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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) - PowerPoint PPT Presentation
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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)
Experiments and Requirements
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.
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?
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?
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?
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?
Target Performance from Previous Experiments
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
Progress with Polarized 3He
SLAC (1990s) , ~ 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
Polarized 3He Progress
Hall A Polarized 3He TargetThree 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: 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
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 uncertainty @ target chamber @ 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 cellsabsolute 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 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
Options for A1n-A running from Gordon
Option Cost Performance ------------------------------------------------------------------------------1) Transversity target as is 200K 1/3 Luminosity2) 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.”