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Title: Measurement of tokamak error fields using plasma response and its applicability to ITER

The nonlinear response of a low-beta tokamak plasma to non-axisymmetric fields offers an alternative to direct measurement of the non-axisymmetric part of the vacuum magnetic fields, often termed “error fields”. Possible approaches are discussed for determination of error fields and the required current in non-axisymmetric correction coils, with an emphasis on two relatively new methods: measurement of the torque balance on a saturated magnetic island, and measurement of the braking of plasma rotation in the absence of an island. The former is well suited to ohmically heated discharges, while the latter is more appropriate for discharges with a modest amount of neutral beam heating to drive rotation. Both can potentially provide continuous measurements during a discharge, subject to the limitation of a minimum averaging time. The applicability of these methods to ITER is discussed, and an estimate is made of their uncertainties in light of the specifications of ITER’s diagnostic systems. Furthermore, the use of plasma response-based techniques in normal ITER operational scenarios may allow identification of the error field contributions by individual central solenoid coils, but identification of the individual contributions by the outer poloidal field coils or other sources is less likely to be feasible.
Authors:
 [1] ;  [1] ;  [2] ;  [1] ;  [3] ;  [1] ;  [2] ;  [1] ;  [4] ;  [1] ;  [3]
  1. General Atomics, San Diego, CA (United States)
  2. ITER Organization, Saint Paul Lez Durance (France)
  3. Columbia Univ., New York, NY (United States)
  4. Columbia Univ., New York, NY (United States); Ecole Polytechnique Federal de Lausanne (EPFL), Lausanne (Switzerland)
Publication Date:
Grant/Contract Number:
FC02-04ER54698
Type:
Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 54; Journal Issue: 7; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Research Org:
General Atomics, San Diego, CA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; error field; magnetic island; locked mode; tokamak; ITER
OSTI Identifier:
1351080

Strait, Edward J., Buttery, Richard J., Casper, T. A., Chu, M. S., Hanson, Jeremy M., Garofalo, Andrea M., Gribov, Y., La Haye, Robert J., Reimerdes, H., Schaffer, M. J., and Volpe, F. A.. Measurement of tokamak error fields using plasma response and its applicability to ITER. United States: N. p., Web. doi:10.1088/0029-5515/54/7/073004.
Strait, Edward J., Buttery, Richard J., Casper, T. A., Chu, M. S., Hanson, Jeremy M., Garofalo, Andrea M., Gribov, Y., La Haye, Robert J., Reimerdes, H., Schaffer, M. J., & Volpe, F. A.. Measurement of tokamak error fields using plasma response and its applicability to ITER. United States. doi:10.1088/0029-5515/54/7/073004.
Strait, Edward J., Buttery, Richard J., Casper, T. A., Chu, M. S., Hanson, Jeremy M., Garofalo, Andrea M., Gribov, Y., La Haye, Robert J., Reimerdes, H., Schaffer, M. J., and Volpe, F. A.. 2014. "Measurement of tokamak error fields using plasma response and its applicability to ITER". United States. doi:10.1088/0029-5515/54/7/073004. https://www.osti.gov/servlets/purl/1351080.
@article{osti_1351080,
title = {Measurement of tokamak error fields using plasma response and its applicability to ITER},
author = {Strait, Edward J. and Buttery, Richard J. and Casper, T. A. and Chu, M. S. and Hanson, Jeremy M. and Garofalo, Andrea M. and Gribov, Y. and La Haye, Robert J. and Reimerdes, H. and Schaffer, M. J. and Volpe, F. A.},
abstractNote = {The nonlinear response of a low-beta tokamak plasma to non-axisymmetric fields offers an alternative to direct measurement of the non-axisymmetric part of the vacuum magnetic fields, often termed “error fields”. Possible approaches are discussed for determination of error fields and the required current in non-axisymmetric correction coils, with an emphasis on two relatively new methods: measurement of the torque balance on a saturated magnetic island, and measurement of the braking of plasma rotation in the absence of an island. The former is well suited to ohmically heated discharges, while the latter is more appropriate for discharges with a modest amount of neutral beam heating to drive rotation. Both can potentially provide continuous measurements during a discharge, subject to the limitation of a minimum averaging time. The applicability of these methods to ITER is discussed, and an estimate is made of their uncertainties in light of the specifications of ITER’s diagnostic systems. Furthermore, the use of plasma response-based techniques in normal ITER operational scenarios may allow identification of the error field contributions by individual central solenoid coils, but identification of the individual contributions by the outer poloidal field coils or other sources is less likely to be feasible.},
doi = {10.1088/0029-5515/54/7/073004},
journal = {Nuclear Fusion},
number = 7,
volume = 54,
place = {United States},
year = {2014},
month = {4}
}