CCD-world: Pleas help TASS

[Tom Droege]

The following was posted to CCD-world:

Mark,

Thanks for al the good advice.  I am slowly moving toward a continuous
flush with dry Argon.  This after a good bake out.  Just keep a small
positive pressure and operate like a proportional chamber.  I have done a
lot of that.  ( At Argonne in the HEP group many years ago).  The people at
Fermilab (where I am retired) tell me that super insulation does not work
at room temperature.  Of course it is a good general insulator.  But the
radiation shield division scheme that makes it really effective in vacuum
systems does not work when the primary loss is convection and conduction, I
am told. 

Thanks again,

Tom  

At 11:06 AM 5/5/00 -1000, you wrote:
>The following was posted to CCD-world:
>
>As a possible alternative to Tom's lack-of-vacuum camera enclosures one
>might try static fluxh & fill with *dry* nitrogen or other gas (not that
>expensive from Airco) to get as much moisture as possible out of the
>enclosure. If you basically flush the enclosure for a while (hours?)
>then valve it off at static pressure there won't be much exchange with
>outside air as long as you don't get thermal pressure changes to "pump"
>the leaks.
>To get cold, you need to solve aother problem - thermal capacity, since
>your TEC's are limited, you need to reduce the heat input - try a good
>layer of what we called "superinsulation" at Argonne National  lab -
>alternate layers of nylon mesh (the kind ballerina skirts are made from)
>and aluminized mylar film. A stack of this 2" thick with an overlapping
>wrap will insulate a LN2 pipe without any vacuum, so it approaches the
>R-value of vacuum without the mess. Since you aren't trying to get that
>cold, less thickness would be ok.
>
>As a getter, Drierite needs to be baked really well and you need to
>start pretty dry to get it to work, and more importantly you need
>surface area exposure - I'm not sure your .25" tube will give you enough
>circulation to dry the enclosure though the tube will be dry :-) Try
>enclosing a layer of drierite in filter paper ( to keep the dust in)
>inside the enclosure. This surely isn't the approach you'd take in a
>cryogenic camera, but this might be "good enough"!
>
>hope the ideas help,
>--
>    mfw
> Mark Waterson
> University of Hawaii - Institute for Astronomy - Haleakala
>Observatories, Maui
> 808-876-7600 x108  Office     808-243-5892   Observatory
>
>
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