Paper Written: July 1970 Paper Issued: July 1970 (EXPI .

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Paper written:July 1970Paper issued:July 1970SLAC-PUB-780(EXPI) and (ACC)THE STANFORDSTORAGE RING - SPEAR*BurtonRichterStanford Linear AcceleratorCenterStanford University,Stanford, California94305I.SPEAR (StanfordGENERALDESIGN FEATURESPositron-ElectronAsymmetricRing) consistsring of magnets threaded by an aluminumvacuum nearlybeams of electronsand positronsby making the beams collidecircularbeam by the rf voltagecapabilityoperatingan increasein the initialThe ring will operate in the so-calledzero crossingcollision*Work supportedI-This publicationby the U. ,S. Atomicwill be in Englishregions.a singlewill collidewithThe other potential‘Xerntechnik”t)Commission.and thusmode whereindesign of SPEAR,Energyinand in the magnet the Reviewconfigura-be installedoperatingand a single bunch of positronsbecause of the asymmetric(To be printedIn its initialconnecteddesigned to operate at energiesmaximumangle at one of the two low-betapoint,1).regionsof the single cavity which willin the number of rf cavitiesbunch of electronsisenergy of about 2.5 GeV eachThe magnets of the ring are however,up to 4.5 GeV, and an increasecirculatingA high luminosityin one of two long 71low-beta71 interactionarcs of unequal length3 (see a maximumrequiresin which counter-132 The ring is composed of the two matched low-betation SPEAR is limitedthe ring.circulate.of a singleis not at the

centerof the second low- beta section,ratherlarge.resultin greatlySince a collisionexceedingbut is ratherin a region where beta isbetween the two beams at such a point wouldthe thresholdfor the incoherenttwo-beamthe beams will be made to miss each other by a local perturbationorbitsgeneratedThe limitingby an electricluminositymined by the incoherentrent densityfield.of SPEAR,two-beamp, and p, and the beam energy.circulatingtoE-4.currentControlSPEARForis limiteddimensionsBelow 2 GeV the luminosityapertureto be exceeded,the controlproblemproblems.of single-beamrf cavitylenses to controloscillationin a luminosityby the apertureinsertions).coherenttodensity is nothave faced inkinds of instabilities.electricof the electronthe tune-versus-energycharacteristicsof the Landau damping.proportionalWedevices to aid in controllingfrequenciesthe frequencythe limitinginclude a fast feedback system foroscillations:frequenciesabove 2 GeV theThe beam currentring projectsof variousThese devicesisto E2.which most storagering with variousparametersof the storage ringcurrentproportionalis the controlthe cur-rf power and is proportionalto split the synchrotronof octupole lenses to controlstrengthis limitedis deter-design luminosityof the beam to maintainresultsin a luminosityto equip the storagesplit the betatronspeciallimitsAt energiesto the beam energy if the limitingearly days of operationthese instabilitylimitis outside the low-betaresultingThe most difficultare planningthe maximumby the availableof the transversemust be proportionaltheirrings,This instabilityat an energy of 2 GeV each beam.beam current(the limitingas with other storageinstability.density set by the incoherentE-3.of equilibriumin the beams in a manner which depends on the guidefield1O32 cm-2 see-linstability,quadrupolelenses toand positronbeams; aof the two beams: sextupoleof the lattice:and a setspread in the beam and to vary the

The two interactionregionshave been designed with a 5 meterbetween the faces of the quadrupolefeel that these relativelymagnets closestlong interactionof apparatusused for experimentationis capable.The interactionlong,35 feet transverseline of 10 clearanceThe interactionMAGNETis a separatedis composedfive such cells.mentum vectorpoint.Wefor the kindsof which SPEARof a pit which is 40 feetclearanceto the beamwillalso allow 10 feet of verti-latticecomposed of zero-gradient1. ) The long arc connectingthe two low-betacells while the short arc is composed ofbeta functionscell in the long arc.(P,,Py),and mo-The short arc must havethan the long arc in order to close the the two regionsin the standardand shorteningcell by roughlySince the firstone-halfand second derivativesof the cell straightbation on the transferthe interactionof three quadrupolesWe havethis by keeping the bending msgnet and quadrupoleidenticalPropertiesfunction2 shows the structure,jr]) for a standardat the centerLATTICEof six standardFigurechosen to accomplishsmallenergiesThe basic cell is composed(See Fig.average radiusshort requiredspaceabove the beam line.and two bending magnets.sectionat the higherregion buildingsbending magnets and quadrupoles.and lengthswillto the beam, and gives a verticalThe SPEAR latticea smallerto the interactionpoint is above the centerII.insertionsregionsdriftmatrixof the low-betaregion,a value of a few meterssection,the three meterfieldsstraightmeter to make the cells for aof the beta functionthis makes a negligibleare verypertur-of the cell.insertionp, is nominallyby varyingare shown in Fig.3.5 cm and is continuouslythe currents-3-in Ql,At the centeradjustableQ2, and Q3.Theofup to

