Download ppt - Polarized 3 He Target for 12 GeV Experiments J. P. Chen, August 15, 2012, JLab Experiments and requirements Target performance from previous experiments

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?


Hall A 2) GENII (Super BB)

Luminosity: 1037?

60 uA ? 60 cm? 15 amg?

metal target chamber required


use convection cell



Windows: thin?

metal and/or coating required? need collimator?

Walls: thin metal?


fringe field from SBB? (distance?)

Polarimetry: 3%?



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


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%



Hall C 2) A1n

Luminosity: 1037?

60 uA ? 60 cm? 15 amg?

metal target chamber required


use convection cell



Windows: ok

metal and/or coating required? need collimator?

Walls: ok


fringe field from SHMS bender? (distance?), SHMS pivot?

Polarimetry: 3%?


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.”