Multi Anode Photomultiplier Tube Reliability Assessment for the JEM-EUSO Space Mission

1 MB·English

by  H. Prieto-Alfonso

Multi Anode Photomultiplier Tube Reliability Assessment for the JEM-EUSO
Space Mission
H.Prieto-Alfonsoa,∗,L.DelPerala,M.Casolinob,c,K.Tsunob,T.Ebisuzakid,M.D.Rodr´ıguezFr´ıasa,forthe
JEM-EUSOcollaboration
aSPaceandAStroparticle(SPAS)Group,UAH,Madrid,Spain
bEUSOTeam.RIKEN,Japan
cINFNRomaTorVergata,Roma,Italy
dComputationalAstrophysicsLaboratory.RIKEN,Wako,Japan
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n Abstract
a
Reliabilityassessmentisconcernedwiththeanalysisofdevicesandsystemswhoseindividualcomponentsareprone
J
to fail. This reliability analysis documents the process and results of reliability determination of the JEM-EUSO
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2 Photomultipliertubecomponentusingthemethods217Plus,Quantumefficiencydegradationandradiationhardness
assurance. In conclusion, the levels of damage suffered by the PMTs which comprise the focal surface of JEM-

] EUSO Space Telescope, are acceptable. The results show as well that the greatest contribution to the failure is due
t
e to radiation SET. The guaranteed performance of this equipment is a 99.45%, an accepted value of reliability thus
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fulfillingtheobjectivesandtechnologicalchallengesofJEM-EUSO.Itshouldbenotedthatthereliabilityvaluesof
-
s theStandard217Plus,despitebeingastandardimproved,andanupdatedversionofMIL-HDBK-217Plusdoesnot
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have sections that include the analysis of radiation of space electronic equipment. The recommendation from this
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. studyistheinclusionofallrealfailureeffectsmayfaceanelectronic,mechanical,opticalspaceequipment.
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i Keywords: JEM-EUSO,PMT’s,Reliability.
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y
h
p 1. Introduction JEM-EUSO is being designed to operate for 5 years
[ onboard the ISS orbiting in a Low Earth Orbit (LEO)

1 JEM-EUSO [1, 2] is a large imaging telescope de- aroundtheEarthatanaltitudeofabout400km. Asfor
v signed to study the Ultra-High Energy Cosmic Rays any mission to be operated in space, JEM-EUSO must
8 (UHECR)atenergiesabove1020 eV,asrepresentedby comply with specific requirements, i.e. high radiation
0 Figure 1. Looking downward the Earth from the In- doses,unaccessibilityandremotecontrolledoperations.
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ternational Space Station (ISS) it will detect such cos- That is why the reliability analysis and radiation hard-
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0 mic ray particles observing the UV light generated by nessassuranceisextremelyimportantinordertodeter-
. Extensive Air Showers (EAS) while the UHECRs de- mine the tolerance and redundacy requirements within
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velop in the atmosphere. The scientific objectives of thesystemaspreviousstudiesshowincaseofFieldPro-
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5 the mission include charged particle Astronomy and grammable Gate Array (FPGA) which also applies to
1 a promising branch of Astrophysics, called Astropar- PMTs[4,5,6].
v: ticle Physics, with the aim of extending the measure- The design and the construction of the JEM-EUSO
i ment of the energy spectra of the cosmic radiation be- telescopeisarealtechnicalchallenge,asitinvolvesthe
X yond the Greisen-Zatsepin-Kuzmin (GZK) effect [3], useofnewtechnologiesfromthelaboratoriesofbothin-
ar together with the detection of Extremely High Energy dustrialandresearchcentersinareasasdiverseaslarge
Gamma Rays (EHEGR) and Extremely High Energy optical and accurate Fresnel lenses, a novel technique
Neutrinos(EHEN). of photo detection highly sensitive with very accurate
resolution,andveryinnovativeanaloganddigitalelec-
tronicsaswell.
∗Corresponding Author: H. Prieto-Alfonso, Univer-
The paper is organized as follows. First of all, we
sity of Alcala´, Alcala´ de Henares, 28871, Madrid, Spain;
Email:[email protected]. have explained the considerations we have taken into
PreprintsubmittedtoElsevier January26,2015
oftheperformanceofthePMT,whichmeanthereliabil-
ityofthetransmissionofthesignal, qualityofthesig-
nal, neither the degradation of the performance during
operationofthePMT(Backgroundevents),theseevents
canbestudiedinotherpapers. Intheanotherhand,this
studywillconsiderthePMTasasemiconductor, since
most of the element are composed by alkali materials,
considerationspreviouslymadebydifferentstudiesin-
cludingtheoryoftheprincipalmanufacturerofPMTas
Hamamatsu[8].insuchawaywewillproceedwiththis
studytakingintoaccounttheconsiderationsalsomade
bypreviousstudiesandtheories[9,10,11].
