View
40
Download
0
Category
Preview:
DESCRIPTION
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 - PowerPoint PPT Presentation
Citation preview
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
Recommended