Spallation UCN source at RCNP/TRIUMF

S. Kawasaki, Y. Masuda, S.C. Jeong, Y. Watanabe KEKK. Hatanaka, R. Matsumiya RCNP

K. Matsuta, M. Mihara Osaka UniversityY. Shin TRIUMF

1

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• He cryostat test

– UCN Polarizer• UCN polarizer using super conducting magnet• Polarized UCN guide

• Summary and Outlook 2

UCN Production with Super-fluid He

3

Features・ Spallation Source

High cold neutron fluxclose to superfluid He from target

・ Superfluid He for UCN converterLong storage lifetime

　 　　 depend on phonon up-scatteringτs = 36 s at THeII = 1.2 Kτs = 600 s at THeII = 0.8 K

(Cf. SD2 : Ts = 24ms)

important to keep THeII < 1K

UCN Production Spallation Neutron 　　　　↓ D2O Moderator (300K, 20K)　 Cold Neutron ～ meV

↓ Phonon scattering in He-II　 Ultra Cold Neutron 　～ 100neV

UCN Production with Super-fluid He

4

dispersion curve of phonon

factor stracture Dynamic : ),(

r wavenumbe: ,

),(4 2

qS

kk

qSkk

bdEd

fi

i

f

M. R. Gibbs, et alJ. Low Temp. Phys. 120 (2000) 55

multi phonon excitation

single phonon excitation

neutron dispersion curve

uiuii

uu dEdEEEdEdN

dEEddEEP

)()()( He

dq

mqqS

dEqdk

mbNdEEpP c

nuu

n

22322

He 2,)(

34)(

S(q,ħω）

UCN Production rate

Cold neutron excite phonon in super-fluid He and become UCNFree from Liouville’s theorem : use large phonon phase space in He-II

Current UCN Source

5

Proton beam400MeV 1μA

UCN

4He pumping 3He pumping

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

Flux simulation

6

neV210VA01.0

meV/A14.4

b34.14

cm1019.2

Ni1

n2

2

322H

　 　 　c

e

k

m

b

N

Production rate 9 UCN/cm3/s

single phonon excitation 14 UCN/cm3/s

including multi phonon excitation

PHITS Simulation 20K D2O ： Free gas modelFlux at resonant energy

proton beam : 400MeV×1μA

dq

mqqS

dEqdk

mbNdEEpP c

nuu

n

22322

He 2,)(

34)(

Geometry

Simulated flux and phonon stracture factor

Single phonon excitation

/meV/sn/cm109.3 )( 28dEEd i

UCN Production in 2008

7

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

UCN Production in 2008

8

proton beam 1μA × 600 sec　 UCN density 15 UCN/cm3 Ec = 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

Assuming50K D2O 6 UCN/cm3/s80K D2O 4 UCN/cm3/s

lifetime Storage rate ProductionUCN P

9

10

UCN Production in 2011

11

　 Storage Lifetime : 81 sec

　 Improvement of bottle surfaceAlkali cleaningbaking temperature 　 140℃

UCN density15 → 26 UCN/cm3 Ec = 90neV180 → 320 UCN/cm3 @ UCN bottle

UCN count after valve openingproton beam : 1μA × 40s

Cooling Power of Cryostat

12

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 heatingenergy 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 rateafter proton beam impingement

proton beam : 400MeV, 1μA, 1200s

UCN Source Improvement

13

Year IP τs THeII Improvement

2002 200nA 14 s 1.2K

June 2006 1μA 29 s 0.9K 3He cryostat

Nov. 2006 1μA 34 s 0.8K Reduce HeII film perimeter (8.5 cm → 　 5 cm)

July 2007 1μA 39 s 0.8K Remove 3He contamination

April 2008 1μA 47 s 0.8K Fomblin coating

Dec. 2009 1μA 61s 0.8K Alkali cleaning

Feb. 2011 1μA 81s 0.8K High temperature baking (140 )℃

lifetime Storage rate ProductionUCN P

Finally, UCN density 26 UCN/cm3 Ec = 90neV

New UCN source

14

ImprovementsHorizontal extraction

avoid gravity potentialD2O moderator optimization

more cold neutron fluxIncrease volume of He-II bottle

more production volumeNew cryostat

Large heat exchanger keep He-II temperature lowerHigh proton current 1 uA × 400 MeV : current→10 μA × 400 MeV @ RCNP→ 40 μA × 500 MeV @ TRIUMF

Horizontal extraction

15

UCN energy spectrum (Geant 4 simulation)

Gravity potential

Current source : vertical extraction Gravity potential 102 neV/m×1.2 m

New source : horizontal extraction• Avoid gravity potential• improve conductance

×2.5 effective transportNew source

Old Source

1.2m

210 neVbottle potential

10 K D2O

He-II

300 K D2O

Graphite W-Target

h2

h1

d

D2O Moderator Optimization

h1h2

d

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

16

Old source vs. New source

17

cold neutron flux across He-II bottle compared with old source

by PHITS simulation

proton current400 MeV × 1 μA @ RCNP

Cold Neutron Flux

10 K D2O

He-II

300 K D2O

GraphiteTarget

300K D2O

10K D2OH

e-II

graphitelead

target

Old source New Source

20% improvement

New D2O Moderator

10 K D2O

He-II

300 K D2O

GraphiteW-Target

D2O Moderator

Thermal moderator (300K)Volume=7x104 cm3

Cold moderator (10K)Volume=2x105 cm3

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

18

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 by charge particles and recoil energy of charge particles produced by high energy neutrons and photons.

low energy neutrons and photons by using Kerma data base.

