Radiation Studies forMu2e Experiment

V. PronskikhFermilab

August 21, 2012

2

Basics of Mu2e experiment muon converts to electron in the presence of a nucleus, coherent conversion: 1) neutrinos are not emitted 2) nucleus remains intact 3) signature – 105 MeV monoenergetic electron

muon converts to electron in the presence of a nucleus, coherent conversion: 1) neutrinos are not emitted 2) nucleus remains intact 3) signature – 105 MeV monoenergetic electron

Explanation: SUSY, second Higgs doublet, large extra dimensions, leptoquarks, etc.

Best limit : (90% C.L.) from SINDRUM II-136×10 Search for Charged Lepton Flavor Violation, rate in SM -51<10

Beam power 8 kW, two batches of 4E12 protons from the booster every 1.33 secondData-taking 3 years, apparatus lifetime ~5 years at 2×107 s/yr

3

ProductionSolenoid Transport

Solenoid

DetectorSolenoid

ProductionTarget Collimators

StoppingTarget Tracker

Calorimeter

(not shown: Cosmic Ray Veto, Proton Dump, Muon Dump, Proton/Neutron absorbers,Extinction Monitor, Stopping Monitor)

Mu2e apparatus

protons

2.5T~5T

2.0T

1.0T

e-

m-, p-

MARS15 model developed

4

Main Issues Object: • Primarily, Mu2e apparatus with 8-GeV proton beam, also

applicable to COMET, Muon Collider, Project X, Neutrino Factory and other superconducting setups in high radiation fields

Main goal:• Maximize useful particle production, minimize background

particle yieldsIssues:• Quench: power density and dynamic heat load of

superconducting (SC) coils. • Integrity and lifetime of critical components: integrated dose in

organic materials, i.e. epoxy, insulator. • Radiation damage to superconducting and stabilizing materials:

atomic displacements (DPA), integrated particle flux • Damage to electronics (single event upsets (SEU), lifetime) • Safety aspects: shielding, nuclide production, residual dose, etc.

5

Requirements to Mu2e Heat and Radiation Shield

• Absorber (heat and radiation

shield) is intended to prevent

radiation damage to the magnet

coil material and ensure quench

protection and acceptable heat

loads for the lifetime of the

experiment

– Total dynamic heat load on the coils – Peak power density in the coils– Peak radiation dose to the insulation and epoxy – Displacements Per Atom (DPA) to describe how radiation affects

the electrical conductivity of metals in the superconducting cable

6

Displacement per atom (DPA)• DPA (displacement per atom). Radiation damage in metals,

displacement of atoms from their equilibrium positions in a crystalline lattice due to radiation with formation of interstitial atoms and vacancies in the lattice.

• A primary knock-on (PKA) atom is formed in elastic particle-nucleus collisions, generates a cascade of atomic displacements.

• A PKA displaces neighboring atoms, this results in an atomic displacement cascade. Point defects are formed as well as defect clusters of vacancies and interstitial atoms (time scale=ps).

• Residual Resistivity Ratio degradation (RRR, ratio of the electric resistance of a conductor at room temperature to that at the liquid He one), the loss of superconducting properties due to change of conditions of electron transport in metals.

7

Mu2e LimitsQuantity DPA, 10-5 Power

density, µW/g

Absorbed dose, MGy

Dynamic heat load, W

Specs 4-6 30 7 100

• DPA limit: RRR degrades from ~1000 to 100. After this RRR reduction we must warm-up and anneal Al (once a year).

• Definite cooling requirements lead to limits on peak power density calculated based on the heat map

• Dynamic heat load limit depends on cooling system

8

Requirements: Peak power density

T plot for T0 =4.6K (liquid He temp)Tc = 6.5K; (supercond+field)Tpeak = Tc-1.5K = 5.0K.Peak coil temperature starts to violate allowable value based on 1.5 K thermal margin and 5 T field after 30 µW/g

MARS15

Power density, µW/gVolume temperature, K

17.9 µW/g4.8 K

pp

9

Requirements: Absorbed dose to organic materials

7 MGy before 10% degradationof ultimate tensile strength (shear modulus).

Mu2e apparatus lifetime is 5 years

Current LHC limit 25-50 MGy overthe lifetime

also Radiation Hard Coils, A. Zeller et al, 2003, http://supercon.lbl.gov/WAAM

Ultimate tensile strength degradation

UTS/UTS0

e-, γ, n

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Requirements: RRR vs DPARRR(DPA) =

