核电工程外文翻译国际空间站空间站上进行的阿尔法磁谱仪ams02实验.docx
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核电工程外文翻译国际空间站空间站上进行的阿尔法磁谱仪ams02实验.docx
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核电工程外文翻译国际空间站空间站上进行的阿尔法磁谱仪ams02实验
翻译原文
AlphaMagneticSpectrometer(AMS02)experimentontheInternationalSpaceStation(ISS)
AbstractTheAlphaMagneticSpectrometerexperimentisrealizedintwophases.Aprecursorflight(STS-91)withareducedexperimentalconfiguration(AMS01)hassuccessfullyflownonspaceshuttleDiscoveryinJune1998.Thefinalversion(AMS02)willbeinstalledontheInternationalSpaceStation(ISS)asanindependentmodulein
early2006foranoperationalperiodofthreeyears.ThemainscientificobjectivesofAMS02includethesearchesfortheantimatteranddarkmatterincosmicrays.InthisworkwewilldiscusstheexperimentaldetailsaswellastheimprovedphysicscapabilitiesofAMS02onISS.
KeywordsAlphaMagneticSpectrometer,InternationalSpaceStation,Antimatter,Darkmatter
Introduction
Apossibleexistenceofcosmologicallylargedomainsofantimatterorastronomical"antiobjects"andthenatureofdarkmatterintheuniversearefundamentalquestionsofthemodernastroparticlephysicsandcosmology.
TheAMS02experimentthankstoitslargeacceptance(~0.65m2)anditsparticleidentificationcapability,willstudythesefundamentalaspectswithunprecedentedsensitivity.Thisrequiresthemeasurementofthephysicalquantitiessuchasparticlemomentum,chargeandvelocitywithhighestpossibledegreeofconfidence.
Anunambiguousproofofexistenceofcosmicantimatterwouldbeobservationofantinuclei(Z>2)incosmicrays.Anobservationevenofasingleantiheliumorheaviernucleiwoulddemonstratethatprimordialantimatterindeedexistsanditisnottoofarfromus.TheAMS02willbeabletodistinguishasingleantiheliumnucleiamong~10^9estimatedbackgroundparticlesover3years.
Theprojectisrealizedintwophases.InJune1998,abaselineconfigurationoftheexperimenthasdownonthespaceshuttleDiscoveryfor10daysmissionon51.70orbitataltitudesbetween320and390km.Fromthismission(STS-91)wegatheredpreciousinformationondetectorperformanceinactualspaceconditionsandonpossiblebackgroundsources.
AMS01hasalsomeasured,forthefirsttime,withsuchanaccuracyfromspace,cosmicrayfluxesinGeVregioncoveringalmostthewholeEarthsurface.Thedetectorlayout,performanceandthephysicsresuitsofAMSO1duringSTS-91flight(AMS-0l)aredescribedindetailelsewhere.
InthisworkwewilldiscusstheexperimentalconfigurationaswellasthephysicscapabilitiesofAMS02ontheinternationalSpaceStation.
2.DetailsoftheAMS02experiment
TheAMS02isalargeacceptance,highprecisionsuperconductingmagneticspectrometerdesignedtomeasurecosmicrayspectraofindividualelementswithZ<--25uptoTeVregion.ItcanalsomeasurethehighenergygammaraysuptofewhundredsGeVwithverygoodysourcepointingcapability.Fig.lshowsthedetailsofAMS02experiment.
Thereareatotalof227,300electronicschannelseachproviding16bitsofinformationwitheventratesupto2kHcorrespondingtoatotalrawdatarateofover1Gbit/s.TheDAQelectronicswillreducetheeventsize,throughproperfiltering,totheallocateddownlinkdatarateof2Mbit/s.
AllelectronicsandmechanicalpartsofAMS02aretestedforoperationinvacuum.Theeffectoftotalionizationdose(upto6Gy/year)onallcriticalcomponentsisextensivelytested.
Thedetectorhasbeendesignedtoidentifythecosmicraysbutatthesametimeminimizingthemultiplescatteringandlargeanglenuclearscatteringoccurringinsidethetrackingpartofthedetector.Largeacceptanceforantiheliumsearch,goodparticlerigidityandvelocityresolutionsaswellastheirredundantmeasurementsandh/erejectionof>10^6wereotherkeyparametersforitsdesign.
TheAMS02willweigh6760kgandwillhaveapowerconsumptionof2kW.
InthefollowingtheAMS02sub-detectorswillbedescribedfromuptodownstream.2.1TransitionRadiationDetector(TRD)
TheTransitionRadiationDetectorisdesignedtoseparatea/psignalstodistinguishe+andpfromrelativebackgrounds(pande一respectively)witharejectionfactorof103一102intheenergyrangefrom10~300GeV.ThisrejectionfactorcombinedwiththeElectromagneticCalorimeterwillprovideanover-alle+/prejectionfactorof10^6at90%ofe+efficiency.
Thedetectorconsistsof20layersof6mmdiameterstrawtubesalternatingwith20mmlayersof10humpolyethylene/polypropylenefiberradiator.Thetubesarefilledwitha80%~20%mixtureofXe÷CO2at1barfromarecirculatinggassystemdesignedtooperateinspacefor>3years.Thewallmaterialofstrawtubesisa72μmkaptonfoil.Theupperandlower4layersruninthexdirection(paralleltoAMS02magneticfield)whilecentrallayersrunintheperpendicularydirectiontoprovidebi-dimensionaltrackingandparticleidentification.
