A Proposal to Move from the LEP Topological to an LHC
Functional Control System Architecture
Michel Rabany
CERN / AT Division, 1211 Geneva 23
Abstract
Our knowledge of the fundamental particles of matter is governed by the available particle energy inaccelerators. In order to address this issue, and physicists have been designing ever larger accelerators andcolliders for the last forty years engineers. This has led to increasing complexity of both the components
and the control signals that have to be relayed to and from an operations centre. Whereas simple cabling
was more than sufficient for the early accelerators, distributed control systems are now essential for large
accelerators. At CERN, such developments were pioneered by distributing computers around the SPS
accelerator, which were then interconnected through proprietary communication links. Networking with
an emerging Token Ring was a major breakthrough for the LEP collider. While the evolution ofaccelerator control systems has matched the progress of technology, industry has, for its part, developed
very attractive generic solutions to meet the needs of manufacturers for automation, control andsupervision. The clear advantages of industrial control solutions in today's economic climate lead us toconsider their integration into modern accelerator systems. Following an analysis of the actual LEP
control system, an evolution of its architecture is proposed for the control of the LHC.

INTRODUCTION
During the 1960’s, the ever increasing need for data processing was an incentive for the development ofcomputer technology. Experimental physics is certainly one of the most demanding applications in thisrespect. Concurrently, the ever increasing need for energy in the collision of particles leads to thedevelopment of ever larger accelerators. Accelerator control requires communication with the equipmentfrom an operations centre, in the same way that musicians in an orchestra need their conductor. The
economic necessity of reducing the numbers and the sizes of the cables to reasonable dimensions led to
today’s distributed computer control architecture. Our pioneering activity in this domain sheltered us fromthe outside evolution, steered by industrial needs. The benefit we can expect from using industrial controls
certainly requires adaptation of our control architecture for optimal integration. Since 1990, CERN hastaken an increasing interest in industrial controls for many applications, which leads us to believe thatthey will be extensively used in LHC.

THE EVOLUTION OF THE MACHINES
Created in February 1952, CERN started operating its first proton and nuclear accelerator, a SynchroCyclotron of 600 MeV, in 1957. The machine, essentially a magnet, was 5 m in diameter. At the end of
the 1950’s the PS, a circular proton accelerator of 26 GeV for which CERN was built, delivered its firstbeam. The PS circumference is ~630 m. Then the ISR was constructed in 1971, the world’s first proton
collider, of 63 GeV and 940 m in circumference. Next came the SPS, a 450 GeV proton synchrotron
accelerator, launched in 1976, 7,000 m in circumference and, finally, in 1989 LEP, a 110 GeV electronpositron collider, 27,000 m.
Control of the equipment inevitably relies on cables for the transmission of electrical signals.As themachines were small enough, laying cables from the equipment to a central control room for the SC andthe PS was not a problem. The construction of the ISR and the upgrading of the PS at the end of the1960’s provided the opportunity to introduce the emerging computer control technology within acentralized computer architecture. The size of the SPS called for pioneering distributed computer controlarchitecture, in order to keep the computers near the equipment. The result was a system based on Norsk
Data ND100 computers, connected in a TITN star configuration [1]. The LEP, the world’s largest collider,also depends upon a distributed computer control architecture, but the computers are connected to a Token
Ring running around the accelerator [2] (Figure 1).

Acc. ctrl
room
Acc. ctrl
room
The PS in 1959 (Ø 200 m)

The PS at the end of the 1960’sAcc. ctrl
room

Acc. ctrl
room
The SPS in 1976 (Ø 2.3 km)
Legend:The LEP in 1989 (Ø 8.6 km)

computer(s)Figure 1. Evolution of accelerator basic control architecture.