19

Total

Energy deposit

Neutron Photon

Heat Deposit by 1μA proton beam

Heat (W) / 1μA proton bem

400 MeV 500 MeV

300K D2O

Vessel (Al) 1.10 1.73

D2O 4.12 6.60

sum 5.22 8.33

20K D2O

Vessel (Al) 0.76 1.16

D2O 3.67 5.48

sum 4.43 6.64

He-II

Vessel (Al) 0.06 0.09

He-II 0.04 0.04

sum 0.10 0.13

• Heat deposit on He-II

100 mW @ 400MeV ×1μA @ RCNP

(current intensity)

1W @ 400MeV ×10μA @ RCNP

5.2W @ 500MeV × 40μA @ TRIUMF

　　　　　　　　 Duty cycle ~ 　 20 ％20

He-II Cryostat

Improvements• Large heat exchanger

effective heat transfer from He-II• Large exhaust duct

high power pumping

21

•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

He-II temperature 　＜ 1K

3He-4He Heat Exchanger

22

6N cupper

Inside 3He horizontal finsoutside He-II perpendicular fins

Outside Inside

×8 surface area

Summary of improvement

23

• 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

Construction

24

He cryostat

D2O moderator and UCN guide

Already Installed @ RCNP

3He pumping4He pumping

D2O cryostat

UCN guide

D2O Moderator test

25

Experimental Layout

Measure cold neutron spectrum from D2O moderatorTOF Measurement

• proton beam • power : 400MeV × 80 nA• width : 100μs

• D2O Ice temperature : 5K, 15K ,40K ,60K

Cold Neutron Spectrum

26

peak velocity calculated from peak shift

m/s 1600ms 8.1ms 3.3

mm 2707mm 5219

tL

Near DetectorL = 2707mm

peak = 1.8msTD2O = 5K

Far DetectorL = 5219mm

peak = 3.3 msTD2O = 5K

Moderator size ~ 1 m　　 20 % of TOF length

Detail analysis is under way

TOF distribution ex. D2O temperature : 5K

D2O Temperature dependence

27

Temperature dependence60K : High energy shift<40K : No shift

Next test•　 Wide temperature range •　 TOF length : 10m avoid moderator size effect

Cooling test

• Cooling test– Use 4He instead of 3He– achieve 1.2K– if 3He is used as same

vapor pressure　→　 0.6K

28

UCN Polarizer

29

Polarizer

UCN Polarizer using super conducting magnet

Serebrov et.al. NIM A 545 490-492 (2005)

UCN energy 　 < 210 neV (guide potential)

magnetic potential 　 60 neV / T3.5T field → 　 210 neV

reduce reflection at Al window (54 neV) effective transmission ( gain energy )

3.5T

distance from center

B10T

1T

100mT

10mTHe-II

200μm Al window

10μm Al foil

magnet0 20 40 60 80 100

Al window position

5cm

Xe

Material for Polarized UCN Guide

• Diamond Like Carbon (DLC)– density 　 2 ～ 3 g/cm3 　　 (depend on sp2 : sp3 ratio)– potential ～ 250 neV– Depolarization 10-6/bounce

We test several kind of DLC30

PolarizerRequirement

Potential HighDepolarization Low

DLC Potential Measurement

31

Neutron Reflectometer (TOF) @ KUR

Direct Beam

Neutron reflectometer @ KUR TOF measurement

λ 　 = 　 0.3 – 0.7 nmfix detector pointuse chopper

systematic error 　～　 10%• 　 beam divergence• 　 chopper opening angle

Results

32

Sample d Company VF

(neV)C6F6 1μm Nanotec

Corp.

C 1μm Nanotec Corp.

Ta-C 250nm NanoFilm

Ta-C high density

250nm NanoFilm

total reflection

Sample d Company VF

(neV)C6F6 1μm Nanotec

Corp.110

C 1μm Nanotec Corp.

150

Ta-C 250nm NanoFilm 230

Ta-C high density

250nm NanoFilm 260

Results

33

fittingC6F6 Fitting with |R|2

VF

Reflectivity is not 1 ( total reflection)　 deflection : bending of Si substance (380μm)

2

22

''kkkkR

k k’

k (nm-1)

Reflectivity : ratio of direct beam

Depolarization

34

Silica

DLC sample

BeCu+DLCspin holding time 　～ 1000sec

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• 5 times 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 μA35

Thanks !!

36

Ultra Cold Neutron

37

Ultra Cold Neutron　　 energy ～ 100 neV　　 velocity ～ 5 m/s　　 wavelength ～ 50 nm

interaction　　 gravity 　 100 neV/m　　 magnetic force 60 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

Neutron flux optimization by changing the distance from 39 to 44, 49 and 54 cm.

h1

Neutron flux optimization by changing the thickness of the upper D2O from 20 to 25 and 30 cm.

h2

Cold neutron flux (1)

38

Neutron flux optimization by changing the diameter of the D2O from 75 to 60, 50 and 40 cm.

Final geometry:

h1=44cm

h2=30cm

d=75cmd

From MC simulations:

For the new source at 500MeV, the cold neutron flux is 1.8 times larger than the prototype source at 400MeV.

Cold neutron flux (2)

39

Recoil Ionization

Energy deposits (3)

40

Neutron Photon

Energy deposits (4)

41

Super conducting magnet

42

Magnet design

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

43

UCN Polarizer Fe foil : potential 　 VF = 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

Material for Polarized UCN Transport

44

Fermi potential Ni 　 210neV SUS316 190neV BeCu 168neV SiO2 90neV

onoff

onoff

NNNN

SiO2 cell

sample

OK

Depolarization

45

onoff

onoff

NNNN

SiO2

DLC sample

H0 = 20mGaussBeCu+DLC(C6F6)spin holding time 　～ 200sec