Plasma Models for Real-time Control of Advanced Tokamak Scenarios
D. Moreau, D. Mazon, M.L. Walker, J.R. Ferron, K.H. Burrell, S.M. Flanagan, P. Gohil, R.J. Groebner, A.W. Hyatt, R.J. La Haye, J. Lohr, F. Turco, E. Schuster, Y. Ou, C. Xu, Y. Takase, Y. Sakamoto, S. Ide, T. Suzuki and ITPA-IOS group members and experts
Nuclear Fusion 51 (2011) 063009 (14pp)
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 modelling and was initially explored on JET
(Moreau et al 2008 Nucl. Fusion 48 106001). This paper deals with the general applicability of this strategy for simultaneous
magnetic and kinetic control on various tokamaks. 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 to both JT-60U and DIII-D data. On JT-60U, an existing series of high bootstrap current (~70%),
0.9 MA non-inductive 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 system identification experiments were carried out in the loop voltage (Vext) control mode (as opposed to current
control) to avoid feedback in the response data from the primary circuit. 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. 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 essential plasma parameter profiles to
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-principles plasma modelling.