Actuator Management via Real-time Optimization for Integrated Control in Tokamaks
A. Pajares and E. Schuster
European Physical Society (EPS) Conference on Plasma Physics (CPP)
Milan, Italy, July 8-12, 2019
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Abstract
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In ITER, only a limited number of actuators is available to carry out
a great variety of control tasks, some of which may be closely coupled.
Safe operation while attaining high plasma performance will require an
integrated Plasma Control System (PCS) that has the capability of
simultaneously regulating as many aspects of the plasma dynamics as
possible. Moreover, such integrated PCS must include supervisory and a
ctuator management systems. The goal of such systems is to determine
and assign in real time the authority of each control task over the
available actuation mechanisms depending on the plasma state. In this
work, an integrated controller with actuator management capabilities
is proposed for simultane- ous control of the central safety factor,
q0, the edge safety factor, qedge, the total stored energy, W , the
bulk toroidal rotation and/or line-average electron density. Figure 1
shows a simplified schematic of a possible PCS architecture in which
the integrated controller proposed in this work could be embedded. The
integrated controller is based on zero-dimensional, control-level models
of the plasma dynamics, and is synthesized using nonlinear, robust
Lyapunov techniques to ensure high performance despite nonlinear,
unknown plasma dynamics. The actuator management algorithm employs the
time-varying, plasma-state-dependent control priorities to decide which
actuators are utilized for each control task. The actuator management
problem is solved as a real-time optimization problem, providing
substantial flexibility to include changing control objectives in the
form of time-varying constraints. Also, this scheme allows for performing
the two main kinds of actuator sharing envisioned for ITER: Simultaneous
Multiple Mission (SMM) sharing and Repurposing (RP) sharing [1]. The
proposed control algorithm is tested in one-dimensional simulations
using the Control Oriented Transport SIMulator (COTSIM) code.
[1] D.Humphreys et al., Novel aspects of plasma control in ITER, Phys. Plasmas 22, 021806 (2015).
