Polarized 3He Target

On Behalf of the JLab Polarized 3He Target Group

Mingyu Chen

University of Virginia

January 28, 2021

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Introduction to 3He Polarization

● Polarized target for study the spin structure of nucleon. ● Free neutron mean lifetime: 880.2 s.

● The unpaired neutron carries the majority of the 3He nucleus  polarization.

● Polarized 3He is a good effective polarized neutron target.

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Spin Exchange Optical Pumping (SEOP)

1. Optical Pumping

2. Spin Exchange

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Polarized 3He Targets Performance Evolution

Pumping  

chamber

1-inch  sphere

Target chamber

Transfer  tube

GEn (E02-013): Started to use Rb/K hybrid alkali cell.

Transversity (E06-010):

Started to use narrow band laser.

● 12 GeV era Target Cell:

 Target chamber length: 40 cm ● Beam Current: 30uA

Reached over 50% in beam  

polarization

Luminosity: ~ 2.2x1036 cm-2s-1  

● Convection Cell (instead of diffusion  cells used in the 6 GeV era)

→ convection allows for more uniform  polarization between target and  

pumping chamber

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Target Activities

Target Activities at JLab:

People at JLab:

• PhD students: Junhao Chen (W&M, Todd Averett), Mingyu Chen (UVa, Xiaochao Zheng), Murchhana Roy  (University of Kentucky, Wolfgang Korsch), Melanie Rehfuss (Temple, Zein-Eddine Meziani) • Postdoc: Arun Tadepalli, William Henry, Jixie Zhang

• Engineers/Designer (Bert Metzger)

• Installation (Walter Kellner, Hall C technicians)

• Supervisor/coordinator (Jian-ping Chen)

Overview of Activities:

• Design to fit the polarized 3He into Hall C (first time), construction (Bert)

• Develop pulse NMR (Mingyu)

• Upgrade and commissioning EPR (Melanie, Todd, Junhao, Sumudu Katugampola from Uva) • Commissioning NMR (Junhao, William)

• Field mapping (Jixie et al.)

• Field direction measurement (Murchhana, Arun)

• Reference cell and cooling jets (Todd)

• Target ladder alignment (Alignment group, Bert, Arun)

• Installation (Walter Kellner, Hall C technicians, Bert, alignment group et al.)

• Slow control system (Brad Sawatzky, Ethan Becker, Junhao, Arun, William, Mahlon Long, Mark Taylor,  Chris Carlin,Mindy Leffel)

Target Activities at User Institutes:

• Cell fabrication and testing: UVa (Gordon Cates), W&M (Todd Averett)

• k0 measurement: W&M (Todd Averett), UVa

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Polarized 3He Target in Hall C

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EPR

PNMR

Polarimetry for 3He in Target Cell

1. Adiabatic Fast Passage Nuclear  

Magnetic Resonance (AFP-NMR)  

● Magnetic Resonance of 3He Nucleus

● Sweep the holding field under AFP  

condition to flip the Nucleon spin  

direction back and forth.

● Relative measurement, calibrate with  

water NMR or EPR.

2. Pulse NMR  

● Use resonance RF pulse at 3He Larmor  

frequency to tilts the Nucleon spin to a  

certain angle.

● Relative measurement, calibrate with  

AFP-NMR.

● Implemented for the first time on  

polarized 3He target.

3. Electron Paramagnetic  

Resonance (EPR)

● Magnetic resonance of the alkali atoms

● Resonance shifted due to polarized 3He,  

get the resonance frequency difference  

by flipping the 3He polarization direction.

● Get 3He polarization from resonance  

frequency difference. Absolute  

measurement.  

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NMR  

(by Junhao Chen)

● AFP-NMR was the primary method to  

measure the 3He target polarization  

during the production run.  

● Two pairs of pumping chamber pickup  

coils: one in longitudinal direction,  

another one in transverse direction

● Two pair of target chamber pickup coils:  upstream and downstream  

● Target chamber pickup coils are also  

used to study convection speed

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EPR System

(by Melanie Rehfuss and Junhao Chen)

● EPR provides absolute polarimetry.

● EPR polarimetry provided calibrations to NMR system.

● Used a photo diode with D1 light filter to collect D2 light.

● The uncertainty for target polarimetry is about ±3%.

● EPR FM Sweep ● EPR AFP Sweep

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Pulse NMR

(by Mingyu Chen)

● Advantage: Took shorter time to complete  

measurement, less depolarization compare to  AFP-NMR.

● PNMR was performed at transfer tube which was  calibrated by AFP-NMR at pumping chamber.

● For most of the measurements, polarization from  PNMR agrees with NMR within ±2%.

● However, the drift of holding field magnitude over  time changed PNMR signal amplitude and  

introduce additional uncertainty.

● Still need to do detailed analysis to characterize  

this effect on PNMR signal and determine the  systemic uncertainty for PNMR.

● Current fit for the signal by the FID fitting  A0 

function to obtain PNMR amplitude .  S(t)=FID(t)=A0cos(ωt+ϕ0)e−t /T2+a∗t+b ● Obtain PNMRamp/NMRamp ratio in order to  calibrate PNMR with NMR.

