De la Rive-Box, M

Gröbner, Oswald

Kemp, D

Keyser, R

Kohler, K

Neet, D

Sagnell, B

Schaffer, G

Tausch, L

Verelst, H

Wagner, F

Wolstenholme, P

CERN Document Server

EXPERIENCE WITH COMPUTER CONTROL APPLIED TO THE CERN INTERSECTING STORAGE RINGS (ISR)M. de la Rive Box, O. Grebner, D. Kemp, R. Keyser, K. Kohler, D. Neet, B. Sagnell, L. Tausch, G. Schaffer,H. Verelst, F. Wagner~ P. WolstenholmeCERN, Geneva, Switzerland. (* Visitor from Institute of Technology, Gliwice, Poland)(presented by R. Keyser)AbstractThe paper discusses briefly the computer systemand its interfaces with the ISR and with operators.In this framework the applications of the computer inthe ISR activities are described.1. IntroductionWhen the control system for the IntersectingStorage Rings at CERN was being studied 1), it wasdecided to incorporate a computer for the supervisionof the large quantity of hardware involved. Thecomputer functions are to present data, suitablyprocessed, to the operators and to carry out changesin settings as requested. The computational activityin these two functions can be considerable, as thecomputer may be asked for example, to present dataon beam orbits analysed into harmonic components ofthe ISR circumference, and then to apply a controlcorrection aimed at reducing some of these componentsto zero. Thus, our computer system is made to per-form closed-loop functions, at present closely super-vised by the operators, and as experience is gainedin the behaviour of the ISR, these and others willbe performed as part of complete setting-up routines.The major applications of the computer systemare the control of 300 power supplies in the beamtransfer lines and the storage rings, data collectionfrom over 100 beam observation stations and data col-iection, recording and display on an extensive ultra-high vacuum system. These and other applicationsdescribed in this paper are operational and routinelyused by the operators.2. Comput er HardwareThe computer used is a Ferranti Argus 500 whichhas a 24-bit word length, 8 sets of accumulators formulti-programming convenience, 24,576 words of 1 ~score store and a fixed head disc store of 640 000words capacity. The 34 ms worst-case disc accesstime permits several programs a second to be run.Operator communication is achieved by means ofthree teleprinters and a graphic and alpha-numericdisplay system, driving 4 display screens.General purpose input systems comprise a digitalscanner which reads up to 8000 contacts at up to 600 mfrom the control room, and puts all the data into thecomputer memory each 112 ms, and 12 analog scannersin the various equipment buildings, reading up to3500 signals selected by a reed-relay scanner anddigitised by integrating d.v.m. techniques.There is qo all-embracing output system, eachmajor control system being interfaced as a separatecomputer peripheral. Minor requirements are met byusing a general-purpose unit, together with a smallrange of digital input and output cards. A Camacsystem has been added in order to facilitate theinterfacing of small control systems. A data linknetwork between the computers ~sed for ISR physicsexperiments and the Argus will use Camac hardware.For maintenance back-up, and also for softwareand hardware development work, we have installed asecond Argus 500, with only 20 480 words of corestore, a disc store, a teleprinter and a card reader.3. SoftwareA multi-programming executive has been developedat CERN 3). This contains drivers for the variousinput-output devices together with schedulers for thecore store, the display module store and the disc.Under control of the executive, up to seven appli-cation programs may be in execution at a given time.Normally copies of all the application programs arekept on the disc and are brought into core store bythe executive, according to requests by operators.However, there are a few programs which are coreresident, primarily for monitoring purposes or aspart of the interface between the operator and thesystem.At present in the on-line machine, 12K of corestore is dedicated to system coding, re-entrant rou-tines, input-output bUffers etc., and 4K to core-resident application programs leaving 8K availablefor sharing among disc-kept application programs.About half of the disc storage is so far filled withdata and programs.The decision taken early in the project to pur-chase a second computer has been fully justified bylater experience. Although one important justificationfor the second computer was hardware back-up for theon-line computer, the main use of the second computerhas been in permitting program