skip to main content


Title: Error field optimization in DIII-D using extremum seeking control

A closed-loop error field control algorithm is implemented in the Plasma Control System of the DIII-D tokamak and used to identify optimal control currents during a single plasma discharge. The algorithm, based on established extremum seeking control theory, exploits the link in tokamaks between maximizing the toroidal angular momentum and minimizing deleterious non-axisymmetric magnetic fields. Slowly-rotating n = 1 fields (the dither), generated by external coils, are used to perturb the angular momentum, monitored in real-time using a charge-exchange spectroscopy diagnostic. Simple signal processing of the rotation measurements extracts information about the rotation gradient with respect to the control coil currents. This information is used to converge the control coil currents to a point that maximizes the toroidal angular momentum. The technique is well-suited for multi-coil, multi-harmonic error field optimizations in disruption sensitive devices as it does not require triggering locked tearing modes or plasma current disruptions. Control simulations highlight the importance of the initial search direction on the rate of the convergence, and identify future algorithm upgrades that may allow more rapid convergence that projects to convergence times in ITER on the order of tens of seconds.
 [1] ;  [2] ;  [3] ;  [1] ;  [1] ;  [4] ;  [1] ;  [1] ;  [1]
  1. General Atomics, San Diego, CA (United States)
  2. Oak Ridge Associated Univ., Oak Ridge, TN (United States)
  3. Univ. of California San Diego, La Jolla, CA (United States)
  4. Columbia Univ., New York, NY (United States)
Publication Date:
Grant/Contract Number:
FC02-04ER54698; AC05-06OR23100; FG02-04ER54761
Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 56; Journal Issue: 7; Related Information: M.J. Lanctot, K.E.J. Olofsson, M. Capella, D.A. Humphreys, N. Eidietis, J.M. Hanson, C. Paz-Soldan, E.J. Strait and M.L. Walker, "Error field optimization in DIII-D using extremum seeking control," Nucl. Fusion 56, 076003 (2016).; Journal ID: ISSN 0029-5515
IOP Science
Research Org:
General Atomics, San Diego, CA (United States)
Sponsoring Org:
Country of Publication:
United States
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; error field optimization; real-time control; non-axisymmetric fields
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1255456