Akiyama, A

Katoh, T

Kubo, Ta

Nakamura, T T

Yamamoto, N

Yoshida, M

CERN Document Server

MAGNET POWER SUPPLY CONTROL SYSTEM IN KEKBACCELERATORST. T. Nakamura,  A. Akiyama,  T. Katoh,  Ta. Kubo,  N. Yamamoto,  M. Yoshida,KEK, Tsukuba, JapanAbstract  There are more than 2500 magnet power supplies forKEKB storage rings and injection beam transport lines.To construct a control system for such a large number ofpower supplies, one of the important things is to reducethe cost of the interface between the power supplies andthe control computers. For this purpose we developed thePower Supply Interface Controller Module (PSICM) of3U Euro-Card mounted in each power supply. PSICMsand a local control computer are connected by ARCNETSTP cables in a daisy-chain manner. A PSICM has amicroprocessor which communicates with the localcontrol computer. Magnet power supply control system iscarefully designed to satisfy conditions for efficient beamhandling. A PSICM can change the power supply currentwith an arbitrary tracking curve which is sent from thecontrol computer. An arbitrary number of PSICMs canstart tracking synchronously with each other by using anexternal trigger signal. The KEKB magnet power supplycontrol system has been operated since Dec. 1998.  Itssoftware design and functions are discussed.1  INTRODUCTIONKEKB is an asymmetric electron-positron collider at 8× 3.5 GeV/c, which is dedicated to B-meson physics.  Itsoperation was started in December 1998.  The KEKBaccelerator control system[1] has been constructed basedon EPICS toolkit[2].  EPICS provides core mechanism forthe distributed control system.  EPICS runtime database isrunning on a VME based local control computer called anIOC (Input/Output Controller).  There are about 100 IOCsin the KEKB accelerator control system.  We use a UNIXserver as the host computer.The number of  magnets (including auxiliary coils)used in the two storage rings is 4607, and the number ofpower supplies for them is 2245.  1711 of them are thepower supplies for steering magnets.  To connect such alarge number of power supplies to the IOCs, we adoptedARCNET as a field bus and developed the Power SupplyInterface Controller Module (PSICM) [3], which is anARCNET interface board for the power supply.  APSICM has the shape of 3U Euro-card format (100mm ×160mm) with a DIN 64-pin connector and can be pluggedinto the power supply.  The ARCNET allows to useseveral kinds of media.  We adopted shielded twisted-pair(STP) cable as the media and HYC2485 as the mediadriver.  This configuration allows up to 20 ARCNETnodes to be connected on single segment in the daisy-chain manner.  The STP cable includes an auxiliarytwisted-pair for the external trigger signal other than theARCNET use.While ARCNET and PSICM reduced a great deal ofwiring cost, there are other control paths between IOCsand  subsystems of the magnet power supply system[4].The power supply output current is monitored by a digitalvoltmeter with scanner.  They are connected to the IOCusing GPIB.  The PLC based interlock system of thepower supplies has a connection with an IOC throughModbus Plus[5].  These subsystems are not discussed inthis paper.There are 274 magnet power supplies for the KEKBinjection beam transport lines.  They are also controlled inthe similar manner.2  FUNCTIONAL REQUIREMENTS ANDDESIGNAlthough KEKB storage rings do not need synchronousramping of magnetic fields for the acceleration,synchronous operation of magnet power supplies is stillimportant.  For efficient beam handling, beam opticsshould be changed without loosing stored beam.  Toachieve this, the magnet power supply control system hastwo features.  One is the synchronous operation ofPSICMs.  A PSICM can receive an external trigger signalto start current tracking.  The external trigger signalgenerated by the IOC in the central control room isdistributed to the IOCs in the local control rooms throughthe software trigger system[6].  From an IOC to PSICMs,the trigger signal is sent through the auxiliary twisted-pairin STP cables for the ARCNET.  Using the externaltrigger signal, PSICMs can start tracking synchronouslywithin 0.1ms or less.The other feature is a flexible tracking curve.  ThePSICM is designed to receive arbitrary tracking data.This feature is useful for fine synchronous operation.Using a proper tracking curve, it is possible to compensatefor  the delay of magnetic field against the current setting,which is caused by the delay of the power supply and thedelay of the vacuum chamber.  This feature gives usanother benefit even for the asynchronous operation.  