EURECA Conceptual Design Report

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Contents lists available at ScienceDirect

Physics

of

the

Dark

Universe

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / d a r k

EURECA

Conceptual

Design

Report

The

EURECA

Collaboration

G. Angloher

n

_,

_E.

_Armengaud

b

_,

_C.

_Augier

g

_,

_A.

_Benoit

f

_,

_T.

_Bergmann

k

_,

_J.

_Bl

_¨umer

i ,j

_,

_A.

_Broniatowski

e

_,

_V.

Brudanin

h

_,

_P.

_Camus

f

_,

_A.

_Cazes

g

_,

_M.

_Chapellier

e

_,

_N.

_Coron

c

_,

_G.A.

_Cox

i

_,

_C.

_Cuesta

s

_,

_F.A.

_Danevich

l

_,

_M.

_De

J

´esus

g

_,

_L.

_Dumoulin

e

_,

_K.

_Eitel

j

_,

_A.

_Erb

o

_,

_A.

_Ertl

o

_,

_F.

_von

_Feilitzsch

o

_,

_D.

_Filosofov

h

_,

_N.

_Fourches

b

_,

_E.

_Garc

_´ıa

s

_,

_J.

Gascon

g

_,

_G.

_Gerbier

b

_,

_C.

_Ginestra

s

_,

_J.

_Gironnet

g

_,

_A.

_Giuliani

e

_,

_M.

_Gros

b

_,

_A.

_G

_¨utlein

o

_,

_D.

_Hauff

n

_,

_S.

_Henry

p

_,

G. Heuermann

i

_,

_J.

_Jochum

r

_,

_S.

_Jokisch

j

_,

_A.

_Juillard

g

_,

_C.

_Kister

n

_,

_M.

_Kleifges

k

_,

_H.

_Kluck

i

_,

_E.V.

_Korolkova

q

_,

_V.Y.

Kozlov

j

,

H. Kraus

p

,

V.A.

Kudryavtsev

q

,

J.-C.

Lanfranchi

o

,

P. Loaiza

m

,

J. Loebell

r

,

I. Machulin

u

,

S. Marnieros

e

,

M. Mart

´ınez

s

_,

_A.

_Menshikov

k

_,

_A.

_M

_¨unster

o

_,

_X.-F.

_Navick

b

_,

_C.

_Nones

b

_,

_Y.

_Ortigoza

s

_,

_P.

_Pari

a

_,

_F.

_Petricca

n

_,

_W.

Potzel

o

_,

_P.P.

_Povinec

t

_,

_F.

_Pr

_¨obst

n

_,

_J.

_Puimed

_´on

s

_,

_F.

_Reindl

n

_,

_M.

_Robinson

q

_,

_T.

_Rol

_´on

s

_,

_S.

_Roth

o

_,

_K.

_Rottler

r

_,

_S.

Rozov

h

_,

_C.

_Sailer

r

_,

_A.

_Salinas

s

_,

_V.

_Sanglard

g

_,

_M.L.

_Sarsa

s

_,

_K.

_Sch

_¨affner

n

_,

_B.

_Schmidt

i

_,

_S.

_Scholl

o

_,

_S.

_Sch

_¨onert

o

_,

W. Seidel

n

_,

_B.

_Siebenborn

i

_,

_M.

_v.

_Sivers

o

_,

_C.

_Strandhagen

r

_,

_R.

_Strauß

o

_,

_A.

_Tanzke

n

_,

_V.I.

_Tretyak

l

_,

_M.

_Turad

r

_,

A. Ulrich

o

_,

_I.

_Usherov

r

_,

_P.

_Veber

d

_,

_M.

_Velazquez

d

_,

_J.A.

_Villar

s

_,

_O.

_Viraphong

d

_,

_R.J.

_Walker

b ,i

_,

_S.

_Wawoczny

o

_,

M. Weber

k

_,

_M.

_Willers

o

_,

_M.

_W

_¨ustrich

o

_,

_E.

_Yakushev

h

_,

_X.

_Zhang

p

_,

_A.

_Z

_¨oller

o a_CEA,_Centre_d_’Etudes´ Nucl´eairesdeSaclay,IRAMIS,91191Gif-sur-YvetteCedex,France

b_CEA,_Centre_d_’´EtudesNucl´eairesdeSaclay,IRFU,91191Gif-sur-YvetteCedex,France

c_CNRS,_Institut_d_’_{Astrophysique}_Spatiale,_Universit_´e_Paris_11,_Orsay_91405,_France

d_CNRS,_Universit_´e_de_Bordeaux,_ICMCB,₈₇_avenue_du_Dr._A._Schweitzer,_Pessac_cedex,_33608,_France

e_Centre_de_{Spectroscopie}_Nucl_´eaire_et_de_{Spectroscopie}_de_Masse,_UMR8609_IN2P3-CNRS,_Univ._Paris_Sud,_Orsay_Campus,_91405,_France

f_Institut_N_´eel,_CNRS,₃₈₀₄₂_Grenoble_cedex_9,_France

g_IPNL,_Universit_´e_de_Lyon,_Universit_´e_Lyon_1,_CNRS_/_IN2P3,₄_rue_E._Fermi,_Villeurbanne_69622,_France h_Laboratory_of_Nuclear_Problems,_JINR,_Dubna_141980,_Russian_Federation

i_Karlsruhe_Institute_of_Technology,_Institut_f_¨_ur_{Experimentelle}_Kernphysik,_Karlsruhe_76128,_Germany

j_Karlsruhe_Institute_of_Technology,_Institut_f_¨_ur_Kernphysik,_Karlsruhe_76021,_Germany

k_Karlsruhe_Institute_of_Technology,_Institut_f_ur_¨ _{Prozessdatenverarbeitung}_und_Elektronik,_Karlsruhe_76021,_Germany

l_Institute_for_Nuclear_Research,_MSP₀₃₆₈₀_Kyiv,_Ukraine

m_Laboratoire_Souterrain_de_Modane,_CEA-CNRS,_Modane_73500,_France

n_{Max-Planck-Institut}_f_ur_¨ _Physik,₈₀₈₀₅_M_unchen,_¨ _Germany

o_{Physik-Department}_E15,_Technische_Universit_¨at_M_unchen,_¨ _Garching_85747,_Germany

p_University_of_Oxford,_Department_of_Physics,_Keble_Road,_Oxford_OX1_3RH,_UK q_University_of_Shefﬁeld,_Department_of_Physics_and_Astronomy,_Shefﬁeld_S3_7RH,_UK

r_{Eberhard-Karls-Universit}_¨at_T_¨_ubingen,_T_ubingen_¨ _72076,_Germany

s_Laboratorio_de_F_´ısica_Nuclear_y_Astropart_´ıculas,_Pedro_Cerbuna_12,_Universidad_de_Zaragoza,_Zaragoza_50009,_Spain

t_Comenius_University,_Department_of_Nuclear_Physics_and_Biophysics,_Bratislava_84248,_Slovakia

u_NRC_“Kurchatov_{Institute”,}_Kurchatov_sq._1,_Moscow,_Russia

a

r

t

i

c

l

e

i

n

f

o

Keywords:

Darkmatter WIMPs Directdetection Cryogenicbolometers EURECAexperiment

a

b

s

t

r

a

c

t

The EURECA (European Underground Rare Event Calorimeter Array) project is aimed at searching for dark matter particles using cryogenic bolometers. The proponents of the present project have decided to pool their strengths and expertise to build a facility to house up to 1000 kg of detectors, EURECA, consisting in the ﬁrst instance of germanium and CaWO 4crystals. The shielding will be provided through a large water

tank in which the cryostat with detectors will be immersed. The EURECA infrastructure will be an essential tool for the community interested in using cryogenic detectors for dark matter searches. Beyond European detectors, it will be designed to host other types of similar cryogenic detectors, requiring millikelvin operating temperatures. In particular, this includes the germanium detectors currently in use by the SuperCDMS team, following the current collaborative work performed by the EURECA and SuperCDMS collaborations. EURECA

2212-6864/$-seefrontmatterc ₂₀₁₄_The_Authors._Published_by_Elsevier_B.V._This_is_an_open_access_article_under_the_CC_BY_license₍_http://_{creativecommons.org}/_licenses/_by/ 3.0/).

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will have two stages. The ﬁrst phase aims at a sensitivity of 3 ·10 −10_{pb and will involve building the}

infrastructure, cryostat and shielding, and operating 150 kg of detectors. The second phase will be completed with 850 kg of additional detectors, the relative weight between the different detectors being decided by the collaboration according to the physics reach. A sensitivity of 2 ·10 −11_{pb is}_{aimed for}_at_the_second_stage.

EURECA will ideally beneﬁt from the planned extension of the deepest underground laboratory in Europe – LSM. With a site-independent design, it can also be hosted in other locations at similar or deeper sites such as SNOLAB.

c

2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license ( http://creativecommons.org/licenses/by/3.0/).

1. Executivesummary

The EURECA (European Underground Rare Event Calorimeter

Array)projectispartofthequestforunderstandingthecomposition ofouruniverseandinparticularthelargefraction,26.8%[1 ],ofits un-knownmass-energydensitycalleddarkmatter.Thisquestion,raised 80yearsago,hasstillnoanswerandthereisaﬁerceracetowardsthe directdetectionofdarkmatterparticles.Manyastrophysical obser-vationsconvergeontheassumptionthatitwouldconsistofparticles stillunknown,asyetundetectedandfugitive,presentsincetheearly momentsoftheuniverse.

