UTA

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UTA Digital hadron Calorimetry using the GEM
concept J.Li, A.White, J.Yu 5/30/02
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• Requirements for DHCAL
• General
• Thin sensitive/readout layer for compact
  calorimeter design
• Simple 1- or 2-level hit recording for energy
  flow algorithm use
• On-board amplification/digitization/discrimination
  for digital readout noise/cross-talk
  minimization
• Flexible design for easy implementation of
  arbitrary cell size
• Minimal intrusions for crackless design
• Ease of construction/cost minimization

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(B) Gas Amplification Specific - Sufficient gain
for good S/N for MIPs - Minimized cross-talk
between cells - Readout path isolated from
active volume - Modular design with ease
module-to-module continuity for supplies,
readout path - Digital readout from each cell -
Pad design (to avoid x-y strip complications) -
Keep HV low for safe/reliable use - Keep
electronics simple cheap/reliable
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GEM (Gas Electron Multiplier) Approach
GEM developed by F. Sauli (CERN) for use as
pre-amplification stage for MSGCs. GEM also can
be used with printed circuit readout allows
very flexible approach to geometrical
design. GEMs with gains above 104 have been
developed and spark probabilities per incident ?
less than 10-10. Fast operation -gt Ar CO2 40 ns
drift for 3mm gap. Relatively low HV ( few x100V
per GEM layer) (cf. 10-16kV for RPC!)
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From CERN-open-2000-344, A. Sharma
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Initial design concept for gas amplification DHCAL
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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 !