Polarized 3He Target for 12 GeV Experiments J. P. Chen, February 12, 2013, Hall A Meeting

Introduction

Target performance for 6 GeV experiments

12 GeV experiments and requirements

Upgrade plan and status

Principle for Polarizing Targets

• Polarization

• Brute Force:

Zeeman split: energy level split in a magnetic field B

Boltzmann distribution: spin up (+ state):

spin down (- state):

• Magnetic moment

much easier to polarize electron (atom) than polarize proton (nuclei)

large B (~15T) , low T (~10mK) to have significant polarization for proton

NN

NNP

kTBeN /~

kTBeN /~

m1~ pe

Dynamic Nuclear Polarization (proton)

Spin exchange Optical Pumping for 3He

Rb 3He

Two step process:

• Polarize Rb by optical pumping

•Transfer Rb atomic (electron) polarization to 3He nucleus by spin-exchange interaction

History: Spin Milestones

• Nature: (www.nature.com/milestones/milespin) 1896: Zeeman effect (milestone 1) 1922: Stern-Gerlach experiment (2) 1925: Spinning electron (Uhlenbeck/Goudsmit)(3) 1928: Dirac equation (4) Quantum magnetism (5) 1940: Spin–statistics connection(7) 1946: Nuclear magnetic resonance (NMR)(8) 1950-51: NMR for chemical analysis (10) 1973: Magnetic resonance imaging(15) 1975-76:NMR for protein structure determination (16) 1990: Functional MRI (19) 1991: Magnetic resonance force microscopy (21) 1997: Semiconductor spintronics (23) 2000s: Breakthroughs in nucleon spin/nucleon structure study? ?: Applications of nucleon spin physics?

M edical A pp licationM ed ical A pp lication Ð lung d iagnos tics by M agnetic R es onance Im ag ing (M R I)

#H e-M R I#H e-M R I

#H e S p in #H e S p in dens ity dens ity M R IM R I

Inhaled B ronchodilatorInhaled B ronchodilator

A s ym ptom atic A s thm atic

C o urte s y o f T . A lte s e t al., U nive rs ity o f V irg inia

C o urte s y o f W . H e il, U niv . M ainz

JLab Polarized 3He Target

Performance for 6 GeV 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 uA55-60%

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 diametter

thin (0.1mm) windows, thick wall (~1mm)

Pumping chamber:

2.5” diameter sphere for early 6 GeV experiments

3.5” for GEn

3.0” for transversity series

Uniform field region: 10-3 level

gradient: < 30 mg/cm

All three coils have been mapped, well studied

Asymmetry Measurements for Spin Experiments

• Double spin symmetries for polarized beam on polarized targets

• Figure of Merit (FOM) depends on luminosity, beam and target polarization (squared) and dilution factor (squared)

LfPPFOM tb *** 222

]s cm [ *I -12L

NN

NNfPP tb

A 1

Polarized 3He Progress

Hybrid: Increase Spin-Exchange efficiency

Rb K

KRb

K 3He

K 3He

Lasers: Narrow-width

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% Total uncertainty @ target chamber @ 3-5% Cross-check with elastic asymmetry (typically ~5% level)

12 GeV Experiments Requirements

Plan for Polarized 3He Target Upgarde

12 GeV Polarized 3He Target RequirementsExp Density Length Pol. Current Lumi Polarimtery

A1n-A: 23 days, A- , BigBIte, thin window/collimation, BB field shield/compensation

prop 10 amg 60 cm 55% 30 uA 3x1036 3%

accept 10 amg 40 cm 55% 15-30 uA 1-2x1036 3%

GENII:50 days, A-, BigBite/SuperBB, thin window/coll., BB/SBB field shield/comp.

prop. 10 amg 60 cm 60% 60 uA 6x1036 3%

acceptable: 5/8 FOM

SIDIS: 64 days, A-, BigBIte/SuperBB, vertical polarization(?) and fast spin flip (2 min)

prop 10 amg 60 cm 60% 40 uA 4x1036 3%

acceptable 5/8 FOM

d2n-C, 29 days, A-, HMS/SHMS

prop 10 amg 60 cm 55% 30 uA 3x1036 3%

accept 10 amg 40 cm 55% 15 uA 1x1036 3%

A1n-C , 36 days, A, HMS/SHMS

prop 10 amg 60 cm 60% 60 uA 6x 1036 3%

acceptable 10 amg 40 cm 60% 60 uA 4x 1036 3%

Note: Another two approved experiment E12-10-006 and E12-11-007 (both related to SOLIDS),

requirements for 3He target already achieved

Considerations for Upgrade Plan

Goal: meet experiment needs within budgetary/manpower/schedule constraintsconsider both Hall A and C together.

Schedule: A1n-A in 2016 d2n-C in 2017 (A1n-C follow immediately if possible)

Options: 1) use the (transversity) target system as it is with almost no change 2) upgrade to have FOM by a factor of 3 first (A1n-A, d2n-C. maybe SIDIS) 3) full upgrade to have FOM by a factor of 8 (GENII, A1n-C)

Series discussions/iterations: JLab 3He group, engineering group, user 3He groups, experimental proponents, Hall A/C and Physics Division management.

option 1) too strong impacts on experiments 3) not enough resource (manpower/ cost) Decision: Go with option 2 for A1n-A in 2016, d2n-C in 2017 work in parallel (best effort) or afterwards to further upgrade to 3)

Upgrade Plan

First Step: 40 cm target to reach ~60% polarization with 30 uA1. Cells with convection flow2. Single pumping chamber with 3.5” diameter sphere3. Shield pumping chamber from beam radiation damage: 4. New oven design/over support5. Pulsed NMR, calibrated with EPR and water NMR 6. Measure EPR calibration constant 0 to operation temperature (user responsibility)7. Metal end-windows desirable (optional for 30 uA, must for 60 uA, user responsibility)8. Using existing magnets, supports, and most components.

Second Step: upgrade to (possibly 60cm) ~60% pol with 60 uA to meet A1n-C and GENII requirements Best effort, i.e., depends on resource availability

Upgrade Status: Convection Cell

New convection style cell (single pumping chamber) • “Protovec-I” tested at UVa, is at Jlab now

• 3D measurement of the cell, transferred into CAD model

• Made customized mount and oven bottom piece

• Start to do test on this convection cell soon

From Jie Liu

Polarimetry

Pulse NMR @ JLab

RF StopsDecay starts

•Pulse NMR compared with regular NMR•Pulse NMR signal vs time

Lasers

New narrow-width laser• Problem: Comet laser (25W, 0.2nm width) production was discontinued!

• Found two new vendors: QPC and Raytum

• Purchased one QPC laser (25W, 0.3nm width) (Hall C) and tests underway

• Raytum visit and demo @ JLab

• Possible upgrade to our existing Coherent lasers by Raytum

Summary

Polarized 3He target is central to JLab spin experiments

Outstanding performance for 6 GeV experiments (13)

Seven high-impact 12 GeV polarized-3He experiments/requirements

Upgrade plan and status