Vacuum 60 (2001) 123}129

Vacuum control and operation of the ESRF accelerator system

Daniela Schmied

ESRF, BP 220 - 38043 Grenoble Ce&dex, France

Abstract

The reliability of large vacuum systems is largely dependent on the installed hardware and on the proceduresestablished for the production, installation and interventions on such systems.

Nonetheless, an essential role is the control of these systems which implies its remote operation, careful survey andproper protection. This allows the operation of the vacuum system* to a certain extent* without expert assistance butalso enables a careful survey of the vacuum system for preventive maintenance or for the identi"cation of failures. Thispaper presents some control and operation aspects which became important items for the operation of such a system asa result of the experience gained. ( 2001 Elsevier Science Ltd. All rights reserved.

1. Vacuum control

1.1. ESRF vacuum control layout

The aim was to adopt a uniform technical solu-tion that leaves open the possibility of a speci"ccustomised operation.

The vacuum system is treated as a sub-set of theoverall machine control. With the advantages ofrapid developments, improved equipment manage-ment and also, from the operation point of view,a common user interface and archiving, PC-basedcustomised control is used for speci"c local main-tenance or interventions. This allows a continuousoperation even with various system downtimes.

The successful operation of large vacuum sys-tems must be based on the distributed intelligence,i.e., intelligent instrumentation and a reliable com-munication infrastructure.

Most commercial vacuum controllers are micro-processor-controlledwhich means that a signi"cantamount of speci"c operation and error handlingcan be performed by the equipment itself. This

results in a faster and simpler control of the equip-ment. The installed vacuum control units are com-mercially available equipment and most of themare o!-the-shelf products (Fig. 1).

The general control structure is split into di!er-ent levels. The vacuum instrumentation located onthe lowest level is connected via dedicated controlinterfaces to front end computers on an intermedi-ate level. This software handles the routing of re-quests coming from various applications. Thesecomputers are connected to the server computersvia a network, the man}machine interface being atthe highest level.

The control structure is designed as an openconcept, which allows upgrades and modi"cationsof the actual system. In order to maintain identicalaccess to the di!erent device groups an access pro-tocol has been de"ned guaranteeing an identicalinterface for each family of similar vacuum equip-ment, independent of the hardware and the di!er-ent application programs [1,2].

In order to obtain a simple and reliable control,a server}client architecture has been adopted. The

0042-207X/01/$ - see front matter ( 2001 Elsevier Science Ltd. All rights reserved.PII: S 0 0 4 2 - 2 0 7 X ( 0 0 ) 0 0 3 6 4 - X

Fig. 1. Control layout of ESRF vacuum system.

interface software on the front end computers arethe servers who respond only to requests comingfrom the various applications (Fig. 2).

An important feature is the #exibility withoutexpert assistance.

The main functionality of the vacuum applica-tion program is to visualise the current status of thevacuum equipment, to be able to modify it, todisplay all relevant physical data and to indicateerrors or faulty equipment. This application shouldbe similar to a common man}machine interface ofthe accelerator in order to ease control and troubleshooting by the operation crew (Fig. 3).

In order to improve the #exibility of the controlsystem, it has been structured such that the user canaccess and modify di!erent vacuum items, i.e. tomodify process relay trip levels or assignments oreven add additional equipment to the applicationor historical database. This is realised by means ofdynamic update of the vacuum device parametersor the application program's con"guration. Re-starting the application programs or dedicatedinterface software automatically restores thenecessary con"guration data from a database. Thisallows a dynamic update of any modi"cation to the

vacuum system with the guarantee of having a validupdate at all control levels.

The protection of the vacuum equipment by theinterlock system has been separated from the vac-uum control system in order to improve the reliabil-ity and to provide a redundancy of the system (Fig. 4).

1.2. Database

The multitude of the di!erent vacuum systemsfor the accelerators and beam lines implies the useof databases. The use of these systems reduces theordeals of maintenance and improves the under-standing of the system behaviour. Commercialdatabase management systems allow access fromwithin the control application via high-level lan-guages as well as the possibility of interfacing withcommercial packages like data analyser tools [3].

Information concerning the dynamic vacuumcontrol system con"guration is stored in adatabase, which contains:

f The description of the vacuum system, whichconcerns its physical layout like names, posi-tions, etc.

124 D. Schmied / Vacuum 60 (2001) 123}129

Fig. 2. Cold cathode gauge device server model.

