[Halld-tracking-hw] NO FDC meeting tomorrow Thu 03/29, short update below

[Lubomir Pentchev]

Dear all,

Bill, Dave, Beni will be missing tomorrow, so we decided to cancel this 
meeting.

After we found the main source of the oxygen contamination, the rough 
surface in the G10 groove, we are investigating further the effect of the 
different O-ring types. Using the testing chamber with the groove coated 
we tried different O-rings at different places and got these results for 
the oxygen:

two Buna-N in the spacer ring and one EPDM in the G10 groove - 280ppm 
two EPDM in the spacer and one EPDM in the G10 - 560ppm
two Buna-N in the spacer and one Buna-N in the G10 - 290ppm
two Viton in the spacer and one Viton in the G10 - measuring right now

Even we were satisfied with the Buna-N results, there are reports of 
higher outgassing for this material, including in the NASA data base.
That's why we decided to try Viton. By the end of the week we will decide 
about the O-ring material and plan to start replacing the O-rings in the 
third package at the beginning of the next week. Preparation for that at 
Blue Crab have started.

Best regards,
  Lubomir