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Spallation UCN source at RCNP/TRIUMF

Spallation UCN source at RCNP/TRIUMF. S. Kawasaki , Y. Masuda, S.C. Jeong , Y. Watanabe KEK K. Hatanaka , R. Matsumiya RCNP K. Matsuta , M. Mihara Osaka University Y. Shin TRIUMF. Contents. UCN Production with super-fluid He

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Spallation UCN source at RCNP/TRIUMF

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  1. Spallation UCN source at RCNP/TRIUMF S. Kawasaki, Y. Masuda, S.C. Jeong, Y. Watanabe KEK K. Hatanaka, R. Matsumiya RCNP K. Matsuta, M. Mihara Osaka University Y. Shin TRIUMF

  2. Contents • UCN Production with super-fluid He • Current UCN source • Storage lifetime • UCN density • New UCN source • Improvement • horizontal extraction • cooling power etc. • Preparation Status • D2O Moderator test • Hecryostat test • UCN Polarizer • UCN polarizer using super conducting magnet • Polarized UCN guide • Summary and Outlook

  3. UCN Production with Super-fluid He UCNProduction Spallation Neutron 　　　　↓ D2O Moderator (300K, 20K) Cold Neutron ～meV ↓ Phonon scattering in He-II Ultra Cold Neutron　～100neV • Features • ・Spallation Source • High cold neutron flux • close to superfluid He from target • ・Superfluid He for UCN converter • Long storage lifetime • depend on phonon up-scattering • τs = 36 s at THeII= 1.2 K • τs = 600 s at THeII = 0.8 K • (Cf. SD2 : Ts = 24ms) • important to keep THeII < 1K

  4. UCN Production with Super-fluid He Cold neutron excite phonon in super-fluid He and become UCN Free from Liouville’s theorem : use large phonon phase spacein He-II neutron dispersion curve multi phonon excitation single phonon excitation UCN Production rate S(q,ħω） dispersion curve of phonon M. R. Gibbs, et al J. Low Temp. Phys. 120 (2000) 55

  5. Current UCN Source 4He pumping 3He pumping UCN Proton beam 400MeV 1μA UCN source He-II bottle Φ16cm , L 41cm, Volume = 8L Al of 2mm thickness, inner wall coated with nickel Surrounded by D2O moderator (ice, water) Cryostat keep He-II the temperature by 3He pumping 3He is pre-cooled by 4He pumping UCN guide Φ8.5 cm, L = 3 m 1.25m high from He-II bottle

  6. Flux simulation PHITS Simulation 20K D2O： Free gas model Flux at resonant energy proton beam : 400MeV×1μA Geometry Single phonon excitation Production rate 9 UCN/cm3/s single phonon excitation 14 UCN/cm3/s including multi phonon excitation Simulated flux and phonon stracture factor

  7. UCN Production in 2008 Storage life time measurement UCN is produced and hold in the UCN bottle and guide proton beam : 0.2μA, 100s After time delay UCN valve open and counting Storage Lifetime : 47 sec wall loss rate 1cm hole

  8. UCN Production in 2008 proton beam1μA ×600 sec UCN density 15 UCN/cm3Ec = 90neV 180 UCN/cm3 @ UCN bottle UCN production rate 4 UCN/cm3/s (14 UCN/cm3/s : simulation) Free gas model is used in simulation effective temperature is more higher Assuming 50K D2O 6 UCN/cm3/s 80K D2O 4 UCN/cm3/s

  9. UCN Production in 2011 • Storage Lifetime : 81 sec • Improvement of bottle surface • Alkali cleaning • baking temperature140℃ UCN density 15 → 26 UCN/cm3Ec = 90neV 180 → 320 UCN/cm3 @ UCN bottle UCN count after valve opening proton beam : 1μA × 40s

  10. Cooling Power of Cryostat Heat load on super fluid He Super fluid film flow thermal radiation etc. is balanced with cooling power of cryostat T = 0.77K During proton beam impingement extra heat road from neutron-capture γ heating energy loss of charged particles Extra heat load 　→　He-II temperature rise up →　3He temperature rise up →　3He flow rate rise up → balance at new point T = 0.83K Temperature and Flow rate after proton beam impingement proton beam : 400MeV, 1μA, 1200s

