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P. Geltenbort Ultra-Cold and Cold Neutrons: Physics and Sources, St. Petersburg --> Moscow, 1 - 7 July 2007 1

Ultra-Cold Neutron Sources:from the past to the future

UCN – properties and keystones

early sources

sD2 at PSI, TUM, Mainz, LANL, NCSU, and ILL

sLHe at ILL, TUM, and RCNP, and SNS

thanks to the beautiful slides ofJ. Bazin, D. Bondoux, A. Frei, R. Gähler, P. Harris, W. Heil, P. Huffman, T. Ito, Y. Masuda, J.M. Pendlebury,

A. Pichlmaier, C. Plonka, R. Stöpler, M. van der Grinten, A. Young, O. Zimmer, and R. Golub (book)

turbine at ILL, PNPI


Properties of UCN

λUCN ~ 1000 Å

Ekin (~ 5 ms-1) = 100 neV (10-7 eV)

~ 10-7 eV / TeslaMagnetic field∆E= μn B

~ 10-7 eV / MeterGravity∆E=mn g ∆h

~ 10-7 eVFermi potential

UCN are totally reflected from suitable materials at any angle of incidence, hence storable!

UCN are furthermore storable by gravity and/or magnetic fields

Interaction with matter:UCN see a Fermi-Potential EF

EF ~ 10-7 eV for many materials, e.g.

- beryllium 252 neV- stainless steel 200 neV

Long storage and observationtimes possible (up to several minutes)!

High precision measurements ofthe properties of the free neutron

(lifetime, electric dipole moment, gravitational levels)

That’s why we are here!

TUCN ~ 2 mK

Ultracold neutrons, that is, neutrons whose energy is so low that they can be contained for long periods of time in material and/or magnetic bottles

V n

V n < V c r it

V n > V c r it


UCN discovery

… by extracting neutrons from the low energy tail of the Maxwellian distribution in the source


Reactor core

Cold source

Vertical guide tube

Neutron turbineA. Steyerl (TUM - 1985)

The UCN/VCN facility PF2


The Vertical Cold Source (VCS)


Generating Ultracold Neutrons (UCN)“Steyerl turbine”Doppler shifting device

Very cold neutrons

Ultracold neutrons

Steyerl turbineat FRM-I (Munich)

Steyerl turbine (2nd generation)at PF2 / ILL10 years later


Principle of the neutron turbine

TOF data as a function of axial velocity


The PF2 beam facility

PF2: Physique Fondamentale 22nd installation for fundamental physics

4 positions for Ultracold Neutrons (UCN)

- MAM [14x10 cm2]

- EDM [7x7cm2]

- UCN [10x5 cm2]

- TES [4x4 cm2]

v = 5 ms-1

ρ = ~50 cm-3 (at the experiment)

1 position for Very Cold Neutrons (VCN)

v = 50 ms-1

Φ = 108 cm-2 s-1- VCN beam


Other versions of the neutron turbine

Radial turbine, Kashoukeev et al (1975), Bulgaria

12 flat mirrors like the fins of a paddle wheel~ 1000 rpm

Super-mirror turbine, Utsuro et al (1988), Kyoto

less turbine blades (32 instead of 690)flat (instead of curved) mirrorsIncreased yield for velocities above UCN range

“Crystal” turbine, Dombeck et al (1979), Brun et al (1980), ANLLater revisisted in LANSCE at LANLBragg reflection from a moving crystalLarger velocity neutrons can be reflected


Source of polarized cold and UCN at PNPI

Φth ~ 2x1014 n cm-2 s-1

ρ ~ 16 cm-3

(1 l)

(Al +58Ni(Mo))

(1 l)

UCN yield as a function of source temperature (hydrogen)Highest gain (66) with D2 at 17K

see next talk by A. Serebrovon the impressive activities at PNPI in this field


UCN source using horizontal extraction

Dimitrovgrad, Kosvintsev et al (1977)

UCN are produced in a water cooled convertor of zirconium hydridelocated inside a stainless steel guide with several bends


UCN facilities – Status and Future

More UCN facilities in the futureworldwide

- PSI (CH)- Mainz / Munich (D)- ILL (F)- LANL / NIST / SNS/

NCSU / (LENS) (USA)- RCNP / JPARC (J)


The importance of cooling the neutrons

(M. Pendlebury)

