OVERVIEW OF THE LARGE HELICAL DEVICE (LHD) CONTROLSYSTEM AND ITS FIRST OPERATION
K.Yamazaki, H.Yamada, K.Y.Watanabe, K.Nishimura, S.Yamaguchi, H.Nakanishi, A.Komori,
H.Suzuki, T.Mito, H.Chikaraishi, K.Murai, O.Motojima and the LHD Group, NIFS, Toki, JAPAN
Abstract
The first plasma operation of the Large Helical Device(LHD) fusion system has been successfully performed on
March 31 in 1998 by means of the Central (‘Chu-oh’ inJapanese) Control System (COCOS) connected to ~50
subsystems using hard-wired interlock, optical-fiber
timing and computer information network. From January
1998, the protective supervision system of COCOS went
into service and the vacuum pumping control systemstarted operation. The cryogenic control and the coil
power supply control systems were utilized to cool down
and energize the superconducting coils. The sequential
control and timing control systems of COCOS havesuccessfully started operation for a first plasma production.
A variety of machine operations and plasma experiments
will be continued on LHD using these flexible, reliable
and advanced control systems.

(1) LHD operation scenario and its control concept.
(2) Central control system COCOS with hardwired interlock, soft sequential control andoptical timing control units.
(3) FDDI/ATM network architecture.
(4) Client/server LHD Man-machine-interface System(LMS) using Windows NT with Visual Basic.
(5) Control sub-systems relevant to machinecommissioning, such as vacuum pumping control,
cryogenic control, and coil power supply control
systems.
(6) Real-time control data monitoring system with
VME (VxWorks), Windows NT using Visual C++
and/or Unix workstation using Java.
(7) Distributed control systems for plasma diagnostics,
and advanced data acquisition system by Windows
NT network.

1 INTRODUCTION
Helical confinement systems have distinctive merits ofsteady-state operations for fusion reactors. The Large
Helical Device (LHD)[1-3] (Fig.1), the superconducting
helical fusion machine with the major radius of 3.9 m,
the minor plasma radius of 0.6 m and the magnetic fieldstrength of 3 Tesla, has been completed after the 8-year
construction schedule in Toki-City, Japan. This is aworld-largest helical fusion experiment aiming at steadystate operation by means of superconducting coil system.
One of the main objectives of this LHD project is todemonstrate steady-state operations of helical fusion
plasmas that can be extrapolated to the future fusion
reactor. For these purposes the National Institute for
Fusion Science (NIFS) had been established in 1989 andthe LHD machine construction was started in 1990.
As for the LHD main control system (see Figure 2), in
April 1996 we started the real construction of the Central(‘Chu-oh’ in Japanese) Control System (COCOS), the
LHD Man-machine Interface System (LMS) and the LHD
experimental network [4-5]. In addition to this central
control system, about 50 sub-control systems have been
constructed. These systems are composed of a variety ofcomputers such as UNIX engineering workstations,Windows NT personal computers (PCs), VME computer
boards with real-time OS and programmable logic
controllers (PLC).
In this paper, we will explain the overview of the
LHD control system in the following:

Figure1: Photograph of LHD (Large Helical Device)

Figure2: Photograph of LHD Central Control Room

2 MACHINE OPERATION AND
CONTROL CONCEPT
2.1 LHD Operation Scenario
The LHD system consists of a variety of complicatedsystems that should be worked cooperatively. In order toclarify that, the LHD normal operation modes wereclassified into six modes (Fig.3); shut-down mode,
facility operation mode, vacuum pumping mode, coilcooling mode, coil operation mode and plasma experimentmode. These modes are related to the personnel entrance
permission with respect to electricity and vacuum, themagnetic field hazard and the X-ray radiation production,
respectively.
The LHD coil system is cooled down once or twice ayear after pumping out the cryostat. It takes a few weeks
to cool down or warm up the helical and poloidal magnets,
which should be operated safely and reliably, and theplasma experiment will be carried out flexibly. Thesemagnets will be operated for about 10 hours per day, andthe number of short-pulsed plasma operations with 10
second duration will be typically 50 - 100 shots per day.
The LHD is also going to be operated in steady state(more than one-hour pulse length) and requires interactive
control of the machine and the plasma.
For the analysis and protection of abnormal operation(for example, coil quench, electric power failure or
earthquake accidents), the following six modes were
defined; “1Q mode” (quick coil-current dump mode for coilquench protection), “1M mode” (medium coil-current
decay mode), “1S mode” (slow coil-current decay mode),“2 mode” (plasma shut-down mode), “3 mode” (nextsequence stop mode) and “4 mode” (warning mode). Thesesignals are used in the interlock design, and its concepts
had been successfully demonstrated in the real LHD
experiment.
Shut-Down Mode
Facility Operation ModeCentral Control Systemseveral years