Manyexperimentsaroundtheworld,alllocatedinunderground environments,aimto trackdown thepresence oftheseparticles. Amongthese,EDELWEISS,locatedattheLSMlaboratory,andCRESST, installedattheGranSassolaboratory,arecryogenicexperiments in-volvingsolidstatedetectorscooledtoverylowtemperatures.

TheexperimentsattheLHChavenotshownanyhintssofar,asof March2013,ofSUSY,thefavouredtheoryprovidinganatural candi-datefordarkmatter.However,thequestionoftheexistenceofdark matterintheuniverseandthequestionofwhichtheorydescribes bestbeyondstandardmodelphysicsaredifferent.Assuch,direct de-tectiondarkmatterexperimentsremainmuchinasituationwhere theattainmentofcontinualimprovementonupperlimitsfor WIMP-nucleoncrosssectionsthroughenhancingthedetectors’sensitivities remainsaveryimportantobjective.

Inthepresentsituation,wherewedonotyethaveexperimental proofofSUSY,norconvincingevidenceoftheexistenceofWIMPs bydirectdetectionexperiments,thenextgenerationofdirect detec-tionexperiments,providinganincreaseofsensitivitybytwoorders ofmagnitude,willbeneededtotackletheissueofthedarkmatter nature.TherecentavatarsoflowmassWIMPhints,notconsidered yetasevidence[2 ],confirmthatseveralexperimentswith comple-mentarydetectionprincipleswillbeneededtoestablishaconclusive demonstrationofsignalidentification.Thespecificstrengthsof cryo-genicdetectors,namelytheirverygoodenergyresolution,excellent discriminationagainstbackgroundandtheredundancyofferedby theuseofmultipletargetnucleiinthesamecryogenicinfrastructure, equipEURECAwithasignificantadvantagefortheidentificationofa darkmattersignal.

Theproponentsofthepresentproject,mostlyoriginatingfromthe EDELWEISS,CRESSTandROSEBUDcollaborations,thereforehave de-cidedtopooltheirstrengthsandexpertisetobuildafacilitytohouse upto1000kgofdetectors,EURECA,consistingintheﬁrstinstanceof germaniumandCaWO4detectors.Thedetectorswillbemountedin

subunitsoftowers,housedina6-m3_cryostat,_with_shielding_provided

byalargewatertank.InnovativecryogenicswillrelyonEuropean expertiseintheﬁeld,andtogetherwithadaptablecablingand elec-tronicsoptions,theEURECAinfrastructurewillbeanessentialtoolfor thecommunityinterestedintheuseofcryogenicdetectorsfordark mattersearches.BeyondEuropeandetectors,itwillbedesignedto hostothertypesofsimilarcryogenicdetectors,requiringmillikelvin

operatingtemperatures.Inparticular,thisincludesthegermanium detectorscurrentlyinusebytheSuperCDMSteam,followingthe cur-rentcollaborativeworkperformedbytheEURECAandSuperCDMS collaborations.

EURECAwillhavetwostages.Theﬁrstphaseaimsatasensitivityof 3_·10−10_pb_and_will_involve_building_the_{infrastructure,}_cryostat_and

shielding,andoperating150kgofdetectors.Thesecondphasewill becompletedwith850kgofadditionaldetectors,therelativeweight betweenthedifferentdetectorsbeingdecidedwithinthe collabora-tionaccordingtothephysicsreach.Aﬁnalsensitivityof2·10−11_pb

isaimedfor.

EURECAwillideallybeneﬁtfromnewspaceprovidedbyanew plannedextensionoftheLSM,acavityprojectcalledDOMUS. Fur-thermore,thesiteofFr´ejusisbestsuitedtothisresearchbeingthe deepestinEurope.Withasite-independentdesign,itcanbehosted inotherlocationsatsimilardepthsorevendeepersiteslikeSNOLAB. Suchauniquefacility,plannedtooperatelong-term,willbe de-signedtoensureanexceptionallyradio-pureenvironmentinorderto provideoptimalsensitivityfordarkmattersearchescurrentlyunder design.

2. Science

Thissectiondescribesthecurrentcontextofdarkmattersearches andtheplacethatEURECA,theEuropeanUndergroundRareEvent CalorimeterArray,willoccupywithinthescientiﬁclandscape. Table 1 summarisestheobjectivesofEURECA,splitintotwophases,starting withatargetmassof150kginPhase1andreachingthedesignvalue of1000kginPhase2:

Table 1

ObjectivesofEURECA

EURECA Goals

Phase1

Crosssection(SI) 3·10−10_pb

Masstobeoperated 150kg

Residualbackground(allsources) 10−2_evts_/_kg_/_y_in_ROI

Dutycycle 70%

Timeofoperation 1year

Phase2

Crosssection(SI) 2·10−11_pb

Masstobeoperated 1000kg

Residualbackground(allsources) <10−3_evts_/_kg_/_y_in_ROI

Dutycycle 70%

Timeofoperation 3years

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Figure 1. ThesensitivitiesobtainedbytheexperimentsEDELWEISS-II(green)[6], CDMS(grey)[10],EDELWEISS-CDMScombined(cyan)[11],ZEPLIN-III(magenta)[12] andXENON100(blue)[13];thepotentialsensitivityofEDELWEISS-III(dashedgreen) witha12000kg·dbackground-freeexposure;andthepositionthattheproposed ex-perimentsofSuperCDMS(dashedgrey)[14],XENON1T(dashedblue)[15]andEURECA (Phase1:upperdashedred,Phase2:lowerdashedred)willplayintheirimprovement. ThesensitivityforEURECAPhase2isaspresentedinTable1,withoneevent/t/y as-suminga50:50masssplitofGe:CaWO4,5-(15-)keVthresholdfor200kg(300kg)of Geanda10-keVthresholdforCaWO4aspresentedinthisCDR.SensitivityforPhase1

is15%scaledbymassfromPhase2,for70%dutycycleofoneyear.(Forinterpretationof thereferencestocolourinthisﬁgurelegend,thereaderisreferredtothewebversion ofthisarticle.)

2.1. Scientiﬁcenvironment

TheEURECAprojectispartofthequestforunderstandingthe com-positionofouruniverseandinparticularthelargefraction,26.8%,of itsunknownmass-energydensitycalleddarkmatter[1 ].This ques-tion,raised80yearsago,stillhasnoanswerandthereisaﬁercerace towardsthedirectdetectionofdarkmatterparticles.

Manyastrophysicalobservationsconvergeontheassumptionthat it wouldconsist ofparticlesstillunknown, asyet undetectedand fugitive,presentsincethebirth ofthe universe.Whiletheoretical models have providedmany candidates,which span50orders of magnitudeofmassandcrosssection,themostmotivatedcandidates aretheweaklyinteractingmassiveparticle(WIMP),theaxionand possiblyasterileneutrino.Inanycase,darkmatterrequiresphysics beyondthestandardmodelofparticlephysics.

ThefavouredcandidatefordarkmatterisaWIMPrelatedtonew physicsattheTeVscale.AmongthevariousWIMPcandidatesatthis scale,themostappealingisthelightestsuper-symmetric(SUSY) par-ticle(LSP),theneutralino,whichisembeddedinaconsistentmodel, e.g.theminimalsupersymmetricstandardmodel(MSSM).TheMSSM postulatesthattheeffectivescaleofSUSYbreakingisaroundaTeV andthatthereisanadditionalsymmetrycalledR-paritywhichwould keepthelightestSUSYparticlestable.Otherextensionsofthe stan-dardmodelprovidesuitableWIMPdarkmattercandidates,e.g.the lightKaluza-Kleinparticle(LKP)inextra-dimensionaltheories[3 ]and thelightestT-oddparticle(LTP)inLittleHiggsmodels[4 ].

TheparameterspaceofWIMPsislargelycoveredbytheproposed cryogenicdirectdarkmattersearch,whichcouldprobedarkmatter particles withamass intherangefromGeVto TeVwitha spin-independentWIMP-nucleoncrosssectiondowntoafew10−11 _pb.

Currentdata,obtainedattheLHC,donotshowanyhintofSUSY particlesinproton-protoncollisionsforatotalintegratedluminosity of10.5fb−1 _[₅_]_up _to_an _energy_of√_s ₌₈_TeV._No_indication_of

particlespredictedbyextra-dimensional modelsorbyLittleHiggs modelshaveshownupeither.However,theremainingparameter spaceisplannedtobeinvestigatedaftertherestartoftheLHCin 2015,withﬁnalintegratedluminositygoalsof250fb−1_by₂₀₂₀_and

3000fb−1_by_2030.

Nonetheless,thediscoveryofacandidateparticlefordarkmatter attheLHCalonedoesnotprovethatitistheCDMparticlerequired bycosmology.Forthatpurpose,thedetectionofcosmologicalWIMPs isnecessary.Conversely,thedetectionofcosmologicalWIMPswould shownewphysicsbutnotprovethattheyareSUSYparticles.Forthat purpose,identiﬁcationandinvestigationatacceleratorsisnecessary. ThesynergybetweentheLHCandthenextgenerationofdarkmatter searchesisobviousandconstitutesanexcitingperspective.

Inthepresentsituation,wherewedonothaveexperimentalproof ofphysicsbeyondtheStandardModelattheLHC,norconvincing evidenceoftheexistenceofdarkmatterparticlesbydirectdetection experiments,theEURECAproject,byoperatingcryogenicdetectors ofuptoonetontargetmassandaddressinganincreaseofsensitivity bytwo(three)ordersofmagnitudeathigh(low)mass,asshownin Fig. 1 ,isanessentialtooltotacklethemysteryofdarkmatter.

