getters/molecular (fwd)

[Tim Abbott]

Re-distributed, with permission:

> From reed at noao.edu Fri Feb  9 07:47:42 1996
> Date: Fri, 9 Feb 96 10:47:38 MST
> From: reed at noao.edu (Richard Reed X267)
> Message-Id: <9602091747.AA01380 at bigx.tuc.noao.edu>
> To: tmca at cfht.hawaii.edu
> Subject: getters/molecular
> 
> 
> >From KPNO Tucson, our word without authority is that we use a ceramic
> pellet called Lindy5 for the 5 mico size of the traps.  A 150-200
> cc canister is attached to the back end of the LN2 tank(away from the
> ccd)  There is a potential for generating a small amount of ceramic "dust"
> due to the temperature cycling.  The dust could end up on the ccd if
> conditions are just right.  It is easily removed with a short puff of
> de-ionized air.  
> 
> We prepare the canister of Lindy5 by baking it in a vacuum oven at 
> 250 deg C and 10-3 torr for 24-48 hours.  The dewar with CCD is prepared
> by elevating the temperature to 50 deg C while pumping at 10-5 torr.
> We will usually do this operation for as long as the dewar is avialable.
> (within reason of course)  We then cease pumping, vent to dry N2 and
> remove the back plate of the dewar.  We then install the 250 deg C
> canister on the 50 deg C LN2 tank and immediately close the dewar and
> start to pump.
> 
> What does this buy us?  We typically service our many dewars only once
> a year at our summer shutdown.  Sometimes we will put them on the
> pump if they are not being used but that is more for a "warm fuzzy"
> feeling, not that it is necessary.
> 
> We electropolish the dewars and they are assembled clean.  It is
> a shame we have to put a "dirty ccd" in them.  The O-rings are
> very lightly coated with vacuum grease.  I think we have had
> good success with this technique.  No creeping crude on CCDs
> etc.
> 
> Rich Reed
> 
> 


-- 
Timothy M. C. Abbott                http://www.cfht.hawaii.edu/~tmca/tmca.html