1.0E-07 1.0E-06 1.0E-05 1.0E-04 1.0E-030

100

200

300

400

500

600

700

800

900

1,000lower limit upper limit

DPA

RRR

Broeders, Konobeyev, 2004

Range 4-6E-5

NRT model of DPA – from KEK measurement

; 0.357 – 0.535scales NRT to experiment

DPA Modeling Status• Codes using NRT model (MARS15, FLUKA,

PHITS) agree quite well (10-20%).• Industry standard NRT and state-of-the-art

models (BCA-MD) differ by a factor of 2 to 3 in some cases

• More experiments at high-energy neutron spectrum are necessary to benchmark models

• More data on non-annealable (irreversible, transmuted DPA) are important for experiments with spallation targets (Mu2e, COMET, Project X etc.)

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12

Experiments at JINR, DubnaDecember 2011

d beam

The samples were placed at the depth of 10 cm insidethe target

“On proposal to measure irreversible DPA”,Mu2e-doc-1996-v1, October 2011

d beam

0.8-2 AGeV deuterons, total fluence ~ 4E13 d

Secondary neutron fluence ~ 1-3E7 n/cm^2/s

Cryogenic measurements are needed

Synergy with ADS program at JINR

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Secondary neutron spectra of Mu2e PS coils, KVINTA and GAMMA3 at 3 GeV, a

Reactor

Mu2e coilsKVINTA d at 3 GeV

GAMMA3 d at 3 GeV

30 MeVspallation

Reactor spectrumarb. units

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MARS15 DPA model development

• Based on ENDF/B-VII, calculated for 393 nuclides• NRT (industry standard) corrected for experimental ηη – ratio of number of single interstitial atom vacancy pairs (Frenkelpairs) produced in a material to the number of defects calculated usingNRT model

0 50 100 150 200

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Al

NiCu PdAg Pt

Au

PbK

V

Fe

Nb

Mo

Ta

W

Mg

Ti

CoZn

Zr

Cd

Gd

ReGa

Sn

experimental data

defe

ct p

rodu

ctio

n ef

ficie

ncy,

A

10-5 10-3 10-1 101 103 105 107 10910-2

10-1

100

101

102

103

104

d (

NR

T),

b

En, eV

27Al

65Cu

Al

Broeders, Konobeyev, 2004

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DPA for 8-kW beam power baseline

3.2*10-5 yr^-1

Limit 4-6*10-5

16

3.1*109 cm^-2s^-1

3.1x1021 n/m2 over lifetime

Neutron flux >100 keV

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Power density, mW/g

18 µW/gLimit ~30 µW/g

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Limits and design valuesQuantity MARS15 LimitsPeak Total Neutron flux in coils, n/cm2/s 8.3*109

Peak Neutron flux > 100 keV in coils, n/cm2/s 3.1*109

Peak Power density, µW/g 18 30

Peak DPA 3.2*10-5/yr 4-6*10-5

Peak absorbed dose over the lifetime, MGy 1.65 7

Dynamic heat load, W 20 100

• Radiation damage is a key issue for experiments at the Intensity Frontier

• Models are developed and experiments are proposed to understand and address the issue

• Current Mu2e design solutions are safe during the lifetime of the experiment but more work is needed for fine tuning, value engineering and upgrade (Project X)

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Alternative HRS designsW, 5cm

Fe (Cu, WC), 20cm

BCH2, 12 cm

Fe (Cu, Cd), 3cm

Tungsten, WC, U-238 5 multilayer cases

Tungsten/copperTungsten/copper Cases #1-#10

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1

2

3

4

5

6

7

8

9

10

3E-05 8E-051 2 3 4 5 6 7 8 9 10

1a 0.000019487

0.00004949800000

00001

0.00005504700000

00001

0.000047227

0.00004245100000

00001

0.000030902

0.000014404

0.00007759400000

00002

0.0000169

0.0000165

2a 0.00001423

0.00003536900000

00001

0.00004179600000

00001

0.000042179

0.00003894000000

00001

0.000018056

0.00000776750000

000001

0.000055521

0.000015784

2.14070000000001

E-05

3a 2.22900000000001

E-07

0.0000015873

0.0000009618

0.0000010201

0.00000059434

0.00000085351

2.41710000000001

E-07

0.0000011562

0.000000418

0.000000593

Peak DPA in Coils, yr^-1

WC

W

U-238

multi#1

multi#2

multi#3

multi#4

multi#5

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W Cu

coils

L(W)=235 cm, L(Cu1)=365 cm, L(Cu2)=560 cmE

p = 3 GeV @1 MW, C target: ~190 tonnes of W/130 tonnes of Cu

Mu2e @ PX preliminary design

22

Accidental mode

Peak values for 1 ms: 1E-14 DPA, 0.1 µJ/g

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Radiation quantities at TS1DPA=2.2E-6/yr, Power density= 0.5E-3 mW/g, Absorbed dose = 1.1E4 Gy/yr,