2.2. Scientiﬁccase

Manyexperimentsaroundtheworld,alllocatedunderground,aim attrackingdownthepresenceofdarkmatter.EDELWEISS[6 ,7 ], lo-catedattheLaboratoireSouterraindeModane(LSM)undertheFr´ejus mountain,andCRESST[8 ,9 ],installedattheGranSassolaboratory,are ‘cryogenic’experimentsinvolvingsolidstatedetectorscooledtovery lowtemperatures.Theystillhavenotshownevidenceofthese parti-clesandwillbelimitedinthecomingyearsintheirsensitivitybythe sizeofthecryostatshousingthedetectors.

Cryogenicdetectors,asdemonstratedbythelatestpublished re-sults,exhibitexcellentcapabilityfortheirexploitationinfacilitiesfor thedirectdetectionofdarkmatterparticles.Thequalityofthenext generationofcryogenicgermaniumdetectors,withsigniﬁcantly im-proveddiscriminationpoweragainstbackgroundevents,issuchthat onecananticipatetorunmassesoftheorderof100-1000kgwithout signiﬁcantbackground.

TheteamsoftheEDELWEISSandCRESSTcollaborations,together withotherEuropeanteams,inparticularfromtheROSEBUD collab-oration,leadinginnovativeR&Donnewscintillatingdetectors,have decidedtopooltheir strengthsandexpertisetobuildafacilityto houseupto1000kgofdetectors:EURECA.

Suchanextremelysensitivesearchshouldbecarriedoutinthe bestpossibleenvironment,thatisinthedeepestsiteinEurope,to reduceasmuchaspossiblethecosmicmuon-inducedbackgrounds. ThisledtheEURECAcollaborationtofavourtheFr´ejussiteastheideal locationoftheexperiment.

Withthecurrentbaselinedesign,consistingofashieldofalarge watertankinwhichwillbeimmersedthecryostathousingthe de-tectors,EURECAistoolargetofitwithintheexistingcavityofthe Fréjuslaboratory.Itwillideallybenefitfromtheextensionofthe laboratory,theDeepObservatoryforMultidisciplinaryUnderground Science(DOMUS),plannedtobeduginconjunctionwiththealready startedsafetytunnel(diggingfromFrancereachedthepositionofthe currentLSMlaboratoryinMarch2013)oftheFréjusroadtunnel.In caseofcancellationofthisextensionproject,analternativedesign ofamixedwater

/

denseshieldmayallowEURECAtoﬁtwithinthe availablespaceofthelab.

EURECAwillconsistofasinglecryostat,installedinadedicated watertankandwillhave twostages.Theﬁrst phasewill involve acryostatandshieldingwith150kgofdetectorswhilethesecond phasewillbecompletedwith850kgofadditionaldetectors.The two-phasedapproachprovidesuswiththeopportunitytohaveastaged productionofthelargenumberofindividualdetectors.

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targetnucleiinordertobeabletoprovethattheobservedratesand energyspectraofapossiblecandidateshowtheexpectedcorrelation ofaWIMPsignal.Itwillbedesignedtooperatevarioustypesof cryo-genicdetectors:germaniumbolometerscurrentlydevelopedwithin EDELWEISS,measuringheatandionisationsignals;andCaWO4

scin-tillatingbolometersallowingmeasurementoflightandheatsignals, developedbyCRESST.R&Disongoingtocharacteriseother scintillat-ingtargets,speciﬁcallythoseincludingnucleiwithenhanced sensitiv-itytospin-dependentinteractions,andlow-massWIMPs.Depending ontheachievedperformance,oneofthesematerialscouldbe incor-poratedasanadditionaltargetinEURECA,mostlikelyinthesecond phase.

ForgermaniumdetectorsdevelopedwithinEDELWEISS,the in-creaseofsensitivitywillbeobtainedinthreeways:decreaseofthe localradioactivebackgroundbyselectionofmaterialsandimproved surfacetreatment,increasedrejectioncapabilityagainstgammarays andbetas,andimprovement ofenergyresolutionsallowinglower thresholds.Thesethreeavenuesofdevelopmentarebeingpursued withinEDELWEISS-III,andtheobtainedresultsallowtoextrapolate totherequiredsensitivityforEURECA.

Scintillation-phonondetectorsprovideanexcellentsuppressionof gammabackground.Sofarthispotentialcouldnotyetbefullyshown duetoeffectsrelated toan alphabackground, thisiswhyefforts toincreasethesensitivityarethereforedominatedbyavoidingand taggingthealpharelatedbackgrounds.

Differenttypesofrecoilingnucleicantosomeextentbe distin-guishedwithinonedetectormodule.WiththepresentlyusedCaWO4

detectorsoftheCRESSTexperiment,oxygenrecoilscanclearlybe dis-tinguishedfromtungstenrecoilsbytheirdifferentlightyield(ratio betweenlightandphononsignal).Thus,suchdetectorsarecapableof partiallydiscriminatinganeutronbackgroundfromasignalcaused byaWIMPheavierthan∼20 GeV.

Thedetectorsmentionedaboveusedifferentreadoutschemes, whichwillneedﬂexibilityinthedesignofwiringandelectronics housingoftheEURECAcryostat.Suchﬂexibilitywillalsobeakey featureallowingtohouseothertypesofdetectors.

Othertypesofdetectors arebeingdevelopedwithin aparallel projectleadbytheAmericanteamofSuperCDMS,thesuccessorof theCDMScollaboration.Thisprogram,whosegoalistooperate150 kgofgermaniumdetectors,isverysimilartoEURECAPhase1.Indeed, theverysimilarqualityofdataobtainedsofarbytheEDELWEISSand CDMScollaborationsledthetwoteamstocombinebothdatasets toproduceanimprovedlimitrelativetoeachindividualresult[11 ]. Thesuccessofthiscollaborativeworkledthetwocollaborationsto startmoreconcreteworkonthedesignoftheirnextgenerationof theprojectsdescribedabove,inordertopossiblyexchangedetectors andfurthercombinefuturedatasets.

Other100-kgtotonne-scaleprojectsarebeingpursuedwithliquid noblegases.Self-shieldingeffectsandcapabilityofthelocalisationof interactionsaredistinctivefeaturesofliquidnoblegastwo-phase technology.ThemostadvancedareXENON1T(two-phaseliquidXe, 1000-kgfiducialmass),LUX(two-phase liquidXe,100-kgfiducial mass),andXMASS(single-phaseliquidXe,100-kgfiducialmass).

Withtheirlowthresholdandgoodenergyresolution,the cryo-genicdetectorsexhibitverygoodpotentialforreliablydetecting low-massWIMPs.Theverydifferentdetectiontechniquesmakethetwo approachescomplementary,astronganddecisiveadvantageincase apossiblecandidateisseenbyoneofthedetectorsandneedstobe cross-checkedandconﬁrmedbytheother.

Insummary,suchauniquesetupinEurope,plannedtooperate long-term,willbedesignedtoprovideanexceptionallygood radio-pureenvironment.Itwillbedesignedtohouse,intheﬁrstinstance, detectorsdedicatedtothesearchfordarkmatter.Inparticular, elec-tronicsandcablingwillbe designed tooperate differenttypesof cryogenicdetectors,whethersemiconductorssuchasgermanium,or scintillatingtypeasCaWO4,oranyothercryogenicdetectors.

3. Infrastructure

AlthoughEURECAcanbeplacedinanysuitablysizedunderground location,discussionherefollowsthepreferredlocationoftheLSM extension(DOMUS).Aviewoftheoveralllayoutoftheproposednew spaceisshowninFig. 2 .Herewedescribetheinterfacesbetweenthe hostlaboratoryandtheEURECAfacility.Table 2 summarisessomeof thekeyfeaturesoftheEURECAinfrastructure.

Figure 2. Positionofthenewfacility,towardsthetopoftheimage,withrespectto theexistingroad(lowermost)andlaboratoryspace(shaded).

Table 2

KeyfeaturesoftheEURECAinfrastructure

Infrastructure Baselineoption

Space

EURECAvolume 10×24-mfootprint×12-mheight Cryostat 2-mdiameter×2-mheight Watershieldtank 8-mdiameter×12-mheight Waterbuffer 6.5-mdiameter×12-mheight Infrastructurebuilding 6×8-mfootprint×12-mheight,3or4

storeys

Cleanroomsuite 48-m2_footprint_×_3-m_height

Cryogenics 6×5-mfootprint×3-mheight Power,volume,ﬂowsanddatarate

Powerpeak 270kW

Powerrunning 230kW Low-Rnairﬂux 150m3_/_h

Watervolume 400m3

Coolingneed equivalentto8m3_/_h_of_water

Shieldingwaterrecirculation 2m3_/_h

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Figure 3. Layoutofthemainwatertank(left)containingthecryostat,adjacent infras-tructureandcleanroomtower,andwaterstoragetank(right)withinthe50-m-long halloftheDOMUSlab.Proximitycryogenicsareshownwithinthecoldboxconnected tothecryostat.Clearanceofatleast1mhasbeenincludedbetweenthecavernwalls andtheexperimentalinfrastructure.Theyellowlineindicatestheﬂoorspaceavailable withinthecurrentLSM,althoughwiththereducedheightofonly10m.(For interpre-tationofthereferencestocolourinthisﬁgurelegend,thereaderisreferredtotheweb versionofthisarticle.)