If we try to compare PMT with ICs, the only rea-
sonweconsidertheirrelationshipisbecausetheICand
PMT in a reliability model are considered as system
Figure 1: JEM-EUSO telescope onboard the Interna-
themself,however,accordingtothisassumption,theIC
tionalSpaceStation[2]
is the closest electronic component to the PMT in the
reliability standards we have so far [12, 13]. Table 1
showsmaindifferencesamongPMTs,VTsandICs.
accounttomakethereliabilityanalysis,thenabriefex-
planationofpossiblefailuresofPMTareshowninsec-
tion 3, along with the elements that compose the PMT Table 1. Differences among PMTs, VTs and ICs de-
in section 4. In section 5 the reliability analysis of the vices.
PMT has been performed and finally in section 6 the
conclusionsandresultsoftheanalysisarepresented. Element Material FeatureSize PhysicalConditions OperatingVoltage(V)
Anode 2”<Size≤30”
PMT Cathode:(AgOCs,(SbKcS) mm AffectedbyVibration 500<V≤3000
Dynode:(AgMg),(CuBe) AffectedbyShock
AffectedbyLight
2. TechnicalSpecificationsofJEM-EUSOPMTs Vacuum Anode:Ni(Nickel) 1.5”<Size≤25”
Tube Cathode:W(Tungsten) mm AffectedByVibration 10<V≤15000
Grid:Ni(Nickel) AffectedByShock
The focal surface is a spherical curved surface, 1.5”<Size≤25”
Integrated SiO2(SiliconDioxide) nm VibrationResistance 2.3<V≤5
its area amounts to about 4.5 m2 and it is cov- Circuit ShockingResistance
Affectedbytemperature
ered with about 5,000 Multi-Anode PhotoMultiplier
Tubes (MAPMT) Hamamatsu R11265-03-M64 MOD:
MAPMT designed for this space mission. The fo- The PMTs used in JEM-EUSO have been specially
calsurfacedetectorconsistsofPhoto-DetectorModules designed and manufactured by Hamamatsu and are in-
(PDMs), each of which consists of 9 Elementary Cells tendedforthisspacemission. Withtheaimtoimprove
(ECs).TheECimplements4unitsofMAPMTs.There- the technical specification of the PMT for the JEM-
fore,about1,233ECsorabout137PDMsarearranged EUSOSpacetelescope,Hamamatsu,theJapanesecom-
onthewholefocalsurfacewith384,000pixels[7]. pany, has developed dedicated PMTs according to the
Standards that describe PMTs reliability have not JEM-EUSO Space requirements. Tables 2 & 3 show
beendevelopedsofar,howeverwehaveconsideredthe technical characteristics of the PMT, with a spectral
caseofVacuumTubes(VT)andIntegratedCircuits(IC) window in the UV enough broad to observe both the
becauseofthesimilarityamongthemandPMTs. This fluorescence as Cherenkov light generated in the EAS.
hasbeendoneinordertodevelopamodelforthePMT Againratioof106 addedtoacathodesensitivityof90
electronicsbehaviourtakingasreferencethemostsim- µA/lm allows the detection of low light levels with a
ilarelementintermsoffunctionality. verylowdarkcurrentof0.4nA.ThePMTisoperative
This study of the reliability of the PMT is a statisti- inawidetemperaturerange. Table4listsnominalvolt-
calstudy,notaperformancestudy,referredtothefailure ageratiosforthedynodeofthePMTs.
ratesofthePMTunderthedifferentsmechanismoffail-
ure,suchacracksintheenvelope,electromigration,and
multipleelectronicbehavioursuchasshort-circuits. In
anycase,thispapernevertriestosimulatethereliability
2
Table 2. Technical specifications of the JEM-EUSO We can classify failures in two types according to
PMT[14] theireffectsonthedevice: catastrophicandpartialfail-
ures.
Parameter Description
SpectralResponseRange 185to650nm
Windowmaterial/Thickness UltraVioletglass/0.8mm 3.1.1. CatastrophicFailure
PhotocathodeMaterial Bialkali Acatastrophicfailureisasuddenandtotalfailureof
Photocathodeminimuneffectivearea 23×23mm2 somesystemfromwhichrecoveryisimpossible.Catas-
Dynodestructure MetalchannelDynode
trophicfailuresoftenleadtocascadingsystemsfailure.
