Tracker Meeting June 21, 2000 Present: (sorry, as usual I didn't manage to get all of the names) Pisa: Ronaldo + 3 others Trieste: Guido et al. Perugia: Mauro SLAC: Gary, John, BJ, Taka, Ossie, Hartmut, Eduardo, Robert, Martin UCSC: Masa, Tsune, Wilko Hytec: Eric, Erik Eric presented preliminary requirements on the shear modulus of the adhesive bond versus strength of adhesive. The principal general conclusion is that a rigid adhesive won't work. Temperature changes will likely shear the bond. He proposes to use a factor of 4 safety to account for an indefinite number of temperature cycles. RTV looks fairly comfortable within the requirements. He studied 3 different bond thicknesses from 100 to 400 microns. His write-up is on the Hytec FTP site (HTN-102050-017) and also on the Tracker web page at UCSC: http://scipp.ucsc.edu/groups/glast/mechanical/HTN- 102050-017.pdf (Note that access to the UCSC GLAST page is by the same user identification and passwords as the Stanford GLAST page). Ossie has a sample of 3M transfer adhesive. He will order some Nusil RTV-type stuff, with carbon loading for conductivity (the one that doesn't eat copper---see last week's minutes). Eric recommended sending samples out to external vendors for measurement of shear modulus and shear strength of the adhesive. He recommends to use ASTM standards. Temperature dependence is an issue to be addressed in such tests. Also surface preparation. These characterization tests don't need to be done with real detectors. We will use temperature cycling to test the concept in the end with real detectors (baby detectors making up a full length ladder). We will test poisoning of the detectors by adhesives at UCSC, where a test station is nearly ready to go. We learned that 14 new baby detectors have arrived from Japan. It was decided that Ossie and Eduardo will make plans for next week for material tests to be carried out at SLAC (in particular for the adhesives). UCSC will start putting together a new ladder test, using rails to support the ladder in a plane. There still are some questions about the type of adhesive to use for bonding the thin lead to the face sheet. Eric tentatively thinks that epoxy might still be okay for that. There was some discussion of the use of lead versus tungsten. The old figure of merit was modulus*CTE. Hytec finds that that works well for thin lead trays. However, Eric has found that for Super-GLAST trays this figure of merit doesn’t hold. In that case, tungsten is superior to lead even if rigidly bonded, as far as reducing stress in silicon. Ossie reported that he has found that the price of W is about half of what he reported before. There are lots of suppliers of thin W foils. Thick foils run about $270/kg. Thin foils run about $650/kg. Ossie reported on the flatness of the ladder-gluing fixture. It is out by 2.5 mils (about 64 microns). John is taking it to the main shop where they have new machines. That should get it good to about 0.5 mils (12 microns). Ossie reported that some Si wafers should be back by next Tuesday metalized. A glue pump to use for potting tests has been located. They will use the existing tray measuring table as a test bed. Another x table (5 ft long) is available that might be useful later. It is old and tired and has some problems with chatter. Ossie found a vendor that will do cutting of dummy wafers. He will get price information from them. Ronaldo reported that an engineer and a physicist will visit UCSC for 3 weeks. Another physicist will visit SLAC to work on tracker software. The expected time frame is the 2nd half of July through the 1st half of August. They would like to get a complete readout section to set up in Pisa. Stanford is making a VME module for them, and UCSC can supply the front-end hardware (perhaps one of the SuperGLAST layers of the BTEM, which will not be used in the balloon flight). Wilko is putting together some programs to be able to exercise the system from a PC rather than using VxWorks. Ronaldo said that his people can help with that when they arrive. Eduardo reported that he received one wafer from the STM run that did not succeed. There is no news on the new STM run. Hartmut reported that he received comments on detector specs and has amended the specs. He will put the new version on the web. Martin requested that they be sent also to Darren Marsh. Ohsugi is already talking to engineers working on the mask. Hartmut will check on the expected date to begin fabrication. Eduardo reported that the beamtest MC now agrees well with data. The number of hits per layer, for energy correction, looks good. There are still some small problems with beam definition in the MC (width of beam, etc). He has talked to NRL folks and said that they find the energy deposition in Si to be wrong in GLASTSIM. Action Items: 1. Ossie: order a sample of the Nusil conductive adhesive. 2. Ossie and Eduardo: make plans for materials tests to be carried out at SLAC in preparation for construction of new ladder test structures, in particular the shear modulus and bond strength of the adhesives. 3. UCSC: make plans for construction of new ladder modules and a support holder with rails and slots to keep the ladders flat. 4. Ossie: get price information for cutting of dummy wafers. 5. Hartmut: check on the schedule for beginning of Si detector fabrication at Hamamatsu.