加速器准直

TS6H-EngineeringSurveysIDavidMartinReviewofAcceleratorAlignmentFIGCongress2010FacingtheChallenges–BuildingtheCapacitySydney,Australia,11-16April20101/16ReviewofAcceleratorAlignmentDavidMARTIN,FranceKeywords:accelerator,alignmentSUMMARYThehistoryoftwentiethcenturyscienceandtechnologyisintimatelytiedtothedevelopmentofparticleacceleratorsandthediscoveriesmadeusingthem.Todaythebreadthofscienceconcernedby,andstudiedusingparticleacceleratorsistrulystaggering.Itrangesfromattemptstounderstandtheoriginofouruniverseandwhatconstitutesmatterandradiation;toquestionsconcerningtheprocessesthatsustainlife;toabetterunderstandingofarchaeologyandpalaeontology.Virtuallyallaccelerators,regardlessoftheirscientificapplicationrequireprecisealignmenttooperatecorrectly.Thefieldofacceleratoralignmentoverlapsthefieldsofmetrologyandtraditionalsurveyingandgeodesy.Standardmeasurementprecisionismillimetrictosub-millimetricoverdistancesrangingbetweenseveralhundredmetresuptonearly30km.Newandplannedmachinesgobeyondeventhisandrequiremicro-metrealignmentprecisiononthesamescales.Theuseofspecialisedtechniquesandinstrumentsareneededtoguaranteethattheserequirementscanbemet.Thispaperwillprovideaverygeneraloverviewandcharacteristicexamplesofdifferenttechniques,instrumentation,andresultsrelatedtothefieldofacceleratoralignment.InterestedreadersarereferredtoacomprehensivecollectionofarticlesconcerningparticleacceleratorandexperimentalignmentavailableontheInternationalWorkshoponAcceleratorAlignment(IWAA)website().TS6H-EngineeringSurveysIDavidMartinReviewofAcceleratorAlignmentFIGCongress2010FacingtheChallenges–BuildingtheCapacitySydney,Australia,11-16April20102/16ReviewofAcceleratorAlignmentDavidMARTIN,France1.INTRODUCTIONAparticleacceleratorisadevicethatuseselectricfieldstoaccelerateionsorchargedsubatomicparticlessuchaselectronsandprotonstohighspeedswhilemaintainingtheminwell-definedtrajectories.Beamsofhigh-energyparticlesareusefulforbothfundamentalandappliedresearchinthesciences.Fundamentalparticlephysicsseekstounderstandtheelementaryconstituentsofmatterandradiationandtheinteractionsbetweenthem.Elementaryparticlephysicistsusemachinesthatacceleratebeamsofelectrons,positrons,protons,andanti-protons,interactingwitheachotherorwiththesimplestnuclei(e.g.hydrogen)atthehighestpossibleenergies,generallyhundredsofGeV1ormore.Nuclearphysicistsandcosmologistsusebeamsofatomicnuclei2ofatomssuchasironorgold,toinvestigatethestructure,interactions,andpropertiesofthenucleiandofcondensedmatteratextremelyhightemperaturesanddensitiessimilartothoseimaginedtohaveoccurredinthefirstmomentsoftheBigBang.Interactionsorcollisionscanbeprovokedbetweentheparticlebeamandafixedtargetorbetweentwoparticlebeamscirculatinginoppositedirectionswithintheaccelerator.ExamplesofthesetypesofacceleratorsareCERN,DESY(upuntil2007),SLAC(upuntil2008),KEKandFERMIlab.Anotherbranchofparticleacceleratorscienceworkswithwhatisreferredtoassynchrotronradiation.Synchrotronradiationlightsourcescanbecomparedtosupermicroscopes.3Highenergyelectronspassingthroughbendingelectromagnets(dipoles),orthroughperiodicmagneticstructurescomposedofmanymagnetswithaspecialrepeatingrowofNandSpolesthatforcetheelectronsintoasinusoidalorhelicalpath4;emitextremelybrightandcoherentbeamsofhighenergyphotonsintheultravioletandX-rayregionsoftheelectromagneticspectrum.Applicationfieldsforlightgeneratedbysynchrotronradiationlightsourcesincludechemistry,earthscience,condensedmatterphysics,biology,andlifesciencesandtechnology.ExamplesofthesetypesofacceleratorsaretheESRF,APS,SPRING-8,DIAMOND,theCanadianandAustralianLightSources(CLSandALS),tonameonlyafew.Atthetimeof1Theelectronvolt(eV;1GeViseV)isaunitofenergyusedinphysics.Bydefinition,itisequaltotheamountofkineticenergygainedbyasingleunboundelectronwhenitacceleratesthroughanelectricpotentialdifferenceofonevolt.Bymass-energyequivalence,theelectronvoltisalsoaunitofmass.Itiscommoninparticlephysics,wheremassandenergyareofteninterchanged,touse,where(aconstant)isthespeedoflightinavacuum(from).2Nucleiareatomsstrippedoftheirelectronsleavingonlyprotonsandneutrons.3Withoureyeswecanobservethemacroscopicworld.However,toseeatoms,whichhavedimensionsoftheorderofatenthofananometre(i.e.10-9m),weneedtouseadifferentformoflight,onethathasamuchshorterwavelengththanvisiblelight.ThistypeoflightisknownasX-rays.SynchrotronlightsourcesproduceveryintenseandbrightX-rays.X-rayshavemanywell-knownapplicationsinmedicine,buttheycanalsobeusedtorevealimportantinformationabouttheorganisationoftheatomsthatmakeupamaterial.4Thesedevicesarecalledwigglersorundulators.TS6H-EngineeringSurveysIDavidMartinReviewofAcceleratorAlignmentFIGCongress2010FacingtheChallenges–BuildingtheCapacitySydney,Australia,11-16April20103/16writingtherearecloseto70synchrotronradiationlightsourcesintheworldbeingusedbyanevergrowingnumberofscientists.Virtuallyallaccelerators,regardlessoftheirscientificapplicationrequireprecisealignmenttofunctioncorrectly.Thefieldofacceleratoralignmentoverlapsthefieldsofmetrologya