Polarized 3 He Target for 12 GeV Experiments J. P. Chen, February 12, 2013, Hall A Meeting - PowerPoint PPT Presentation

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Polarized 3 He Target for 12 GeV Experiments J. P. Chen, February 12, 2013, Hall A Meeting

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  1. Polarized 3He Target for 12 GeV Experiments J. P. Chen, February 12, 2013, Hall A Meeting • Introduction • Target performance for 6 GeV experiments • 12 GeV experiments and requirements • Upgrade plan and status

  2. Principle for Polarizing Targets Polarization Brute Force: Zeeman split: energy level split in a magnetic field B Boltzmann distribution: spin up (+ state): spin down (- state): Magnetic moment  much easier to polarize electron (atom) than polarize proton (nuclei) large B (~15T) , low T (~10mK) to have significant polarization for proton

  3. Dynamic Nuclear Polarization (proton)

  4. Rb Spin exchange Optical Pumping for 3He • Two step process: • Polarize Rb by optical pumping • Transfer Rb atomic (electron) polarization to 3He nucleus by spin-exchange interaction 3He

  5. History: Spin Milestones • Nature: (www.nature.com/milestones/milespin) • 1896: Zeeman effect (milestone 1) • 1922: Stern-Gerlach experiment (2) • 1925: Spinning electron (Uhlenbeck/Goudsmit)(3) • 1928: Dirac equation (4) • Quantum magnetism (5) • 1940: Spin–statistics connection(7) • 1946: Nuclear magnetic resonance (NMR)(8) • 1950-51: NMR for chemical analysis (10) • 1973: Magnetic resonance imaging(15) • 1975-76:NMR for protein structure determination (16) • 1990: Functional MRI (19) • 1991: Magnetic resonance force microscopy (21) • 1997: Semiconductor spintronics (23) • 2000s: Breakthroughs in nucleon spin/nucleon structure study? • ?: Applications of nucleon spin physics?


  6. JLab Polarized 3He Target Performance for 6 GeV Experiments

  7. Hall A polarized 3He target 55-60% • longitudinal, transverse and vertical • Luminosity=1036 (1/s) (highest in the world) • High in-beam polarization 55-60 % • Effective polarized neutron target • 13 completed experiments 7 approved with 12 GeV (A/C) 15 uA

  8. Hall A Polarized 3He Target Three sets of Helmholtz coils to provide polarization in 3-d

  9. Target Cell / Field Uniformity Target chamber: 40 cm long, ~2 cm diametter thin (0.1mm) windows, thick wall (~1mm) Pumping chamber: 2.5” diameter sphere for early 6 GeV experiments 3.5” for GEn 3.0” for transversity series Uniform field region: 10-3 level gradient: < 30 mg/cm All three coils have been mapped, well studied

  10. Asymmetry Measurements for Spin Experiments Double spin symmetries for polarized beam on polarized targets Figure of Merit (FOM) depends on luminosity, beam and target polarization (squared) and dilution factor (squared)

  11. Polarized 3He Progress

  12. 3He Rb Rb K K K K 3He Hybrid: Increase Spin-Exchange efficiency

  13. Lasers: Narrow-width With new Comet (narrow-width) lasers, polarizations > 70% Left: Blue is current lasers, Red is Comet laser Right: Absorption spectrum of Rb

  14. Polarization Measurements • 3He NMR in both pumping chamber and target chamber: ~2-3% • only longitudinal in target chamber • 3-d in pumping chamber • both field sweep and RF • field uniformity/ stability • temperature/ density • Water calibration in target chamber: ~ 2-3% • flux • field sweep • EPR in pumping chamber, absolute: ~ 2-3% • k0 • temperature/ density • Diffusion from pumping to target chamber: 2-3% • Total uncertainty @ target chamber @ 3-5% • Cross-check with elastic asymmetry (typically ~5% level)