several months

Vessel Baking

Magnet Operation Mode
Discharge Cleaning
Magnetic field

The latest mission of the LHD project was to produce
a first plasma as soon as possible, and as reliable aspossible. On the basis of above-stated operation scenarios,
the designed control system is composed of the central
experimental control system and several sub-supervisory
facilities which are connected by the FDDI-LAN in
addition to hard-wired interlock/sequence control and firsttiming optical signals (Fig.3).
The real construction of the main unit of the COCOS
was started in April, 1996 based on the following design
philosophies;(1) Flexibility for the physics experiment,(2) Reliability for the large engineering machine and(3) Extensibility for the central control system.
The design philosophy (1) requires human-friendly
man-machine interface and advanced real-time plasma
control systems, the item (2) requires reliable protective
interlock systems with hardwires, and the philosophy (3)leads to the requirement of distributed and modularized
control/ monitoring systems.
Figure 3 shows the outline of this system architecture.
The conventional hard-wired logic system has been used
between COCOS and about 50 sub-systems in addition to
the FDDI computer network communication. The initial
LHD operation should be carried out reliably on theschedule. The central boards with programmable logic
controllers
directly connected to sub-systems withhardwires were used for this initial purpose. Especially,
the simple protective interlock system in COCOS wasquite helpful to connect among a variety of complicatedsubsystems, some of which had been behind schedule.
The computer systems such as man-machine interface
may sometimes suffer from programming bugs and will
waste a lot of time, however they should be used finallyas flexible experimental tools. We decided to developthese friendly computer control systems step by step. The
optical triggering signals were used in the fast timing
system for sequential control of plasma discharges in
addition to hard-wired signals and computer digital signals.

VacuumPumping System

Vacuum Pumping Mode

Coill Cooling Mode

2.2 Control Concept and its Architecture

Cryogenic Systemseveral months
Discharge Cleaning
Coil Power Supply Systemnightnext day~10 hours

Plasma Experiment mode
Plasma Production
Plasma Heating
Plasma Diagnostics

10 sec or≥ 1 hour pulses

NIFS Campus LAN(ATM CLUSTER)

CENTRAL CONTROL SYSTEM

Reliable Operation

Flexible ExperimentCentralOperation
ConsoleMan Machine
Computer(Windows-NT)

Sequence
Control andInterocks(PLC)

Hard-wired

Fast Timing(VME)

Optical

LHD
Experiment
Cluster

Control
Information
Network(FDDI Switch)

LAN

time

Figure 3: Six Operation Modes on LHD.

LHD SUB-SYSTEMS

Figure 4: Outline Architecture of LHD Control.

3 CENTRAL CONTROL SYSTEM
3.1

COCOS Overview

On the basis of the LHD operation scenarios, thedesigned control system is composed of the COCOS
central unit (Fig.5) and several tens of sub-supervisory
facilities which are connected by the hard-wired interlock
and soft sequential control link in addition to the
FDDI/ATM communication network [4-5].
At the beginning of the LHD proposal (morethan10
years ago), the control system was considered based on thecentralized control “process computer”. Around several
years later the UNIX engineering workstation system with
VME computer connected by Ethernet-LAN was proposed.
Now, some client-server systems by personal computers(PCs) are added for control and data acquisition. Thesevarious systems are presently connected by the advanced
FDDI / ATM switching network system.

directly connected to sub-systems via hardwires was used
for the quick and reliable operation of LHD. Especially,
the reliable protective interlock system is available in
COCOS. The fast timing system with 64 channel opticalsignals (accuracy: < 1 micro-second, setting-up interval: 1
ms ~ 10 hr) was distributed to sub-systems. The feedback
control for plasma current, position and cross-sectional
shape will be carried out in the near future using
intelligent VME control systems, such as applications offuzzy logic or neural networks in addition to standard PID
plasma control algorithm.

3.2

For flexible and elaborate experimental setup, the LHD
Man-machine System (LMS) is installed for experimental
operation using Windows NT, Oracle 7 and Visual Basic.
This is a client/server system based on 3-Layer standard
model (presentation, transmission and data house, anddevice control layer). This system is used for (1)presentation of operation mode, (2) setting-up of
experimental condition, and (3) supervision of machinedata. At present 8 clients and 2 servers for LMS areconnecting to 6 subsystems, and will be extended to all
sub-systems in the future. The details of this system arepresented in this conference [6].