Fig. 3. Vacuum high-level control.

f Communication path de"nition related to theequipment interface and the network address in-cluding the necessary communication parameters.

f Physical characteristics describing each part ofthe equipment (calibration, process relay assign-ments, set points, trip levels).

D. Schmied / Vacuum 60 (2001) 123}129 125

Fig. 4. Storage ring vacuum interlock layout.

The historical data archiving and retrieving be-comes an important feature with time. It enablespreventative maintenance, troubleshooting incase of failures or quali"es vacuum conditions.In the case of the ESRF, data is processed ina common database for accelerators and beamlines.

The data archiving must be #exible and easy touse which implies access tools to include new sig-nals or modify the data collection process. Thiscan be con"gured by selecting either a time stampof a minimum period of 10 s and/or changes ofone or more signals which are triggered by ade"ned value change checked in a period ofa minimum of 10 s.

Up to 3 Gbytes of vacuum data an year arestored. To date, eight years of data archives areavailable. This requires convenient and powerfulgraphic programs to browse and display historicaldata. In addition, it should be compatible for theuse by common spreadsheets or specialised dataanalysis programs. Initially this common databasewas not available and the vacuum data were storedin dedicated "les with di$culties of correlatingvacuum data with other accelerator data and the

increasing complexity to extract important amountsof data.

The increasing number of equipment, interven-tions, failures and maintenance work make theestablishment of a proper vacuum database man-datory.

This database contains all installed or availablehardware such as chambers, supports, valves,pumps, computers, controllers and raw materials.

A di!erent feature is the systematic recording ofinterventions, faulty equipment, material failuressuch as leaks, radiation damaged cables, leakagecurrents on connectors, gauges, feedthroughs, etc.in a data-based e-log for accelerators and beamlines.

This database, developed under Filemaker Prohas been exported on the Internet and allows every-body to access it from various platforms.

In addition, the whole documentation concern-ing the speci"c vacuum control and interlocklayout of the accelerators and beam lines areavailable on the Internet. This has proved toease the maintenance burden and release the expertassistance in many cases where problems havearisen.

126 D. Schmied / Vacuum 60 (2001) 123}129

2. Interlock

2.1. General concept

The concept is to provide a fail-safe vacuumsystem which allows, to a certain extent, its opera-tion by non-experts. In order to improve the relia-bility and allow a certain redundancy it has beendesigned independent of the control system asa hardwired stand-alone system, which remainsalso operational during shutdown periods withdown times of the various systems. In order to ful"lthis requirement the use of intelligent units at thelowest level is necessary and therefore the interlocksystem has been based on programmable logicalcontrollers.

PLC provides expansion capability, communica-tion mechanisms, supervision tools or archivingtools. These units are used extensively in industryto control continuous and/or sequential processes.These systems are designed to sustain harsh indus-trial environment.

2.2. ESRF vacuum interlock system

At the ESRF the same interlock strategy hasbeen applied for the accelerators, storage ring, frontends and beam lines.

The vacuum interlock system is based onmodules, which consists of all vacuum equipmentin between two gate valves or windows. A moduleconsists at least of a Pirani gauge, invertedmagnetron gauge, pump and pre-pumping valve.Depending on the size and complexity of thesystem, several PLCs can build up the interlocksystem.

Apart from the continuous survey and process-ing of trigger signals, which a!ord protection forgauges, residual gas analysers and pumps, eachPLC performs operation of sequential processes.This concerns the operation of gate valves, shuttersand absorbers related to other safety systems suchas personal safety system, FE or experimental inter-locks.

The remote operation via the control systemallows a safe access to control these itemsand allows diagnostics in case of interlocks orfailures.

3. Operation

Continuous and careful survey is necessary toidentify vacuum-related problems in time andallow to perform preventive maintenance. At theESRF these surveys consist of total pressure, par-tial pressure and temperature measurements.

3.1. Total pressure measurements

3.1.1. Pirani gaugesThese are chie#y used as high-pressure gauges

necessary during interventions and for completionof the total pressure measurement for the interlocksystem. The stability of these gauges is satisfactory.At the ESRF the Pirani gauge measurements areused for the interlock system to protect Cold Cath-ode gauges, sputter ion pumps, residual gas ana-lysers, to be started at high pressures, and for NEGpump activation.

