From jdotson Sat Jul 13 15:15 CDT 1996
Date: Sat, 13 Jul 1996 15:15:14 -0500
From: jdotson (Jessie Dotson)
To: novak@clark.phys.nwu.edu
Subject: pumped pot work at yerkes 7/9-7/12
Cc: samuel@irastro.gsfc.nasa.gov


Giles,

Samuel and I installed a calibrated GRT on the pot and successfully
cooled down the dewar.  We came up with a crude test to look for plugs
at both room temperature and at LN2 temperature.  We pumped on the
reservoir while applying a back pressure of helium to the capillary.
We were able to confirm the line was open by briefly eliminating
the back pressure and observing the decrease in the reservoir
pressure.  Hopefully we can develop this test further so that we can
quantify the capillary impedance in both temperature ranges (which would
allow us to diagnose partial blockages as well as complete blockages).

We successfully cooled the dewar to He4 without blocking the capillary
and ran the pumped pot.  After Samuel left for Madison I heated the
pot and observed the resulting temperature range.  The results were
somewhat surprising - the temperature responded weakly for a large
range of input powers.  We didn't have enough helium to keep the dewar
cold over the weekend so the dewar is slowly warming up.

Over the weekend I'm going to do the calculations suggested by friday's
test.  I'll send you a summary when I'm done.

Monday Samuel and I will start working on a plan of action
incorporating what we learned from last week's test and what Samuel
learns from his visit to Madison.  More cryogens should be delivered
monday afternoon so we can do another run.

I think we will want to seriously consider setting up to log
temperatures, pressures and heater voltages on computer.  I think
we'll also want to revisit the method of attaching the capillary to
the reservoir.  An indium seal rather than a threaded expoxy seal
would greatly increase our ability to investigate systems with
varying flow impedance.  We may even want to redesign the pot slightly
to allow for better heat sinking to thermometers and heaters.

cheers
Jessie