[Halld-tracking-hw] FDC Prototype Gas leak discussion

[Fernando J. Barbosa]

Hi Tim,

I have a few concerns about the re-design to address the gas leaks with 
foam gaskets. I suggest getting more information on the foam gaskets:

a. material composition
b. outgassing
c. adhesive
d. long term performance with Ar-CO2
e. radiation "hardness".

Most foam gaskets and contact adhesives loose their properties over 
time. In particular, most foam gaskets loose their elasticity and 
crumble, even with closed cell compositions. I am concerned that after 2 
years of operation leaks will develop.

Because the FDC is such a complex detector, there is likely room for 
improvement in several areas and the prototype serves as a good model 
for further tests and modifications. I know that a number of remedies 
have been tried. I, however, would like to see a document detailing 
systematic tests and results with the prototype, i.e. a test report. A 
lot of effort has been devoted to the nominal design with O-rings over 
the years and Bill has worked very hard to get it working. I am 
concerned that we will have a complete re-design of the "sealing" 
approach before assessing all the risks and root causes of the problem 
with the prototype.

Best regards,
Fernando


Best regards,
Fernando




Tim Whitlatch wrote:
> Hi All,
>
> Here are my notes from the discussion of the gas leaks in the FDC full 
> scale prototype.
>
> 1. Causes and potential fixes for the production  packages were discussed
> 2. Some known and Possible causes of leaks include leaks through the 
> rohacel bonding boudaries, deflection of unsupported wireplane pc board 
> under o-ring, grounding vias on pc board, bond voids on cathode 
> sandwich, protrusion of traces (3-4 mils) on pc board, not enough 
> compression on o-ring, too much compression on rohacel, not enough 
> stifnness in outer channel supports.
>  
> Action items
>
> a. Develop test plan for testing existing design, slightly changed 
> design and addition of G10 ring to support bolts and gas seal (Bill Crahen)
> b. Get worst case additional material to Simon for background analysis 
> (Bill Crahen)
> c. Perform background analysis on increased material (Indiana U?)
> d. Gather all changes needed for production pc board (Kim Shinault).
>
> Cheers,
>
>        Tim
>
>
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