  11. UCN Source Improvement Finally, UCN density 26 UCN/cm3Ec = 90neV

  12. NewUCN source • Improvements • Horizontal extraction • avoid gravity potential • D2O moderator optimization • more cold neutron flux • Increase volume of He-II bottle • more production volume • New cryostat • Large heat exchanger • keep He-II temperature lower • High proton current • 1 uA × 400 MeV : current • →10 μA × 400 MeV @ RCNP • → 40μA ×500 MeV @ TRIUMF

  13. Horizontal extraction Gravity potential 210 neV bottle potential 1.2m Old Source UCN energy spectrum (Geant 4simulation) • Current source : vertical extraction • Gravity potential102 neV/m×1.2 m • New source : horizontal extraction • Avoid gravity potential • improve conductance • ×2.5 effective transport New source

  14. D2O ModeratorOptimization MC simulation by PHITS Parameter optimization h1 : distance from target to He-II h2 : thickness of upper D2O d : diameter of D2O h1 = 44 cm h2 = 30 cm d = 75 cm d 10 K D2O h2 He-II h1 300 K D2O W-Target Graphite d h1 h2

  15. Old source vs. New source 10K D2O He-II 300K D2O 10 K D2O target He-II graphite lead 300 K D2O Old source New Source Target Graphite cold neutron flux across He-II bottle compared with old source by PHITS simulation proton current 400 MeV × 1μA @ RCNP 20% improvement Cold Neutron Flux

  16. New D2O Moderator • D2O Moderator • Thermal moderator (300K) • Volume=7x104 cm3 • Cold moderator (10K) • Volume=2x105cm3 • Solidification of D2O • capacity of GM cryostat (SRDK-408): 44W@40K • D2O latent heat at solidification=314J/g • average cooling power between 300K and 10K=60W • 7days to solidify D2O • 7days to cool solid D2O down to 10K 10 K D2O He-II 300 K D2O W-Target Graphite

  17. Energy deposit • MC simulations of energy deposit by the code PHITS2 • proton energy is 500MeV. • 360MeV/p is deposited in the W-target. • 140MeV/p leaves the target in the form of neutrons and photons. • energy deposit includes ionization bycharge particles and recoil energy of charge particles produced by high energy neutrons and photons. • low energy neutrons and photons by using Kerma data base.

  18. Energy deposit Total Neutron Photon • Heat deposit on He-II • 100 mW @ 400MeV ×1μA @ RCNP • (current intensity) • 1W @400MeV ×10μA @ RCNP • 5.2W @ 500MeV × 40μA @ TRIUMF • Duty cycle ~20％

  19. He-II Cryostat He-IItemperature　＜ 1K Improvements • Large heat exchanger effective heat transfer from He-II • Large exhaust duct high power pumping • Iso-pure He (light blue) • UCN Moderator • 3He (violet) • 4He (blue) • Coolant • iso-pure He and 3He are cooled down by • evaporated 4He gas • Liq. He • 1K pot (4He pumping) • 3He pumping

  20. 3He-4He Heat Exchanger 6N cupper Inside 3He horizontal fins outside He-II perpendicular fins ×8surface area Outside Inside

  21. Summary of improvement • UCN bottle volume ×1.5 • Increase cold neutron flux×1.2 • Horizontal extraction×2.5 • avoid gravity • avoid reflection total ×5 same proton current and more proton current

  22. Construction He cryostat UCN guide D2O cryostat 4He pumping 3He pumping D2O moderator and UCN guide Already Installed @ RCNP

  23. D2O Moderator test • Measure cold neutron spectrum from D2O moderator • TOF Measurement • proton beam • power : 400MeV × 80 nA • width : 100μs • D2O Icetemperature : 5K, 15K ,40K ,60K Experimental Layout

  24. Cold Neutron Spectrum Near Detector L = 2707mm peak = 1.8ms TD2O = 5K TOFdistribution ex. D2O temperature : 5K peak velocity calculated from peak shift Far Detector L = 5219mm peak = 3.3 ms TD2O = 5K Moderator size ~ 1 m 20 % of TOF length Detail analysis is under way