3.3

Figure 5: Central Unit of COCOS
Top: central operation console, four central control
computer, central supervision panel and largescale display in the central control room.
Lower left: VME timing board, central sequencecontrol board, and I/O board in the basement of
the control building.
Lower right: protective interlock board and so on in
the LHD building.
The central control system COCOS is composed of thecentral control unit (including central operation console,
central sequence control board, central control computer,central supervision panel, large-scale display, and the
VME timing board), the torus instrumentation unit (torus
supervision computer, torus supervision VME board andprotective interlock board), the LHD Man-machineinterface System (LMS), the control data monitoring
system, the LHD experimental LAN and the uninterrupted
power supply (UPS) systems. This system is provided
with a variety of computers such as UNIX engineering
workstations, Windows NT personal computers, VME
computer boards with real time OS (VxWorks) andprogrammable logic controllers (PLCs).
The outline of this system architecture was shownin Figure 4. The central control board with PLCsLMS

LHD Experimental Network

In the LHD experiment, we may have three kinds ofdata from the LHD computer systems: machine operation
data (from main torus and plasma heating system), plasma
diagnostics acquisition and control data, and plasma
analysis data. These kinds of data should be transferred to
the NIFS Campus ATM network. As shown in Fig.6,
three network sub-clusters are used in the LHD
experimental cluster. For machine control data , we added
a fire wall system for safety. Plasma diagnostics data andanalysis data are strongly coupled and we are trying toinstall ATM switches between diagnostics sub-cluster andexperimental analysis sub-cluster. The large-scalecomputer system for theoretical analysis using
experimental data is connected to the LHD experimental
computers via this ATM campus LAN system.
Res earc h Ba sis Clus te rATM

Large-S cal e Simulati on Clus te r

ATM

LHD Experi mental Cl uster

A TM
ATM
E xperimental Analysis S ub-Cluster

LHD Operation S ub-Cluster
Operational Information LAN
FDD I (SW-H UB)FDDI (SW-HU B)

FDDI Swi tch

Fi re Wal l
FDDI (SW- HUB)

Device Control LAN

Diagnostics Sub-Cluster ATM
FDDI (SW-HU B)

Data A quisition LAN
FDDI (SW-HU B)

Diagno stics Control Lan

Figure 6: LHD experimental network connected to
NIFS campus LAN.

4 TYPICAL SUB-CONTROLSYSTEMS
According to the above-mentioned operation scenarios,
various sub-systems started operation in turn. Typicalsubsystems among ~50 systems are described below,
which are connected to the central control system bymeans of three kinds of signals; PLC interlock hardwire
ON/OFF signals, timing optical-fiber signals and TCP/IP
computer network signals.

4.1

Vacuum Control

The initial important device at the machine start-up is
the vacuum pumping system that consists of pumps,
valves, pressure gauges and so on. Its device controllers
are installed in the basement of the LHD building and four
PCs are installed in the central control room for remoteand automatic operation. More than 100 of status flags areprogrammed for operation and interlocks. The software is
now in progress for upgrading the control system.

4.2 Cryogenic Control
Since the cooling scheme of the LHD system is fairly
complicated, a reliable and flexible duplex control system
is required for cryogenic control. Figure 7 shows the LHD
cryogenic control system (TESS) arrangement [7] whichis composed of two clusters: helium refrigerator control
and cooling objet control for helical coil, poloidal coil andsuperconducting bus lines. The control system is based on
open system and consists of Unix workstation, VMEVxWorks controllers, LAN and operation graphic
consoles. This system is composed as a duplex
Workstations
for Programming

Graphic Terminals
for Operation

Color
Hard Copy

redundancy system that significantly improves the reliable
operation with fault diagnoses of each component. The
VME controllers are used as a pair of one in service andthe another in waiting. Two VME controllers are identicalin both hardware and software. In case the running VME
has trouble, the service is instantly switched over to theanother VME controller which is in the waiting mode.
The workstation and LAN are also duplicated, andcontrolled by the master workstation. The network is the
optical duplex link type LAN that is compatible with
Ethernet. At present the upgrade of the automatic
operation programming is being in progress.