THE EVOLUTION OF INDUSTRIAL CONTROLSThe industrial products
Industrial controls really took off with the advent of Programmable Logic Controllers. PLCs appeared in
the United States around the year 1969 in response to the automotive industry which wanted to develop
automated production lines that were able to follow the evolution of the models [3]. This led to thedevelopment of products from two of the largest manufacturers, Modicon and Allen-Bradley. Europe camein two years later with products from Merlin-Gerin and Alspa. The first aim was to replace the cabledsolutions which were very rigid and costly. The first specifications for the PLCs included operation in aharsh industrial environment, simple implementation and low cost.
PLCs are designed to work in a harsh environment caused by three main types of aggression:• physical and mechanical: vibrations, shock, humidity, temperature, etc.
• chemical: corrosive gas (chlorine, hydrogen sulphide, sulphur oxide, etc.), metallic dust, etc.
• electrical: electromagnetic and electrostatic interference, etc.
PLCs are designed to provide a simple tool for the user.
• The design of an application is made easy by the presence of a programming console, which ismatched to the mind and the needs of the process technician. Attaching the software to the hardware isa simple task of filling in parameters. The modularity of the hardware and the flexibility of thesoftware allows for easy reconfiguration.
• The operation and supervision are provided through specific consoles. These consoles are easily
configurable through application enabling programs, without programming, to perform a wide
variety of functions:• PLCs can provide• graphics screen editing• alarm monitoring and logging• control• data acquisition• report generation• real-time and historical trending• data analysis

•• help for maintenance• etc.
Large installations are controlled by Distributed Control Systems which, in addition, offer:• access to multiple clusters of PLCs through LANs or peer to peer communication links• distributed applications running on different platforms

The industrial users
It is difficult today to find an industrial sector that does not use automation. The following industries
account for two thirds of the market: motor, metallurgy, textile-wood-paper, chemicals-petroleum andenergy. The last third is split between mechanics, machine-tools, agro-food and the tertiary sector. [4]Usersmechanics
machine-tools
agro-foodtertiary

motor
metallurgy
textile-wood-paper
chemicals-petroleum
energyFigure 2

The manufacturers
The world-wide market for PLCs was estimated at $2.5 billion in 1987 and is approximately $5.5 billion
today. The growth rate for revenue is around 10% per year, with Europe and the United States being thelargest PLC markets. According to Siemens [5] in 1992, as well as stated in Control Engineering [6] in
1995, Siemens and Allen-Bradley were manufacturers number one and two for sales . Mitsubishi ceded its
position in third place to Schneider, mainly because of company regrouping. The market for Distributed
Control Systems is still led by their inventor, Honeywell (1975), followed by ABB, Yokogawa, Baileyand Siemens.

OthersMitsubishiSchneider

3020A-B

5040Siemens

The world market shares for PLCs and DCSs are illustrated below.

1992
1995

100Figure 3. -World PLC market share

Siemens

BaileyYokogawa

15ABB

Honeywell

201050Figure 4. -World DCS market share

CONTROL NEEDS OF AN ACCELERATOR
An accelerator is made up of equipment that can be classified into two categories:• the utilities which are characterized by their capacity to supply a product or provide a service. In thiscategory, we find
• the production and distribution of:• water: raw, drinking, cooled, chilled, heated, demineralized, waste, etc.
• electricity: high voltage, medium voltage, low voltage, security network, no-break
supply, 48V security network, etc.
• air: ventilated, compressed, conditioned, heated, exhausted, etc.
• gas: nitrogen, helium and gas mixtures for detectors, etc.
• cooled helium: liquid, fluid, superfluid, etc.
• etc.
The evolution of the physical processes which are involved is slow in comparison to the particle
production process of the accelerator. These utilities have a very simple interface with theequipment of the accelerator. Their process is of the continuous type. It consists ofmaintaining a few specific physical parameters within limits that have been specified withthe objective of not affecting the particle production in the accelerator. These parameters are,for example, temperature, pressure, voltage, etc. Industrial actuators and sensors are theircontrol elements.
•and the services for:• access control• fire detection• radioprotection• etc.
These are made of sequential processes which do not contribute to the particle production in theaccelerator. They are slow processes. Industrial actuators and sensors are their controlelements.
•the production equipment which is characterized by direct involvement in the particle production. In
this category, we find
• the electromagnetic equipment and their power supply: dipoles, quadrupoles, sextupoles,kickers, etc.
• the electric equipment: radiofrequency cavities• the electrostatic equipment: deflectors, separators, etc.
• the beam instrumentation: electrostatic pick-up’s, beam scanners, intensity monitors, etc.
• etc.
The particle production process involves a perfect synchronization between the thousands ofpieces of equipment spread along the accelerator. The current of the power supplies and theelectric field in the radiofrequency cavities are tightly coupled. The physical phenomena
which govern the production of particles are fast. Electromagnetic, electric and electrostaticequipment are the actuators and beam monitors are the sensors. They are not industrial.
Industrial actuators and sensors are not their control elements.