3.1. Generalexperimentinfrastructure

Aschematicforthehousingoftheexperimentisshownin Fig. 3 .Thedetectorswillbeplacedinacryostatwithinawatertankto shieldagainstneutronsandgamma-rays.Abuildingislocatednext tothetankthroughwhichaccesstothecryostatwillbeprovided. Anadditionaltankwillbeplacedinthevicinityoftheexperiment forstorageofwaterwhenaccesstothecryostatisrequired.Some elementsofthecryogenicssystemwillbelocatedinimmediate prox-imitytothecryostat,housingthedetectors.Theotherelementsof thecryogenicsystems,especiallylargeplant(compressors,cryogenic machines)pronetocontributenoiseandvibration,willbeplacedat somedistancefromthecryostat.Furtherdetailsareprovidedbelow.

3.1.1. Housingoftheexperiment

Thedetectorcryostatwillbesurroundedbyatleast3mof ultra-purewater,ineachdirection,withinastainlesssteelwatertank.Next tothiswillbetheinfrastructuretowerwhichwillincludespacefor storageofmaterials,slowcontrolandDAQsystems,water purifica-tionplant,andacleanroom.Thecleanroomisplacedatthetopofthe towerandservesasaccesstothewatertankwithcleanroomintegrity extendingintothewatertank.Thetankissealedatthepointof en-trybymeansofanairlocktopreservethelow-Rnatmosphere.All connectors(electrical,cryogenic,vacuum)throughthewatercontain bends,orincludesufficientsolidshielding,topreventadirectpath forneutrons.Anadditionalwatertankislocatedbythesideofthe towerforuseasawaterstoragelocationwhenaccesstothecryostat isneeded.Theextratankwillbematchedinheighttothewatertank tominimisetheamountoffloorspaceused,butwillbeofasmaller volumesincenointernalaccessisrequired.

Foracryostatwithaheightanddiametereachof2m,thewater tankwouldneedtohaveadiameterof8mandaheightof12m.This includesaclearanceofabout4mabovethewaterlevelforaccess andcranes.Analternativesizeforthewatershieldispresentedin Appendix A .Thethicknessofthetankwallswillbeupto20mm, withtheprecisethicknesstobedeterminedthroughstandarddesign procedures(forexampleFEAanalysis)intheTDR.Theinternalsofthe watertankwillrequiresurfacepassivationafterthoroughcleaning, withelectro-polishingbeingalikelymethodforthelatter.

Withawatertankof8-mdiameter,theadjacenttowercouldhave similardimensions.Afootprintof8×6mprovidesadequate clean-roomspace(see Section 3.3 ).Averticalspaceof12mcould accom-modatefourfloors.Abuildingthistallwithinacurvedcavernshown inFig. 4 ,wouldallowspaceforthecleanroomoverpressurefanstobe placedontopofthebuilding.Sufficientspacewouldthenalsoexistto allowaflowofairtocooltheoverpressurefans.Thelowermostfloor

Figure 4. PositionofthewatertankwithinthecrosssectionofthenewDOMUS laboratory,approximatelytoscale.Thewidestpartofthehallis18.2m.Thecylindrical envelopeforthewatertankistoscalewithinthecrosssection,andhasaheightof12 mandadiameterof8m.

couldhousemostofthewaterpurificationplant.Anexceptiontothis wouldbetheRn-strippingcolumn(ifused),whichwouldlikelybetoo talltobehousedwithinasinglelevel.Themiddlefloororfloorscould bededicatedtoslowcontrolandDAQ,whilst theuppermostfloor orfloorscouldcontainthecleanrooms.Alllevelscouldalsoprovide someformofstorage.

Anon-detailedanalysisusingthelaboratorycross-sectionshown inFig. 4 andassumingaregularcylindricalshapeforthewatertank suggestssitingthetankwitha1-mclearancefromthecranebeam wouldallowahorizontaldistanceof2.0mtothewallononeside,and 5.0montheotherside.Notethatthe1-mclearanceshowninFig. 4 is mostlimitedintheverticaldirection,leavingahorizontalclearance of1.1mbetweenthetopofthetankandthecranebeam.Structural integrityusingFEAwillbeinvestigated,withcloseattentiontothe topofthewaterstoragetankwherethewaterlevelmayapproach closertothetopofthetank.Ifﬂoorspaceisconsideredmore pre-cious,adifferentshapeforthetopofthewatershieldtankshouldbe considered,allowingtheexperimentalhousingtobesituatednearer tothesideofthecavern.Sloping,orstepping,thetopsectionofthe watertanksabovethewaterlevelwouldallowthetanktobeplaced nearerthecavernwall,butdependsinpartontherequirementson thereachofthecraneinternaltothattank.Thisdependsonwhether thecraneneedsthecapabilityofhorizontalmovementacrossthefull radiusofthetank,andwhetherthisisneededaroundthefullarcof 2

π

.

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3.1.2. Cryogenicsystems

Acryogenicunit,positionedimmediatelyadjacenttothewater tankforcloseproximitytothecryostat,housesthe1-Kpotandstill, theheatexchangersandthe3_He_condenser._The_valves_for_the_fast

precoolingofthedetectorarraywillalsobesituatedinsidethis cryo-genicunit.Theunitwillhavedimensionsofabout1.5× 2.5m,and willbemountedonthesamebaseplateasthedetectorarray, con-nectedbyarigidcryo-line.

Theremainderofthecryogenicsystemconsistingofpumps, com-pressorandgasstoragewillbeplacedinaseparatecavernupto100 mfromthedetectorstoreducemicrophonics.Possiblelocationsare thesidesofaccesstunnelsoraseparatecavitycutintotherock.5 m3_is_required_for_gas_storage,_with_the_compressor_{approximately}

2.5_×2_×2m,andafurther1.5_×1_×2mrequiredforoilﬁltration. Afootprintofatleast6× 5mwouldberequiredfortheseitems,if allofthemareonthesamelevel.

Thelinestothe3_He_and4_He_pumps,_as_well_as_the_liquid

he-lium(LHe)transferline,willpassbetweenthemaincavernandthe acousticallydecoupledcryogenicfacility.Thecryogenicunitwillbe decoupledfromvibrationbyflexiblesectionsanddampingstructures thatareoptimisedforthespectrumofthevibrationofthepumpsand theheliumliquefier.Theseflexiblesectionswillalsoallowthe nec-essarymovementoftheplatformsbyseveralcmwhenemptyingor fillingthewatershieldingtanks.

Fulldetailsofthecryogenicsystemareprovidedinthededicated Section 4 .

3.1.3. Undergroundstorageofdetectorsandothermaterials

Cosmicrays(neutronsandprotons)interactingwithdifferent ma-terialsat thesurfaceproduceradioactive isotopes.Some ofthese isotopeshavearelativelylonghalflifeand,aftermaterialsand com-ponentsaremovedundergroundandinstalledinthedetectors,may contributeto thebackground eventratecompromisingthe detec-torsensitivity.TheprimeconcernfortheEURECAexperimentisthe Gecrystalsandcopper.Boththesematerialswillbepresentinlarge quantities.Irradiationofcopper bycosmicrayswillproduce 60_Co

amongstotherradionuclideswithshorterhalflives,whereas expos-ingGetocosmicrayswillgiveseveralisotopes,themostproblematic being68_Ge_and65_Zn.

Theestimatesofneutronﬂux intensityatdifferentdepthsand copperactivationshowthatcoppercanbesafelystoredatashallow depthofabout10m.w.e.Thiswillgiveasaturationactivityofless than0.3

μ

Bq

/

kgwhichiswellbelowthetoleratedupperlimitof about10

μ

Bq

/

kg.Coppercanbestoredinanundergroundstorage placeinoneoftheinstitutionsandquicklymovedtotheprocessing siteandthenundergroundreducingthetimeofirradiationbycosmic rays.

InducedactivityinGecrystalsismoreproblematicandagreater depthforstorageisrequired.Theexposuretocosmicraysatthe sur-faceshouldbeminimisedandthecrystalswillbestoredunderground beforeandafterdetectorpreparation.Thedecaysof68_Ge_and65_Zn

givepeaksatabout10keV.Incaseofahigheventrateatthese en-ergies,wewillremovetheregionaroundtheseactivationlinesfrom thedarkmatterdataanalysis.

MoredetailsaregiveninAppendix B .

3.1.4. Heavyliftingequipment

Cranagewillbeneededbothinsidethewatertanksforremovalof thecryostatthermalshielding,andaccesstothebolometertowers; andexternallyforuseasthetanksarebuiltupandcomponentsof theinfrastructureareadded.Thecraneinsidethetoweristherefore likelytoberatedtoasafeworkingloadofnogreaterthan1t.This maybeincreasediftheinternalshieldingcannotbesplitintosmaller components(seebelowregardinginternalgammashielding).For ex-ample,a15-cm-thickCushieldofdiameter1.6mwouldweighnearly 3t.FurtherdetailsofthecleanroomcraneareinSection 3.3 .Thecrane

outsidethewatertank,inthemainexperimentalhall,willneedtobe ofahigherrating,upto8t.

Placementofaliftpassingalongtheoutsideofthebuildingto allowtheeasytransportofgoodsuptotheupperfloorswouldbe beneficial.Aworkingloadof1tmaybesufficientforthis.

Accesswillbeneededforheavyequipmenttobeplacedin loca-tionssuchasthecleanroom(laminarﬂowcabinets,otherfurniture), orsidecaverns(cryogenicplant).Somemovementofequipmentwill be withportable ﬂoorcranesandpallet-trucks,whichare readily availablewithworkingloadsofuptoatleast3t.