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1 2 3 4 5 6 7 8

Coils, W

Radiation quantities at TS3

Q(coll, up) = 20.5 W; Q(coll, down) = 0.41 W

Material: bobbins and flanges: (5083): Si 0.4%, Fe 0.4%, Cu 0.1%, Mn 0.4%, Mg 4%, Zn 0.25%,Ti 0.15%, Cr 0.05%, Al 94.25% coils: NbTi 8.27%, Cu 9.51%, G10 15.53%, Al 66.69%

Peak DPA 1E-6/yr, power density 5E-4 mW/g, absorbed dose 1E4 Gy/yr

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Residual activation of PS parts

1E-5 1E-4 1E-3 1E-2 1E-1 1E+0 1E+1 1E+2 1E+3 1E+4 1E+51E-05

1E-04

1E-03

1E-02

1E-01

1E+00

1E+01

1E+02

1E+03

1E+04Al stabilizer

Tirr=365 dTirr=30 d

Cooling time, days

Resi

dual

acti

vatio

n, m

Sv/h

r

1E-5 1E-4 1E-3 1E-2 1E-1 1E+0 1E+1 1E+2 1E+3 1E+4 1E+51E-05

1E-04

1E-03

1E-02

1E-01

1E+00

1E+01

1E+02

1E+03

1E+04HRS average

Tirr=365dTirr=30d

Cooling time, days

Resi

dual

acti

vatio

n, m

Sv/h

r

Also calculated for walls, beam dump, end cap, cryostat, many parts of the PS hall

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Residual dose from Mu2e target

Distance from the target, cm

Dose, Sv/hr (first method)

Dose, Sv/hr (second method)

30 12.98 12.9100 1.15 1.56

1-st method: MARS15 for contact dose,scaling factor for the target size, scaling factorfor distance, correction for finite target size2-nd method: residual nuclei from MARS15,Activities (DeTra), activities to doses usingspecific gamma-ray constants

• Excellent agreement betweenthe two methods.• High dose on contact but not very high at a distance• Typical shielding should be enough

• Precise methods for residual dose determination are developed.• First method should be moreprecise for extended targets.

On contact 20 kSv/hr

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Decay heat of target0 20 40 60 80 100 120 140 160 180 200

1E-03

1E-02

1E-01

1E+00

1E+01

1E+02

1E+03

1E+04

1E+05mb

Ta-1

72

Re-175

Ta-1

78

Re-180

Re-181

Ir-181

Ir-182

Ir-183

Ir-184

Ir-186

Pt-187

Au-188

Au-189

Pt-191

Au-193

Au-196

0.00E+00

5.00E-03

1.00E-02

1.50E-02

2.00E-02

2.50E-02

3.00E-02

3.50E-02

4.00E-02

fraction

0 50 100 150 200 250 300 350 4000

2

4

6

8

10

12

Time from start of irradiation, d

Dec

ay h

eat,

W

~1400 nuclides

Decay heat of the target was determined using MARS15+DeTra codes to be 11.3 W (1 year of irradiation), which is negligible compared to the dynamic heat load (~800 W)

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Beam absorber (dump)

~1E8 n/cm2/s

The proposed beam dump represents itself a Fe or Al box with dimensions 150x150x200 cm, surrounded by 100 cm thick concrete walls from each side, with the albedo trap towards the beam entrance window with sizes 250x250x100 cm, and the beam entrance window 150x150x100 cm.

29

Airflow activation

0 2 4 6 8 10 12 14 16 18 200E+00

5E+07

1E+08

2E+08 Hadron flux between dump pins, cm^2 s^-1

Top Bottom

Pin number

7.8 Ci – made in fins w/o transit time of airborne activity, (depends on vent rate and release point to outdoors distance,21 Ci – released in the target hall, Max 28.8 Ci a yearIf we assume 500 cfm of air to target hall and release near P-bar, annual activated air <21 Ci

30

Surface/ground water and air

Based on MARS15 simulations of the hadron flux and star density, using the Fermilab standard Concentration Model at the design intensity, the average concentration of radionuclides in the sump pump discharge will be 24 pCi/ml due to tritium and 2 pCi/ml due to sodium-22. This is 2% of the total surface water limit if the pumping is performed once a month (conservative scenario). Build-up of tritium and sodium-22 in ground water at 1.2E20 protons per year will be as low as 6.2E-8 % of the total limit over 3 years of operation. Air activation and flow estimations show that at 500 cfm, for the configuration without a pipe connecting the target region to the beam dump (average hadron flux over the whole hall volume is 5.5E6 cm-2s-1), the maximum annual activity released from the target hall is less than 29 Curies. ~ 7% of the Lab’s air release limit.