Numberofstages 12
Weight 27g Thetermismostcommonlyusedforstructuralfailures,
Operatingambienttemperature -30to+50◦C but has often been extended to many other disciplines
Storagetemperature -30to+50◦C wheretotalandirrecoverablelossoccurs. Failuressuch
VoltageSupply(anode-cathode) 1100VDC
as cracks in the glass envelope, electrodes no longer
Averageanodecurrent 0.1mA
connectedorshort-circuited,resultinginuselessornon-
existentsignalsattheoutputareconsideredcatastrophic
Table 3. Electronic characteristics of the JEM-EUSO
failuresinPMTs.
PMTat25◦C[14]
Parameter Min Typ. Max. Unit 3.1.2. PartialFailures
CathodeSensitivity Luminous(2856K) 70 90 - µA/lm Partial failures are fails in a system or part of a sys-
AnodeSensitivity Luminous(2856K) - 90 - A/lm
Gain(CurrentAmplification) - 1×106 - - tem from which recovery of part or all the system is
AnodeDarkCurrent(EachAnode) - 0.4 4 nA possible. These kind of failures include temporal fail-
(After30min.storageindarkness)
AnodePulseRiseTime - 0.6 - ns ures. Failures such as high dark current (noisy tube),
CathodeSensitivity
AnodeTransitTime - 5.1 - ns
UniformityRatioBetweenAnodes N/A 1:3 1:5 N/A gain drifts, decrease of cathode sensitivity, resulting in
PulseLinearity ±2%Deviation - 0.2 - mA incorrect or degraded signals at the output are consid-
(EachAnode) ±5%Deviation - 0.4 - mA
eredpartialfailures.
Due to long-term stability problem, an aging period
Table 4. Nominal voltage distribution ratios for JEM- has to be applied whenever tubes have not been oper-
EUSOPMTswhereDynodesfrom3to10havevoltage atedforalongtime. PMTswhichdonotreachafairly
distributionratio1[14] constant gain after that period can be regarded as fail-
ing. This clearly indicates that the reliability of PMTs
Electrodes K Dy1 Dy2 Dy3 Dy10 Dy11 Dy12 G.R P is closely connected to the mode of operation (volt-
Ratio 2.3 1.2 1.2 1 1 1 1 1 0.5
age,meananodecurrent,etc.) andtothespecifications
which are expected from these tubes. It is also clear
thatphotomultipliersaremorelikesystemsthancompo-
3. PMTReliabilityAnalysis nentsasfarasreliabilityisconcernedduethenumerous
characteristics affecting their operation (cathode sensi-
3.1. PMTFailureRate tivity,noise,gain,etc.) [15].
ThereliabilityanalysisofthePMTisacriticaltopic
Failure rate is the frequency with which an engi-
inground-basedexperimentsandspacemissionswhere
neered system or component fails, expressed, for in-
the proper working condition of PMT’s are crucial for
stance, in failures per hour. It is often denoted by the
the success of the experiment. The reliability of the
Greek letter λ and is important in reliability engineer-
JEM-EUSOPMTsshouldbehighduetothebigamount
ing. The failure rate of a system usually depends on
ofPMTnecessarytoimplementthewholefocalsurface
time,withtheratevaryingoverthelifecycleofthesys-
oftheJEM-EUSOSpacetelescope. Thepropagationof
tem. Inpractice,theMeanTimeToFailure(MTTF) 1,
λ failureratecausedbythisamountofcomponentsmakes
isoftenreportedinsteadofthefailurerate. Thisisvalid
mandatory the usage of high reliable components. As
andusefulifthefailureratemaybeassumedconstant,
usual,twotypesoffailuremustbedetermined[15].
often it is used for complex units or systems, electron-
The main scope of the reliability analysis could be
ics,andisageneralagreementinsomereliabilitystan-
summarized to assess that PMT design satisfies the re-
dards (Military and Aerospace). Failure rates are im-
quired quality/reliability objectives and mission spec-
portantfactorsintheinsurance,finance,commerceand
ifications and to assess the quality and reliability are
regulatory industries and fundamental to the design of
maintained at prescribed levels. The analysis consists
safesystemsinawidevarietyofapplications.
ofthreemainsections:
3
• To define the overall purpose, scope , nomencla- levelofcriticality. InteractionsbetweenHardware
ture, and general reference material for the relia- and SW might be assessed in HSIA (Hardware-
bilityanalysis. Software Interaction Analysis) in a later stage of
the project, to verify the reaction of SW after any
• Todefinetheanalysismethodsusedandthecalcu-
HWfailure.
latedfailureratesofsystemcomponents.
