Burn Control in Fusion Reactors via Nonlinear Stabilization Techniques
E. Schuster, M. Krstic and G. Tynan
Fusion Science and Technology, vol.43, no.1, pp. 18-37, January 2003
Abstract
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Control of plasma density and temperature magnitudes, as well as their profiles, are among
the most fundamental problems in fusion reactors. Existing efforts on model-based control use
control techniques for linear models. In this work, a zero-dimensional nonlinear model involving
approximate conservation equations for the energy and the densities of the species was used to
synthesize a nonlinear feedback controller for stabilizing the burn condition of a fusion reactor.
The subignition case, where the modulation of auxiliary power and fueling rate are considered as
control forces, and the ignition case, where the controlled injection of impurities is considered as an
additional actuator, are treated separately.
The model addresses the issue of the lag due to the finite time for the fresh fuel to diffuse into
the plasma center. In this way we make our control system independent of the fueling system and
the reactor can be fed either by pellet injection or by puffing. This imposed lag is treated using
nonlinear backstepping.
The nonlinear controller proposed guarantees a much larger region of attraction than the previous
linear controllers. In addition, it is capable of rejecting perturbations in initial conditions
leading to both thermal excursion and quenching, and its effectiveness does not depend on whether
the operating point is an ignition or a subignition point.
The controller designed ensures set point regulation for the energy and plasma parameter b
with robustness against uncertainties in the confinement times for different species. Hence, the
controller can increase or decrease b, modify the power, the temperature or the density, and go from
a subignition to an ignition point and vice versa.