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Fusion Engineering and Design 83 (2008) 276–279
Application of PLC to dynamic control system for liquid He cryogenic
pumping facility on JT-60U NBI system
A. Honda
∗
, F. Okano, K. Ooshima, N. Akino, K. Kikuchi, Y. Tanai,
T. Takenouchi, S. Numazawa, Y. Ikeda
Fusion Research and Development Directorate, Japan Atomic Energy Agency, 801-1 Mukouyayama, Naka-shi, Ibaraki-ken 311-0193, Japan
Available online 7 March 2008
Abstract
The control system of the cryogenic facility in the JT-60 NBI system has been replaced by employing the PLC (Programmable Logic Controller)
and SCADA (Supervisory Control And Data Acquisition) system. The original control system was constructed about 20 years ago by specifying
the DCS (Distributed Control System) computer to deal with ∼400 feedback loops. Recently, troubles on this control system have increased due
to its age-induced deterioration. To maintain the high reliability of the cryogenic facility, a new control system has been planned with the PLC and
SCADA systems. Their attractive features include high market availability and cost-effectiveness, however, the use of PLC for such a large facility
with ∼400 feedback loops has not been established because of insufficient processing capability of the early PLC. Meanwhile, the recent progress
in the PLC enables to use the FBD (function block diagram) programming language for 500 function blocks. By optimizing the function blocks
and connecting them in the FBD language, the feedback loops have been successfully replaced from DCS to PLC without a software developer.
Moreover, an oscillation of the liquid He level, which often occurs during the cooldown mode of the cryopumps, can be automatically stabilized
by easily adding a new process program in the PLC. At present, the new control system has worked well.
© 2008 Elsevier B.V. All rights reserved.
Keywords: JT-60U; NBI; Cryopump; DCS; PLC; Cryogenic system
1. Introduction
The main objective of the JT-60U is to study a high- plasma
for long pulse operation towards a steady state tokamak reac-
tor. A neutral beam injector (NBI) is a major actuator to control
plasma profiles such as temperature, current and rotation. There
are 12 positive-ion-based NBI (P-NBI) units and one negative-
ion-based NBI (N-NBI) unit on JT-60U. The P-NBI unit has
demonstrated power injection of 2 MW, 85 keV for 30 s. The
N-NBI unit has injected a power of 3.2 MW, 320 keV for 21 s.
Both units are composed of two ion sources and one beamline.
Deuterium gas is introduced into the ion source to produce the
source plasma at the fueling rate of 3–5 Pam
3
/s. A large mount
of deuterium gas of 2–3 Pam
3
/s is also injected into the neutral-
izer cell to neutralize the ions. However, the residual gas in the
beamline between the neutralizer cell and the NBI port should be
reduced to avoid the interaction of high energy D
0
and the resid-
∗
Corresponding author. Tel.: +81 29 270 7454; fax: +81 29 270 7459.
E-mail address: honda.atsushi@jaea.go.jp (A. Honda).
ual gas (D
2
). Moreover, the pressure in the accelerator column
of the N-NBI ion source should be reduced to avoid the strip-
ping loss in it. To quickly remove the residual gas molecules
along the beam path, a large cryopump with a pumping speed of
1400 m
3
/s is within each unit. A large cryogenic facility supplies
liquid helium (He) to cool down the cryopanel below 3.7 K in
each pumping unit [1].
The key to the control of this cryogenic facility is to dynami-
cally balance the liquid helium (He) level between units, which
is sensitive to the gas load of the cryopump. The original control
system, which was fabricated 20 years ago, employed expen-
sive DCS (Distributed Control System) computers with a total
of about 400 control loops. It had worked well for 20 years;
however, troubles on this control system have increased due
to its age-related deterioration. The most serious issue is that
the DCS computers were discontinued about 10 years ago and
are no longer available for backup supply. Thus, we have con-
structed a new control system with high reliability. The new
system is required and to be easily programmable with com-
mercially available components. Though a large control system
with ∼400 feedback loops has not been established in the early
0920-3796/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.fusengdes.2008.01.005