Plasma Models for Real-Time Control of Advanced Tokamak Scenarios
D. Moreau, D. Mazon, M. L. Walker, J. R. Ferron, S. M. Flanagan, P. Gohil, R. J. Groebner, R. J. La Haye, E. Schuster, Y. Ou, C. Xu, Y. Takase, Y. Sakamoto, S. Ide, T. Suzuki and ITPA-IOS group members and experts
IAEA Fusion Energy Conference
Daejon, Korea, 11-16 October 2010
Abstract
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An integrated plasma profile control strategy, ARTAEMIS, is being
developed for extrapolating present-day advanced tokamak (AT) scenarios
to steady state operation. The approach is based on semi- empirical
(grey-box) modeling. It was initially explored on JET, for current
profile control only (D. Moreau, et al., Nucl. Fus. 48 (2008) 106001).
The present paper deals with the generalization of this strategy to
simultaneous magnetic and kinetic control. The determination of the
device-specific, control-oriented models that are needed to compute
optimal controller matrices for a given operation scenario is discussed.
The methodology is generic and can be applied to any device, with
different sets of heating and current drive actuators, controlled
variables and profiles. The system identification algorithms take
advantage of the large ratio between the magnetic and thermal diffusion
time scales and have been recently applied, in their full version, to
both JT-60U and DIII-D data. On JT-60U, an existing series of
high-bootstrap-current (~70%), 0.9 MA noninductive AT discharges was
used. The actuators consisted of four groups of neutral beam injectors
aimed at perpendicular injection (on-axis and off-axis), and co-current
tangential injection (also on-axis and off-axis). On DIII-D, dedicated o
pen-loop modulation experiments were carried out. The reference plasma
state was that of a 0.9 MA AT scenario which had been optimized to
combine non-inductive current fractions near unity with 3.5 < beta_N < 3.9,
bootstrap current fractions larger than 65%, and H98(y,2)=1.5. DIII-D
was operated in the loop voltage (Vext) control mode (as opposed to
current control) to avoid feedback in the response data from the
primary circuit. Actuators other than Vext were co-current, counter-current
and balanced neutral beam injection, and electron cyclotron current drive.
Power and loop voltage modulations resulted in dynamic variations of
the plasma current between 0.7 and 1.2 MA. It is concluded that the
response of several essential plasma parameter profiles to the specific
actuators of a given device can be satisfactorily identified from a
small set of experiments. This provides, for control purposes, a readily
available alternative to first-principle plasma modeling.