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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
Dmitriy Toporkov Possibility to obtain a polarized molecular hydrogen target
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M.Stancary et al.
Intensities achieved from different ABS
Dmitriy Toporkov Possibility to obtain a polarized molecular hydrogen target
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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
Dmitriy Toporkov Possibility to obtain a polarized molecular hydrogen target
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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
Dmitriy Toporkov Possibility to obtain a polarized molecular hydrogen target
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Intensity of the H2 molecular beam ( free beam )
T.Wise et al. NIMA 336(1993) 410
Dmitriy Toporkov Possibility to obtain a polarized molecular hydrogen target
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Shielding by the skimmer
Two effect which may to providesaturation of the intensity
Dmitriy Toporkov Possibility to obtain a polarized molecular hydrogen target
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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
Dmitriy Toporkov Possibility to obtain a polarized molecular hydrogen target
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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
Dmitriy Toporkov Possibility to obtain a polarized molecular hydrogen target
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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
Dmitriy Toporkov Possibility to obtain a polarized molecular hydrogen target
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TARGET THICKNESS VS BEAM INTENSITYEFFICIENCY OF BEAM INJECTION INTO THE CELL
Dmitriy Toporkov Possibility to obtain a polarized molecular hydrogen target
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Dmitriy Toporkov Possibility to obtain a polarized molecular hydrogen target
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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
Dmitriy Toporkov Possibility to obtain a polarized molecular hydrogen target
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Energy dependenceof H2 molecule vsthe magnetic field
Dmitriy Toporkov Possibility to obtain a polarized molecular hydrogen target
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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
Dmitriy Toporkov Possibility to obtain a polarized molecular hydrogen target
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Diaphragm
Oven slit
Magnet
Beam receiver
Schematic view of the arrangement.
Dmitriy Toporkov Possibility to obtain a polarized molecular hydrogen target
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Suggested source of polarized molecules
D=20 cm
Dmitriy Toporkov Possibility to obtain a polarized molecular hydrogen target
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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
Dmitriy Toporkov Possibility to obtain a polarized molecular hydrogen target
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Monte Carlo simulation of flow through the cylindrical channel
degree
L/d=100
Dmitriy Toporkov Possibility to obtain a polarized molecular hydrogen target
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Radial density distribution at 100 cm distance from the capillary with d m
L/d=100
ab. unit
Dmitriy Toporkov Possibility to obtain a polarized molecular hydrogen target
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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
Dmitriy Toporkov Possibility to obtain a polarized molecular hydrogen target
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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.
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