UTA

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UTA GEM updates J.Li, A.White, J.Yu 5/9/02
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Preparations for prototype construction

• Test GEM chamber designed at UTA
• - allows varying layer configurations
• - straightforward gas, HV etc.
• Main issue is acquisition of GEM foils
• - contact with GEM inventor, F.Sauli, CERN
• 
  ?

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GEM test chamber J.Li, UTA
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• Most foils made in CERN printed circuit workshop
• Approximately 1,000 foils made
• Big project for COMPASS expt. 31x31 cm2 foils
• Most difficult step is kapton etching Sauli
  has offered to reveal trade secrets in context
  of formal collaboration.
• Fastest route buy a few foils from Sauli
• 10x10 cm2 foils 70?m holes 140?m pitch
  300
• - Foils HV tested/verified at CERN.

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• Sauli - procure a fully assembled, dismountable
  detector for usbut prefer our design
• Also Edik Tsyganov at UT Southwestern Med.
  has working multi-gem detector
• Ultimately we want to able to make our own foils.
• Some interesting GEM details

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CERN GDD Group electron-micrograph of GEM foil
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CERN GDD Group electron-micrograph of GEM foil
hole
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GEM Issues

• Gain uniformity ( 15) should not be a big
• issue for digital mode operation
• Discharges single/double GEMs
• - single GEMS OK for G ? 1500
• - double GEMs
• double detectors obtained cascading a Gas
  Electron Multiplier (GEM) as
• preamplification, and a second GEM, a MSGC or
  other devices as second
• amplifier permit to reach gains above 10000
  before discharge under very
• high rates and exposure to heavily ionizing
  tracks. GDD group Web site

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Single GEM gain/discharge probability
A.Bressan et al NIM A424 (1998) 321
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-gt We need to determine particle flux vs.
particle type (MIP, neutral, heavily ionizing)
from detailed simulation. -gt Variations of hole
sizes, shapes affect the discharge probability
and hence operating region.
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• CONCLUSIONS
• Learning more about GEMs
• Source(s) of GEM foils identified
• Test Chamber designed
• Need studies of particle fluxes in calorimeter
• Need !