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)  Discussion on cost, manpower, schedule consideration (All)

Experiments and Requirements

12 GeV Polarized He3 Experiments Total 7 approved experiments using polarized He3 target Hall A: 1) A1n: BigBite/HRS, upgrade luminosity (3x10 36 ?) candidate for early running 2) GENII: SuperBigBite+…, demanding luminosity (10 37 ?) 3) SIDIS(SBB): SuperBigBite+…, less demanding than GENII? 4) SIDIS(T): SoLID, as proven performance (1x10 36 ), later 5) SIDIS(L): SoLID, as proven performance (1x10 36 ), later Hall C: 1) d2n (2016?) upgrade luminosity (3x10 36 ?) 2) A1n (follow d2n?) demanding luminosity (10 37 ?) Will focus discussion on 1) and 2) from both halls.

Experimental requirements Hall A 1) A1n (early round?) Luminosity: 3x10 36 ? 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?

Experimental requirements Hall A 2) GENII (Super BB) Luminosity: ? 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?

Experimental requirements Hall C 1) d2n (2016?): 29 PAC days Luminosity: ideal >3x10 36 ?, acceptable: 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?

Experimental requirements Hall C 2) A1n Luminosity: ? 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?

Target Performance from Previous 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

Progress with Polarized 3 He SLAC (1990s),  ~ 10 amg, P ~ 35%, L~ neutron-cm -2 s -1 JLab ( ), 10 amg, 35% -> ~60%, (up to 15 uA) GDH/Gmn:1998/1999, 10 amg, 35%, cm A1n/g2n: 2001, 10 amg, 40%, <10 36 testing Duality/SAGDH: 2003, 10 amg, ~40%, <10 36 ice-cone GEn: 2006,  10 amg, ~50%, 4*10 35 hybrid Transversity/+5: 2009, 10 amg, 55-60%, narrow Laser Future: A1n (early round?) improve luminosity to 3x10 36 ? convection +volume increase ? GENII (SBB) improve luminosity to ? metal cell, …? SIDIS (SBB) ? Hall C: d2n (2016?) 3x10 36, fit Hall C pivot? special consideration? A1n (follows d2n?) 10 37

Polarized 3 He Progress

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 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: 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

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

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%  0 temperature/ density  Diffusion from pumping to target chamber: 2-3% cell specific information parameters for modelling Total target 3-5% Cross-check with elastic asymmetry (typically ~5% level)

Upgrade to Meet Experimental Needs design consideration and options

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?

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 2 nd 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: ~ $ K (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

Options for A1n-A running from Gordon Option Cost Performance ) 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 M 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.”