3.2. Interfaceswiththehostlaboratory

3.2.1. Electricity

Powerconsumptionandheatloadsfromanumberofitems de-tailedinthissectionaretobeconsidered.Thepowerconsumptionof thecurrentLSMisapproximately200kW,withelectricitysupplied at400kVA.Anestimationforthepowerdrawnbymanyitemsis includedin Appendix C .Thissuggeststhepowerrequirementsfor EURECAwillbearound450kVA(270kW).Itemsincludedinthatlist aresummarisedhere.

Thetotalpowerdrawnfromthecryogenicplantisestimatedtobe 130kW.Itemsconsideredforthisarethecompressor,vacuumpumps, refrigerator,electronicsandthepossibilityofwatercooling,ifneeded, atatotalrateof8m3

_/

_h._Other_items_likely_to_draw_large_amounts

ofpowerarethewatershieldpuriﬁcationplant(20kW),low-Rnair supply(30kW),DAQandslowcontrol(12kW),andcleanroomplant (9 kW).Furtherdetailsabouteach ofthesearecontainedintheir dedicatedSectionsbelow.

3.2.2. Computinginfrastructure

ComputingwillbeneededforcontrolofDAQ(detectorandveto), slowcontrol(detectorandwaterpuriﬁcation)andcryogenicsaswell asforgeneraluseforcommunications,monitoring,logbookentries, etc.EDELWEISS-IIIwillprovideatestbedfortheEURECADAQ,which willinturndictatepartofthecomputinginfrastructurerequirements. TheDAQwilloperateatroomtemperatureandrequireaircooling. MoredetailsaregiveninSection 7.1 .

Allocationmustbemadeforlocaldatastorageandslowcontrol machinestoincludedatalogging.Bothcryogenicandwater puriﬁca-tiondata,alongwithinformationaboutambientconditions (temper-ature,pressure,Rnlevels,etc.)willbestored.

3.2.3. Coolingwateranddrainage

Theamountofcoolingwaterrequireddependsontheamountof heatproduced,andcannotbeaccuratelyknownuntiladesignofthe cryogenicsystemhasbeenfinalised.Initialestimateshavequoted thatpartsofthecryogenicplantneedeitherwatercoolingatarateof 8m3_of_water_per_hour,_or₁₄₀₀₀_m3_of_air_per_hour._The_{fire-fighting}

circuitshavepreviouslyprovidedwaterforcoolingsystemswhich wasdisposedofafteruse.

3.2.4. Laboratorycooling

Theheatproducedbythecryogenicplant,vacuumpumps, com-puting,DAQ,waterandairpuriﬁcation

plantswillneedtobeextractedfromthelaboratory.Thefirstorder estimateofpowerconsumptionisshowninSubsection 3.2.1 .Apower consumptioncorrespondingto30%ofthetotalelectricalpowerhas beenassumedforprovisionofcooling.Itwillbepossibletoprovidea moreprecisefigureoncedetaileddesignsofthecryogenics,DAQand waterpurificationplanthavebeenfinalised.Thesewillbeincluded withinthefutureTDR.

3.2.5. Low-radonairsupply

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Figure 5. SchematicofthelowRnairfacility.

withinaregimewherebyonlythevolumeabovethewateris sup-pliedwithlow-Rnair,witharesidualRnconcentrationinairofa “few” mBq

/

m3_[₁₈_]._In_this_instance,_a_system_of_the_same_scale_as

thatoperatingintheLSMforNEMOandEDELWEISScouldprovide thenecessaryﬂowoflowRnair.

Thecurrentsystemconsistsofacompressor,airbufferanddryer atonelocation,withafootprintofapproximately6_×1m;and sev-eralﬁlters,anaircoolerandaseriesofcarbonadsorptioncolumnsat anotherlocation,withafootprintofapproximately5×2m.Theair cooler,andthetonneofcarbon,arecooledto₋50◦C.Powerdrawn bythisisestimatedtobearound30kWwhenrunningforboth EDEL-WEISSandNEMO.Thesystemprovides150m3

_/

_h_of_air_with_a_factor

1000reductionforRn,tolessthan15mBq

/

m3_._A_schematic_of_the

currentRnreductionfacilityisshowninFig. 5 .

Further details about Rn progeny deposition are provided in Section 3.3 .

ThecurrentRnmonitoringsysteminuseattheLSMcouldbeused formonitoringthelocalenvironmentofEURECA.Ifagreater sensi-tivityisrequired(dependentonsimulationstoshowhowlowaRn concentrationinairweneed),itwouldbepossibletoincreasethesize oftheelectrostaticcollectionvesselandoperatethePINdetectorata highervoltage,aswasdonewiththeSuperKamiokandeRndetector. Further,anumberofsimilarsystemsatdifferentlocationsaroundthe caverncouldbeinoperationsimultaneously.

3.2.6. Low-radonwatersupply

Simulationshaveshownthatitisnecessarytoincludea3-m thick-nessofwatertoefﬁcientlysuppressthegammabackground.Thisis inexcessofthe70cmofwaternecessarytoreducetheneutron back-groundtobelowthesensitivityofthedetector.RequirementsforRn inwateraretobelessthan100mBq

/

m3_._GERDA_used_a_similar

vol-umeofwaterandobtainedU,Th,K,Pbcontaminationsbelowppt levels,withaveryefﬁcientremovalofparticleswithsizes

>

1

μ

m [19 ].EURECAwilloperatewithasimilarlylowlevelofcontaminants inthewater.

Workingwiththebaselineofawatertankofdiameter8mand aheightof12mcontaining8mdepthofwater,EURECArequires around 400m3_of_ultra-pure_water_for_one_cryostat._An_additional

tankcapableofstoringtheentirecapacityofwaterfromtheshielding tankwillalsoberequired.

Wewillrequireatwo-stagepurificationprocess.Aschematicof thewaterpurificationplantisshowninFig. 6 .Feedwaterisinitially passedthroughasystemconsistingoffiltrationandreverseosmosis severaltimesbeforeenteringasecondstage.Upto70%ofthe wa-termaybelostduringtheinitialstage.Thesecondstageconsistsof ultrafiltration,electrodeionisationandmembranedegasification,and formspartofthecontinuouspurificationloopwhichwillbe neces-sarytomaintainthecleanlinessofthewater.UVtreatmentand

/

or coolingmayalsobenecessaryduringthesecondstage,tolimit bac-terialgrowthwhichwouldreduceopticaldepth.Fortheﬁrststage puriﬁcation,afootprintofaround4_× 2misenvisaged,depending

Figure 6. Schematicofthewaterpuriﬁcationplant.Theabbreviationsare:UF, ultra-ﬁltration;RO,reverseosmosis;EDI,electrodeionisation;andUV,ultraviolet.

onfinaldesign.Thesecondstagemay(againsubjecttofinaldesign) fitintoafootprintofaround6 × 4m.However,ifabuffertankis usedwithinthe(secondstage)purificationloop,anadditionalspace oftheorder10m3_may_be_needed.

OfparticularconcernarethelevelsofRninwater.Thisisnotonly forRndaughtersactingasasourceofbackgroundwithinthewater butalsoforthepossibilityofoutgassingofthewaterincreasingtheRn concentrationwithintheairofthecleanroom,whichwillbeattimes opentothewatertank.Borexinousea6-mtall,approximately40-cm diameterRn-strippingcolumn.Waterﬂowsinonedirection (down-wards),withacounterﬂowofN2,toachieveaRnlevelof3mBq

/

m3

(reductiontothislevelachievedaftermanycyclesthroughthe purifi-cationloop)[20 ].Thefootprintfortheirsystemisabout1×1m.An alternative,asusedbySuperKamiokande,wouldbetouseavacuum degasifierwiththepre-treatmentofRn-reducedairtoincreasethe degasificationefficiency.

FormonitoringtheRnconcentrationinwater,asimilarsystemto thatcurrentlyemployedattheLSMformonitoringRninaircanbe used,whichisbasedonthedesignemployedbySuperKamiokande [21 ].Withthisdetector,waterispassedthroughamembrane degasi-ﬁerallowinggastoﬂowintoachamberofRn-reducedairwhichis fedintothemonitoraswiththe‘standard’Rn-in-airdetector.Quoted sensitivityisaround1mBq

/

m3_of_Rn_in_water_for_a_one-day

mea-surement.Itwouldbebeneﬁcialtohaveatleasttwosuchdetectors; onemonitoringtheRnconcentrationwithinthewatertank,andthe otherattheoutletoftheRndegasiﬁcationunit.

Itmaybenecessarytoinstallanadditionalresin-basedRnfilter withinthefirst-stagepurificationprocess.Suchastepwoulddepend onthequalityofthefeedwater,likelydependentonitsorigin.

Aninputﬂowrateofupto10m3

_/

_h_is_foreseen_with_{recirculation}

dependentoncontaminationarisingfromthesystem.

Forthecryostatoutershell,anumberofpossibilitiesexist.Ideally Cuwouldbeused.However,Cu isknownto corrodeindeionised water[22 ],necessitatingapolymer(orother)coating.Hence,PMMA (acrylic,Perspex),asdiscussedinSection 4 ischosenasoutershellfor thecryostat.

Itmaybepossibletousestainlesssteelforthepipework. How-ever,theuseofpolymersispreferredtopreventmetallic contamina-tionwithinthewater.Metallicparticulatescanaidthetransportof bacteria.PVDFandPEarebothfavouredinultrapurewatersystems. Materialscontainingﬂuorineusedherewouldbesufﬁcientlyfarfrom thedetectorsforittobeofnoconcernwith(

α

,n)reactions.

