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.”