4.3 Coil Power Supply Control
For the achievement of excellent plasma, high accuracyof coil current control is required. The coil power supply
control system is composed of VME controllers and Unix
workstations. The required performance criteria of thissystem are (1) current control error is within 0.01 % in
the steady state operation, (2) 0.1% error permissible forsetting current value within 1 second in the normal
operation, and (3) overshoot of current is prohibited. The
current regulator in the VME machine is based on thestate variable control theory to uncouple the mutual
coupling between coils. At present P and PI control
scheme is applied and the superconducting coil system has
been operated successfully.

4.4 Real-Time Machine Monitoring System
We installed two real-time machine data monitoring
system; one is a slow and reliable system coupled to the
COCOS, another is a fast and flexible system forHard Copy
Printer

Printer

Cryogenic Control LAN for He Refrigerator
in Service

INS64

Personal Computers
Workstations
X-Terminals
for Programming &for Monitoring

Graphic Terminals
for Operation
Color

Router

Cryogenic Control LAN for Cooling Objects
in Service in Waiting in Service in Waiting in Service in Waitingin Waiting

Reflective
VME Controllers Memory
Integrated
for He Refrigerator
Workstation

VME Controllers
for Helical Valve-Box

VME Controllers
for Poloidal Valve-Box

Helical CoilHelicalValve-Box

Poloidal Coil
Poloidal
Valve-BoxHe
Refrigerator
Workstations for
Remote Maintenanceto LHD Main Control LAN

Integrated
VME
Controller

Reflective
Memory

LHD Central Control System

Figure 7: Cryogenic Control System

VME Controllers
for SC Bus-Lines

SC Bus-Lines
Current Leads

experimental data handling, as shown bellow.
For reliable machine supervision one of the data
monitoring systems is based on Windows-NT using 1300
channel VME boards within COCOS [4-5]. This treats
with a variety of signals such as machine temperature,mechanical stress, vacuum gauge signal, magnetic fieldstrength and so on. These are used as both protective softinterlock signals for LHD operations and real-time slow
display with sampling time of 1~10 s. The man-machineinterface of this monitoring system was programmed by
Visual C++. In this system the relational database Oracle
is used.
For flexible real-time data monitoring, another LHD
data monitoring system with 512 channel VME and theUNIX workstation was also constructed [8]. The samplingtime is 1 second for real-time data, and 1 milli-second forbatch data by the same acquisition system. Full Javacomputer software on WWW Browser was used in thissystem and will be extended to 4000 channels in the
future. To manage Data, relational database (SyBase) wasused in this system. The special data compression scheme
is adopted here.

4.5 Diagnostics Control and Data Acquisition
High quality data from the various plasma
diagnostics is key to good experiment and good physics.
Here the data acquisition and control for diagnostics weredivided and connected by FDDI switch as shown in Fig.6.
The data acquisition system [9] is using distributed andobject-oriented technology. The plasma data from ~20
diagnostic instruments are managed by CAMAC-VME
and Windows-NT distributed systems. The typical raw
data amount is a few 100MB per each shot, and maximum
10GB per day. It adopted the object-oriented database. For
diagnostics control, the system is parallel to thediagnostics data acquisition system. Figure 8 shows thephotograph of this diagnostics system with more than 50
clients and 30 servers (Windows-NT) .

Figure 8: Photographs of Diagnostic client PCs in theCentral Control Room (upper) and a cluster of server
computers in the Diagnostics Computer Room(lower right)

5

SUMMARY

The first plasma operation of the Large Helical Device(LHD) fusion system has been successfully carried out
just on schedule after eight-year construction period.
This has been achieved by the help of the Central Control
System (COCOS) connected to ~50 subsystems using
hard-wired interlock, optical-fiber timing and computer
network information. From January 1998, the protective
supervision system of COCOS went into service and thevacuum pumping control system was started. The duplex
cryogenic control system and the high-accuracy coil power
supply control system were used to cool down andenergize the superconducting coils. Sequence control andtiming triggering systems of COCOS have successfully
started operation for a first plasma production. The
COCOS man-machine system for monitoring and timing
is based on Windows NT personal computers (PCs) with
Visual C++. The LHD Man-machine interface System(LMS) based on Windows NT PCs with Visual Basic also
stated in service and communicates with several subsystems. The plasma diagnostics control and dataacquisition system is also based on Windows NT
client/server distributed system. The real-time monitoring
system using Unix workstation with Java programmingis also running. Using these flexible, reliable andadvanced control systems, a variety of machine operations
and plasma experiments will be continued on LHD.

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