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Possibility to obtain a polarized hydrogen

molecular target

Dmitriy ToporkovDmitriy Toporkov

Budker Institute of Nuclear PhysicsBudker Institute of Nuclear Physics

Novosibirsk, RussiaNovosibirsk, Russia

XIV International Workshop onXIV International Workshop on

Polarized Sources, Targets and Polarized Sources, Targets and PolarimetersPolarimeters

12-16 September 2011, St.Petersburg, RUSSIA

Dmitriy Toporkov Possibility to obtain a polarized molecular hydrogen target

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• Introduction• Intensity limitation in ABS • Source of polarized molecules• High directivity capillary source of molecules• Separating magnet for molecules• Conclusion

CONTENTS

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M.Stancary et al.

Intensities achieved from different ABS

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0( ) ( 1)cos

2nQdI n

d

n )-1

= I0cosn

Ifoc.= I0 max2 T (1-Att )

atomic fraction

T – transmission factor1 – Att – attenuation due to residual gas scatteringmax

2 – maximum accepted solid angle

Beam intensity from ABS

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Factors limiting the intensity from ABS

• Increasing a size of the source of atoms with increasing throughput (Belov’s talk)• Intra-beam scattering• Pressure bump in the ABS• Attenuation by the residual gas

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Intensity of the H2 molecular beam ( free beam )

T.Wise et al. NIMA 336(1993) 410

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Shielding by the skimmer

Two effect which may to providesaturation of the intensity

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v/vmax 0.25 vmax 2*105 cm/sec

1.5*10-14cm-2 this is from attenuation atomicbeam by 300K residual gas

For 20K beam temperature should be largerFor given cm*secImax = 1/(*X) ~ 5*1017 at/cm2

For parallel beam and v being the velocity spread

Intra-beam scattering

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Attenuation of the beam by residual gas - well understood process

I(p) = I0*exp( -x*p/p0 )

Relative velocitiesof particles correspond roomtemperature

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INJECTION OF BACKGROUND GAS AT DIFFERENT POSITION

ATTENUATION OF THE BEAM ISDEPENDENT FROM THE POSITIONOF THE GAS INJECTIOJN

NOT MANY EXPERIMENTAL DATAAVAILABLE

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TARGET THICKNESS VS BEAM INTENSITYEFFICIENCY OF BEAM INJECTION INTO THE CELL

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Orthohydrogen S = 1 L = 1, 3 … oddParahydrogen S = 0 L= 0, 2 … evenAt room temperature concentration ratio in normal hydrogen C o-H2 /Cp-H2 = 3:1Magnetic moment of molecule is dependent on S and L.Magnetic moment of o-H2 molecule for mI= -1, mJ= -1 equals 5n = 5*0.5*10-23

CGS=2.5*10-3B

Magnetic properties of H2 molecule

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Energy dependenceof H2 molecule vsthe magnetic field

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First (to my knowledge) spatial separation of o-H2 molecules in inhomogeneous magnetic field have been done by Frisch R. and Stern О. [F r i s c h R. und S t e r n О., Ztschr. f. Phys., 85, 4, 1933].

Magnetic separation of the beam of H2

mm

Cross sectionof the magnet system

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Diaphragm

Oven slit

Magnet

Beam receiver

Schematic view of the arrangement.

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Suggested source of polarized molecules

D=20 cm

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Molecular flow through the long tube

~ L>>d

Intensity in forward direction is the same as fromthe orifice, but total flow is less by a factor 3L/4d

For further estimation L/d = 100, d=0.1m

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Regular microporous membrane with pores of 0.3 m in diameter and 30 m thickness have a geometrical transperancy of about 70% could be fabricated by the method of deep X-ray lithography [G.N.Kulipanov et al. Nucl. Instr. And Meth. A359, 404(1995)]

Capillary ring array D = 20cm, width = 0.5cm

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The total area of the source is about 30 cm2. Assuming geometrical transparency of 50% this area should contain 2*1011capillaries. If we set a flux through a single capillary 1*1010mol/sec the density of the molecules before a capillary should be in the range of1*1018mol/cm3. Total flux of molecules 2*1021mol/sec

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Monte Carlo simulation of flow through the cylindrical channel

degree

L/d=100

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Radial density distribution at 100 cm distance from the capillary with d m

L/d=100

ab. unit

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Number of poletips – 32Magnetic poletip field 4 T

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Spatial distribution of molecules at the exit of the separating magnet from a single capillary

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Monte-Carlo simulation has shown that the fraction of molecules from a single capillary that reached an entrance aperture of the magnet and focused to its axis has a value of 2.3*10-3. The fraction of the focusing molecules in the flow is ¼ ( ¼ is p-H2molecules, ¼ is defocused and ¼ has a magnetic moment close to zero).Estimated fraction of the focusing molecules is about 0.6*10-3 of the total flux or 1*1018 mol/sec

Results of simulation

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Conclusion• Intensities of polarized beams from the Atomic

Beam sources seems have reached it’s limit of about

1017at/sec.

• Proposed source of polarized ortho-hydrogen (o-H2 )

molecules probably will provide intensity by order of

magnitude higher.

• An opening questions are preservation of polarization

of molecules under injection into the storage cell and

realization of huge differential pumping system needed

to get good vacuum condition.