CN

A. Serebrov et al.,

JETP Lett. 59 (1994) 757

Yu. N. Pokotilovski, NIMA 356 (1995) 412pulsed source, separation of production and storage volume


Project of UCN factory

A.P. Serebrov et al, NP-63-1997-2206

UCN Gain factor as a function of sD2 temperatureNormalized to UCN yield at room temperature


p beamSpallation target

n-Guide

Cold sD2moderator (τ~30ms)30 litres

UCN storage volume, 2-3 m3

D2O moderator, 3m3

Membrane

UCN guides toexperiments

Shutter

appr

ox 5

m

(A. Pichlmaier)

2 mA, 600 MeV1% duty cycle


Conclusion

• The PSI UCN source construction iswell under way

• Source R & D– sD2 properties

– Wall coatings

• Physics Program– EDM

– n Lifetime

– other proposals welcome

Start-up in 2008(A. Pichlmaier)

ρ(UCN) ~ 2000 UCN cm–3

(in the storage volume)


MiniMini--DD22 ((schemescheme))

(A. Frei)


Safety aspectsSafety aspects1. Reactor is source of high neutron and gamma flux

2. UCN device will be located inside the biological shield of FRM-II

3. Deuterium is a dangerous (explosive) material

4. Other experimental facilities are planned to work on FRM-II

We must guarantee

low level ofradiation dose

Decouplingof UCN from FRM-IIDouble-wall

concept of barriers

(A. Frei)


Mini-D2: UCN-source for the FRM-II

SR6 Through going beam tube concept.

UCN

Cryo & PreModerator Supply

MiniD2 Source

(R. Stöpler)

The talks of A. Frei and R. Stöpler in the last session on Saturday will provide much more detailed information


45° 40°

Chemie

Chemie Neutronen - Spin - Filter

Ultrakalte NeutronenD C

A

B

ThermischeKern

Reaktor-tank

Säule

45° 50°

Reflektor

Wasser

Fuel elements:Zirconium hydride ( Zr / H ~ 1 )moderator with 8% by weight U Uranium: ( 20% 235U )

σ(n,f)T≈ 300 K ≈ 580 barn

σ(n,f)T≈ 600 K < σ(n,f)T≈ 300 K

Reactor power excursion is limited by theprompt negative temperatur coefficientof the reactivity

n

Pulse mode:Control rod ( B ) is shot outof the reactor core

TRIGA-Mainz

DC-operation: 100 kW

T≈ 600 K

Pulse : 40 ms ( FWHM )Pulse peak-power : 250 MW ( 5×1015 n/cm2/s )Repetition rate: 1 Pulse / 5 min

(W. Heil)


sD2 UCN source at TRIGA reactor in Mainz

(W. Heil)

b) c)

a)

≈ 3 m


Results

(W. Heil)

0 2 4 6 8 10 12 14 16 18 20

1

10

100

1000

#co

un

ts /

0.1

s / M

J

time [s]

no foil (4.55 mole) Ni-foil (4.65 mole) Cu-foil (4.35 mole) Background

All the details you will find in W. Heil’s talk later in this session!!


LANSCELANSCE

UCN Source

Proton Linac(Los Alamos Neutron Science CEnter)

FP12


Schematic

Graphite

Tungsten targetBeryllium

UCN Guide to experiment

Polyethylenemoderator

Flapper valve

SD2 volume

58Ni coated wall

7 in.

1 m

(T. Ito)


0

10

20

30

40

4 8 12 16

τ SD

(mse

c)

T (K)0 0.1 0.2 0.3 0.4

Para Fraction

Measured for the first time: UCN lifetime in SD2

τpara = 1.2 ± .14 (stat) ± .20 (syst)

C. L. Morris et al., Phys. Rev. Lett. 89, 272501 (2002)

PhD Thesis: Chen-Yu Liu

confirmed: F. Atchison et al., Phys. Rev. Lett. 95, 182502 (2005)

Experimental surprise: UCN lifetime depends strongly on

para-D2 content

Prototype Source Key Results

(T. Ito)


Compare to previous record for bottled UCN of 41 UCN/cm3 (at ILL) A. Saunders et al., Phys. Lett. B 593, 55 (2004)

confirmed: F. Atchison et al., Phys. Rev. C. 71, 054601 (2005)

After learning how to control

para-D2concentration

Within 50% of expected fluxes (MCNP simulation)

Measured: 466 ±92 UCN/cm3/μC

Predicted: 750 UCN/cm3/μC

Very High Densities Achieved

(T. Ito)


Area B Schematic

UCNA betaspectrometerSD2 UCN Source

Proton beam

Polarizermagnets

(T. Ito)


Status & Plans• 2005 run

– Source & UCNA experiment commissioning– The UCN flux measured inside the source reasonable but the flux

coming out of the shielding package substantially lower than expectation, and the spectrum very soft, indicating that the Fermi potential of the guide coating is low.

