Robust Nonlinear Control of the Minimum Safety Factor in Tokamaks
A. Pajares and E. Schuster
Proceedings of the 2021 IEEE Conference on Control Technology and Applications (CCTA)
San Diego, California, USA, August 8-11, 2021
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Abstract
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Tokamaks are torus-shaped devices whose goal is
to produce energy by means of thermonuclear fusion reactions.
This is achieved by using helical magnetic fields to confine
a plasma, i.e., a very hot ionized gas, so that the necessary
conditions for fusion (i.e., high pressure and confinement time)
are achieved. The safety factor is a measure of the pitch of
the magnetic-field lines, and plays an important role in the
magnetohydrodynamic stability and confinement properties of
the plasma. In particular, the minimum value of the safety
factor across the plasma spatial domain is often closely related
to the maximum achievable plasma pressure. In this work,
a robust, nonlinear, model-based controller for the regulation
of the minimum safety factor is presented. The controller is
synthesized via Lyapunov theory, and robustified against model
uncertainties by means of Lyapunov redesign techniques. The
controller is tested, together with a controller for the plasma
thermal energy, in one-dimensional simulations using COTSIM
(Control Oriented Transport SIMulator) for a DIII-D scenario.
