1. Radiation Studies for Mu2e Experiment V. Pronskikh Fermilab 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 Search for Charged Lepton Flavor Violation, rate in SM Beam power 8 kW, two batches of 4E12 protons from the booster every 1.33 second Data-taking 3 years, apparatus lifetime ~5 years at 2×10 7 s/yr 2

3. Production Solenoid Transport Solenoid Detector Solenoid Production Target Collimators Stopping Target 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e     3 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 yields Issues: 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. 4

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 5

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. 6

7. Mu2e Limits QuantityDPA, 10 -5 Power density, µW/g Absorbed dose, MGy Dynamic heat load, W Specs4-6307100 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 7

8. Requirements: Peak power density T plot for T 0 =4.6K (liquid He temp) T c = 6.5K; (supercond+field) T peak = T c -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/g Volume temperature, K 17.9 µW/g 4.8 K p p 8

9. Requirements: Absorbed dose to organic materials 7 MGy before 10% degradation of ultimate tensile strength (shear modulus). Mu2e apparatus lifetime is 5 years Current LHC limit 25-50 MGy over the lifetime also Radiation Hard Coils, A. Zeller et al, 2003, http://supercon.lbl.gov/WAAM 9 Ultimate tensile strength degradation UTS/UTS0 e-, γ, n

10. Requirements: RRR vs DPA Broeders, Konobeyev, 2004 Range 4-6E-5 10

11. 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.) 11

12. Experiments at JINR, Dubna December 2011 12 d beam The samples were placed at the depth of 10 cm inside the 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

13. Secondary neutron spectra of Mu2e PS coils, KVINTA and GAMMA3 at 3 GeV, a Reactor Mu2e coils KVINTA d at 3 GeV GAMMA3 d at 3 GeV 30 MeV spallation Reactor spectrum arb. units 13

14. MARS15 DPA model development Based on ENDF/B-VII, calculated for 393 nuclides NRT (industry standard) corrected for experimental η η – ratio of number of single interstitial atom vacancy pairs (Frenkel pairs) produced in a material to the number of defects calculated using NRT model 14 Al Broeders, Konobeyev, 2004

15. DPA for 8-kW beam power baseline 3.2*10 -5 yr^-1 Limit 4-6*10 -5 15

16. 16 3.1*10 9 cm^-2s^-1 3.1x10 21 n/m 2 over lifetime Neutron flux >100 keV

17. Power density, mW/g 17 18 µW/g Limit ~30 µW/g

18. Limits and design values QuantityMARS15Limits Peak Total Neutron flux in coils, n/cm2/s 8.3*10 9 Peak Neutron flux > 100 keV in coils, n/cm2/s 3.1*10 9 Peak Power density, µW/g 1830 Peak DPA 3.2*10 -5 /yr4-6*10 -5 Peak absorbed dose over the lifetime, MGy 1.657 Dynamic heat load, W 20100 18 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)

19. Alternative HRS designs 19 W, 5cm Fe (Cu, WC), 20cm BCH2, 12 cm Fe (Cu, Cd), 3cm Tungsten, WC, U-238 5 multilayer cases Tungsten/copper Cases #1-#10

20. WC W U-238 multi#1 multi#2 multi#3 multi#4 multi#5 20

21. W Cu coils L(W)=235 cm, L(Cu1)=365 cm, L(Cu2)=560 cm E p = 3 GeV @1 MW, C target: ~190 tonnes of W/130 tonnes of Cu 21 Mu2e @ PX preliminary design

22. Accidental mode 22 Peak values for 1 ms: 1E-14 DPA, 0.1 µJ/g

23. Radiation quantities at TS1 DPA=2.2E-6/yr, Power density= 0.5E-3 mW/g, Absorbed dose = 1.1E4 Gy/yr, 23

24. Radiation quantities at TS3 24 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

25. Residual activation of PS parts 25 Also calculated for walls, beam dump, end cap, cryostat, many parts of the PS hall

26. Residual dose from Mu2e target 26 Distance from the target, cm Dose, Sv/hr (first method) Dose, Sv/hr (second method) 3012.9812.9 1001.151.56 1-st method: MARS15 for contact dose, scaling factor for the target size, scaling factor for distance, correction for finite target size 2-nd method: residual nuclei from MARS15, Activities (DeTra), activities to doses using specific gamma-ray constants Excellent agreement between the 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 more precise for extended targets. On contact 20 kSv/hr

27. Decay heat of target 27 ~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)

28. 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. 28

29. Airflow activation 29 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 year If 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 30 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 -2 s -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 31 Stopping target Monitor (HPGe detector)

32. CRV neutron flux 32

33. Stopping target monitor (Ge crystal) radiation damage 33 Neutron flux total: 5600 n/cm 2 /s (MARS15) Neutron flux: En>100 keV ~5400 n/cm2/s Gamma flux: 3.4E4 photons/cm2/s Degradation of detector resolution (asymmetry of gamma peaks) by atomic displacements (DPA) in Ge (peak 1E-8/yr). For this HPGe, FWTM increase is ~25% in 5 days (study is needed for a particular neutron spectrum and detector type) Fermilab has an 241Am-Be neutron source (En=4.5 MeV) 6E7 n/s -> 5500 n/cm 2 /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 new DPA model in MARS15 Publishing results... … work in progress 34

35. Thank you ! 35

36. Back up slides 36

37. Mu2e hall MARS15 model Production Solenoid Transport Solenoid Detector Solenoid V. Pronskikh, Radiation damage, NuFact’12, July 23-28, Williamsburg 37

38. Mu2e Requirements. RRR vs DPA Broeders, Konobeyev, 2004 Range 4-6E-5 V. Pronskikh, Radiation damage, NuFact’12, July 23-28, Williamsburg 38

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, PHITS V. Pronskikh, Radiation damage, NuFact’12, July 23-28, Williamsburg 39