3.1.2. Cold cathode gaugesThe pressure monitoring system and interlock

system at the ESRF is based on inverted magnetrongauges. They provide a reliable and stable opera-tion in the dynamic pressure range of the acceler-ator. These gauges are easy to handle. The strikingof gauges does not present any operational pro-blem. Special attention should be given to the elec-trical connection, since, apart from the HV supplyof the gauge, the measured currents are in the10}9 A range (Fig. 5), which implies carefulearth/mass connections for all connected gaugesand controllers. Important electrical leakage cur-rents occur on the electrical connection due tohumidity or radiation.

3.1.3. Hot cathode gaugesThe aim was to use these gauges as a reference in

a few places. The use of these gauges, in order toachieve reliable and stable measurements is farmore complex compared to the cold cathodegauges. Due to the observed problems such asunstable operation due to frequent "lament trips,important heating while mounting on a CF38 withphotoelectron shielding, a fair amount of gaugefailures and sensitivity to the radiation backgroundwhich required additional shielding, these gauges

D. Schmied / Vacuum 60 (2001) 123}129 127

Fig. 5. Cold cathode gauge leakage currents.

have not been included in the pressure monitoringsystem.

3.1.4. Sputter ion pumpsRecent commercial ion pump power supplies

provide the possibility of obtaining reliable measure-ments of the ion pump current in the low 10~7 Arange. This gives interesting information about thepressure distribution in-between the gauges duringoperation. At the ESRF they are frequently used tolocalise leaks or malfunctioning the pumps.

3.2. Partial pressure measurement

Each accelerator section is equipped with a resid-ual gas analyser which is accessible by the vacuumapplication and data logging which allows the con-tinuous follow up of a de"ned number of partialpressure measurements in order to qualify thevacuum.

For special requirements such as leak detection,bakeout or RGA maintenance the providedsuppliers system based on PC is used.

In order to achieve reliable measurements a con-siderable amount of work on system maintenanceis necessary as well as procedures to de"ne the

various operation parameters. The analyser needsto be shielded from the radiation background.

3.3. Temperature measurement

Initially installed to control and monitor thebakeout, the thermocouples have been included inthe standard vacuum monitoring and data archi-ving as they have proved to be an interesting tool totrace heating problems which may cause sub-sequent vacuum failures.

Thermocouples proved to be simple to handleand inexpensive. Special care has to be taken dur-ing their installation, with cabling and reliable "x-ing aspects. It appears that apart from obviouscritical spots like absorbers, ceramic chambers, thesystem should be #exible to allow the relocationand installation of further thermocouples, if re-quired. This concerns not only the installed hard-ware but also their remote operation.

4. Performance and outlook

Interventions during shutdown periods aresometimes di$cult with regard to performing the

128 D. Schmied / Vacuum 60 (2001) 123}129

necessary tasks while the control and data archi-ving system is not operational. In addition, theexisting temperature monitoring system is not #ex-ible enough to ful"l all needs concerning bakeoutand machine diagnostics.

Therefore we plan to modify the existing PLCsystems installed in each accelerator section. Thisshould allow the provision of redundancy in termsof interlocks for a safe bakeout operation but alsoin-situ control of the NEG pump power suppliesduring their activation.

Additional thermocouples, only for machinediagnostics, will be installed and connected tothe PLC used for the temperature monitoring andinterlock.

Finally the installed PLC units are connected tothe FE computer via serial interface instead ofa "eld bus which results in a partial loss of impor-tant o!-the-shelf feature such as reliable intra-PLCcommunications or alarm handling.

Moreover, it would appear that due to ageing,more and more interventions are required. Oneway of improving the e$ciency of the bakeout isto add data acquisition modules to the bakingcontrol rack, capable of transferring data by means

of wireless LAN to the control room. The goal is toallow the operation crew, present 24 h a day, tohave a full survey of the pressure and temperaturedata for each of the interventions. At present, twoprototypes are under test.

Acknowledgements

The author would like to thank J. Meyer, R.Kersevan and M. Hahn for the fruitful discussionsand I. Parat, P. Guerin and E. Burtin for theirsupport.

References

[1] Strubin PM, Tro"mov NN. First experience with controland operational models of vacuum equipment in the ADdecelerator. New York: CERN.PAC99, 1999.

[2] Strubin PM, Tro"mov NN. Control and operationalmodels for Vacuum equipment, CERN-LHC-97-005-VAC,preprint.

[3] Pool J. Databases for accelerators control } an operationsviewpoint. CERN.PAC95, Dallas, Proceedings IEEE,Piscataway, 1995.

D. Schmied / Vacuum 60 (2001) 123}129 129