• To state conclusions, including the overall system 3.3. ComponentReliabilityAnalysis
reliability. TheanalysiswasconductedfortheJEM-EUSOPMT
inaccordancewiththe”PartsStressAnalysis”Method
3.2. RationalForExcludedItems giveninMIL-HDBK-217-F[16,17].
The following elements are excluded from this as- Following assumptions were made during analysis
sessment: foreachcomponentandthestressanalysis:
• Uniformity.AllelementswhichcomposethePMT
• Structural elements, as far as they are controlled must be statistically identical (within the same
by demonstrating positive Margin of Safety when batchnumber).
applyingFactorofSafetytodesignstrength,inor- • Independent trials. The success or failure of any
dertowarranteethestructuralcapacityofthesys- componentmustnotaffecttheoutcomeofthenext
tembeyondtheexpectedloads. IndeedtheFactors trial.
of Safety are related to reliability. Design is then • Constant rate of failure. The rate of failure from
qualified and the Hardware Manufacturing tested onetrialtothenextmustremainconstant.
foracceptance. Fatigueandfractureanalysismay • SpaceEnvironment
beappliedtoidentifyresistanceversuslifetimeof • Ambienttemperature(−30◦Cto40◦C)
themission(inthiscase5yearsinsteadof3years • Junctiontemperature125◦Cto150◦C
arerequired). • DutyCycle∼20%
• Cycling Rate = 5840 ∼ (16 days × 30 days × 1
• Nonelectronicopticalelements,likelensesandfil-
year)
ters, shall be demonstrated to meet the required
• Electricalstress≤0.5
functional performance by a proper dimensioning
at End of Life conditions and the application of
life Safety Factors, so that their degradation does 4. PartialfailureevaluationofJEM-EUSOPMTs
not degrade the mission during the required mis-
4.1. QuantumEfficiencyDegradation
sionlapseoftime. Underastructuralpointofview
they shall be treated with the same philosophy of Definitely,thelifetimeofthePMTislinearlydepen-
structuralitems. dentoftheworkingconditionswhenusingitaswellas
for the charged applied on it. The following equations
• Passive thermal control, like Multi Layer Insula-
canexplainclearlythissituation
tion (MLI) and thermal washers, shall be demon-
stratedtomeettherequiredthermalperformances QE(t)= QE e−t/τ (1)
0
byaproperdimensioningatEndofLifeconditions
and the application of Life Safety Factors, so that where QE0 is the quantum efficiency of a new unused
theirdegradationdoesnotdegradethemissiondur- PMT;τisthelifetimeofthecathodePMTunderwork-
ingtherequiredmissionlapseoftime. ing conditions. As the PMTs lifetime is depending of
theuse,τisnotagoodparametertocharacterizePMTs
• Hardness and connectors are controlled by using byitsdependenceontheworkingconditions.
qualified materials and by applying the required
SafetyFactorsinthedesignphase. Manufacturing QE(q)= QE e−q/τq (2)
0
byqualifiedproviders,integrationbyverifiedpro-
where τ is the lifetime of the cathode PMT under
cedure, verification campaign shall warrantee the q
charges applied on it. In many cases, this value is
required level of reliability. These values will be
roughly2-3C/cm2.
assessedinafuturepaper.
However, in case of evaluating the time dependent
• Software (if any) is controlled by on ground quantumefficiency,thenextrelationisassumedbecause
SW Quality Assurance according to the identified ofthelinearityofbothequations:
4
functioning.
t q
= (3)
τ τq Q(t)= Q e−t/τ =19.975% (6)
EO
Therefore, in order to perform the analysis of the In other words, a loss of 0.15% of the quantum effi-
Q(q), the q is necessary to be evaluated, where q, is
ciencyin5yearsperPMTasseeninFigure4wherethe
thechargecollectedatthecathode,expressedinC/cm2
first5yearsofdegradationareexpressedbytheredline
whichisdeterminedasfollows:
overtheblueline. Accordingtothisstudy,thequantum
e−·φ ·t·E ·Q efficiencydegradationisabsolutelynegligible. Itcanbe
q= γ γ EO (4) alsosaidthatitisrelatedtothelowlevelofillumination
Ei·S
PMT thePMTsaregoingtobeexposedtoduringthetimeof
Since q is the relation between the charge collected themission.
per unit area, some considerations have been taken
into account in order to express it including the intrin-
sic/physical parameters of the material. To express the
Charge, into couloumbs, for instance it is necessary to
considertheeffectofthegainasthequalityofthema-
terial to amplify the photo-current received, and this
photocurrent is basically the product of the electron’s
chargebythefluxofphotonsreceivedaswellasbythe
product of the initial quantum efficiency of the mate-
rial,whichistheamountofelectronsproducedperpho-
tonperceived. Thedivisionoftheequationisrelatedto
theunitareanecessarytoexpressthechargecollected.
