Polarized 3 He 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

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

Dynamic Nuclear Polarization (proton)

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

History: Spin Milestones Nature: ( : 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) : NMR for chemical analysis (10) 1973: Magnetic resonance imaging(15) :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?

JLab Polarized 3 He Target Performance for 6 GeV Experiments

Hall A polarized 3 He target longitudinal, transverse and vertical Luminosity=10 36 (1/s) (highest in the world) High in-beam polarization % Effective polarized neutron target 13 completed experiments 7 approved with 12 GeV (A/C) 15 uA 55-60%

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

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: level gradient: < 30 mg/cm All three coils have been mapped, well studied

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)

Polarized 3 He Progress

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

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

Polarization Measurements 3 He 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% 0 temperature/ density Diffusion from pumping to target chamber: 2-3% Total target 3-5% Cross-check with elastic asymmetry (typically ~5% level)

12 GeV Experiments Requirements Plan for Polarized 3 He Target Upgarde

12 GeV Polarized 3 He Target Requirements ExpDensity 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 3x % accept10 amg40 cm55%15-30 uA1-2x % GENII:50 days, A-, BigBite/SuperBB, thin window/coll., BB/SBB field shield/comp. prop. 10 amg60 cm60%60 uA 6x % acceptable: 5/8 FOM SIDIS: 64 days, A-, BigBIte/SuperBB, vertical polarization(?) and fast spin flip (2 min) prop 10 amg60 cm60%40 uA4x % acceptable5/8 FOM d2n-C, 29 days, A-, HMS/SHMS prop10 amg 60 cm55%30 uA3x % accept10 amg40 cm55%15 uA 1x % A1n-C, 36 days, A, HMS/SHMS prop 10 amg60 cm60%60 uA6x % acceptable10 amg40 cm60%60 uA4x % Note: Another two approved experiment E and E (both related to SOLIDS), requirements for 3 He target already achieved

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)

Upgrade Plan First Step: 40 cm target to reach ~60% polarization with 30 uA 1. Cells with convection flow 2. Single pumping chamber with 3.5 diameter sphere 3. Shield pumping chamber from beam radiation damage: 4. New oven design/over support 5. Pulsed NMR, calibrated with EPR and water NMR 6. Measure EPR calibration constant 0 to operation temperature (user responsibility) 7. Metal end-windows desirable (optional for 30 uA, must for 60 uA, user responsibility) 8. 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

Upgrade Status: Convection Cell 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 From Jie Liu

Polarimetry

Pulse JLab RF Stops Decay starts Pulse NMR compared with regular NMR Pulse NMR signal vs time

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 JLab Possible upgrade to our existing Coherent lasers by Raytum

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