Transcript Высокоинтенсивный источник поляризован

Possibility to obtain a polarized
hydrogen molecular target
Dmitriy Toporkov
Budker Institute of Nuclear Physics
Novosibirsk, Russia
XIV International Workshop on
Polarized Sources, Targets and
Polarimeters
12-16 September 2011, St.Petersburg,
RUSSIA
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CONTENTS
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Introduction
Intensity limitation in ABS
Source of polarized molecules
High directivity capillary source of molecules
Separating magnet for molecules
Conclusion
Dmitriy Toporkov
Possibility to obtain a polarized
molecular hydrogen target
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Intensities achieved from different ABS
M.Stancary et al.
Dmitriy Toporkov
Possibility to obtain a polarized
molecular hydrogen target
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Beam intensity from ABS
dI ( ) Q0 (n  1)
n

cos  = I0cosn()
d

2
Ifoc.= a I0  max2 T (1-Att )
a - atomic fraction
T – transmission factor
1 – Att – attenuation due to residual
gas scattering
max2 – maximum accepted solid angle
l  ( q2 s n )-1
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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Two effect which may to provide
saturation of the intensity
Shielding by the skimmer
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Possibility to obtain a polarized
molecular hydrogen target
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Intra-beam scattering
For parallel beam and Dv being the velocity spread
Dv/vmax ~ 0.25
vmax ~ 2*105 cm/sec
s~ 1.5*10-14cm-2 this is from attenuation atomic
beam by 300K residual gas
For 20K beam temperature s should be larger
For given s a ~ 2*10-20 cm*sec
Imax = 1/(a*X) ~ 5*1017 at/cm2
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/(l0p0) )
Relative velocities
of particles
correspond room
temperature
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 IS
DEPENDENT FROM THE POSITION
OF THE GAS INJECTIOJN
NOT MANY EXPERIMENTAL DATA
AVAILABLE
Dmitriy Toporkov
Possibility to obtain a polarized
molecular hydrogen target
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TARGET THICKNESS VS BEAM INTENSITY
EFFICIENCY 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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Magnetic properties of H2 molecule
Orthohydrogen S = 1 L = 1, 3 … odd
Parahydrogen S = 0 L= 0, 2 … even
At room temperature concentration ratio in
normal hydrogen C o-H2 /Cp-H2 = 3:1
Magnetic moment of molecule is dependent on S
and L.
Magnetic moment of o-H2 molecule for mI= -1,
mJ= -1 equals 5mn = 5*0.5*10-23 CGS=2.5*10-3mB
Dmitriy Toporkov
Possibility to obtain a polarized
molecular hydrogen target
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Energy dependence
of H2 molecule vs
the 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
Cross section
of the magnet
system
mm
Dmitriy Toporkov
Possibility to obtain a polarized
molecular hydrogen target
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Schematic view of the arrangement.
Beam receiver
Oven slit
Diaphragm
Dmitriy Toporkov
Magnet
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~ L>>d
Intensity in forward direction is the same as from
the orifice, but total flow is less by a factor
3L/4d
For further estimation L/d = 100, d=0.1mm
Dmitriy Toporkov
Possibility to obtain a polarized
molecular hydrogen target
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Capillary ring array
D = 20cm, width = 0.5cm
Regular microporous membrane
with pores of 0.3 mm in diameter
and 30 mm 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)]
Dmitriy Toporkov
Possibility to obtain a polarized
molecular hydrogen target
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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 of
1*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
L/d=100
degree
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  0.1m m
ab. unit
L/d=100
Dmitriy Toporkov
Possibility to obtain a polarized
molecular hydrogen target
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Number of poletips – 32
Magnetic poletip field 4 T
Dmitriy Toporkov
Possibility to obtain a polarized
molecular hydrogen target
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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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Results of simulation
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
Dmitriy Toporkov
Possibility to obtain a polarized
molecular hydrogen target
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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.
Dmitriy Toporkov
Possibility to obtain a polarized
molecular hydrogen target
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