development in paral-lel with hardware development or ISH runs. Newapplication programs can be largely debugged in thesecond computer, although it is usually necessary tocomplete the check-out with access to the specialisedinstrumentation and sometimes under operational con-ditions (e.g. the presence of a beam).To date all programs have been written in assem-bly language, the programming being confined to asmall number of specialists rather than a largernumber of occasional programmers. About 7 man-years440 -of programming effort have been invested, equallydivided between system development and applicationprograms.4. Computer - ISR InterfaceBrief specifications of the programs associatedwith each system are available for display on theCRT screens. Often used commands can be associatedwith a set of buttons; pressing the button is equi-valent to typing the command.Rather than using general-purpose computerinput-output systems for all control applications,we have preferred to regard each major sub-systemas a peripheral, which is independent of the othersas far as the computer interface. Where possible,manual control facilities are switched into the sub-system at the computer end of the data transmissionlink. Thus for little extra cost manual controlfacilities are provided the check-out of which lar-gely tests the computer control mode. Our expe-rience has been that where for economic or technicalreasons this philosophy could not be followed thedevelopment has been more difficult than otherwise.Editing facilities are available (back-spaceand delete). Further, there are instructions whichwill abort a program in execution or remove repeti-tive commands waiting to be completed.It has proven to be essential to re-assure ope-rators that everything is normal if any action takesmore than a few seconds. Such messages are conve-niently displayed on CRT screens.6. Functions Already Implemented6.1 Beam Transfer Channels5. Interface between the System and the OperatorThe label, clauses and in some cases the parameterlist, may be omitted. For example,The operator communicates with the computer viaone of six terminals. Each terminal consists of akeyboard, printer and/or CRT. The operator commandsa particular function by typing a line of the formIn purely monitoring applications, such as va-cuum pressure display or orbit measurement, general-purpose scanning systems have been used. Here, wehave found it highly desirable to allow the com-puter full access to all relevant status data, andto allow such operations as calibrations to be per-formed automatically by the computer.Beam currents are monitored, and beam positionsat the beginning and at the end of each channel arecomputed, by a program which takes calibrations ofindividual pick-up electrodes into account and per-forms periodic measurement of electronic~ offsets.Beam currents, percentage losses and beam positionscan be displayed or recorded as convenient.Magnet power supplies are set up by the computerfor each run according to lists of values stores onthe disc. The routines incorporate switch-on, magnetcycling and checks for correct functioning. Steeringof the beam can be performed by specifying to thecomputer the number of mm the beam has to be dis-placed at a certain position detector (e.g. lumi-nescent screen). It was in this way that the firstbeam was steered through channel TTl. Further pro-grams can record settings, or check them against alist and signal discrepancies to the operator.program name, clauses (parameter list)labelXSET (FS 26)would set the auxiliary power supplies to the valuescontained in the file FS 26. All programs and filesare identified by means of names of four characters.Profile data from secondary emission grid moni-tors are read by the computer and can be used tocompute beam emittance~.6.2 InjectionClauses in the command allow the operator tospecify where his output should be sent or can re-quest the command to be repetitively carried out atgiven intervals of time or on given PS pulses. Forexample,LSVG, FP, IN = IS(lM)lH (Sll)would run the program LSVG to list on the Fast Prin-ter (FP) every minute for the next hour, the pres-sures in Sector 11 as given oy tlie vacuum gauges·.A standard set-up procedure is the optimisationof injection into a storage ring using closed-loopcontrol to minimise the betatron oscillation ampli-tude. This is done by adjusting injection positionand angle and predicting the minimum (the apex of acone) in about five steps. The computer programquickly achieves excellent results and releases theoperator from a delicate tuning procedure.6.3 Monitoring