momentumvector 77 has been made zero in the centralallow this variationin /3y withoutspoilingregion of the insertthe momentumtomatch to the rest ofthe ring.The normalbe variedtune of each ring is around “,- 5.2,Lfrom roughlymomentumphysically4.5 to 5.7 with littlematch over this region,the quadrupolethe match is satisfactoryThe very strong quadrupolesrationsvaryingmomentummachine.large so that it is etsand described.A.Magnetsbe machinedaluminumfrom rolledthe full I l/2 %is designed withoutthis chromaticthe normalcorrections.aberrationcells of themagnets per cell which allowsDESIGN DETAILSof the ring which may be of interestBoth the bending magnets and the quadrupoleswillaber-to be reduced to zero.In this section some of the design detailswillThese chromaticto injectthroughoutWe have designed for three sextupoleboth horizontalof QFI.ring guidefieldof the storagehave shown that the best way to correctis to distributethe positionaberrationsspread for which the injectionCalculationsover a region ofnext to the inter-than is usual in a strong focusingare sufficientlymust beQ2 and Q3 in the insertionaction region make the chromaticmuch largera perfectQFl in the insertionHowever,withoutThese tunes canTo maintaindifficulty.moved from its nominal position.Av z & l/4v 5.1.Ysteel plate.since we find fabricationAll magnet coils willof aluminum-4-are of conventionaldesign andbe made ofcoils to be considerablycheaper

than fabricationcoil capable of handlingextremelycasting.Theseby compensatingformisalignments.on the sextupolemagnets areloose and the iron cores of these magnets will therefore,All magnets are capable of operatingmagnetswith an auxiliaryof the main coil.deviationshave shown that the tolerancesto 4.5 GeV, but in the firstB.the closed-orbitand small quadrupoleCalculationsbe providedabout 1% of the ampere turnscoils can be used to eliminatefield errorsEach magnet willof copper coils.up to a maximumstage of SPEAR power willbe made byfield equival.ectbe suppliedto run theonly to about 2.5 GeV.--RFThe rf system willrun at a frequencyharmonicof the orbit frequency.availableat turn-onof 1010Initially,there willradiationAt the injectionlifetimeconsiderablyenergy of 1.5 GeV the momentumPowerThe energy lossat 2 GeV is 110 kV and the maximumis 300 kV giving a quantum fluctuationsec.on the 31stbe one rf expected to be 160 kW to 200 kW total.per turn in synchrotrona.vailableof about 42 megacyclesrf voltagein excessacceptanceiszk 0.5%.C.InjectionWe plan to inject electronsand positronsinto the storageof 1.5 GeV using the beams of the 20 GeV Stanfordthe ring in the one-bunchparticleslinac.mode describedin two 7-ns burstsLinearWith the 20 pps injectionthe instantaneousrepetitionIn fillingto accepting1.5 psec pulse of the 20 GeVThis bad duty cycle match can be only partiallythe linac gun and increasingAccelerator.above, we are limitedduring the nominalring at an energycurrentrate determinedcompensatedby modulai-ingduring our acceptanceby the radiationdampingtln-ie.

timesin the he positronThe injectionfillingsystemrate is expected to be 6 min peris a relativelystandardbeam-bump-of aluminumextrudedin a crossVacuum--The vacuum chambersectionwill be fabricatedof our design includingthe absorptionof synchrotronshown in Fig.4.chamberand a lower x-rayof the vacuum chamber,rugated to furtherreflectioncapacityrequiredto fabricatecoefficientwhere synchrotronstainlessthan steel.willstrike,willbe cor-rate.ion pumps of our own design for most of the pumpon the ring.These pumps use the relativelyThe componentslow qualityon the pumps.Fig.The pump is made from pieces of stainlessand supportedby insulatorsIn tests with ion pump cellsl/2”in diameter,per meter1200, 45, and 5 I/s/mfor hydrogen,pumpingspeed is nearly1.8 kG which correspondssteel tubing spot-weldedindependentheliumplates.we have achieved pumping speedsof pump for nitrogenand argon,of magneticor carbon monoxiderespectively.field down to fieldsin our design to 0.75 GeV circulatingring will also be supplied with one 80 liter/setstraightfieldbetween two 0. 080” thick titaniumof about 500 liters/setmag-of one of these pumps are shown inrequiredtogethersteelThe inside surfacenetic field of the bending magnets near the pole edge for the magnetic5.isand has a lower gas desorptionradiationreduce the gas desorptionbycross sectionover the more conventionalis easierWe plan to use distributedoff heat generatedThe vacuum chamberradiation.We chose aluminumbecause an aluminumcoefficientthe water passage to carryconventionalandTheof aboutbeams.Theion pump persection to hold the ring at high vacuum when no beams are stored andthe magnets are off.-6-