• 2006 run– Guide tube before PPM was replaced with stainless steel tube– New source insert (flapper valve) was built and tested– Increased UCN flux observed, however the flapper valve was

unreliable• 2007 run

– Run started in mid June– A new source insert will be installed– Additional polyethylene moderator was installed– Additional proton beamline diagnostic was installed– Continue with the source and experiment commissioning and data

taking for beta asymmetry experiment

(T. Ito)

Listen carefully to A. Young’s talk on 5th July!


Development of an Ultracold Neutron Source at the PULSTAR Reactor

Albert R. YoungNorth Carolina State University

(courtesy of A. Young)


NCSU PULSTAR Reactor

• Sintered UO2 pellets• 4% enriched• 1-MW power• Light water moderated and

cooled • Just issued a new license for

about 10 years of operation

Source located in thermal column (outside reactor proper)

28 ft

Core



Source Schematic

• Lead shield -reduce gamma heating, maintain reactivity

• Floodable Helium Nose Port• Heavy Water Thermal

Moderator• CH4 cold moderator, 1 cm

thick cup around SD2• 1 liter SD2• 18 cm diameter, 58Ni-coated

guides



UCN Transport Simulation

Transport efficiency around bend and down approx 3 m of guide

~ 30% (no foils)~15% (Al isolating foil)

Y.-P. Xu and A. R. Young



Expected Results at 1 MW

• 5x1011 n/cm2/s CN Flux in Deuterium• 0.8x104 – 1.5x104 n/cm3/s UCN Production• ~250-400 UCN/cm3 Limiting Density • >30 UCN/cm3 Useful Density



• Funding obtained from DOE INIE program starting in 2003 and NSF in 2004 (NSF provided equipment money)

• First licensing amendments complete, full source safety analysis and license amendment under way (3 person team)

• New scattering kernels for cryogenic materials developed

• Validation of Monte Carlo model of thermal flux in graphite thermal column (now removed to make room for new source)

• New nose port designed, constructed and test fitP li i i i d i f ti l

Current Activities



8.9 A neutrons are needed to create UCN in 4He

(M. Pendlebury)


Superthermal sourceUCN storage cryostat

Golub et al (1983), at ILL

P. Geltenbort Ultra-Cold and Cold Neutrons: Physics and Sources, St. Petersburg --> Moscow, 1 - 7 July 2007 38(Y. Masuda)


UCN production rate vs λn

1.19±0.18 UCN cm-3 s-1 expected, 0.91± 0.13 observedSee C.A.Baker et al., Phys.Lett. A308 67-74 (2002)

Multiphonon production

Single-phonon production

(P. Harris)


Calculating the UCN density in the super-fluid 4He

The UCN production rate per unit volume = (4.55 ±0.25) x10−8 (dΦ/dλ) at 8.9 Å.

C. A. Baker et al, NIM A, 308 (2003) 67.

Thus, for (dΦ/dλ) at 8.9 Å = 2.5 x10+8 /cm2/s/Å,

the production rate in the superfluid is 11 UCN/cm3/s.

If the UCN mean survival time in the super-fluid is 150 s,

then, after having the cold beam on for 150 s,

the UCN density will be 11 x 150 x (1− e−1) = 1080 /cm3

(M. Pendlebury)


H17

requirement for He source: λ = 8.93 Å ± 1%Crystal: Intercalated graphite K-IHOPG stage 1

reflected beam crosses above H18

Cryo-EDM

Area ≈ 100 m2

D9

D3H18

New H17 for FIGARO and Cryo-EDM; general setup; top view (ILL reactor hall)

80× 80 for Cryo-EDM

15× 80 for FIGAROH171

H171: 15× 80 for FIGARO

beam stop for CRYO-EDMAxial separation to H16 and H18 ≈ 70 cm

H172 absorberGRANIT

(R. Gähler)

P. Geltenbort Ultra-Cold and Cold Neutrons: Physics and Sources, St. Petersburg --> Moscow, 1 - 7 July 2007 42(O. Zimmer)

superthermal UCN production at MEPHISTO (FRM-II):

"HELIMEPHISTO“, soon at the ILL

… much more details and the latest and “hotest”news will be given by O.Zimmer just after the coffee break!

