Journal
NUCLEAR FUSION
Volume 56, Issue 7, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/0029-5515/56/7/076003
Keywords
error field optimization; real-time control; non-axisymmetric fields
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Funding
- U.S. Department of Energy, Office of Science, Office of Fusion Energy Sciences [DE-FC02-04ER54698, DE-AC05-06OR23100, DE-FG02-04ER54761]
- U.S. Department of Energy, Office of Science, Office of Workforce Development for Teachers and Scientists (WDTS) under the Science Undergraduate Laboratory Internships Program (SULI)
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DIII-D experiments have demonstrated a new real-time approach to tokamak error field control based on maximizing the toroidal angular momentum. This approach uses extremum seeking control theory to optimize the error field in real time without inducing instabilities. 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.
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