Integrated Current Profile, Normalized Beta and NTM Control in DIII-D
A. Pajares, W.P. Wehner, E. Schuster, N. Eidietis, A. Welander, R. La Haye, J.R. Ferron, J. Barr, M. Walker, D. Humphreys, A. Hyatt
Fusion Engineering and Design, 146 (2019) 559–562.
Abstract
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There is an increasing need for integrating individual plasma-control
algorithms with the ultimate goal of simultaneously regulating more
than one plasma property. Some of these integrated-control solutions
should have the capability of arbitrating the authority of the individual
plasma-control algorithms over the available actuators within the
tokamak. Such decision-making process must run in real time since its
outcome depends on the plasma state. Therefore, control architectures
including supervisory and/or exception-handling algorithms will play
an essential role in future fusion reactors like ITER. However, most
plasma-control experiments in present devices have focused so far on
demonstrating control solutions for isolated objectives. In this work,
initial experimental results are reported for simultaneous current-profile
control, normalized-beta control, and Neoclassical Tearing Mode (NTM)
suppression in DIII-D. Neutral beam injection (NBI), electron-cyclotron
(EC) heating & current drive (H&CD), and plasma current modulation are
the actuation methods. The NBI power and plasma current are always
modulated by the Profile Control category within the DIII-D Plasma
Control System (PCS) in order to control both the current profile and
the normalized beta. EC H&CD is utilized by either the Profile Control
or the Gyrotron categories within the DIII-D PCS as dictated by the
Off-Normal and Fault Response (ONFR) system, which monitors the
occurrence of an NTM and regulates the authority over the gyrotrons.
The total EC power and poloidal mirror angles are the gyrotron-related
actuation variables. When no NTM suppression is required, the gyrotrons
are used by the Profile Control category, but when NTM suppression is
required, the ONFR transfers the authority over the gyrotrons to the
NTM stabilization algorithm located in the Gyrotron category. Initial
experimental results show that simultaneous control of different
aspects of the plasma dynamics may improve the overall control and
plasma performances. Also, the potential of the ONFR system to successfully
integrate competing control algorithms is demonstrated.