P. Geltenbort Ultra-Cold and Cold Neutrons: Physics and Sources, St. Petersburg --> Moscow, 1 - 7 July 2007 43(courtesy of Y. Masuda)

P. Geltenbort Ultra-Cold and Cold Neutrons: Physics and Sources, St. Petersburg --> Moscow, 1 - 7 July 2007 44(Y. Masuda)

P. Geltenbort Ultra-Cold and Cold Neutrons: Physics and Sources, St. Petersburg --> Moscow, 1 - 7 July 2007 51(courtesy of Y. Masuda & O. Zimmer)

compressed Al2O3 powder (50 nm)


SNS at ORNLSNS at ORNL1.4 MW Spallation Source1.4 MW Spallation Source

(P. Huffman)


FNPB FNPB BeamlineBeamline

Double monochromator

Selects 8.9 Å neutronsfor UCN via sLHe

(P. Huffman)


ULTRA COLD SOURCEintegrated in a possible 3rd cold neutron source at the ILL

(J. Bazin)


• SD2 behaviour under radiation

• In pile cryostat concept

• UCN storage tube

• Overall integration

• Preparation of detailed design phase

SD2 UCN source at ILL: feasibility study

(courtesy of D. Bondoux)


γ and n fluxes --> radiolysis phenomena

Water Ice

Sudden releaseof stored energy

Experimental investigations

Water & heavy water icesolid methanesolid mesitylene…

but not for solid deuterium

Major issues for a SD2 UCN source

Level of released energy / « crystal » quality?Period of occurrence / experiments?

UCN source at ILL: SD2 behaviour under radiation



UCN source at ILL: SD2 cryostat concept

Helium

“Ejection” whencooling off

Mini D2 (old design)

~ + 2 KSD2

Inner skin

Outer skin

Outer skinHe flow

Inner skin (coated Al?)

He flow

Helium

Plateexchanger

1/8 model

~ + 1 K

SD2

Exchanger skin, Be

Exchanger skin

SD2

He flow

A promising concept but a challenging technology!



UCN source at ILL: SD2 cryostat concept

solidliquid (19 K)

CN flux (40 K) ~ 2.4e13 n/cm2-s

ILL concept advantages:

- reduced temperature excursion from He to SD2- reduced heating power (ratio ~ 5) due to cryostat reduced mass (geometry & material)- less thermo-mechanical constraints when re-heating SD2 (SD2 thermal expansion)

ILL concept main drawback:

- innovative concept needing extensive validations (prototype)

SD2 temperature effect:5 K → 8 K UCN density divided by 3

ILL HFR γ & n heating level:~ [0.2…0.4] W/g!



UCN source at ILL: overall integration

Thermal screen~ 100 K

LHe in~ 8 g/s @ 4-5 K

LHe out~ + 225 W & + 3 K

1,5 mm Al - 45 MPa @ 20 bar

1,5 mm LHe

1,5 mm Al

10 mmLH

1,5 mm Al

1 mmBe4 mm

2 mm

Double wall guide~ 100 K --> 300 K

8030

190

100 cm3 SD2 @ 5-6 K, ~ 10 W

390 cm3 LH @ 20 K, ~ 12 W

SD2 UCN source& LH pre-moderator



UCN source at ILL: overall integration

SD2 5-6 K

Heliquefactionrefrigeration

LHe, 4K He 25 K

D2 / Heheat

exchanger

He 300 K

Ortho D2300 K1 bar~100 l

Normal D2300 K1 bar

~100 l.

PurifierLiquefaction

Catalyse~ 100 cm3

He / 18 KHe 25 K

He, 4K

He / 100 K

He 300 K

LD2 25 KExpe.



Ultracold Nanoparticles


Ultracold neutrons are still a fancy and powerful tool for fundamental physics studies and much stronger UCN sourcesare not too far from now!

Thank you, merci beaucoup and besten Dankfor your attention!

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