31

DS MARS15 model

(U)p (L)eft (R)ight D(own) (T)op (B)ottom

Stopping targetMonitor (HPGedetector)

32

CRV neutron flux

-6000 -5000 -4000 -3000 -2000 -1000 0 1000 20001E+06

1E+11

1E+16 n from all w/B-shield w/iron at upstream layers

X, mm (Mu2e)

neut

rons

/cm

^2/2

yea

rs

En >0.001 eVEn >100 keV

-6000 -5000 -4000 -3000 -2000 -1000 0 1000 20001E+06

1E+11

1E+16 n from all w/Li-shield w/BMCN conc at upstream layers

X, mm (Mu2e)

neut

rons

/cm

^2/2

yea

rs

02000

40006000

800010000

1200014000

1600018000

200001E+04

1E+09

1E+14n from all w/Li-shield w/BMCN conc

at left layers

Z, mm (Mu2e)

neut

rons

/cm

^2/2

yea

rs

02000

40006000

800010000

1200014000

1600018000

200001E+04

1E+09

1E+14n from all w/B-shield w/iron at left

layers

Z, mm (Mu2e)

neut

rons

/cm

^2/2

yea

rs

33

Stopping target monitor (Ge crystal) radiation damage

Neutron flux total:5600 n/cm2/s (MARS15)

Neutron flux:En>100 keV ~5400 n/cm2/s

Gamma flux:3.4E4 photons/cm2/s

• Degradation of detector resolution (asymmetry of gammapeaks) by atomic displacements (DPA) in Ge (peak 1E-8/yr).• For this HPGe, FWTM increase is ~25% in 5 days (study isneeded for a particular neutron spectrum and detector type)• Fermilab has an 241Am-Be neutron source (En=4.5 MeV)6E7 n/s -> 5500 n/cm2/s at 30 cm from source

from V.Borrel, NIM A 430 (1999) 348, n-type HPGe detectors

γ

34

To do• Heat and Radiation Shield optimization

– second groove for FNAL extinction monitor– material reduction in the upstream part– Considering alternative designs

• Hot Cell and PS hall shielding studies• Cask optimization• TS coils neutron internal shielding studies• CRV shielding optimization• Cryogenic measurements at Dubna (?)• Implementation and benchmark of a newDPA model in MARS15• Publishing results... … work in progress

35

Thank you !

36

Back up slides

37

Mu2e hall MARS15 model

Production Solenoid

Transport Solenoid

Detector Solenoid

V. Pronskikh, Radiation damage, NuFact’12, July 23-28, Williamsburg

38

Mu2e Requirements. RRR vs DPARRR(DPA) =

= 2.7E-6 Ω*cm

= (Mu2e requirement)

- DPA using NRT model withcorrection for defect productionefficiency

1.0E-07 1.0E-06 1.0E-05 1.0E-04 1.0E-030

100200300400500600700800900

1,000lower limit upper limit

DPA

RRR

– from KEK measurement(RRR degradation from 457 to 245)

; 0.357 – 0.535

Broeders, Konobeyev, 2004

Range 4-6E-5

V. Pronskikh, Radiation damage, NuFact’12, July 23-28, Williamsburg

39

DPA Model in MARS15 • Norgett, Robinson, Torrens (NRT) model for atomic displacements per

target atom (DPA) caused by primary knock-on atoms (PKA), created in elastic particle-nucleus collisions, with sequent cascades of atomic displacements (via modified Kinchin-Pease damage function n(T)), displacement energy Td (irregular function of atomic number) and displacement efficiency K(T), Ed – energy to nuclear collision.

Td in Si K(T)

M. Robinson (1970)

R. Stoller (2000), G. Smirnov

All products of elastic and inelastic nuclear interactions as well as Coulomb elastic scattering of transported charged particles (hadrons, electrons, muons and heavy ions) from 1 keV to 10 TeV. Coulomb scattering: Rutherford cross-section with Mott corrections and nuclear form factors for projectile and target. 10% agreement with FLUKA, PHITSV. Pronskikh, Radiation damage, NuFact’12, July 23-28, Williamsburg