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3.3. Cleanrooms

Weplanforatleasttwocleanroomareas,onewithinthewater tankandtheotheratthetopoftheinfrastructuretower.Thelatter willbeusedfordetectorpreparationanditwillbethroughthisthat accesstothewatertankwillbeprovided.Anoptionexistsforhaving eitherthewatertankandthecleanroomastwoseparatecleanrooms, eachwithitsownlow-Rnairsupplyandvent;orhavingtheairsupply tothewatertank,inturnoverpressurisingthecleanroom.Thetwo mustbemechanicallydecoupledtopreventunnecessaryvibration ofthedetector,butalsosealagainsttheoutsidetomaintain cleanli-nesswithin.Additionalcleanroomspacemaybeavailableforgeneral facilityuseelsewherewithintheundergroundlaboratory.

Inadditiontothecleanarea,extraspacemustbeavailablefor changingrooms,andthestorageofbothcleanroomandeveryday clothing.Aclean-offareaandamaterialshatchwillrequirespaceas theywillneedadoubleairlocksystem.

Externaltothecleanroom,spacemustbemadeavailableforthe interfacesbetweeninsideandoutsidethecleanrooms.Provisionmust bemadeforgascylinderplacement,liquidnitrogen(LN2)dewar

stor-age(ifboil-offofLN2istobeusedasapurgegas),andthesupplyand

disposalofwater.

3.3.1. Cleanroomaroundcryostat

Sincethereexistsarequirementforthecryostattobeshielded byultra-purewater,thenthewatertankmustbeconsideredtobea cleanroom.Accesstothecryostatwillbeviathewatertank,initially throughtheadjacentman-tower,theupperﬂoorofwhichwill func-tionasacleanroom.AlikelycategorywouldbeISO6to7(class1000 to10000,respectively).

Low-Rnaircouldbeintroducedatthetopofthewatertank,further ﬁlteredtotherequirementsofthecleanroom.Anoverpressurewill bemaintainedwithinthetank,although theoptionofusing boil-offfromLN2willbeconsideredduringdetectoroperations.Careful

considerationmustbegiventodeadzonesofairwithinthetank.It maybenecessarytopipethecleanairdowntothebottomofthe tankwhilethecryostatisopen.Thewaterwillalreadyhavealow concentrationofRn.

Theentrancefromthecleanroomwillleadontoaplatforminthe tankabovethe levelofthewater. Thisisenvisagedto beasolid structureofstainlesssteel.Twotrapdoorswillbelocatedintheﬂoor, oneattheedgeprovidingaccesstothebottomofthewatertank;the otherinthecentreallowingaccesstothecryostat.

Acranewillbeincludedwithinthewatertank,likelywithaload limitof1tonne.Thecranewillbeusedformovingshields,andforthe detectortowers.Theminimummovementnecessaryforthecrane willneedtobedeﬁned(fordetectortowerplacement)aswillthe reachofthecrane.Ifaccessisrequiredtothewholevolume, modiﬁ-cationswillbeneededtotheplatformatthetopofthetanktoenable ittobetemporarilymoved.

Spacemustbeavailableforthesixdetectorthermalshields.One optionwouldbetoincludeaﬂoorstageataroundthelevelofthe openingofthecryostat.Adequatedrainagewouldhavetobe consid-ered,e.g.useofagrilledﬂoor,aswouldaccessofthecrane.

3.3.2. Cleanroomfordetectormountingandpreparation

Thecleanroomlocatedatthetopﬂoorofthetowerwillbefor detectormountingandpreparation.ThiswillbeaISO7cleanroom containinglaminarﬂowcabinetsofISO5.

Sincewewillhavemultipletargetmaterials, andthereforethe possibilityofmultiplegroupsworkingwithinonearea,thereshould beatleasttwoofthesededicatedareas.Returnairfromthecleanroom willbepassedtotheinputoftheairhandlingunit,tominimisethe inputoflow-Rnair.

Storageandmountingspacewithinthiscleanroomwillbeneeded forindividualdetectors,thosemountedontobaseplates,andthose

mountedintowers.Consideringthatindividualtowersofdetectors maybeupto1-mlongandupto30-cmdiameter,adequatestorage spaceneedstobeplanned.

Apparatusforcleaningwillbeneeded.Thisincludesanultrasonic bath,aclean(deionisedandﬁltered)watersupplyforrinsing,awater disposalroute,fumehoodsandstoragecabinetsforworkwith haz-ardouschemicalsandsolventssuchasdichloromethane,andagas supply.Mainswatercanbeinputtothecleanroom,withsmallscale ﬁlteringoccurringtherein.Gascylindersand

/

orLN2dewarscouldbe

placedexternaltothebuildingandgaspipedintothecleanroom. Abuildingofdimensions6 × 8mhasbeenpresentedwithin Section 3.1 .Ifthisprovidesinsufficientfloorspaceforthecleanroom, alternativesofalargerfootprintorpartiallysubmergingthebuilding willbeconsidered.CleanroomoverpressureandHEPA-filteredfans willbeplacedontopofthebuilding.

3.3.3. Radonprevention

222_Rn _decay _leads _to _deposition _of _the _relatively _long-lived

progeny210_Pb_onto_surfaces_exposed_to_Rn.210_Pb_decays_mainly_by

emission oftwo

β

s andan

α

beforereachingthestable206_Pb._In

ordertoreducethebackgroundtobelowoneevent

/

tonne

/

yearin theWIMP-searchregionofinterest(ROI),specialcaremustbetaken toreducesuchdepositionontosurfaceswhichareindirectviewof thedetectorcrystals.Alow-Rnenvironmentmustbesupplied for mountingthedetectorsintotheEURECAcryostat.

The222_Rn_level_inside_the_current_LSM_laboratory_is_10–15_Bq

_/

m3_due_to_the_ventilation_system_supplying_air_from_outside_of_the

mountainat7000m3

_/

_h_(two_laboratory_volumes_per_hour)._Low-Rn

airisalsosuppliedtoareasofthecurrentlaboratorytoamaximum rateof150m3

/

_h_with_a_measured_{concentration}_at_the_exit_of_the

low-Rnfacilityoflessthan15mBq

/

m3_._Further_details_of_the_system

arepresentedin Section 3.1 .AnaverageRnlevelintheproximityof theEDELWEISS-IIcryostatattheLSMoflessthan100mBq

/

m3_has

beenachieved,withairsuppliedfromthissystematarateof0.5m3

_/

h.

WeplantouseasimilarRnreductionsystemtothatalreadyin placeasaninputtothecleanroomoverpressurefans.Sincethe re-quiredairflowthroughthecleanroomisinexcessofthelow-Rnair flowbyafactorofaround10,wewillrecyclethelow-Rnairsuch thatthefanfilterunitsdrawairinfromtheroomitself,astandard cleanroompractice.

CalculationshavebeenperformedtoestimatetheamountofRn progenydepositedonasurfaceforgivenexposuretimesand concen-trationsofRn.FurtherdetailsaregiveninAppendix D .Foraninitially cleansurfaceexposedto100mBq

/

m3_of_Rn_for₉₀_days,_we_would

expecttoobtain2.5

α

sand5

β

sintheROIpertonneperyearwith arejectionpowerforbothof1.7×104_[₂₃_,₂₄_]._This_activity_is_a

fac-torof∼10toohigh.PossiblemethodsofreducingtheamountofRn withinthecleanroomtoanacceptablelevelwouldbebyincreasing theflowrateofairthroughtheRntrap,andinstallinguptotwo ad-ditionalcharcoalfilters.Thefinalspecificationsforthisimprovement willbedetailedatalaterstage.The90daysprovidesanexampletime forassemblyofthedetectors.

Withinthewatertank,sourcesofRnmayarisefromthePMTsand stainlesssteelofthetank.Amembranedegassingunit(see[21 ]for anexample)willbeincludedwithinthewaterpuriﬁcationcircuitto lowerthelevelofRntobelowtherequired100mBq

/

m3_.

3.4. ElectromagneticShielding

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numbereddocuments.Generalregulationsandgoodpracticeprovide sufﬁcientguidanceforthedesignandimplementationofgeneral ex-perimentinfrastructure.

Specialconsiderationisnecessaryforthespacehousingthe de-tectorsandfront-endelectronicsatthecentreofthecryostat.Here, requirementstypicallygobeyondthegeneralgoodpracticedescribed aboveandaredescribedinmoredetailintherelevantsectionon electronics. Broadly,the detectoraccommodation willneedto be designed andimplementedasa Faradaycage.Inaddition,further shieldingagainstmagneticinterferencemaybecomenecessaryifthis noise contributionis identiﬁedasbeingtoohigh. Typical sources ofmagneticcontributionsarevacuumandrecirculationpumpsand othermotorsandcompressors.Theseshouldbelocatedatsufﬁcient distancefromthedetectorcompartment.