Forinstance,itisnecessarytomultiplytheunitareaby
theIonizationEnergybecauseitisbasicallytheenergy Figure2:JEM-EUSOPMTsQuantumEfficiencydegra-
necesarytoremoveanelectronperunitarea. dationexpressedatdifferenttimeperiods. Accordingto
Where the values considered to calculate the charge thisresults,theQEdegradationisnegligible
collectedareprovidedintable5
ThereforeweconsiderthefailurerateofthePMTdue
Table5: JEM-EUSOPMTsQEparameters to the degradation of the quantum efficiency as the in-
verseofthelifetime,asλ =2.85×10−2 Failures/106
QE
h. Hence,theMTTFis35×106h.
Parameter Value
Since the Quantum efficiency affects some perfor-
InitialQuantumEfficiency(Q ) 20%
EO mancecharacteristicsofthePMTasSensitivityandDe-
Electron’sCharge(e−) 1.6×10−19C
tectivity,theiraffectionandcontributionhasbeenevalu-
PhotonFlux(φ ) 1.2×109ph/s
γ atedinthefollowingsubsections. However,sincetheir
Time(t) 5Years
failure rate is related to the Quantum efficiency, their
PhotonsEnergy(E ) 4.14eV
γ value has not been calculated but considered anyway
Chargecollection(τ ) 2-3C/cm2
q as a contribution to the total failure rate of the QE ex-
IonizationEnergy(Ei) 1.9eV
pressed above. Anyway, its important to higlight that
PhotocathodeActiveSurface(S ) 5.29cm2
PMT SensitivityadDetectivityareexpressionsoftheQEaf-
fection, their study it is necessary to understand the
meaningofthedegradationoftheQE.
Anyway, consideringequation3, thelifetimecanbe
calculatedasfollows: 4.2. PMTsDetectivityDegradation
NoiseEquivalentPower(NEP)isthequantityofinci-
τ ·E ·S
τ= q i PMT (5) dentlightequaltotheintrinsicnoiselevelofadetector.
e−φ ·E ·Q
γ γ EO Inotherwords,thisisthequantityofincidentlightwhen
Finally, according to equation 5 , the lifetime is thesignal-to-noiseratio(S/N)is1[18].
1.264× 1011s. Therefore, the quantum efficiency over TheinversevalueofNEPisthedetectivity(detection
time is as Equation 6 reflects, considering t as 5 year capability). Thedetectivityisameasureoftheleastde-
5
tectable radiant power or detector signal to noise ratio. shows the linearity between the QE and detectivity. In
AhigherDindicatesabilitytodetectlowerlevelsofra- theend,thereductionofthedetectivityisaslowasthe
diantpower[19]. QE. However its reduction is not considerable enough
Therefore,theNEPiscalculatedasfollows: duringtheperiodofthemissionsince0.15%oflossis
acceptableconsideringthat10%ofthresholdlossisac-
hc (cid:32)2I (cid:33)1/2 ceptedbytheJEM-EUSOsciencecomitee.
NEP= D =1.48×10−17W (7)
ηλ q
Wherethevaluesconsideredtocalculatethedarkcur-
rentareprovidedintable6
Table6: JEM-EUSOPMTsNEPcharacteristics
Parameter Value
Planckconstant(h) 6.62×10−34J·s
Speedoflight(c) 3×108ms−1
DarkCurrent(I ) 1.63×10−18A
D
Elementarychargeoftheelectron(q) 1.62×10−19C
Figure3:JEM-EUSOPMTsdetectivitydegradationex-
pressedfordifferenttimeperiods
Hence,ηisexpressedasatimefunctioniscalculated
according to equation 6 and dark current I is deter-
D
minedasfollows: 4.3. PMTsSensitivityDegradation
(cid:18)−φ (cid:19) The responsivity expresses how much electrical sig-
ID =aAT2exp kT0 =1.63×10−18A (8) nal is generated when a given amount of optical flux
(power)isincidentonadetector,anditcanbealsocon-
The values considered to calculate the dark current
sider as the sensitivity of the detector. The electrical
and finally obtain the NEP and therfore the detectivity
quantitycanbecurrentorvoltage[20].