THE LEP CONTROL SYSTEM
As illustrated in figure 1, the LEP control system is a distributed computer control system. The
circumference of LEP has been split into eight equal sectors, in order, for one thing, to have reasonabledistances to supply the equipment with what it needs in order to perform its functions. The controlsystem fits closely with this structure and acts like a funnel for data coming from, and commands going
to, the equipment.
WSX

serverControl centre network

TCP/IP
file servers
TCP/IP

Backbone network

Accelerator & services

Local network

TCP/IPMASTER
PLC

PLC

PLC

FE

PLC

PLC

PLC

PLC

Figure 5. Integrating PLCs today in the LEP Control system
Figure 5 shows the possibilities today of integrating PLCs in the LEP control system. It must be recalledthat the particle production equipment described above is not considered here.
The Front End computer [7] [8] or controller imposes a very rigid frame structure which makes theoriginal structure of the equipment control layer completely disappear. A direct consequence is thedifficulty of integrating an industrial Distributed Control System which the manufacturer has designed togive a central global view of the equipment. It is much easier to use PLCs at a lower level, that is at
network level. However, integrating Master PLCs into the network and reconstructing the supervisory
functions at the level of the accelerator control room can only be done at the expense of considerable
effort. In addition, this structure has the serious drawback of dividing into two parts the responsibility ofthe people in charge of the equipment. This is due to the topological structure.
The pressure to use industrial controls could be satisfied by the possibility of a more global integration.
Splitting the equipment into functional domains (centres) would immediately remove the inconvenienceof breaking the split of responsibility and allow for much better integration of industrially available
control solutions. Moreover, this structure fits much better with the requirements concerning the flux ofexchanged data or commands for the types of equipment concerned. The specific Centre may apply aconstructive filtering to the whole flux of data coming from the equipment to the benefit of the accelerator
operation. Figure 6 shows the resulting functional arrangement.
The organization to functional elements is something which, interestingly, can be adapted to the humanresources structure. The Water Centre, in order to fit with distributed responsibilities, may itself subdivide
in more specialized Centres like Waste Water Centre, Chilled Water Centre, Raw Water Centre, etc., asthere is no intrisic reason to restrict the water processes to a single Centre.

Watercentre

Cryocentre

VacuumcentreProduction
equipment
Accelerator
Control RoomElectr.
centre...
centreFigure 6. The functional approach

CONCLUSION
The vital necessity for our research laboratories[9] to make as much use as possible of industry leads us toadapt our concepts to the industrial world. The industrial world is naturally organized into specificdomains which match the specialization of the individuals from whom expertise is expected. Tendering forequipment on the basis of functional specifications will result in industrial offers from which we can onlyexpect the maximum benefit if we do not impose restrictions on the overall system. This naturally leads
to a functional architecture.

REFERENCES[1] The design of the control system for the SPS, M. Crowley-Milling, CERN 75-20.
[2] The LEP Control System, P.G. Innocenti, Accelerator and Large Experimental Physics Control
Systems, Vancouver, Canada, 1989, pp 1-5.
[3] Les A.P.I., Architecture et applications des automates programmables industriels, G. Michel, Dunod
edition, Paris, 1988
[4] Quelques chiffres sur les API, Robotique Informatique Industrielle, G. Rouchouse, Janvier 1992.
[5] Le marché des API en 1992, Robotique Informatique Industrielle, Mars 1993.
[6] Market update, G. J. Blickley, Control Engineering, January 1995.
[7] Interfacing industrial equipment to CERN’s accelerators and services control system, P. Anderssen,
P. Charrue, R. Lauckner, P. Lienard, R. Rausch, M. Tyrell, M. Vanden Eyden, CERN-SL-95-42 CO.
[8] SPS and LEP Controls: Status and Evolution Towards the LHC Era, R. Rausch, This conference.
[9] Industrial Control Solutions in Research Laboratories, M. Rabany, This conference.