Integrated Control and Actuator Management Strategies for Internal Inductance and Normalized Beta Regulation
A. Pajares and E. Schuster
Fusion Engineering and Design 170 (2021) 112526.
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Abstract
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An integrated-control architecture for simultaneous regulation of the
plasma internal inductance and normalized beta has been designed and
tested in simulations using COTSIM (Control-Oriented Transport SIMulator).
As present-day tokamaks evolve into nuclear-fusion reactors capable of
producing net energy, a significant control-engineering challenge must
be solved: regulating a wide variety of plasma variables, often
simultaneously, by employing only a reduced number of actuators. As a
contribution towards this objective, the present work tackles the problem
of controlling the plasma internal inductance, which is a proxy for the
broadness of the current-density profile, simultaneously with the plasma
normalized beta. Based on zero-dimensional, control-oriented models of
the plasma dynamics, individual Lyapunov-theory-based controllers for
the internal inductance and normalized beta have been developed. These
controllers are integrated by means of an actuator manager that decides,
in real time, how the available actuators are utilized in order to fulfill
as many control objectives as possible. In addition, the actuator manager
is designed to achieve a particular performance metric defined by the
control engineer. This metric could be, for example, prioritizing a
particular control task over the others and/or minimizing the use of a
particular actuator during certain phases of the plasma discharge. Using
COTSIM, which includes one-dimensional models of the plasma current-density
and electron-temperature dynamics, the performance of the integrated-control
framework has been tested in a steady-state scenario for the DIII-D tokamak.
These simulation results yield illustrative insights into the plasma
current-density and electron-temperature controllability with the current
actuation capabilities in DIII-D. Moreover, these simulations show that
the way in which the different actuators are employed during the discharge
(based on the choice of the aforementioned actuator-manager performance
metric) highly determines the value of internal inductance and
normalized beta achieved in steady-state conditions, and therefore,
the final current-profile shape.
