TRANSP-based Closed-loop Simulations of Current Profile Optimal Regulation in NSTX-Upgrade
Z.O. Ilhan, E. Schuster, M.D. Boyer
Symposium on Fusion Technology
Giardini Naxos, Sicily, Italy, September 16-21, 2018
Abstract
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Active control of the toroidal current density profile is one of the
plasma control milestones that the National Spherical Tokamak eXperiment
- Upgrade (NSTX-U) program must achieve to realize and sustain
high-performance, MHD-stable plasma operation. As a first step towards
the realization of this goal, a nonlinear, control-oriented,
physics-based model describing the temporal evolution of the current
profile has been obtained by combining the magnetic diffusion equation
with empirical correlations obtained for the electron density, electron
temperature, and non-inductive current drives in NSTX-U [Fusion Eng.
Des., 123 (2017) 564–568]. The proposed model has then been embedded
into the control design process to synthesize a time-invariant,
linear-quadratic-integral, optimal controller capable of regulating the
rotational transform profile around a desired target profile while
rejecting disturbances. Neutral beam injectors, electron density, and
the total plasma current are used as actuators to shape the current
profile. The effectiveness of the proposed controller in regulating the
rotational transform profile in NSTX-U is demonstrated in this work in
closed-loop nonlinear simulations based on the physics-oriented code
TRANSP. These high-fidelity closed- loop simulations, which are a
critical step before experimental implementation and testing, are enabled
by a flexible framework recently developed to perform feedback control
design and simulation in TRANSP [Nucl. Fusion 55 (2015) 053033 (15pp)].