Polarized 3 He Target for 12 GeV Experiments J. P. Chen, August 15, 2012, JLab Experiments and...
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Transcript of Polarized 3 He Target for 12 GeV Experiments J. P. Chen, August 15, 2012, JLab Experiments and...
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)
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?
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
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
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.”