areprovidedintable7
ηq
R =S = (9)
Table7: JEM-EUSOPMTsI characteristics esponsivity ensitivity hv
D
Hence,ηisexpressedasatimefunctioniscalculated
accordingtoequation6,However,thevaluesconsidered
Parameter Value
tocalculatethesensitivityareprovidedintable8
Richardson’sconstant(a) 1.2×106A/(m2K2)
Absolutetemperature(T)inK 300K Table8: JEM-EUSOPMTssensitivitycharacteristics
Workfunction(φ) 1.52eV
Boltzmann’sconstant(K) 1.38×10−23J/K
CathodeArea(A) 5.29×10−4cm2 Parameter Value
QuantumEfficiency(η) 20%
Elementarychargeoftheelectron(q) 1.62×10−19C
Planckconstant(h) 6.62×10−34J·s
PreviouslywementionedthatthereductionofaPMT
quantumefficiencyisaparameterthatdirectlyaffectsits Opticalfrequency(v) 1×1015hz
performance. Hencethiscanbeseennotonlyasaper-
centage of the ratio of photons entering the number of
subsequentlyemittedelectron. Thequantumefficiency As for detectivity, sensitivity is a parameter related
degradation can be also express in terms of loss of de- to the quantum efficiency. Its behavior allows to ob-
tectivity of the detector, ie as soon as it has reduced serve the performance of the PMTs. Its understanding
the ability of photons that can be detected throughout also contributes to calibrate the instrument in order to
the lifespan and therefore the number of photons pro- guaranteethesuccessofthemission. However,thesen-
duced. ThiseffectisshownbyFigure3, whichclearly sitivityshownbythisstudy,iswithintheparametersof
6
the manufacturer, with a value of about 70.49 µA/lm
overthefirst5yearsandareductionofupto0.1%ofits
λ =π (λ π π +λ π π +
valueduringthesameperiodoftime. P G OB DCO TO EB DCN RHT
(10)
λ π π )+λ π +λ
TCB CR DT SJB SJDT EOS
ThekeyfactorinfailurerateevaluationforPMTac-
cording to 217 Plus is: Failure rate multiplier, solder
joint delta temperature (π ), this value reflects that
SJDT
themostimportantaspecttoconsiderwhenassembling
our electronics system in case of PMT is soldering, a
well known critical parameter to be considered, which
isnowconfirmedandreflectedbythisevaluation.
Table9: PMTConditionValuesaccordingto217Plus
Figure4:JEM-EUSOPMTsSensitivitydegradationex-
pressedfordifferenttimeperiods Condition Value
IntegratedCircuit,PlasticEncapsulated PMT
YearofManufacture 2010
4.4. PMTsperformancedegradationduetoradiation Growthconstant(β) 0.293
Accordingto[21],theamountofPMTsthatwillfail DutyCycle 20%
duringtheJEM-EUSOisabout16includingalltypeof CyclingRate 5840
ActivationEnergyOperating(Eaop) 0.8
radiationsources. Therefore,thefailurerateintermsof
radiationisλ =7.3×10−2Failures/1×106h,hence, ActivationEnergynonoperating(Eanonop) 0.3
RAD Ambienttemperature,operatingin◦C(TAO) 26◦C
theMTTFofabout1.37×107. Thisvalueswillbeex-
Ambienttemperature,nonoperatingin◦C(TAE) 15◦C
plained in detail in the nexts subsections when whole
DutyCycleOperating(DC1op) 0.72
sourcesoffailureareconsideredinordertostablishthe
DutyCyclenonOperating(DC1nonop) 0.28
totalFailureRateoftheJEM-EUSOPMTs. Defaulttemperaturerise(TR )in◦C 25◦C
default
DeltaTemperature(DT )in◦C 26.5◦C
1
CyclingRate(CR ) 482.46
5. Catastrophic failure evaluation of JEM-EUSO 1
PMTsusing217PlusStandard
Reliability analysis using standard 217 Plus is quite
useful since It is basically the latest version of MIL-
HDBK-217-F. Also, the 217 Plus has optional data in-
cluded in order to enhance the predicted failure rate Table 10: PMT Failure Rate Calculations according to
by adding more detailed pertaining to environmental 217Plus
stresses, operating profile factors and process grades.
It also contains default values for the environmental
FailureRateMultiplier(FRM) Symbol Result
stresses and environmental profile as well as many
ReliabilityGrowthFRM πG 6.867×10−3
moreandnewcomponentsmissinginMIL-HDBK-217- Basefailurerate,Operating λOB 8×10−6
F. The failure rate (λp) for plastic encapsulated (non- FRMforDutyCycleOperating πDCO 0.27
hermetic) integrated circuit applicable for the PMT is FRMforTemperatureOperating πTO 12.18
Basefailurerate,Environmental λEB 1.997×10−3
givenbyequation10,andthetheconditionsandvalues FRM,DutyCycle,Nonoperating πDCN 1.11
accordingtothe217PlusstandardareshowninTable9 FRMforTemperatureenvironment πRHT 0
. Thesevaluesallowustoestimatethebasefailurerate Basefailurerate,TempCycling λTCB 8.9×10−5
FRM,CyclingRate πCR 12.10
andfailureratemultipliersforanyenvironmental,with FRM,DeltaTemperature πDT 3.405
operationalaswellasnonoperationalconditionswhich Basefailurerate,SolderJoint λSJB 4.850×10−3
the component is exposed to. The calculations results FFaRiMlur,eSroaltdeeErlJeocitnrticDalelOtavTeresmtrpess πλSEJODST 1.5602.6×3510−3
from the failure rate evaluation made to The PMT are FailureRate=2.334×10−2F/106h
showninTable10.