2.2TimeofFlight(ToF)system
TheToFsystemisdesignedtoprovidefast(firstlevel)triggertotheexperiment,measurementoftimeofflightoftheparticlestraversingthedetectorwithup/downseparationbetterthan10-g,themeasurementoftheabsolutechargeoftheparticle(inadditiontodE/dXmeasuredfromtheSiliconTracker)andtheidentificationofelectronsandpositronfromantiprotonsandprotonsupto1--2GeV.Theexpectedoveralltimeresolutionis≈140psforprotonsandbetterforheaviercosmicraynuclei(seeFig.3forintrinsicresolutions).Itconsistsoffourscintillatorplanes(seeFig.4)readbyatotalnumberof144Hamamatsu85946phototubes.ThedesignofAMS02ToFsystemisdeterminedbytheconstraintofoperationin0.1~0.3Tstraymagneticfield.ThechoiceofPMandtheshapeoflightguidesaredrivenbythisissue.LightguidesareindeedtiltedtoreducetheanglebetweenthemagneticfieldandPMaxis.
2.3SuperconductingMagnet(SCM)
OneofthechallengingfeaturesoftheAMS02detectorisitsstrongsuperconductingmagnet.ItisthefirstlargesuperconductingmagnetusedinspaceandithasabendingpowerofB}LZ}0.8Tm^2whichwillbeessentialtoperformasensitivesearchforantimatter(He)intherigidity(p/Z)rangefrom0.1GVtoseveralTV.
Themagnetconsistsof2}dipolecoilstogetherwith2setsofsmallerracetrackcoils(seeFig.5)withatotalcoldmassofabout2300kg.Theracetrackcoilsisdesignedtoincreasetheoveralldipolefield,tominimizethestraydipolefieldoutsidethemagnet(maxstrayfieldataradiusof3mis4mT)inordertoavoidanundesirabletorqueontheISScausedbytheinteractionwiththeEarthmagneticfield.Allcoilsarewoundfromhighpurityaluminum-stabilizedniobium-titaniumconductor.Themagnetwillbeoperatedatatemperatureof1.8Kandcooledby2500Lofsuperfluidhelium,whichshouldbeoperationalforthreeyearswithoutrefilling(optimizedforheatlosses).
2.4Anticoincidence(AC)
TheAMS02anticoincidencesystem(Fig.6)isdesignedtoassuretotriggeronlyonthoseparticlespassingthroughtheapertureoftheAMS02superconductingmagnet.Itisplacedinsidethemagnetfreeborecoveringtheinnersurfaceofthesuperconductingmagnet.ACsystemconsistsofthinscintillatorslabsreadoutonbothendsbyPMs.
2.5SiliconTracker(ST)
TheSiliconTrackerofAMS02isdesignedtoperformhighprecisionmeasurementsoftherigidityhesignofchargeandtheabsolutechargeoftheparticletraversingit.
Thereareatotalof192ladderswithvariablenumberofsiliconensorsgluedtogetherandreadoutononeextremityythefront-endelectronics.Thelengthsoftheladdersvaryfrom36cmtoaboutwith60cm(activepart)correspondingto≈6.4m^2ofactivedoublesidedsurface.Fig.8showsadetaileddesignofaladderanditsmaincomponents.
Oneofthekeypointsintheassemblingoflongladdersisthatitrequireshighprecisionincuttingofthesensorsandduringtheladderassembly.Fig.9showsthedifferencesbetweenmeasured(throughreferencecrossesoneachsensor)andnominal(perfectlyaligned)positionsofthesensorsof73ladders.
Ther.m.s.ofdistributionisabout4μm.Thereadoutelectronicsisbasedonlownoise,lowpower(~0.7mW/ch),highdynamicrange(士70MIPs)VA_HDRVLSI,preamplifier,shaper,sampleandholdcircuitconnectedtothesiliconsensorsthrough700pFdecouplingcapacitors.
TheperformanceoftheAMS02laddershasbeentestedwithminimumionizingparticlesandwithheavyions.Fig.10showstheresidualsofthereconstructedandexpectedpositionsof400GeVmuonstraversingtheprototypeladders.Theresultingspatialresolutionsareonbending(nonbending)directionsfor400GeVmuonsand20GeV/Aheliumparticlesrespectively.Thetrackercoolingsystembasesonvariableconductiveheat-pipesinwhichthecoolingfluid(C02)runsbythecapillaryforces.Theheatiscollectedby3heat-pipeloopsandthendriventotheradiatorsfordissipation(seeFig.13).Thesystemwilldissipate192W(1Wforeachfront-endhybridpair)andfulfilltherequirementsofoperating(survival)temperaturesof-10℃to+25℃(-20℃to+40℃)and-10℃to+40℃(-20℃to+60℃)forsiliconwafersandfront-endhybridsrespectively.Therequirementforsiliconwafertemperaturestabilityperorbitis3Kandformaximumacceptedgradientbetweenanysiliconwaferfulfills10K.ThetotalweightofSTisabout186kgandthetotalpowerconsumptionis734W.
TheparticleidentificationcapabilitiesoftheAMS-U2proximityfocusedRICHdetectorwillimprovetheconfidenceinthedeterminationofthesignofthecharge,willprovidehighlevelofredundancyrequiredforhighpuritysamplesofpositronsandantiprotons,willperformtheidentificationofisotopesofmassA<~15-20,overamomentumrange1GeV/c
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