E.AssemblyWe plan to preassemblein Fig.the components6 before installationposed of a 30-ft-longthree quadrupoleselementsin the storageconcretecell,aligned with respectring girderand three sextupolesof a normalof the ring into modules as shownon which two bending magnets,are typicallyless the cell straightto the girder,Each module is com-mounted.section.The magnets will bethe vacuum chamberinstalledchecked and all power,water and controlassembly.Installationof this module into the ring requiresconcretesupport girderand one multi-conductorF.and the connectioncontrolinstalledand leak-as a part of modulethe alignmentof theof one water pipe, 3 dc power cablescable.StatusWe have recentlyemphasizingcompletedan extensiveresearchand developmentwork on the ring magnets and on the vacuum begin fabricationfinishcablingThese are theconstructionof the storagering itselfin 1972.-7-programWe expectin the second half of 1970 and to

COLLIDINGBEAM STORAGE RINGS -- eStanfordConstructionFirst1970started1972 e ,ebeams or goalCollidingparticlesMax. energy2.5 GeVPossible4.5 GeVextensionNo. of rings-3Approx.ovoid1shapeDimensions60 mx74Orbit220 mlengthmnNo. of orbit intersectionsLNo. of experimental2zonesApprox.area for experiments2 X (11 m X 12 m)Straightsect. for experiments5mBEAM PARAMETERSReference2 GeVenergyenergy spread-2-1setLuminositycm5 x 10-4Beam life 2 hr.Relative1o32Half crossingangle (vert/horiz)0Beam current(each beam)0.5 ANo. of particles2 x 1o12per beamNo. of bunches per beam3L1No. of particles1012per bunchBunch to bunch time0.7 /.&24 nsHalf bunch length14 cmHaif bunch width at I. P.0.32 cmHalf bunch height at I. P.0.008 cm-8-

SummaryTable (cont’d. ) - 2MAGNETLATTICESPEARNameTotal no. of bending magnets (B)34Max. bending field6.3 kG (2.5 GeV)Radius in bending magnets12.72 mTotal no. of quadrupoles51(Q)Max. field gradient590 g/cmTotal weight of Fe230 tonsTotal weight of CuNo. of identical1superperiods11No. of magnet periodsCompositionLow-beta(0 straight),(F,D, synchr.insertionExperimentalmag.)2x48m(no. x length)straightQ/2 BQOQB Q/22X5msectionEv. third typeMagnet power availablePossibleextensionMachine acceptancehoriz.nx6cmX4.5Machine int. point1.6 m to 8 mVert.ampl.ampl.funct.funct.5cmtolmat int. pointRF SYSTEMFrequency(rf)42.35 MHzRevoltuionfrequency1.36 MHzCorrespondingrevolutionNo. of transmittersNo. of cavities0.73 pstime8(total)1(total)Max. rf power (total)200 kWMax. peak rf voltage (per beam)300 kVMax.180 kWrf power on the beams-9-mr

SummaryTable (cont’d. ) - 3VACUUMSYSTEMSPEARNameRoughing pumps (no. x type)Total pumping speedUHV pumps (no. x type)34 X ionTotal pumping1.7 x lo4 l/setspeedPressurewithoutPressurewith beam 10eg torrbeam 5 X ngSYSTEM1.5 GeVenergylinacused6 min/AspeedEv. filling2 min/Aspeed for opp. signTotal time for fill.process(Imax)6 min2mm X 3 mrAcceptanceAcceptancetorrk l/2%energy spread- 10 -

REFERENCESAND FOOTNOTES1.K. W. Robinson and G. A. Voss,2.P. L. Morton and J. R. Rees, IEEE Trans.3.This configurationintersectingis derivedasymmetricCEAL-TM-149froma previousNucl.Sci. NS-14,is one of the two rings of this previousto begin with a facilityof adding the second ring at a laterluminosityin theThe single ring describedheredesign and allows high energy physicsof lower cost while preservingdate.- 11 -630 (1967).SLAC design which used tworings designed to produce higherenergy range below 2 GeV than this project.experiments(1965) unpublished.the option

FIGURE1.Schematic2.Betatronfunctionsstandardcell of large ayout of SPEAR.(left scale) and momentum(left scale) and momentum4.Crosssection of the extruded5.The components6.The standard SPEAR assemblyaluminumof the distributed(rightscale) in afunction(rightscale) in thevacuum chamber.ion pump.module.function

cdcodzd2-112 METERS 21CELLs:zddcuI III IIBBIRF1262422200I234567DISTANCE IN METERS -Fig. 289IOIII2576-13-B

t-----48i IO100cl& 90METERS 8xI%I \IIpFz80&60RF\\I/7o50403003691215I8212427DISTANCE IN METERS -Fig. 3303335384245576-12-R48