7
6. EstimationofPMTsreliabilityandDiscussions lostof0.55%oftheJEM-EUSOtelescopefocalsurface
in 5 years of operation period according to 217 Plus,
Reliability has many connotations. In general, it radiationfailuresourcesandQuantumefficiencydegra-
referstoanitem’sabilitytosuccessfullyperformanin- dation. WecanuseMTTFratingmoreaccurately,how-
tendedfunctionduringaSpacemission. Thelongerthe ever, in JEM-EUSO focal surface we have 4,932 PMT
itemperformsitsintendedfunction,themorereliableit operating continuously, so, we can expect 27 PMTs to
is. failinfiveoperationyearsaccordingtothisstudy.
Some systems, such as spacecrafts, cannot be re-
pairedafteramajorfailure,whichisobviouslythecase
ofJEM-EUSOPMTs.Inothercases,eventhoughmain-
tenance tasks can be performed offline, they cannot be
performed during a mission. For all of these types of
non-repairablesystems,thetimetosystemfailureisan
importantreliabilitycharacteristic. Theexpectedvalue
isknownasmeantimetofailure(MTTF).[22].
Table11. PMTFailureRatesvalues
(cid:97)RE(cid:97)xelpira(cid:97)ebsisl(cid:97)iiotyn(cid:97)(cid:97)(cid:97)St(cid:97)ud(cid:97)y Radiation QuantumEfficiency 217Plus
FailureRate 7.3×10−2h 2.85×10−2h 2.334×10−2h
Figure5: JEM-EUSOPMTsreliabilityvstimeinclud-
ingmultiplefailuresources
The failure rates calculated before yield the MTTF
Values are listed in Table 11. A MTTF of 8 million
hours (8×106 hours) according to the addition of ev- 7. ApproximatenumberofPMTsfailures
ery PMT failure source. Certainly they do not mean
we can expect an individual device to operate for 913 InordertohaveanideaofhowtheJEM-EUSOPMTs
yearsbeforefailing. MTTFisastatisticalmeasure,and wouldfailduringthetimeofthemission,itisnecessary
assuch,itcannotpredictanythingforasingleunit. As- to determine how this specific failures are going to be
suming that during the useful operating life period the distributed. Thebestwayofdoingthis,istoapplypois-
PMT have constant failure rates, and part failure rates sondistribution.
(λ ) follow an poissonian distribution. In this case, ThePoissonequationforpredictingtheprobabilityof
parts
theMTTFoftheproductcanbecalculatedas: aspecificnumberoffailures(r)intime(t)isasfollows
[23]:
1
MTTF = (cid:80)λ (11) (λt)re−λt
PMT P(r)= (14)
and the probability that the product will work for r!
sometimetwithoutfailureisgivenby: where:
• r=numberoffailuresintime(t)
P(t)=e−MTtTF (12) • λ=failurerateperhour
• t=timeexpressedinhours
Thus,incaseofourJEM-EUSOPMTwithanMTTF
• P(t) = probability of getting specific r failures in
of8·106hrs(Allfailuresourcesincluded)andamission
timet
durationof5years(43,800hrs)ofcontinuousoperation,
Assuming that the population of the PMT’s JEM-
EUSOtelescopefocalsurfacewillusehasafailurerate
Ptc = e−84×3810006 =99,45% (13) (peryear)of5.4failuresorroughly27PMTsaregoing
tofailduringthemissionduetothequantumefficiency
degradation and it is expected to operate during 43800
P (t) shows that the PMT functioning at the end of hours, it is necessary to estimate the especific number
tc
5 years operation period will be operated with 99.45% of failures during mission time. The values from the
of reliability for five years without a failure. Figure 5 estimation were calculated using equation 14, and the
illustrates this situation. In other words, an estimated resultsareshowninFigure6
8
[2] JEM-EUSOwebpagehttp://jemeuso.riken.jp/en/index.html
[3] Greisen, K,Phys.Lett.16, 1648; Zatespin, G.T. And
Kuz’min,V.A.JETPPhys.Lett.4,78.(1966)
[4] Hector Prieto, Katsuhiko Tsuno, Marco Casolino,Luis
del Peral, Toshikazu Ebisuzaki, J.A. Morales de los
R´ıos, G.Sa´ez-Cano and M.D. Rodr´ıguez Fr´ıas, for
the JEM-EUSO Collaboration.”FPGA Reliability Anal-
ysis for the JEM-EUSO Space Mission”.ISBN: 84-
616-2226-X.http://www.ramsinscience.es/posters/Prieto-
ReliabilityWorkInJEMEUSO.pdf.(2012)
[5] H.Prieto, Katsuhiko Tsuno, Marco Casolino, Luis del Peral,
Toshikazu Ebisuzaki, J.A. Morales de los R´ıos, G.Sa´ez-Cano
andM.D.Rodr´ıguezFr´ıas,”ReliabilityworkintheJEM-EUSO
Spacemission”.”39thCOSPARScientificAssembly”.Mysore,
Figure6: ApproximatenumberofPMT’sFailing
India.July(2012).
