Architectural Concept for the ITER Plasma Control System
W. Treutterer, D. Humphreys, G. Raupp, E. Schuster, J. Snipes, G. Tommasi, M. Walker, A. Winter
IAEA Technical Meeting on Control, Data Acquisition and Remote Participation for Fusion Research
Hefei, China on May 6-10, 2013
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Abstract
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The plasma control system is a key instrument for successfully
investigating the physics of burning plasma at ITER. It has the task
to execute an experimental plan, known as pulse schedule, in the
presence of complex relationships between plasma parameters like
temperature, pressure, confinement and shape. The biggest challenge in
the design of the control system is to find an adequate breakdown of
this task in a hierarchy of feedback control functions. But it is also
important to foresee structures that allow handling unplanned
exceptional situations to protect the machine. Also the management of
the limited number of actuator systems for multiple targets is an
aspect with a strong impact on system architecture. Finally, the
control system must be flexible and reconfigurable to cover the
manifold facets of plasma behavior and investigation goals.
In order to prepare the development of a control system for ITER plasma
operation, a conceptual design has been proposed by a group of worldwide
experts and reviewed by an ITER panel in 2012. In this paper we describe
the fundamental principles of the proposed control system architecture
and how they were derived from a systematic collection and analysis of
use cases and requirements. The experience and best practices from many
fusion devices and research laboratories, augmented by the envisaged
ITER specific tasks, build the foundation of this collection. In the
next step control functions were distilled from this input. An analysis
of the relationships between the functions allowed sequential and
parallel structures, alternate branches and conflicting requirements to
be identified. Finally, a concept of selectable control layers consisting
of nested “master controllers” was synthesized. Each control layer
represents a cascaded scheme from high-level to elementary controllers
and implements a control hierarchy. The master controllers are used to
resolve conflicts when several control functions would use the same
command signals as their outputs. They consist of a collection of
potentially conflicting control functions from which one at a time is
exclusively activated by a mode selector signal.
It can be shown that this architectural design is capable of implementing
all of the presently known functional control requirements. Furthermore,
this design takes already into account that the result of future
experiments at ITER will create additional requirements on the functions
or performance of ITER plasma control.
