Model-based Optimal Scenario Planning in EAST
H. Wang, E. Schuster
Symposium on Fusion Technology
Prague, Czech Republic, September 5-9, 2016
Abstract
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Ongoing work in the fusion community focuses on developing advanced
plasma scenarios characterized by high plasma confinement,
magnetohydrodynamic (MHD) stability, and noninductively driven plasma
current. The toroidal current density profile, or alternatively the q
profile, together with the normalized beta, are often used to
characterize these advanced scenarios. The development of these
advanced scenarios is experimentally carried out by specifying the
device’s actuator trajectory waveforms, such as the total plasma current,
the plasma density, and the auxiliary heating and current-drive (H&CD)
sources based on trial- and-error basis. In this work, a model-based
numerical optimization algorithm is developed to complement the
experimental effort of actuator trajectory planning in the EAST tokamak.
The evolution of the q profile 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). In this work, the MDE is
combined with physics-based correlations obtained from EAST experimental
data for the plasma density, temperature, resistivity and non-inductive
current drives to develop a control- oriented nonlinear PDE model. The
optimization objective is to design feedforward trajectories for the
plasma current, density, electron cyclotron heating, neutral beam
injection and lower hybrid current drive that steer the plasma to
desired q profile and βN such that the achieved state is stationary in
time. The optimization is subject to the plasma dynamics (described by
the physics-based PDE model) and plasma state and actuator constraints,
such as the maximum available amount of H&CD power and MHD stability
limits. This defines a nonlinear, constrained optimization problem that
is solved by employing sequential quadratic programming. The optimized
actuator trajectories are assessed in nonlinear transport simulations
in preparation for experimental tests in the EAST tokamak.