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Polarized 3 He Target for 12 GeV Experiments J. P. Chen, August 15, 2012, JLab

Polarized 3 He Target for 12 GeV Experiments J. P. Chen, August 15, 2012, JLab. Experiments and requirements Target performance from previous experiments Upgrade/design / R&D consideration and status (Gordon) Hall C / A compatibility and special consideration (Patricia)

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Polarized 3 He Target for 12 GeV Experiments J. P. Chen, August 15, 2012, JLab

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  1. Polarized 3He Target for 12 GeV Experiments J. P. Chen, August 15, 2012, JLab • Experiments and requirements • Target performance from previous experiments • Upgrade/design / R&D consideration and status (Gordon) • Hall C / A compatibility and special consideration (Patricia) • Discussion on cost, manpower, schedule consideration (All)

  2. Experiments and Requirements

  3. 12 GeV Polarized He3 Experiments Total 7 approved experiments using polarized He3 target Hall A: 1) A1n: BigBite/HRS, upgrade luminosity (3x1036?) candidate for early running 2) GENII: SuperBigBite+…, demanding luminosity (1037?) 3) SIDIS(SBB): SuperBigBite+…, less demanding than GENII? 4) SIDIS(T): SoLID, as proven performance (1x1036), later 5) SIDIS(L): SoLID, as proven performance (1x1036), later Hall C: 1) d2n (2016?) upgrade luminosity (3x1036 ?) 2) A1n (follow d2n?) demanding luminosity (1037 ?) Will focus discussion on 1) and 2) from both halls.

  4. Experimental requirements Hall A 1) A1n (early round?) Luminosity: 3x1036? 30 uA ? 60 cm? 10 amg Average in-beam polarization: 60%? use convection cell separate (shield) pumping chamber from target chamber increase pumping chamber volume (x3?) Windows: thin? possibly metal and/or coating? need collimator Walls: ~1 mm GE180 glass ok? Need shield or compensation coils: fringe field from BigBite (1.5m?) Polarimetry: 3%? EPR (AFP)?, pulsed NMR?, NMR (AFP)?, water calibration?

  5. Experimental requirements Hall A 2) GENII (Super BB) Luminosity: 1037? 60 uA ? 60 cm? 15 amg? metal target chamber required Average in-beam polarization: 60%? use convection cell separate (shield) pumping chamber from target chamber increase pumping chamber volume (x8?) Windows: thin? metal and/or coating required? need collimator? Walls: thin metal? Need shield or compensation coils: fringe field from SBB? (distance?) Polarimetry: 3%? EPR (AFP)?, pulsed NMR?, NMR (AFP)?, water calibration?

  6. Experimental requirements Hall C 1) d2n (2016?): 29 PAC days Luminosity: ideal >3x1036?, acceptable: 1036 ideal: 30 uA on 60 cm? 10 amg acceptable: 15 uA on 40 cm, 10 amg Average in-beam polarization: 55% use convection cell separate (shield) pumping chamber from target chamber increase pumping chamber volume (x3?) in ideal case Windows: regular thickness ok need collimation for forward angle SHMS kinematics Walls: ~1 mm GE180 glass ok Need compensation coils: fringe field from SHMS bender (distance?), new SHMS pivot Polarimetry: 2-3% EPR (AFP)?, pulsed NMR?, NMR (AFP)?, water calibration?

  7. Experimental requirements Hall C 2) A1n Luminosity: 1037? 60 uA ? 60 cm? 15 amg? metal target chamber required Average in-beam polarization: 60%? use convection cell separate (shield) pumping chamber from target chamber increase pumping chamber volume (x8?) Windows: ok metal and/or coating required? need collimator? Walls: ok Need shield or compensation coils: fringe field from SHMS bender? (distance?), SHMS pivot? Polarimetry: 3%? EPR (AFP)?, pulsed NMR?, NMR (AFP)?, water calibration?

