Diffusive Transport of 3 He in the EDM Experiment Steve Lamoreaux

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

What W do we need? We have two cells, 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

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 sec, A=10 -3 cm 2 This is a 1 micron gap around a 6 cm circumference

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

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?

Gradient Requirements Holding Cells: See hreq.pdf for details

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

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

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