cyropumping materials

[ATWOOD at mps.ohio-state.edu]

Posted to CCD-world:
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1.  Put your charcoal in a box lined with filter paper to keep the dust down.

2.  Since charcoal does not trap water at room temperature the only way to
get water out of your Dewar is to pump for a very long time, waiting for the
water to come off the inner surfaces.  If you don't remove the water you can
wind up with the water on your chip as the system warms up or froming clouds
when you backfill your system.  I have gone to cold charcoal to "pump" the
air that diffuses through the o-rings and a WARM, easy to change, canister
of zeolite to pump the water.  Zeolite activated at 350 C will hold the water
partial pressure to a few microns and when you change it you are removing the water
from the system.  In fact one change a few weeks after pumping a Dewar is all
that is required unless it is open for a long time (days).

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