of the Ultra-High Vacuum SystemWhile there are many mnenomics that an operatorhas to learn, together with their parameter lists,this is inevitable with a process that has so manydiverse aspects as an accelerator. Naturally, thetasks of the operator is made as easy as possibleand a number of aids are at his disposal.An important task of the computer is the super-vision of the vac~um instrumentation. A variety ofprograms are used for producing lists or c.r.t. dis-plays of sputter-ion pump currents, valve positionsetc. The operator is able to shorten the lists byimposing restrictions such as currents greater thana given value, valves closed etc. Graphical displays- 441 -of the pressure around the rings are produced fromthe ionisation gauge readings (see Figure). More-over, the computer can automatically calibrate thegauges by switching their modulator potential.Groups of gauges may be turned on or off.6.4 ISR Working Line Adjustment 4)The computer is able to set pole-face windingsand other correction currents to a list correspon-ding to a specified QH-Qv locus over the ISRaperture. Each list is established or modified bya program which computes and applies saturationcompensation at high main magnet field, and pro-grams which permit the operator to change Q and itsderivatives.6.5 Closed Orbit Analysis and Correction 5,6)The computer proved to be an indispensable toolin the presentation to the operator of orbit data.As in the beam transfer system, calibration of thepick-up stations and recording of the offsets inelectronics can be performed by the computer. Onrequest, 224 readings are taken from either ring,the beam positions are calculated and the orbit dis-played.Further programs are used to analyse the beamorbit into its harmonic components. A set of theseharmonics may be selected by the operator, andcorrection magnet currents altered to reduce theamplitude to zero. A further orbit measurement andanalysis will check the corrected orbit. The loopis at present closed in a number of stages by theoperator, but it could be done by the computer inone action, should it be operationally desirable.In this way, orbit corrections have been per-formed vertically and radially. Vertical correc-tion has also been carried out by adjustment ofmagnet positions. Orbit analysis programs computethe required jack movements. The adjustments arecontrolled by the operator, supervised by the com-puter, which displays the positions of the magnetsconcerned. It carries out checks during theadjustment, exercising a veto on further movementif limits would be exceeded.6.6 Orbit BumpsThe computer is used to produce vertical orradial bumps of a given amplitude. To do this, thenecessary power supplies must be adjusted in aconstant ratio to one another, in order not todisturb the stacked beams outside the bump area.This procedure is standard when setting up colli-ding beams for optimum luminosity.6.7 Power Supply SupervisionThe computer is used extensively in checkingthe correct operation of about 180 ISR power sup-plies and 80 beam transfer power supplies, bothduring a run when it checks for faults, drifts etc.and in preparation for a run to establish correctperformance of all functions, check that,zerooffsets and maximum currents are within tolerance,etc.6.8 Logging Functions and Alarm MonitoringDuring the ISR runs the computer sums the num-bers of protons injected, dumped or lost due tovarious causes. This helps in compiling statisticson operation and in radiation monitoring.Beam transfer and ISR magnet power supplies aremonitored regularly and warning of faults, drifts,etc. are presented on a reserved alarm printer.Other important items, such as clearing electrodevoltages, were incorporated in monitor programs asthe need arose.6.9 ISR DevelopmentIn addition to use of standard operational faci-lities, programs have been prepared for particularinvestigations, as for example beam current decayrate evaluation and current loss related to beamscraper position.7. Further Development of the Computer System.Work is being carried out under four mainheadingsautomatic setting up of the machine condi-tions. This is generally a two-stage pro-cess, the setting of standard conditions ina number of components followed by a finetuning procedure. For example, the settingof the transfer line magnets is followed byoptimisation of injection for minimum beta-tron oscillation. To automate the set-up ofthe ISR so as to achieve reproducably highbeam quality is one of our main goals.improvements and extensions to logging andalarm monitoring facilities.communication with ISR physics experiments.This