Thermal stress & cooling of J-Parc neutrino target S . UedaJHF target monitor R&D group Introductionneutrino targetrequirement for targetThermal stressCoolingheat transfer coefficientcooling testsummary

IntroductionBeam 50[GeV] proton,0.75[MW] 31014 [protons / spill] , 5[sec/spill] 3.3[sec](between spills) , 8[bunch/spill]Material graphite or C/C composite Because of; high melting point(~3700) thermal resistanceCooling water coolingShape cylindrical 900mm long(2int) & 12~15mm radius

beam

900mmCooling pipe from one-side

hornTarget

Requirements for targetMore pionThermal shock resistancePossibility to coolThe effects of target radiusLarger radius pion yield decreasesSmaller radiusTemperature increases more thermal stresssurface area decreases difficult to cool The optimization is neededPion yield1.2

1.0

0.8

0.6

0.4

0.2

0

2.5 5 7.5 10 12.5 15 Target Size(mm) [K]Temperature rise at center

Energy deposit

heat distribution in 1pulse (15mm radius) 20%difference cal. w/ MARS

[J/g]r=13mmr=15mm

Thermal stressStress estimation

quasi-static stress (non-uniform heating)

dynamical stress(rapid heating) Material fatigue

after repeating stress(106 times), tensile strength become 0.8 (IG-110). E :Youngs modulus:Poisson ratio:linear expansion coeff.T0:Temperature at center

Material properties Temperature dependence specific heat tensile strength

max temp. rise(G347) r=13mm 234.2[K] almost the same r=15mm 200.6[K] [J/g]

Material properties thermal expansion coeff.(G347) Youngs modulus(G347)

temperature dependence exists these effects should be taken into account. 10-6[1/K][Gpa]

Safety factor Definition safety factor = ( tensile strength / eq )

Result (include fatiguematerial properties) Type tensileeqeq strength[Mpa]r=13[MPa] r=15[MPa] Toyo Tanso IG-4337.229.88.92(3.3)7.48 (4.0)Tokai Carbon G34731.425.16.43(3.9)5.55 (4.5) () is safety factor

These graphite have sufficient safety factor

CoolingRequirement cool down 60kJ in 3.3 sec keep Tsurf under 100

is a key parameter! Q = S(Tsurf - Twater) = S Tsurf = Twater + T Twater T

depends cooling test need to be measuredQ : heat transfer[kW]S : surface area [m2]Tsurf : temp. at surface[K]Twater : temp. of water [K] heat transfer coeff. [kW/m2/K]targetwaterTwaterTsurfQ

Analytical estimation of TT(t)

depends on initial condition Trise(r) heat transfer coeff

=6Temp. rise at 5sec[K]Averaged in z direction

Water temperatureTwater(r)(at Z=900mm) Tsurf = Twater + T to estimate maximum Tsurf , max of Twater is necessary Twater has max at Z=900mm

heat transferT Twater takes maximum value at 0.8sec Water temp.=620[l/min]beam in[]targetwaterZ=0mmZ=900mmbeamQ

& flow rateCalculation result Tsurf T Twater more water flow rate water temp rise : smaller acceptable : lower Relation between flow rate satisfy Tsurf more than6.5[kW/m2/K]20[l/min]->more than5.8[kW/m2/K]Is needed[]allowable

Cooling testPurpose measure the heat transfer coeff.How heat up the graphite with DC current , and cool by flowing water Measurement temperatures,water flow rate ,current

: heat transfer coeff. [kW/m2/K] Q :heat transfer [W] Tsurf :surface temperature [K] Twater :water temperature [K] S :surface area [m2]

Setup of cooling test

Current ~ 1.2kA(20kW) Water flow 8.9 , 12[l/min]Target radius 15mm

Current feeds DC currentthermocouples900mmtargetwater

Cooling test results increase with surface temperature & water flow rate

compared with the condition

extrapolate with theoretical formula [][kW/m2K]6.5[kW/m2/K]at 15[l/min]

Comparison w/ theoretical formula Theoretical formula

Re(T) :Reynolds numberPr(T):Prandtl number(T)Thermal conductivity equivalent diameterResult Data and calculation seems to agree

at 20 [l/min] , expected to satisfies the condition !

Summary Thermal stressmax stress safety factor r=15mm IG-43 7.48[MPa]4.0 G347 5.55[MPa]4.5 cooling calc. relations between flow rater=15mm 15[l/min] ,6.5[kW/m2/K] 20[l/min] ,5.8[kW/m2/K] cooling test possible to cool at more than 20[l/min]

Schedule Next cooling test with more flow rate

We plan to test with 20 [l/min] this month

reference1off-axis-beam high intensity narrow energy bandHornsSuper-K.TargetDecay Pipeq

reference2

reference

referenceT(r) time developmentWhen the target surface is cooled (at r=R)with , temperature difference between Tsurf and Twater atr,time=) : is,

:heat conductivitya:thermal diffusivity

referenceT[K]T[K]

reference6

rQ(r) c q : R

data

POWER :4.2kW~19.4kW flow rate :8.9 ,12[l/min] each data points are averaged

4.24.212.415.219.414.912.2

JPARC neutrino beamlineProton beam kinetic energy# of protons / pulseBeam powerBunch structureBunch length (full width)Bunch spacingSpill widthCycle50GeV(40GeV@T=0)3.3x1014750kW8 bunches58ns598ns~5ms3.53secPrimary Proton beam lineExtraction pointTargetTarget stationmuon monitorbeam dumpNear neutrino detectorDecay volume

J-PARC e disappearanceCPV in lepton sector++decay pipeproton

J-PARCK2KEnergy (GeV)5012Int. (1012ppp)3306beam(sec)3.32.2Power (kW)7505.2

[Gpa]

Water flow 1

900mmtargetwater

Water flow 2

s

900mmtargetwater

S

91cm4cm5cm4.7cm

the contents are