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Magnetic Field Direction Measurement

(by Murchhana Roy)

● A novel air-floated compass was developed and built as  

the commercially available compasses cannot achieve  

the desired level of precision.

● The magnetic field direction was determined from the  

surface normal of the aligned compass mirrors by  

mapping incident and reflected laser beam spots on a  

screen.

● The points were surveyed by JLab alignment group in  

absolute Hall C coordinate system.

● Measured absolute direction of the target  

magnetic field in the Hall C coordinate  

system precisely to about ±0.1°.

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Holding Field Mapping

(by Jixie Zhang and William Henry)

• Measure and correct the field gradient  

and vertical field components caused by  

the magnetic structures surrounding the  

target and fringe field of SHMS HB.

• Use 1D and 3D Hall probe (from Steve  

Lassiter) mounted on a 3-axis movable  

slotted rack .

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Production Cell Performance

(for A1n/d2n experiments)● Target cell polarimetry was  

performed by AFP-NMR in  

pumping chamber and calibrated  

with EPR measurements.  

Reached over 50% polarization  

with 30 uA electron beam.

Polarized 3He  

target polarization  

during A1n  

production running.

Polarized 3He  

target polarization  

during d2n  

production running.

● Still need to do detailed  

analysis to get target  

polarization in target chamber  

with systemic uncertainties.

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Convection Speed Test

Preliminary

● Sent RF pulse to PNMR coil and monitor the evolution of NMR signal at TC Upstream and  TC Downstream, the convection speed will be determined.

● From the two curves of NMR signal amp for TC Upstream and TC Downstream, the time  difference for first NMR amplitude valley is ~2.0 min.

● Since center of two pick up coil is apart by ~13.4 cm, then convection speed is ~6.7 cm/min.

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Production Cells for the Experiment  

● Production cells are fabricated and filled by Gordon’s group at UVa. Professor  Todd Averett at W&M helped to fill some of the cells.

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Summary

● For the first time, install the upgraded polarized 3He target for 12 GeV era in  JLab Hall C. The target reached the expected performance with over 50%  3He polarization in 30 uA electron beam.

● Implement new method of polarimetry (pulse NMR) on the polarized target  cell.  

● Offline detailed analysis for target polarimetry is in progress.

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AcknowledgmentsPeople

Institutions

D. Androic, W. Armstrong, T. Averett, X. Bai, J. Bane, S.  Barcus, J. Benesch, H. Bhatt, D. Bhetuwal, D. Biswas, A.  Camsonne, G. Cates, J-P. Chen, J. Chen, M. Chen, C.  Cotton, M-M. Dalton, A. Deur, B. Dhital, B. Duran, S.C. Dusa,  I. Fernando, E. Fuchey, B. Gamage, H. Gao, D. Gaskell, T.N.  Gautam, N. Gauthier, C.A. Gayoso, O. Hansen, F.  Hauenstein, W. Henry, G. Huber, C. Jantzi, S. Jia, K. Jin, M.  Jones, S. Joosten, A. Karki, B. Karki, S. Katugampola, S. Kay,  C. Keppel, E. King, P. King, W. Korsch, V. Kumar, R. Li, S. Li,  W. Li, D. Mack, S. Malace, P. Markowitz, J. Matter, M.  McCaughan, Z-E. Meziani, R. Michaels, A. Mkrtchyan, H.  Mkrtchyan, C. Morean, V. Nelyubin, G. Niculescu, M.  Niculescu, M. Nycz, C. Peng, S. Premathilake, A. Puckett, A.  Rathnayake, M. Rehfuss, P. Reimer, G. Riley, Y. Roblin, J.  Roche, M. Roy, M. Satnik, B. Sawatzky, S. Seeds, S. Sirca,  G. Smith, N. Sparveris, H. Szumila-Vance, A. Tadepalli, V.  Tadevosyan, Y. Tian, A. Usman, H. Voskanyan, S. Wood, B.  Yale, C. Yero, A. Yoon, J. Zhang, Z. Zhao, X. Zheng, J. Zhou

PhD Candidates Spokespeople  

A.I. Alikhanian National Science Laboratory; Argonne  National Laboratory; Artem Alikhanian National  Laboratory (AANL).; Christopher Newport University;  Duke University; Florida International University;  Hampton University ; James Madison University ;  Jefferson Lab; Kent State University; Mississippi State  University; Ohio University; Old Dominion University;  Rutgers University; Syracuse University; Temple  University; The College of William and Mary; Univ. of  Ljubljana; University of Connecticut; University of  Kentucky; University of Kentucky; University of New  Hampshire; University of Regina; University of  Tennessee; University of Virginia; University of Virginia;  University of Zagreb

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Other People’s Talks

(for A1n/d2n Experiments)

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Backup Slides

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Target Cell Glass Thickness Measurement

• Used ultrasonic thickness gauge to measure the wall thickness of target  chamber. (Mingyu Chen)

• Used laser interference pattern to measure the window thickness of target  chamber. (Christopher Jantz from UVa)

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