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Basic limitation on polarized atomic beam intensity

Basic limitation on polarized atomic beam intensity. Dmitriy Toporkov Budker Institute of Nuclear Physics Novosibirsk, Russia XII International Workshop on Polarized Sources, Targets and Polarimeters Brookhaven National Laboratory, Upton,10-14,2007. CONTENTS. Introduction

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Basic limitation on polarized atomic beam intensity

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  1. Basic limitation on polarizedatomic beam intensity Dmitriy Toporkov Budker Institute of Nuclear Physics Novosibirsk, Russia XII International Workshop on Polarized Sources, Targets and Polarimeters Brookhaven National Laboratory, Upton,10-14,2007

  2. CONTENTS • Introduction • Attenuation by residual gas and pressure bump • Shielding effect of skimmer • Intra beam scattering • Atomic beam focusing at different flow rate • What to measure further? • Conclusion Basic limitation on polarized atomic beam intensity

  3. M.Stancary et al. Basic limitation on polarized atomic beam intensity

  4. = I0cosn(q) • Ifoc.= a I0 p qmax2 T (1-Att ) a - atomic fraction T – transmission factor 1 – Att – attenuation due to residual gas scattering pqmax2 – maximum accepted solid angle l = ( s n )-1 Basic limitation on polarized atomic beam intensity

  5. Formation of the atomic or molecular beam BALZER TMP 2200 2 unit LEYBOLD-HERAUS 1000 2 unit. BALZERS TMP 2200 + KRYOPUMP 3500 KRYOPUMP 1500 2unit + TMP 360 Permanent sextupole magnets B=1.5Т Basic limitation on polarized atomic beam intensity

  6. Intensity of the H2 molecular beam ( free beam ) T.Wise et al. NIMA 336(1993) 410 Basic limitation on polarized atomic beam intensity

  7. Attenuation of the beam inside the magnets T.Wise et al. NIMA 336(1993) 410 M.V.Dyug et al. NIMA 495/1 (2002) 8 H2 beam , dummy magnets system for H1 beam attenuation should be larger H1 beam , cryogenic magnets system Int. Temperature of the inner bore, K Basic limitation on polarized atomic beam intensity

  8. Attenuation of the beam by residual gas - well understood process I(p) = I0*exp( -x*p/(l0p0) ) Relative velocities of particles correspond room temperature Basic limitation on polarized atomic beam intensity

  9. Dependence of the pressure rise in the compression tube on the nozzle throughput for a molecular deuterium beam at a nozzletemperature 100 K. Shown are the measured values (full dots), and those calculated for various peaking exponent. [N. Koch. A studyon the Production of the Intense Cold Atomic Beams for PolarizedHydrogen and Deuterium Targets. DESY-THESIS-1999-015, 1999.] Basic limitation on polarized atomic beam intensity

  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 Basic limitation on polarized atomic beam intensity

  11. In the case when the attenuation is provided by the residual gas scattering the intensity of the beam versus the nozzle throughput can be written as follows I(Q)=a*Q0* (Q/Q0) * exp(-Q/Q0)=a*Q0* x*exp(-x) x*exp(-x) Basic limitation on polarized atomic beam intensity

  12. Two effect which may to provide saturation of the intensity Shielding by the skimmer Basic limitation on polarized atomic beam intensity

  13. H.C.W.Beijerinck and N.F.Verster Physica 111C(1981)327-352 Geometry of the experiment Basic limitation on polarized atomic beam intensity

  14. H.C.W.Beijerinck and N.F.Verster Physica 111C(1981)327-352 Shielding effect of the skimmer For Ar at 300K X = 0.161Kn-1 = 0.174 Re = 29.7(Torr-1 cm -1)P0Dnoz. Basic limitation on polarized atomic beam intensity

  15. S.V. Musanov. Scientific Proc. of TsAGI, v.III, N.4 (1972) 130. In Russian. Basic limitation on polarized atomic beam intensity

  16. For parallel beam and Dv being the velocity spread Dv/vmax ~ 0.25 vmax ~2*105 cm/sec • ~ 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 Flux 1017 at/cm2 and x = 150 cm F(150) = 0.7 F0 Basic limitation on polarized atomic beam intensity

  17. A.Hershcovitch. Phys.Rev.Lett. 63(1989)750 Tremendous pumping speed of about 40000 l/sec for H2 at 2.5 K temperature Focusing is observed at lower densities, but it fall off as the density is increased Basic limitation on polarized atomic beam intensity

  18. Permanent magnets B=1.6 T Superconducting B=4.8 T Focusing magnets • DW = p*a2 = p*m*B/kT • B = 1.6 T DW ~ 1.5*10-2sr a ~ 0.07 rad • B = 4.8 T DW ~ 4.5*10-2 sr a ~ 0.21 rad Basic limitation on polarized atomic beam intensity

  19. Cryogenic Atomic Beam Source Two group of magnets – green (tapered magnets) and red (constant radius) driven independently, 200 and 350 A respectively Cryostat Liquid nitrogen IT Turbo pump Basic limitation on polarized atomic beam intensity

  20. Calculated density along the source axis in 1 mm radius Basic limitation on polarized atomic beam intensity

  21. Intensity of the atomic beam vs current through the coils. The measured value is vacuum in the straight section of the VEPP-3 storage ring. Beam is injected into the storage cell. Basic limitation on polarized atomic beam intensity

  22. Test bench measurements. Beam is injected into the compression tube contained QMA. The size of the tube the same as for injection tube of the storage cell Gas flow = Q R=I3/I2=1.4 Gas flow = 0.14Q R=I3/I2=2.8 Basic limitation on polarized atomic beam intensity

  23. FORWARD INTENSITY OF THE BEAM IS DEPENDENT FROM THE GEOMETRY OF THE NOZZLE Basic limitation on polarized atomic beam intensity

  24. What to measure further to understand the limitation of the • atomic beam intensity?? • Formation of the molecular flow before skimmer • Determination position and dimension of the boundary • surface • 3. Direct investigation of the intra beam scattering • More careful investigation the shape of the nozzle which • can provide more intensity at given position for fixed flow rate • Detail investigation of the focusing property of the magnet • system versus the magnetic field (current driven magnets) Basic limitation on polarized atomic beam intensity

  25. Conclusion Attenuation of the beam by uniform residual gas is well investigated and understood, but we really do not know the pressuredistribution along the beam path. We do not know the shape of the source of atoms, which raise under the expansion of gas through the nozzle. Intra beam scattering is poor investigated experimentally ( only A.Hershcovitch PRL 63(1989)750 has shown that this process totally define the intensity of focused atomic beam at 2K). Further investigations are required to overcome the limitations and get more density and intensity of polarized atomic beams. Basic limitation on polarized atomic beam intensity

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