Vacuum materials

[Peter.Pool at eev.com]

Posted to CCD-world:
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Hi

     Apart from making CCDs,  EEV make vacuum tubes.   In our experience, 
 for the temperature range envisaged for a dewar, the choice of material is 
not too difficult .

     What is most important is a low absorbency surface (not anodised) and 
the ability to remove low vapour pressure contaminants from that surface. 
   A raw machined surface inevitably includes "rolled over" surface features 
which trap machining oil etc.   This is best removed by de-greasing followed 
by acid etching ,  to give an open surface.   Provided this surface is kept 
clean (no finger grease) it will not be a significant outgassing source. 
  If you really want to minimise the surface area, use stainless steel, 
electro-polished after construction.

Peter Pool
EEV CCDs

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