Integrated Current Profile, Normalized Beta and NTM Control in DIII-D
A. Pajares, E. Schuster, W.P. Wehner, N. Eidietis, A. Welander, R. La Haye, J.R. Ferron, J. Barr, M. Walker, D. Humphreys, A. Hyatt
Symposium on Fusion Technology
Giardini Naxos, Sicily, Italy, September 16-21, 2018
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 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. Electron-cyclotron
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 a Neoclassical Tearing
Mode (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 the potential of the ONFR system to successfully
integrate competing control algorithms.