3He Relaxation below 1 K

Jacob Yoder

UIUC

October 6th, 2006

Outline

• Goals

• Proposed method of measurement

• Status / To do

Goals

• Measure relaxation time of 3He on dTPB coated acrylic at temperatures between 0.3 K and 1.0 K

• Measure relaxation time of 3He in the presence of other materials

Proposed method

• Polarized 3He produced by MEOP

• Double cell: 3He polarized at room temp, T1 measured in cold cell

Manifold

RT pumping cell

Cold Cell

V1

V2

3He cycling

1) V1 open V2 open;

Evacuate cells

2) V1 open V2 closed;

Fill with 3He

3) V1 closed V2 closed;

Pump 3He

4) V1 closed V2 open;3He pulled into cold cell as pressure equalizes

5) V1 closed V2 closed;

Measure T1

Repeat

Manifold

RT pumping cell

Cold Cell

V1

V2

Status as of last meeting

• Cryostat reached 0.3 K unloaded

• Magnet built • ~ 1h relaxation

time seen in valve-less pyrex cells

Cool down with dummy cell

• Glass dummy cell cooled to ~1 K

• Anchors did not uniformly cool the cell

• Anchors will need to cover large fraction of the glass surface area

Magnet and NMR setup in place

• Magnet placed around cryostat

• Laser, valve-less double cell, coils put in place

Polarization measured in “cold” cell

• FID amplitude in the cold cell 3.3 V in old location, 2.1 V in cryostat

• T1 of 2500 s before, now T1 ~ 100 s

• T2 in each cell dropped by approximately ½

• Losses are likely due to nearby magnetic materials, which need to be moved away

Relationship between gradients and Relaxation times

mg/cm 12

120

2

242

GsT

Gl

DT

mG/cm 70 1001

2

20

1

GsTDG

BT

Mismatch between implied gradients likely due to highly localized gradient. Wilson seal or ball valve probably the culprit.

Nearby Magnetic Materials

Wilson SealBall Valve

Valve/O-Ring issues• Contamination of the MEOP discharge

– Contamination becomes problematic approximately 2 weeks after filling. This is much longer than the expected fill measurement cycle

• Depolarization of 3He as it passes through the valve– The valve did not reduce the polarization in the “cold”

cell in RT test

• “Real” valved double cell built

To Do• Reduce background gradients by removing

magnetic materials and possibly relocating cryostat +redo room temp test (2 wks)

• Put fill/pumpout manifold in place and test (3 wks)

• Relaxation measurement with pure 3He gas in pyrex cell below 1 K (3 wks)

• 4He wall coating? (2 wks)• Construct/borrow dTPB (?) coated cell and

perform relaxation measurement at working temperature (8-12 wks)

• Test other materials

Costs (to be assumed by Illinois)

• Upgrades to manifold -$500• Glassware -$1000• Materials for new cells 4X -$1200• LHe for tests (6 tests, 250 l/test) -$5265• Contingency (20%) -$1600• Total -$9600