Forthe power supplies with slow response, a proper trackingcurve makes current setting faster without overshoot thanlinear tracking.To make application programming simple, the magnetpower supply control system requires that a controlInternational Conference on Accelerator and Large Experimental Physics Control Systems406International Conference  Accel rator and L rge Experim ntal Physics Control Systems, 1999, Trieste, Italyparameter can be given not only by current in apms, butalso by some abstracted parameter of beam optics such asK1 for a quadrupole magnet, K0 for a steering magnet etc.We generically call such parameters "K-values" forsimplicity.3  FUNCTIONS OF PSICMSince the PSICM has a microprocessor, it is not only anARCNET interface board but also an intelligentcontroller.  The control program is stored in EPROMs onthe PSICM.  It provides advanced functions of the powersupply.  The PSICM provides the following 3 functions;(1) generating control signals to the power supply for thesingle actions such as power on/off, interlock reset,polarity change etc.,  (2) setting output current,  (3)sending the status of the power supply and the PSICMitself.  The status can be sent periodically, on demand orwhen specific status is changed.The PSICM communicates with an IOC through theARCNET.  The elemental unit of the communication is a"message".  The message from an IOC to a PSICM iscalled a "command".  More than one commands can bepacked in single ARCNET packet.  The message from aPSICM to an IOC is only the status with fixed format.To set the output current, the PSICM writes a digitalvalue to the DAC (Digital to Analog Converter) in thepower supply.  There are 3 tracking modes and 2 triggersources.  The tracking modes are as followings.  (1) Thedirect output mode: the output current is set directly to theDAC without tracking.  This mode is only for diagnosticsof the DAC and PSICM itself.  (2) The constant slewingrate mode: the output current is changed with a lineartracking.  The PSICM receives the target current and thetime of the tracking duration from the IOC and writes thelinearly interpolated value to the DAC every 1ms.  Thismode is mainly used for stand alone test of the powersupply.  (3) The wave-generator mode: the output currentis changed with an arbitrary tracking curve.  The PSICMreceives tracking data as an array of currents from theIOC, then sequentially writes them to the DAC everyinternal clock interval which can be a multiple of 1ms.This mode is used for usual operation.The constant slewing rate mode and the wave-generatormode require a trigger to start tracking.  The triggersource is either a "start" command sent from the IOCthrough ARCNET or an external trigger signal sentthrough the auxiliary twisted-pair.4  DRIVER LEVEL SOFTWARELow level software is EPICS Driver support and EPICSDevice support in the IOCs.  The driver support isdesigned to perform communication through theARCNET.  The elemental services of the driver supportare transmitting and receiving single packet.  Inside thedriver support, packets are queued.  There are atransmission queue and a receiving queue for each powersupply independently.The device support is designed to provide two kinds ofservices.  One category includes the services dedicated tothe PSICM.  Each service corresponds to the singlecommand of the PSICM such as power on/off, interlockreset etc.  Using these services EPICS records whichperform the single action can be easily created.  Othercategory includes general purpose services which performsingle packet I/O.  They are nearly same as ones in thedriver support.  Using these services, although EPICSrecord support should directly encode or decode messageson the ARCNET packet, it is rather convenient when arecord issues various commands sequentially.5  MIDDLE LEVEL SOFTWAREMiddle level software provides various logic to thepower supply system.  Most of them are resident in IOCsusing EPICS runtime database which is the collection ofthe EPICS records.  Each power supply has a large specialrecord called the PS-record, which has been developedonly for magnet power supply in KEKB.  Most of thecontrol logic is concentrated in the PS-record andprogrammed in C.5.1  Parameter ConversionThe most complicated logic is current setting.  Since anapplication program may request current setting in term ofa K-value, middle level software must have parameterconversion logic using some information such as magneticfield excitation curve.  The parameter conversion iscarried out typically in the following manner.  (1) A K-value is multiplied by the beam line momentum to yieldan integrated magnetic field strength.  The momentum iskept in an EPICS software record.  Each storage ring orinjection beam transport line has such a momentumrecord.  (2) The integrated magnetic field strength may bemodified by a "fudge" factor and a fudge offset.  They areintroduced to correct the magnetic field excitation curvein an empirical manner.  (3) The integrated magnetic fieldstrength is converted to current using the magnetic fieldexcitation curve.  Each PS-record has the characteristicparameters of the excitation curve of its own magnet.5.2  Asynchronous OperationAsynchronous operation of current setting is theoperation on a single power supply independently of otherpower supplies.  