  25. D2O Temperature dependence • Temperature dependence • 60K: High energy shift • <40K : No shift • Next test • Wide temperature range • TOF length: 10m avoid moderator size effect

  26. Cooling test • Cooling test • Use 4He instead of 3He • achieve 1.2K • if 3He is used as same vapor pressure 　→　0.6K

  27. UCN Polarizer UCN Polarizer using super conducting magnet Serebrov et.al. NIM A 545 490-492 (2005) UCN energy< 210 neV (guide potential) magnetic potential60 neV / T 3.5Tfield →210 neV reduce reflection at Al window (54 neV) effective transmission ( gain energy ) Polarizer B 10T 3.5T 200μm Al window 1T 100mT Xe He-II 10mT Al window position magnet 5cm 0 20 40 60 80 100 10μm Al foil distance from center

  28. Material for Polarized UCN Guide • Diamond Like Carbon (DLC) • density2～3 g/cm3(depend on sp2 : sp3 ratio) • potential ～250 neV • Depolarization 10-6/bounce We test several kind of DLC Polarizer • Requirement • Potential High • Depolarization Low

  29. DLC Potential Measurement Neutron Reflectometer(TOF) @ KUR • Neutron reflectometer@ KUR • TOF measurement • λ=0.3 – 0.7 nm • fix detector point • use chopper • systematic error～　10% • beam divergence • chopper opening angle Direct Beam

  30. Results total reflection

  31. Results Reflectivity is not 1 ( total reflection) deflection : bending of Si substance (380μm) k (nm-1) Reflectivity : ratio of direct beam fitting C6F6 Fitting with |R|2 k k’ VF

  32. Depolarization Silica DLC sample BeCu+DLC spin holding time～1000sec

  33. Summary and Outlook • UCN source with super-fluid He • Current UCN source • proton beam power : 400MeV × 1μA • storage life time : 81 s • UCN density : 26 UCN/cm3 @ EC = 90 neV • New UCN Source • Horizontal extraction • 5times UCN at the same proton power • Polarizer • Outlook • 2013 UCN Production at RCNP beam power → 400 MeV × 10 μA • 2015? Transport to TRIUMF beam power → 500 MeV × 40 μA

  34. Thanks !!

  35. Ultra Cold Neutron • Ultra Cold Neutron • energy ～ 100 neV • velocity ～ 5 m/s • wavelength ～ 50 nm • interaction • gravity100 neV/m • magnetic force60 neV/T • weak interaction • β-decay n → p + e • strong interaction • Fermi potential 335 neV (58Ni) • UCN can confine in material bottle • →Use various experiment • nEDM search, gravity experiment, life time measurement … • Need high density UCN source

  36. Cold neutron flux (1) h2 h1 Neutron flux optimization by changing the distance from 39 to 44, 49 and 54 cm. Neutron flux optimization by changing the thickness of the upper D2O from 20 to 25 and 30 cm.

  37. Cold neutron flux (2) Final geometry: h1=44cm h2=30cm d=75cm d From MC simulations: For the new source at 500MeV, the cold neutron flux is 1.8 times larger than the prototype source at 400MeV. Neutron flux optimization by changing the diameter of the D2O from 75 to 60, 50 and 40 cm.

  38. Energy deposits (3) Ionization Recoil

  39. Energy deposits (4) Neutron Photon

  40. Super conducting magnet Magnet design

  41. Polarized UCN transportation • Good material for polarized UCN transportation • large potential • long spin holding time • Store UCN in cell and measure spin holding time • SiO2 cell＋ sample UCN Polarizer Fe foil : potentialVF = 210 neV inner field 2T VF + μH = 210 neV ±120 neV 330 neV or 90 neV UCN energy Vmax = 170 neV only one spin component can transmit Fe foil Spin Flipper spin flipped UCN cannot transmit Fe foil

  42. Material for Polarized UCN Transport SiO2 cell sample Fermi potential Ni 210neV SUS316190neV BeCu 168neV SiO2 90neV OK

  43. Depolarization SiO2 DLC sample H0 = 20mGauss BeCu+DLC(C6F6) spin holding time　～200sec

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