1. Diffusive Transport of 3 He 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 3 He density so 3 He- 3 He collisions will not hinder diffusive/ballistic flow Flow in pipes: Knudsen’s formula

3. What W do we need? We have two cells, 10000 cm 3 volume. We need an emptying time constant of about 50 seconds (4 time constants to get to 98% clean) So W=1/(200 cm 3 /sec) m=2.2 m 3 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 cm 2, V=10000 cm 3  = 2.5 sec Or, for 10000 sec, A=10 -3 cm 2 This is a 1 micron gap around a 6 cm circumference

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

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

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

10. Ion Mobility in SFHe ~ 2.0 K E > 10 4 V/cm ions detach from vortices