project will link about a dozen com-puters on the CERN site through Camac mo-dules.assistance in ISR machine studies. Furtherautomation of measurements will give usefulassistance to physicists and speed up theirexperiments.8. Concluding RemarksThe computer has shown itself to be an essentialpart of the control system. It has proven veryreliable. In this context, one may mention thatfiles are kept on disc for many months and it israre that their contents become damaged.since the commencement of running-in tests thecomputer has been used by the operators. The com-- 442 -missioning of the computer programs closely followedthe installation and testing of ISR components.The computer system is now used extensively, bothin operation and in testing of equipment.For successful computerisation of an apparatus,it has been found essential that both hardware andsoftware be complete. Incomplete computerisationof a control system often causes dissatisfaction.The last link may only require a small effort butmay greatly enhance the performance.The total investments including engineering andprogramming effort has so far stayed below 2% of theISR construction cost.AcknowledgmentOn the human side, we have encouraged active in-volvement of other groups in the computer project.which is essential if full benefits are to berealised from the investment in time and money. Wewish to express our gratitude for the many contri-butions from our colleagues.References1) D.A.G. Neet. P. Wolstenholme: Proposal for useof a Digital Computer for Data Handling andControl in the ISR Project, CERN/ISR-Co/68-6,1968.2) P. Wolstenholme: Data transmission and computerapplication for the CERN-ISR project. USSR 2ndNat. Conf. on Particle Accelerators, September1970. Also CERN/ISR-CO/70-42 (This has a listof 13 further references) 1970.3) D. Kemp, R. Keyser, L. Tausch: Present status ofthe software for computer control in the CERN ISRproject. Paper presented to the 4th NationalParticle Accelerator Conference, Chicago, 1971.To be published in IEEE Transactions on NuclearScience, Volume NS-18.4) J-P. Gourber, Adjustment of Working Lines in theISR. Paper presented to this Conference.5) J. Borer et al, Instrumentation and Beam Dia-gnostics in ISR, Paper presented to this Confe-rence.6) B. Autin, P.J. Bryant, Closed Orbit Manipulationand Corrections in ISR. Paper presented to thisConference.FigureCRT display of pressuresread from Ultra-highvacuum gauges.- 443 -DISCUSSIONM.J. KNOTT: In your "multi-programming system",do you mean to imply that more than one programcan simultaneously time-share the C.P.D., or thatmany programs are simply "on call" by the operatorR. KEYSER: The system is a time multi-programmingsystem, scheduling up to seven programs in core.M.J. KNOTT Can you also do off-line (background)tasks such as compiling at the same time ?R. KEYSER: Since one of the seven tasks I men-tioned above could be the assembler, the answer is"yes".K. MALLORY I am pleased to find that the ISR,being like sLAe essentially a "steady-state" machine,puts little emphasis on fast response from userprograms.G. SCHAFFER We cannot consider the ISR as asteady-state machine in all respects, for example,not with respect to beam-vacuum interactions. Weneed to implement some fast triggered correlationstudy programs in order to analyse the situationon vacuum pressure instabilities and the mechanismsthat cause sudden beam losses. The development ofour data-acquisition system towards faster responseis included in our program of future work.A. MILLICH To what extent should one monitor beamquality rather than hardware which influences beambehaviour ?R. KEYSER At present, it is difficult for thecomputer to be told how to quantify the quality ofthe beam. If, for example, a badly stacked beamis produced, the experimentalists soon tell us andwe restack. How it is determined that a stackedbeam is deteriorating may be solved by asking theexperimenter'scomputers over the data link that Imentioned. When some ideas are known about whatcauses deteriorations, then we may know what tomonitor.VAN DER BEKEN : The question of monitoring the beamor the hardware depends on the machine involved.For ISR , the loss of the beam might have severeresults; therefore, monitoring the hardware mightbe wiser. In the case of the CPS, one pulse lostis less drastic and monitoring the beam might beacceptable.

Experience with computer control applied to the CERN intersecting storage rings (ISR)

Experience with computer control applied to the CERN intersecting storage rings (ISR)

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