},
journal = {Nuclear Fusion},
issn = {0029-5515},
number = 6,
volume = 55,
place = {United States},
year = {2015},
month = {5}
}