[6] H.Prieto-Alfonso, K. Tsuno,L. del Peral, M. Casolino, T.
Ebisuzaki, J.A. Morales de los R´ıos, G.Sa´ez-Cano and M.D.
8. Conclusions Rodr´ıguezFr´ıasfortheJEM-EUSOcollaboration.”Multi-anode
PhotomultiplierTubeReliabilityanalysisandRadiationHard-
Results from this reliability study are as expected. nessAssurancefortheJEM-EUSOSpaceMission”.”33rdIn-
ThelevelsofdamagesufferedbythePMTswhichcom- ternationalCosmicRaysConference(ICRC)”.RiodeJaneiro,
Brazil.July(2013).
prisethefocalsurfaceofJEM-EUSOSpaceTelescope, [7] Hamamatsu, Photomultiplier tubes-Basics and applica-
areacceptable. Theresultsshowaswellthatthegreat- tions,Chapter1-5,ThirdEdition,2006
est contribution to the failure is due to radiation SET, [8] Hamamatsu, Elemental Technology.
http://www.hamamatsu.com/jp/en/
as predicted by [21]. The guaranteed performance of
technology/innovation/photocathode/index.html
this equipment is a 99.45%, an accepted value of re- [9] BooNEExperimentwebpage.www.boone.fnal.gov.
liability thus fulfilling the objectives and technological [10] JosephR.Lakowicz.Topicsinfluorescencespectroscopy.Vol1:
challenges of JEM-EUSO. It should be noted that the Techniques,Chapter2,page149.
[11] D.Motta, S.Scho¨nert.Opticalpropertiesofbialkaliphotocath-
reliability values of the Standard 217Plus, despite be-
odes. Nuclear instruments & methods in physics research.
ing a standard improved, an updated version of MIL- September2004.
HDBK-217Plusdoesnothavesectionsthatincludethe [12] H.H.Tan.AStatisticalmodelofthephotomultipliergainprocess
with applications to optical pulse detection.Page 55-56, TDA
analysisofradiationofspaceelectronicequipment.The
Progressreport42-68,February1982.
recommendation from this study is the inclusion of all
[13] M.P.Groover,FundamentalsofModernManufacturingSecond
real failure effects may face an electronic, mechanical, Edition,2002JohnWiley&Sons,Inc.
opticalspaceequipment. [14] Hamamatsu. Photomultiplier tube R11265-113-M64 MOD 2,
HAMAMATSUforJEM-EUSOcollaboration,November2011.
[15] J.P.Boutotetal.Recenttrendsinphotomultipliers,pag270-297,
Acknowledgments 1983
[16] MIL-HDBK-217-F, notice 2,Military Handbook: Reliability
Predictionofelectronicequipment.2December1991.
TheJEM-EUSOSpaceMissionisfunderinSpainun-
[17] Handbook of 217 Plus, Reliability prediction Models, United
der projects AYA2009-06037-E/AYA, AYA-ESP2010-
StatesofAmerica,DepartmentofDefense,26May2006.
19082 and the coordinated projects AYA-ESP2011- [18] Hamamatsu.TechnicalInformationSD-12.Characteristicsand
29489-C03 and AYA-ESP2012-39115-C03. We ac- useofinfrareddetectors.2004.
knowledge CAM ASTROMADRID S2009/ESP-1496 [19] PerkinElmerOptoelectronics.Photoconductivecellsandanalog
optooscilators(Vactrols).2001.
and MICINN MULTIDARK CSD2009-00064 Projects [20] JosephA.Shaw.RemoteSensingSystems.MontanaStateUni-
fortheirfinantialsupporttotheSpanishConsortiumin- versity.2012
volvedinJEM-EUSOaswell. H.Prieto-Alfonsowants [21] H.Prieto-Alfonsoetal.,RadiationHardnessAssuranceforthe
JEM-EUSOSpaceMission.2013
toacknowledgethesupportfromInternationalProgram
[22] RelexSoftwareCorporation.ReliabilityArticles,MTTFVersus
Associates (IPAs),which granted one year stay at the MTBF.2009.
RIKENinstitute,Wako-shi,Japan. [23] MohammadModarres,ReliabilityEngineeringandRiskAnaly-
sis, APracticalGuide,Chapter1.Page15-21SecondEdition,
2010.
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9