For this operation, the external trigger isnot used.  PS-record provides 4 methods of currentsetting.  One is called "Direct Setting", in which currentsetting is carried out regardless of magnetic hysteresis.The other 3 methods are "Standardize Setting", "SimpleStandardize Setting" and "Sequence Setting".  In thesemethods, the regular hysteresis loop is more or lessconsidered.  To set lower current by Sequence setting for407example, the current goes up to the maximum currentfirst, then it keeps the maximum current for a moment.Next, it goes down to zero current, then it keeps zerocurrent for a moment.  Finally it goes up to the targetcurrent.  Thus, unless Direct Setting is used, magneticfields is kept on the regular hysteresis loop.  Thesemethods are particularly useful for magnets in theinjection beam transport lines.5.3  Synchronous OperationSynchronous operation of current setting is theoperation on more than two power suppliessimultaneously without loosing beam in the storage ring.In this operation, only Direct Setting is possible.To perform the synchronous operation, frequentnegotiations among power supplies are necessary.  As anarbiter of them, we introduced a server process for eachstorage ring.  It manages the sequence of the synchronousoperation.  The server process runs in the host computerand is programmed in Python.  The synchronous operationis carried out in the following steps.  (1) The serverreceives a request with parameters from an applicationprogram.  The parameters are a set of power supply IDnumbers, a set of K-values to be set and a time of thetracking duration.  These parameters are passed throughEPICS software records.  (2) The server sends the K-values to the PS-records.  (3) Each PS-record converts thegiven K-value to current, then it estimates minimum timeof the tracking duration and sends it back to the server.(4) The server checks the estimated minimum times.  Ifthe application program does not specify a time, themaximum of the estimated times is adopted.  (5) Theserver sends the adopted time to the PS-records.  (6) EachPS-record calculates tracking data and sends them to thePSICM.  (7) Each PS-record checks status of the PSICM.If the PSICM is ready to start tracking, the PS-recordsends "ready" to the server.  (8) The server waits until allPSICMs become ready, then the server generates anexternal trigger signal.  (9) The server checks whether allpower supplies have started tracking.6  APPLICATION LEVEL SOFTWAREApplication programs are developed by many users.They use not only EPICS standard tools such as MEDM,but also write programs in some programminglanguages[7].  The application program which requiresknowledge of beam optics are written by acceleratorphysicists.  In this case, the program is usually written inSAD[8].  SAD is a computer program complex foraccelerator design developed at KEK.  It has scriptlanguage called SADScript in Mathematica style.  UsingSAD, optics calculation and operation of power suppliesare easily combined.Another popular language in KEKB accelerator controlsystem is Python.  Python is a portable, interpretive,object-oriented programming language.  The operatorconsoles for magnet power supplies are mainly written inPython.  Python is easier to learn than C/C++ and moreproductive for beginners.7  CONCLUSIONIntroducing PSICM and ARCNET, wiring between theIOCs and the power supplies became simpler.  ThePSICM also provides rich functions to the power supplies,such as the wave-generator mode and the external triggerto start tracking.  As the middle level software, thecomplicated logic is implemented in IOCs and in thesynchronous operation servers.  The middle level softwaresystematically provides simple but powerful functions tothe application programmers.  Using these functions inscripting languages, SAD and Python, it became mucheasier to develop high level application programs.8  REFERENCES[1] "KEKB control system: the present and the future",N. Yamamoto et al., PAC-99, New York, 29 Mar.-2Apr. 1999[2] http://epics.aps.anl.gov/asd/controls/epics/EpicsDocumentation/WWWPages/[3] "KEKB Power Supply Interface Controller Module",A. Akiyama et al., ICALEPCS’97, Beijing, 3-7 Nov.1997[4] "Magnet Power Supply System for KEKBAccelerator", M. Yoshida et al., EPAC-98,Stockholm, 22-26 June 1998[5] "Interfacing Modbus Plus to EPICS for KEKBAccelerator Control System", J. Odagiri et al.,ICALEPCS’99, Trieste, 4-8 Oct. 1999[6] "Performance of the Timing System of the KEKB",T. Naito et al., ICALEPCS’99, Trieste, 4-8 Oct. 1999[7] "Use of Object Oriented interpretive Languages in anAccelerator Control System", N. Yamamoto et al.,ICALEPCS’99, Trieste, 4-8 Oct. 1999[8] http://www-acc-theory.kek.jp/SAD/sad.html408

Magnet Power Supply Control System in KEKB Accelerators

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