  15. 12 GeV Experiments Requirements Plan for Polarized 3He Target Upgarde

  16. 12 GeV Polarized 3He Target Requirements Exp Density Length Pol. Current Lumi Polarimtery A1n-A: 23 days, A- , BigBIte, thin window/collimation, BB field shield/compensation prop 10 amg 60 cm 55% 30 uA 3x1036 3% accept 10 amg 40 cm 55% 15-30 uA 1-2x1036 3% GENII:50 days, A-, BigBite/SuperBB, thin window/coll., BB/SBB field shield/comp. prop. 10 amg 60 cm 60% 60 uA 6x1036 3% acceptable: 5/8 FOM SIDIS: 64 days, A-, BigBIte/SuperBB, vertical polarization(?) and fast spin flip (2 min) prop 10 amg 60 cm 60% 40 uA 4x1036 3% acceptable 5/8 FOM d2n-C, 29 days, A-, HMS/SHMS prop 10 amg 60 cm 55% 30 uA 3x1036 3% accept 10 amg 40 cm 55% 15 uA 1x1036 3% A1n-C , 36 days, A, HMS/SHMS prop 10 amg 60 cm 60% 60 uA 6x 1036 3% acceptable 10 amg 40 cm 60% 60 uA 4x 1036 3% Note: Another two approved experiment E12-10-006 and E12-11-007 (both related to SOLIDS), requirements for 3He target already achieved

  17. Considerations for Upgrade Plan • Goal: meet experiment needs within budgetary/manpower/schedule constraints • consider both Hall A and C together. • Schedule: A1n-A in 2016 • d2n-C in 2017 (A1n-C follow immediately if possible) • Options: • 1) use the (transversity) target system as it is with almost no change • 2) upgrade to have FOM by a factor of 3 first (A1n-A, d2n-C. maybe SIDIS) • 3) full upgrade to have FOM by a factor of 8 (GENII, A1n-C) • Series discussions/iterations: JLab 3He group, engineering group, user 3He groups, experimental proponents, Hall A/C and Physics Division management. • option 1) too strong impacts on experiments • 3) not enough resource (manpower/ cost) • Decision: Go with option 2 for A1n-A in 2016, d2n-C in 2017 • work in parallel (best effort) or afterwards to further upgrade to 3)

  18. Upgrade Plan • First Step: 40 cm target to reach ~60% polarization with 30 uA • Cells with convection flow • Single pumping chamber with 3.5” diameter sphere • Shield pumping chamber from beam radiation damage: • New oven design/over support • Pulsed NMR, calibrated with EPR and water NMR • Measure EPR calibration constant k0 to operation temperature (user responsibility) • Metal end-windows desirable (optional for 30 uA, must for 60 uA, user responsibility) • Using existing magnets, supports, and most components. • Second Step: upgrade to (possibly 60cm) ~60% pol with 60 uA • to meet A1n-C and GENII requirements • Best effort, i.e., depends on resource availability

  19. Upgrade Status: Convection Cell From Jie Liu • New convection style cell (single pumping chamber) • “Protovec-I” tested at UVa, is at Jlab now • 3D measurement of the cell, transferred into CAD model • Made customized mount and oven bottom piece • Start to do test on this convection cell soon

  20. Polarimetry

  21. Pulse NMR @ JLab • Pulse NMR compared with regular NMR • Pulse NMR signal vs time RF Stops Decay starts

  22. Lasers • New narrow-width laser • Problem: Comet laser (25W, 0.2nm width) production was discontinued! • Found two new vendors: QPC and Raytum • Purchased one QPC laser (25W, 0.3nm width) (Hall C) and tests underway • Raytum visit and demo @ JLab • Possible upgrade to our existing Coherent lasers by Raytum

  23. Summary • Polarized 3He target is central to JLab spin experiments • Outstanding performance for 6 GeV experiments(13) • Seven high-impact 12 GeV polarized-3He experiments/requirements • Upgrade plan and status