3.5. Muonvetosystem

Thewatertankhousingthecryostatwillbetheshieldingforany neutronandgammaactivityfromtheconcreteofthelaboratory(see Section 3.6 )andwillactasanactiveshieldforcosmicmuons.Forthat purpose,thewatertankwillbeequippedwithPMTs.Thedetailed parametersofthePMTsetup(e.g.PMTsize,number,position,trigger threshold)willbedefinedinanoptimisingprocessbasedonMC sim-ulations.Theoptimisationprocesswillincludetheexactgeometryof thesupportstructureofthecryostat,theinfrastructureandcabling pipesfromthetankwalltothecryostatandwillexaminedifferent solutionsforthetanksurfacesuchashighlyreflectivefoils.Alikely configurationwillconsist oftheorderof1008-inchencapsulated PMTsfixedonamountingstructureatthetankwall,bottomandtop. AllPMTswillhavetobeleakcheckedtoensurecompatibilitywith longtermuse.Fromfirstsimulations(Section 8.4 ),thesignal thresh-oldcorrespondingtoanenergydepositof0.2GeVhastobeachieved tosuppressanymuon-inducedneutronbackgroundinthebolometer array.

The simulationsshowthat lessthan ﬁvesinglenuclearrecoils inducedbycosmicmuonsareexpectedfora3tonne·yearsexposure. AllthebackgroundeventslinkedtosinglenuclearrecoilsinEURECA crystalsshowenergydeposits

>

0.2GeVinthewatertank.Forsuch energydeposits,anefﬁciencyfarinexcessof90%istypicalforsuch waterCherenkovvetoes,thusanymuon-inducedsinglenuclearrecoil isexpectedtobevetoed.AsstatedinSection 8.4 ,anupperlimiton theunvetoedsinglenuclearrecoilsis0.3events

/

yearassumingan 0.2GeVenergythresholdforthevetosystem.

EachPMTwillbesuppliedwithanindividualhighvoltagebased onaHVsystem(MPOD2HLXHV-EXmainframehousing10boards with16or32HVchannelseach)toindividuallyadjustthePMT re-sponse.Calibrationandstability

/

puritycontrolwillbeensuredby laserpulses,movablebulbsandradioactivesources.Severaloptions forthedeadtime-freesignal readoutanddataacquisitionare cur-rentlyunderinvestigation.

Themuonvetodatastream(asdigitisedtraces)willbeintegrated intothemaindataacquisitionsystem(seeSection 6 ).

3.6. MonteCarlosimulationsfortheshieldingdesign

Alphaandbetaparticleshaveshortrangeswithinmaterials.The 5-mm-thickcopperscreenswillbesufﬁcient toshieldfromthese sourcesofradiation.

Neutronsandgammas fromrockcanbeefficientlyshieldedby variousmaterials.Asuppressionofgamma-rayandneutronfluxes by aboutsixorders ofmagnitudeis required to reduce the non-discriminatedbackgroundbelowthelevelofdetectorsensitivity.In oursimulationswehaveconsideredbackgroundradiationfromrock andconcreteofthelabwalls. Fig. 7 showstheattenuationofthe gamma-rayfluxfromconcrete beyondthewatershield,asinthe baseline designofEURECA.Ourresultsshowthat3mofwateris

Figure 7. Gamma-rayspectrafromtheThdecaychaincontainedintheconcreteof thelaboratorywallsattenuatedbydifferentthicknessesofwatershielding(givenin metres).

requiredtoattenuatethegamma-rayﬂuxfromthelabwallssothe remaininggamma-rayinducedbackground(beforediscrimination)in theregionofinterestwillbeabout2000peryearinatonneoftarget. Thisleadstoasizeofthewatertankofabout8mindiameterand8 minheightforatonne-scaleexperiment.With3mofwatershield theneutronﬂuxfromrockandconcreteofthelabwallswillbe sup-pressedtoalevelwellbelowthedetectorsensitivity.Moredetailsof simulationsaregiveninAppendix F .

4. Cryogenicsandcryostat

4.1. Cryogenics

ThecryogenicsolutionforcoolingEURECAispresentedinthis section.Table 3 summarisestheaimsofthecoolingsystem.

Table 3

BaselinedesignfortheEURECAcryostatandcryogenics.

Cryogenicsandcryostat

Basetemperature 7mK Coolingpoweratbasetemperature 20μW

Cooldowntime 20daystobasetemperature Cryostatsize 2mdiameter,2mheight Coldvolume 1.5mdiameter,1.5mheight

ThebasetemperaturetobeprovidedbytheEURECAcryogenic systemwillbe7mKtocooladetectormassof1t.Detectorsequipped withNTD-Gesensorscanoperatewithexcellentsensitivityat20mK; but10mKoperatingtemperature(withmargin)isrequiredforthe operationofCaWO4detectors,equippedwithtransitionedgesensors

(TESs).ThecriticaltemperatureoftungstenTESsisaround 15mK withaspreadofafewmK.Forreliablestabilisationoftheoperating temperatureforTESs,abasetemperatureof10mKisrequiredatthe detectorholders,andthus7mKisspeciﬁedasthebasetemperature forthecryogenicsystem.

Thislowtemperaturewillbecreatedby adilutionrefrigerator (DR).Circulatedlow-temperaturegaswithintheDRcircuitwill fur-thercooltwointermediatelow-temperaturestages:aheatintercept at50mKandathermalshieldat500mK.Additionalthermal shield-ingwillbemaintainedat1.8Kand60KbyaHerefrigerator,which willalsoprovidepre-coolingtoallcryogeniccomponentsduringthe ﬁrststageofcool-down.Adiagramofthecryogeniccircuitisshown inFig. 8 .

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Figure 8. DiagramofthecryogenicsystemforEURECA.Numbereditemsreferto:1, pressurisedgaseousheliumcoolingloop;2,pre-coolingheliumloop;3,liquidhelium supply;4,superﬂuidheliumsupply;5,pumpingline(16mbar,returnfromClaudet bath);6,dilution3_He_pumping_line_(return);_7,_dilution3_He_supply.

polarisationof3_He_[₂₅_]_and_with_the_current_design_of_the_CUORE

cryostat[26 ].AfeasibilitystudyonthedesignoftheEURECAdilution refrigeratorhasbeencarriedoutwithintherecentdesignstudyfor EURECA[27 ].

Basedoncompletedstudies [17 ,27 ,28 ] ourdesignincludesthe followingfeatures:

• Athermalshieldbelowroomtemperatureat60K;thethermal loadisdrivenbytheradiativeloadfromroomtemperature;the coolingpowerisprovidedbyapressurisedheliumloop.

• A1.8Klevel,cooledbyapressurisedsuperﬂuidheliumlinkin ordertominimisethemircro-vibrations(avoidingboilinghelium); theheatloadisdrivenby theconductionfromthesupporting strutsandcabling,andtheheatingintroducedbytheelectronics front-end.

• Thedilutionrefrigeratorisoptimisedtominimisetheconductive loadonthecoldeststage:

- Aclosed500mKshieldinterceptsthebulkoftheconductive loadfromstructuralelementsandthedetectorwiring. - Anintermediate50mKstagelimitstheconductiveloadson

thelaststage.

- Anenclosureofthedetectorcompartmentat10mK.

• Low-temperaturedilutionrefrigeratorcomponentsarelocatedin acommoncoldboxwiththeHerefrigerator(i.e.thestillandthe

3_He_{pre-cooling).}

Forcomparison,theCUOREexperiment[29 ,30 ]hasasimilar re-quirementforthecoolingof1tofdetectorswithacoolingpower of5

μ

Wat12mK.CUOREusesseveral40-Kand4-Kcryo-coolersto establishanumberofintermediatestages.FortheEURECAdesign,we decidedagainsttheuseofcryo-coolerstominimisepotentialissues withvibrations.Inaddition,theEURECAsolutionofusinga combi-nationofaHerefrigeratorandadilutionrefrigeratorisfavouredfor reasonsoffastcool-downandhighefﬁciency.

4.1.1. Requirements

Themaindriversforthecryogenicdesignare:

• Abasetemperatureof7mKforadetectortemperatureof10mKis chosenfordetectorsensitivity.Thelargecoolingpower(20

μ

W) isdrivenbytheestimatedthermalrelaxationprocessinthepure copperusedforpartofthelow-backgroundshielding.

• Acoldspacevolumeofupto1.5-mdiameterand1.5-mheight toaccommodate1tofdetectors,andinternalshieldingagainst radioactivity.

• An allocation of cooling power at a temperature

<

4 K for theSQUID-basedcoldelectronics,orotherfront-endelectronics (1.5Watthe1.8-Kstage).

• Materialselectionforthecryogenicpartsinsideexternal shield-ing.

• Minimisationofthevibrationsexportedfromthecryogenic equip-ment,i.e.thecompressorsandpumps,theﬂuids’circulationand phasechanges.

• Lifetimeoftheequipmentlongerthan20years,withtypical mea-surementperiods

>

1year.

• Acool-downtime

<

5daystoreach1Kandafurther

<

15daysto reachoperationalconditions.

4.1.2. Overallcryogenicsystem

Thecryogenicsystemiscomposedofﬁvemainelements,which arethecryostat,containingthedetectors,acryo-line,throughwhich thecoolingtothecryostatisprovided,acoldbox,housingcryogenics, aDRandaHerefrigerator.

Thecryostatwillcontainthedetectorsmountedbelowthemixing chamber,withfront-endelectronicsmountedabove.Thecryo-line connectsthecryostat,placedwithinthewatertank,tothecoldbox. Ourdesignisbasedonatotalallowablelengthofthecryo-lineof20m, althoughtheaimistokeeptheoveralllengthbelow10mtoreduce heatandpressurelosses,andtherequiredamountof3_He._Further

detailsaregivenbelow.

