Duke nEDM Collaboration Meeting

The status of 3He Relaxation Time Measurement at ~400mK

Q. Ye, D. Dutta, H. Gao, W. Zheng, X. ZhuDuke University

R. Golub, P. Huffman, F. DuboseNC State University

May 20, 2008

Duke nEDM Collaboration Meeting

Outline

• Experimental Apparatus

• 2007 Summer Results

• Modifications to the MC & acrylic cell

• 2008 April Results

• Future plan

Experimental Schematics

Detachable cell

Detachable cell mount

d-TPB coated acrylic cell

RF coils

Dilution Refrigerator

pickup coil

4He capillary

3He transfer

Buffer Volume (copper)

MixingChamber

Filled with polarized 3He

Distance between the top polarized 3He cell and the bottom acrylic cell ~ 218.4cm

d-TPB coatedacrylic cell

293.4 cm

IVC

Transfer Polarized 3He

• Transfer polarized 3He onto top of the DR using portable magnetic field – 90% polarization left

Duke nEDM Collaboration Meeting

2007 Results• Cell filled with 1.23mol

super-fluid 4He (~63% full), cooled down to 0.530K

• Total amount of 3He in the cell was 0.00092 mol (polarization~5%)

• 3He relaxation time (~1263 seconds with an AFP loss of 0.5%) at 7.5G holding field

• Hard to cool down the cell filled with super-fluid 4He

Duke nEDM Collaboration Meeting

After Modification0.25mm capillary restrict 4He film flow

Grooves for copper wires to go thru

Gold-plated 99.999% copper wires

2008 Results

Temperature sensor holder

Small copper piece

For the 1.5mm pure copper cooling wire to go through

1/8” copper tubing

Leak found at the joint

Duke nEDM Collaboration Meeting

The leak was found around this region. The hole was filled with stycast 1266.

Heat Input Study

• Lowest MC temp. ~ 44mK with the acrylic cell being empty (~15.3 kOhm)

Duke nEDM Collaboration Meeting

During the filling process, 1Kpot temperature ~ 2.05K (25.8 kOhm)

Still pressure ~ 8.5e-2 mBar

Still turbo power ~ 200W

IVC pressure ~1.2-1.4e-5 mBar

Stable operation

Condensing 4He into acrylic cell volume: ~ 54cc (need ~ 5000 torr 7.5 liter 4He to fill)

3He Relaxation Time

Duke nEDM Collaboration Meeting

• Wall depolarization probability is deduced

3He relaxation time measurements

nEDM experimental cell

• The neutron EDM experimental cell ~ 7.6cm × 10.2cm × 50.0cm (S/V ~ 0.5)

• Scaled 3He relaxation time ~4260s (S/V=1.284) or 4910s (S/V = 1.48).

Duke nEDM Collaboration Meeting

Duke nEDM Collaboration Meeting

Next steps

• Depolarization probability comparable (slightly worse) to that from 1.9K (~2e-7, Q. Ye et al. to appear in PRA)

• Improve 3He relaxation time, how?

– Better coating? How do we quantify coating, using atomic force microscope (AFM)?

• Put on gradient coils along z-axis to study geometric phase effect under nEDM experimental conditions

Duke nEDM Collaboration Meeting

Thank you!