1 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 September 2011, St.Petersburg, RUSSIA

Dmitriy ToporkovPossibility to obtain a polarized molecular hydrogen target 2 Introduction Intensity limitation in ABS Source of polarized molecules High directivity capillary source of molecules Separating magnet for molecules Conclusion CONTENTS

Dmitriy ToporkovPossibility to obtain a polarized molecular hydrogen target 3 M.Stancary et al. Intensities achieved from different ABS

Dmitriy ToporkovPossibility to obtain a polarized molecular hydrogen target 4  q  n ) -1 = I 0 cos n  I foc. =  I 0  max 2 T (1-Att )  atomic fraction T – transmission factor 1 – Att – attenuation due to residual gas scattering  max 2 – maximum accepted solid angle Beam intensity from ABS

Dmitriy ToporkovPossibility to obtain a polarized molecular hydrogen target 5 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 ToporkovPossibility to obtain a polarized molecular hydrogen target 6 Intensity of the H 2 molecular beam ( free beam ) T.Wise et al. NIMA 336(1993) 410

Dmitriy ToporkovPossibility to obtain a polarized molecular hydrogen target 7 Shielding by the skimmer Two effect which may to provide saturation of the intensity

Dmitriy ToporkovPossibility to obtain a polarized molecular hydrogen target 8  v/v max  0.25 v max  2*10 5 cm/sec  1.5* cm -2 this is from attenuation atomic beam by 300K residual gas For 20K beam temperature  should be larger For given    cm*sec I max = 1/(  *X) ~ 5*10 17 at/cm 2 For parallel beam and  v being the velocity spread Intra-beam scattering

Dmitriy ToporkovPossibility to obtain a polarized molecular hydrogen target 9 Attenuation of the beam by residual gas - well understood process I(p) = I 0 *exp( -x*p/   p 0  ) Relative velocities of particles correspond room temperature

Dmitriy ToporkovPossibility to obtain a polarized molecular hydrogen target 10 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 ToporkovPossibility to obtain a polarized molecular hydrogen target 11 TARGET THICKNESS VS BEAM INTENSITY EFFICIENCY OF BEAM INJECTION INTO THE CELL

Dmitriy ToporkovPossibility to obtain a polarized molecular hydrogen target 12

Dmitriy ToporkovPossibility to obtain a polarized molecular hydrogen target 13 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 /C p-H2 = 3:1 Magnetic moment of molecule is dependent on S and L. Magnetic moment of o-H 2 molecule for m I = -1, m J = -1 equals 5  n = 5*0.5* CGS=2.5*10 -3  B Magnetic properties of H 2 molecule

Dmitriy ToporkovPossibility to obtain a polarized molecular hydrogen target 14 Energy dependence of H 2 molecule vs the magnetic field

Dmitriy ToporkovPossibility to obtain a polarized molecular hydrogen target 15 First (to my knowledge) spatial separation of o-H 2 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 H 2 mm Cross section of the magnet system

Dmitriy ToporkovPossibility to obtain a polarized molecular hydrogen target 16 Diaphragm Oven slit Magnet Beam receiver Schematic view of the arrangement.

Dmitriy ToporkovPossibility to obtain a polarized molecular hydrogen target 17 Suggested source of polarized molecules D=20 cm

Dmitriy ToporkovPossibility to obtain a polarized molecular hydrogen target 18 Molecular flow through the long tube ~ 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=0.1  m

Dmitriy ToporkovPossibility to obtain a polarized molecular hydrogen target 19 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

Dmitriy ToporkovPossibility to obtain a polarized molecular hydrogen target 20 The total area of the source is about 30 cm 2. Assuming geometrical transparency of 50% this area should contain 2*10 11 capillaries. If we set a flux through a single capillary 1*10 10 mol/sec the density of the molecules before a capillary should be in the range of 1*10 18 mol/cm 3. Total flux of molecules 2*10 21 mol/sec

Dmitriy ToporkovPossibility to obtain a polarized molecular hydrogen target 21 Monte Carlo simulation of flow through the cylindrical channel degree L/d=100

Dmitriy ToporkovPossibility to obtain a polarized molecular hydrogen target 22 Radial density distribution at 100 cm distance from the capillary with d  m L/d=100 ab. unit

Dmitriy ToporkovPossibility to obtain a polarized molecular hydrogen target 23 Number of poletips – 32 Magnetic poletip field 4 T

Dmitriy ToporkovPossibility to obtain a polarized molecular hydrogen target 24 Spatial distribution of molecules at the exit of the separating magnet from a single capillary

Dmitriy ToporkovPossibility to obtain a polarized molecular hydrogen target 25 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* The fraction of the focusing molecules in the flow is ¼ ( ¼ is p-H 2 molecules, 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*10 18 mol/sec Results of simulation

Dmitriy ToporkovPossibility to obtain a polarized molecular hydrogen target 26 Conclusion Intensities of polarized beams from the Atomic Beam sources seems have reached it’s limit of about at/sec. Proposed source of polarized ortho-hydrogen (o-H 2 ) 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.