Robust Control of the Current Profile and Plasma Energy in EAST
H. Wang, E. Schuster
Symposium on Fusion Technology
Giardini Naxos, Sicily, Italy, September 16-21, 2018
Abstract
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Integrated control of the toroidal current density profile, or
alternatively the q-profile, and plasma stored energy is essential to
achieve advanced plasma scenarios characterized by high plasma
confinement, magnetohydrodynamics stability, and noninductively driven
plasma current. The q-profile evolution is closely related to the
evolution of the poloidal magnetic flux profile, whose dynamics is
modeled by a nonlinear partial differential equation (PDE) referred to
as the magnetic-flux diffusion equation (MDE). The MDE prediction depends
heavily on the chosen models for the electron temperature, plasma
resistivity, and non- inductive current drives. To aid controller
synthesis, control-oriented models for these plasma quantities are
necessary to make the problem tractable. However, a relatively large
deviation between the predictions by these control-oriented models and
experimental data is not uncommon. For this reason, the electron
temperature, plasma resistivity, and non-inductive current drives are
modeled in this work as the product of an “uncertain” reference profile
and a nonlinear function of the different auxiliary heating and
current-drive (H&CD) source powers and the total plasma current. The
uncertainties are quantified in such a way that the family of models
arising from the modeling process is able to capture the q-profile and
plasma stored energy dynamics from a typical EAST shot. A control-oriented
nonlinear PDE model is developed by combining the MDE with the “uncertain”
models for the electron temperature, plasma resistivity, and non-inductive
current drives. This model is then rewritten into a control framework to
design a controller that is robust against the modeled uncertainties.
The resulting controller utilizes EAST's H&CD powers and total plasma
current to regulate the q-profile and plasma stored energy even when
mismatches between modeled and actual dynamics are present. The
effectiveness of the controller is demonstrated through nonlinear
simulations.