Current Profile and Energy Control in DIII-D Plasmas Using Discrete-Time Variable-Structure Control
M. Lauret, W. Wehner, E. Schuster, C. Holcomb, T.C. Luce, J.R. Ferron, M.L. Walker, D.A. Humphreys, B.G. Penaflor and R.D. Johnson
25th Mediterranean Conference on Control and Automation
Valletta, Malta, July 3-6, 2017
Abstract
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One of the most promising candidates to produce clean nuclear fusion
energy is the tokamak, a device magnetically confining an extremely
hot plasma (i.e. an ion- ized gas) where the fusion reactions take
place. To produce nuclear fusion energy using tokamak devices, it is
crucial that the poloidal magnetic flux (characterized by the
so-called q profile) and the plasma internal energy are tightly
controlled to avoid magnetohydrodynamic instabilities and to reach the
high pressures and temperatures that are needed for high fusion-power
density. Simultaneous control of the q profile and the internal energy
is challenging for a number of reasons: the system is nonlinear, there
are significant parameter uncertainties and large disturbances, the
available number of actuators is small, and the actuation authority is
limited from a control perspective. Therefore, a variable-structure
controller is proposed in this work to tackle this plasma control
problem since this type of controllers can typically diminish the
impact of serious disturbances and nonlinearities while still leading
to good performance. Simulations and recent experiments on the DIII-D
tokamak in a challenging high-confinement (H-mode) plasma regime show
that this control approach does indeed lead to good and repeatable
control of the q profile and the internal energy.