4.1.3. Heliumrefrigerator

The He refrigeratorwillprovide cooling ofthe thermalstages at60Kand1.8K,andwillalsobeusedfortheinitialpre-cooling ofthecolderstages.Coolingofthe60Kshieldwillbeachievedwith Hegasat40K,pressurisedto7-15bar.Asanexample,aﬂowof20g

/

s (5mol

/

s)withatemperatureelevationof20Kgivesacoolingpower of2200W.

For the 1.8-K stage, a direct Joule-Thomson expansion of He to16mbarwillcreatea1.8-Kbath.Thiswillbecombinedwitha Claudetbath(seeAppendix E.1 )toprovidepressurisedsuperﬂuidHe (HeII)tothecryostatat1.25bar.TheuseoftheClaudetbathstops microphonicnoiseproducedbyHeboilingwithinthepipe.Acooling powerof10WextractedfromtheHeIIheatpipecreatesan evapora-tionrateof0.05g

/

s

/

W(0.013mol

/

s

/

W).Thisﬂowislowcompared tothe40-Kcoolingloop,allowingtohaveadirectextractionofthe 1.8-Kvapourswithoutcirculationintheregenerativeheat exchang-ers.

AsmallcommercialHerefrigerator,withmodifications,isan op-timalsolutionfortheEURECAcoolingsystem.Thesmallestliquefiers availablefromthemainmanufacturersprovide100Wat4K[31 ], whichisneededforcoolingdowntoatemperatureof4Kwithin about4days.Further,ithassufficientcoolingcapacityduring nor-malrunning.At1.8Kthecoolingpoweristypicallyaquarterofthat at4K.Twoweeksofcoolingareexpectedforreachingoperational conditions.IncorporatingsuchaHerefrigeratorintothecooling sys-temallowssimplificationofthethermalarchitectureofthesystem throughaccessofcoolingstageswithintherefrigeratorandlinking themdirectlytocorrespondingshieldsandstageswithintheEURECA cryostat.

TheHerefrigeratorconsistsofa5m3_gas_tank_for_the_closed_cycle 4_He_storage,_a_compressor_and_pumps._These_items_will_be_placed

atasigniﬁcantdistancefromthedetectorstolimitnoisegenerated bythehighlevelofvibration,particularlyfromthecompressor.The onlylimitisthepumpingspeedforthelow-pressureﬂows(1.8-KHe bathanddilutionstill).Additionalitemsincludeheatexchangers,two gas-bearingturboexpanders,aJoule-Thomsonvalveandthecontrol system,allcontainedwithinthecoldbox.

AsuitableunitisamodiﬁedHELIALMLseriesfridge, manufac-turedbyAir Liquide[31 ].Thisdraws75kWatfullpower,during cool-down,reducingto50kWunderpartloadoncethesystemis attheoperationaltemperature.Anadditionalpumpwillberequired forthe1.8KHe IIwithin theClaudet bath.The compressoris of dimensions2225 × 1960 × 1885mm3_,_and_requires_a_dedicated

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about7m3_is_needed_within_the_cold_box_for_the_items_related_to_the

Herefrigerator.

WiththemodiﬁedHerefrigerator,thefastcoolingphasecanbe managedentirely by thissystemusingthe samecompressor and pumps.ThecoldboxoftheHerefrigeratorcanalsoaccommodate severalelementsoftheDR:the3_He_pre-cooling_and_the_still.

Com-paredtosmallercryocoolers,thethermodynamiccycleofaliquefier (theClaudecycle)is∼10timesmoreefficient.TheClaudetbath, com-binedwithafastcool-downto1.8K,isthemainjustificationtousea smallHerefrigerator,derivedfromaliquefierdesign.

AnexampleofaHerefrigeratorcoupledwithacryostatwitha superﬂuidthermallinkistheNeuroSpincryogenicsystem[32 ].More detailsofthissystemareprovidedinAppendix E.1 .

4.1.4. Dilutionrefrigerator

TheDRcoolsthreeprogressivelycolderstagesat500 mK,50mK and7mK.It iscomposed ofa gashandlingunit (placedwiththe compressoroftheHerefrigerator),aheatexchangerandstillwithin thecoldbox,andthemixingchamberlocatedwithinthecryostat.

Due tothe20

μ

W coolingpower requirementcombinedwith thelowtemperatureof7mK,theperformanceofthedilution re-frigeratordependscriticallyonthepropertiesofthesintered mate-rialusedforthediscretecounter-ﬂowheatexchangers.Theclassical choiceistousesinteredAgheatexchangers.However,commercialAg powdersareknowntoexhibitradioactivityincompatiblewith low-backgroundrequirements.PowerconsumptionbytheDRislikelyto beupto20kWduringcool-down,estimatedtobe15daysfor1t ofdetectormaterial,startingfromatemperatureof1.8K.Thiswill reduceto10kWduringlow-temperatureoperation.

AdesignbasedonsinteredCuhasbeentestedforEURECA[17 ], showing10cm3_of_sintered_Cu_is_necessary_to_achieve_the

require-ments.Examplesareshownin Appendix E.2 .Basedontheseresults weconcludethattheEURECAthermalrequirementsarewellwithin thestate-of-the-art.Theprocurementofcommercialpowderand de-tailsofthesinteringprocesswillbedeﬁnedandcharacterizedduring thetechnicaldesignforEURECA.

Severalcommercialpowdershavebeenidentiﬁedandthe follow-ingpropertieswillbestudiedbeforetheﬁnaldecisiononpurchasing thepowderismade:

• Porositycharacterisation,optimisationofthesinteringprocess. • MeasurementoftheKapitzaresistance.

• Measurementoftheradioactivitylevel.

4.2. Powerbudgetanddetectortowerthermalrequirements

Theestimatedthermalloadonbothstagesisgivenin Table 22 . Atthisstageofthedesign,comfortablemarginsforcoolingpower (

>

100%)havebeenincluded.Table 4 summarisesthecoolingpowers andtheirrequiredgasﬂowsforthedifferenttemperaturestages.

The3_He_isotope _molar_ﬂow_is_driven_by_the_cooling_power

re-quirementonthelowesttemperaturestage(10mK).Theestimation givenhereincludesa100%margin.Thecontributionstoeachstage areshowninmoredetailinTables22 and23inAppendix E.3 .

EURECAdetectorswillbemountedinarraysoftowerswhichwill beheatsunktoeachofthetemperaturestages.Thedesignﬁguresfor thedifferentstagesofthetowersareat75 K,3 K,700 mK,60mK and10mK.The powerbudgetateachstagebothonthe cooling-systemsideandthedetectorsideisshownin Table 5 withfurther detailsofthecontributiontothe10mKstagelistedinAppendix E.3 . Contributionstotheheatloadarefromdissipationofthereadout electronics,dissipationandheatreleaseinthedetectors,and con-ductionthroughthewiring,neglectingtheradiativeloadfromthe detectortowers.Section 5.3 providesdetailsconcerningthe mount-ingofdetectorswithintowers.

Figure 9. EURECAcryostatsketchshowingthethermalshields,Cu,PEandPMMA shieldingagainstradioactivityandotherelements.Oneexampleofatop-loading de-tectortowerisshown.ThecryogeniclineconnectstheHerefrigeratorwiththedilution refrigeratorthroughseveralcoolingloops.

4.3. Cryostatdesign

Adetaileddesignforthecryostatwillbecarriedoutforthe Tech-nicalDesignReport.Herewepresentaconceptofthecryostat em-phasisingonlyitsmainfeatures.

4.3.1. Mainfeatures

Thecryostatwillbeinstalledwithinahigh-puritywatertank.The variouscryogenicstagesarethermallylinkedtotheHerefrigerator anddilutionrefrigeratorthroughacryo-line.

Inadditiontotheoutervacuumcontainer(OVC)atambient tem-perature,thermalshieldsareplacedattemperaturesof60 K,1.8 K, 500 mK,50mKand10mK. Fig. 9 showsaschematicofthe cryo-statcrosssection.TheHerefrigeratorprovidescoolingforthe60K and1.8Kstagesinadditiontotherequiredcoolingpowerforthe readoutelectronics,operatingatatemperatureofaround100K.The detectorvolumeisprotectedbycopper,polyethylene(PE)andacrylic (PMMA)shielding.Thecold-plate,operatingatthebasetemperature of10mKisonepartofthecoppershielding.Thebulkofthecopper shielding,aswellasthePEandPMMAwillbethermallyconnected tothe50mKtemperaturelevel.Thecoolingpowerforthedetector towersisprovidedbyconductionthroughthecold-plateontowhich thecoolingelementswillbemounted.Around10cm3_of_sintered

materialwillbeusedtocouplethecold-platetothelowtemperature Hemixture.

The60Kshieldlimitstheheattransfertothe1.8Kstageand pro-videsalargecoolingpowerforthereadoutelectronics.Itisactively cooledbyhighpressuregaseousHesuppliedat40K,atupto15bar. Themainthermalloadistheradiationfromthe300Kexternalwall. Thetemperaturegradientalongtheshieldisanissuetobeconsidered tocontrolthethermalloadatthe1.8Kstage.Twooptionsare consid-ered:eitherasinglewallcooledbyaheatexchangermountedalong thecylindricalpartoftheshield,oradouble-walledstagecooledby thecold-plate.

Table 6 presentsanoverviewofalltemperaturestagesofthe cryo-stat.FiguresfortheheatbalancearepresentedinTable 7 .Calculations forTable 7 assumeanemissivityofthecoppershieldsof10%,which isaconservativevalueforuncoatedpurecopper.Theexternalwall (PMMA)hasanemissivityof100%.

4.3.2. Cryostatmechanicalinfrastructure