Honeycomb grounding of the GLAST trays

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Honeycomb grounding of the GLAST trays
Alessandro Brez INFN Pisa
Tray electrical conductivity Carbon Carbon,
carbon fiber and Al core have good electrical
conductivity, but are connected together with non
conductive glue. The result is a poor electrical
connection, 10-100W from element to element. EM
tests demonstrated the need to have a good
grounding of the tray parts
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MCM mounting system
To avoid Carbon Carbon chipping, the MCM will be
not mounted by means of M1.6 screws. There will
be holes in the closeout and glued pins will
replace the screws. The MCM will be glued
(Scotchweld 2216 A/B gray). A tool will be used
to take in place the MCM during glue curing time.

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MCM closeout connection
The MCM ground will be electrically connected to
the closeout using pins with conductive glue in
the 3 ground holes.
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CORE CONNECTION SOLUTION 1
MCM closeout
Structural closeout
Connection wire
After the tray is completed, 4 grooves are
machined across the MCM-structural closeout
walls. The grooves are filled with a short
conductive wire and with conductive glue (Nusil
CV2646) The honeycomb is connected to the
structural wall trough the venting hole by means
of a glued wire. The MCM closeout wall is
connected to the MCM ground with a pin glued with
conductive adhesive
Groove filled with conductive glue
Venting hole
Glue joint
Experimental result all the tray parts
(closeouts, face sheet, honeycomb) are connected
with low resistance lt1W
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Core connection Solution 2
1) Add to the honeycomb conductive cylinders (
gold plated kapton tubes ) glued with conductive
adhesive
2) Put conductive glue on the closeout walls when
the tray is assembled, in correspondence to the
conductive cylinders. Push in place the closeout
walls that will compress the cylinders
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Conclusions

• The Minitower experience demonstrated the need of
  a good grounding of the honeycomb
• A solution 1 has been successfully tested
  electrically connecting all the tray parts after
  the tray building.
• A solution 2 with an internal connection of the
  parts, will be tested on the top/bottom trays of
  the EM tower. This solution seems more clean and
  easy. If in some cases this solution fails (Rgt1W
  between closeout and honeycomb), we can
  recuperate the tray using solution 1.
• Note we are testing the connection Al foils / Al
  foil / Carbon Carbon with conductive gluing
  joints. After 1 month from gluing, R?0.1W