  8. Target Performance from Previous Experiments

  9. Hall A polarized 3He target • 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

  10. Progress with Polarized 3He SLAC (1990s) , r ~ 10 amg, P ~ 35%, L~ 1035 neutron-cm-2s-1 JLab (1998-2009), 10 amg, 35% -> ~60% , 1036 (up to 15 uA) GDH/Gmn:1998/1999, 10 amg, 35% , 1036 40 cm A1n/g2n: 2001, 10 amg, 40% , <1036 testing Duality/SAGDH: 2003, 10 amg, ~40% , <1036 ice-cone GEn: 2006, 10 amg, ~50% , 4*1035 hybrid Transversity/+5: 2009, 10 amg, 55-60% , 1036 narrow Laser Future: A1n (early round?) improve luminosity to 3x1036? convection +volume increase ? GENII (SBB) improve luminosity to 1037? metal cell, …? SIDIS (SBB) ? Hall C: d2n (2016?) 3x1036 , fit Hall C pivot? special consideration? A1n (follows d2n?) 1037

  11. Polarized 3He Progress

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

  13. Target Cell / Field Uniformity Target chamber: 40 cm long, ~2 cm diameter, thin (0.1mm) windows, thick wall (~1mm) A1n: 25 cm long SAGDH: special shape (ice-cone) GDH experiment, cell survived 24 uA for half an hour Pumping chamber: 2.5” diameter sphere for earlier experiments 3.5” for GEn (tested 2.5, 3.0 and 3.5”) 3.0” for transversity/d2n/Ay/(e,e’d) Uniform field region: 10-3-10-4 level covers both target chamber (40 cm) and pumping chamber gradient: < 30 mg/cm the larger coils will cover larger region All three coils have been mapped, well studied

  14. 3He - Comet Lasers With new Comet (narrow-width) lasers, polarizations > 70% Left: Blue is current lasers, Red is Comet laser Right: Absorption spectrum of Rb

  15. 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% • cell specific information • parameters for modelling • Total uncertainty @ target chamber @ 3-5% • Cross-check with elastic asymmetry (typically ~5% level)

  16. Upgrade to Meet Experimental Needs design consideration and options

  17. Upgrade to Meet Experimental Needs • Shield pumping chamber from beam radiation damage: • separate pumping chamber away from target chamber • add shielding (tungsten), support shielding • Speed up circulation: convection flow • Target cell for higher current: • glass or metal cell? up to ~30 uA ok for glass cell? • length? 60 cm? (affect magnet design too) • Increase pumping chamber volume: • how much? double chamber? • cost consideration (He3, cell, laser power, ...)? • Magnet: existing ones or new design? • Support structure: upgrade/improvements? • or new design? • Polarization measurement: • pulsed NMR needed for metal cells • absolute calibration (AFP): EPR and/or water?

  18. Options, Manpower, Cost, Schedule? • Goal: meet experiment needs within budgetary constraints • One path: upgrade to have luminosity by a factor of 3 first (A1n-A, d2n-C) • then another a factor of 3 in 2nd stage (GENII, A1n-C) • Length of target cell? • Uniform field region • New magnet design? • Pumping Cell Size? • Costs: 3He gas, cells, lasers, optical-fibers, optics, oven, ... • Mechanical support/motion system • Design manpower /costs • Option A: simple design/existing magnets/minimum modification/not full size • guesstimation: design/engineering: ~ 1-2 man-year (similar to transversity) • cost: ~ $ 370-500K (similar to transversity/d2n...) • Option B: large size pumping cell /mostly new design • guesstimation: design/engineering: ~ 3-4 man-year (similar to GEn) • cost: ~ $ 1M • Need R&D/design activities by the user groups and at Jlab • User contributions are essential

  19. Options for A1n-A running from Gordon          Option                                    Cost           Performance       ------------------------------------------------------------------------------ 1)  Transversity target as is            200K          1/3 Luminosity 2) Trans. w convection (minimal)   300K           1/2 Luminosity     3) Trans. w convection (full)           375K           2/3 Luminosity    4) Double-pumping ch. w conv.     0.5-1.0M      Full Luminosity Gordon: “(We) would like to present you with an idea that might allow the Hall A A1n experiment to remain in the running for early (first?) running…. we advocate going with option 3.”

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