Duke nEDM Collaboration Meeting The status of 3 He Relaxation Time Measurement at ~400mK Q. Ye, D. Dutta, H. Gao, W. Zheng, X. Zhu Duke University R. Golub, P. Huffman, F. Dubose NC 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 4 He capillary 3 He transfer Buffer Volume (copper) Mixing Chamber Filled with polarized 3 He Distance between the top polarized 3 He cell and the bottom acrylic cell ~ 218.4cm d-TPB coated acrylic cell cm IVC

Transfer Polarized 3 He Transfer polarized 3 He 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 4 He (~63% full), cooled down to 0.530K Total amount of 3 He in the cell was mol (polarization~5%) 3 He 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 4 He

Duke nEDM Collaboration Meeting After Modification 0.25mm capillary restrict 4 He film flow Grooves for copper wires to go thru Gold- plated % 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 ~ e-5 mBar Stable operation Condensing 4 He into acrylic cell volume: ~ 54cc (need ~ 5000 torr 7.5 liter 4 He to fill)

3 He Relaxation Time Duke nEDM Collaboration Meeting Wall depolarization probability is deduced 3 He relaxation time measurements

nEDM experimental cell The neutron EDM experimental cell ~ 7.6cm × 10.2cm × 50.0cm (S/V ~ 0.5) Scaled 3 He relaxation time ~ 4260s (S/V=1.284) or 4910s (S/V = 1.48). 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 3 He 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!