Diffusive Transport of 3 He in the EDM Experiment

# Diffusive Transport of 3 He in the EDM Experiment

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## Diffusive Transport of 3 He in the EDM Experiment

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1. Diffusive Transport of 3He in the EDM Experiment Steve Lamoreaux

2. Basic Idea • Superfluid Helium at sufficiently low “looks like” a perfect mechanical vacuum • We are working with low 3He density so 3He-3He collisions will not hinder diffusive/ballistic flow • Flow in pipes: Knudsen’s formula

3. What W do we need? • We have two cells, 10000 cm3 volume. We need an emptying time constant of about 50 seconds (4 time constants to get to 98% clean) • So W=1/(200 cm3/sec) • m=2.2 m3 • For 50 cm length, T=0.3 K, d=2.3 cm • For 100 cm length, d=2.9 cm

4. What is the time constant to empty the cell through a 2 cm diameter hole? For v= 50 m/s, A=3.14 cm2, V=10000 cm3 t= 2.5 sec Or, for 10000 sec, A=10-3 cm2 This is a 1 micron gap around a 6 cm circumference

5. Overall Scheme Collection Volume Helium Level Cell valve Selection Valve charcoal Exp. Cells

6. The Pressurization Problem • What if we have to run with the superfluid pressurized to get a high dielectric strength? • Then we can’t have a free liquid surface • Possible to have the ‘main bath’ pressurized, the cells at low pressure?

7. Gradient Requirements Holding Cells: See hreq.pdf for details

8. Charcoal Conveyor Belt Charcoal coated “conveyor belt” periodically moves charcoal to hot region for cleaning Purification volume

9. Electrical Detection of Scintillations I+ 5000 ion pairs??? per capture I- About 1 pA if collected in 1 msec; 1 fA/rtHz amp provides s/n of 25

10. ~ 2.0 K Ion Mobility in SFHe E > 104 V/cm ions detach from vortices