An

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An Integrated Single Electron Readout System for
the TESLA TPC
Ton Boerkamp Alessandro Fornaini Wim Gotink Harry
van der Graaf Dimitri John Joop Rovekamp Jan
Timmermans David San Segundo Bello Jan
Visschers (NIKHEF) LC Workshop Amsterdam, April
2, 2003
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Essentials for TPCs Geometry length, inner
outer diameter momentum resolution maximu
m drift time B-field momentum
resolution diffusion (gas)
ionisation primary electrons dE/dX ?-ra
ys drifting electrons drift velocity,
diffusion Gas Amplification gain, preamp
noise, discharges, space charge read-out p
reamp noise bandwidth
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Aleph TPC well optimised, but now there is
something new.
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1995 Giomataris Charpak MicroMegas
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1996 F. Sauli Gas Electron Multiplier (GEM)
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Problem Readout of wires (ion)induced charge on
pads, thus wide charge distribution. High spatial
precision from centre-of-gravity
Solutions - Controlled charge leakage between
pads using resistive layers - Chevron
pads - (very) many (small) pads pixels!
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At NIKHEF MediPix 2 pixel sensor Jan Visschers
et al.
Cathode foil
Drift Space
GEM foils
base plate
MediPix 2
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Triple GEM Cu/Kapton/Cu 5/50/5 ?m Pitch/Metal
Hole/Centre 140/85/85 ?m GDD-F. Sauli, CERN
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MediPix chip
Aluminium base plate
O-ring gas seal
Fixation bar
3 mm brass block
printed circuit board
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Chamber with GEM works appropriate - gas gain
of 55 per GEM is reached without sparks - use 3
GEMs to fire Medipix pixels (2000 e-) -
efficiency of collecting primary electrons gt 90
- signal rise time (100 - 200 ns) OK for
Medipix.
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?
Surface charge ?

• 75 percent of surface is covered with insulator
  (polyimide)
• MediPix is in R D stage (chip imperfections,
• low yield, critical parameter settings,
• ongoing software development)

Proof-of-Principle is ongoing...
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• TimePix CMOS chip
• Best pixel geometry hexagonal, square,
  rectangular?
• Best pixel pitch?
• Preamp specifications? Charge signal time
  development,
• amplitude?
• - Multi-threshold required? Detection of electron
  clusters?
• Readout architecture time stamp per pixel, or
• per row column? Output chain?
• Time resolution? Common timing effects?
• power dissipation? Sleeping mode?
• HV breakdown pixel protection?

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Suggestion of Jan Visschers integrate
GEM/Micromegas and pixel sensor
GEM TimePix
Micromegas TimePix

• TimePix GasGainGrid
• by post-wafer processing?
• glue Micromegas on TimePix?

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• If it works
• - Effordable 340 kE/m2 (2003) for TESLA TPC
• - replaces anode wires, readout pads
• readout electronics
• - Best possible TPC performance due to
• the detection of single electrons
• - position and drift time coordinates
• - dE/dX measurement
• - low occupancy (109 channels!), thus
• best possible multi-track separation
• recognition (and suppressing) of ?-rays
• gas can be optimised for lowest possible
  diffusion
• - little back-migrating ion charge.

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• No conclusions yet, but we do have plans
• proof-of-principle with MediPix 2
• Integration of MediPix 2 and Micromegas
• Tests with MediPix 2 GasGainGrid in
• cosmic rays
• muon beam at CERN (H8)
• focussed UV laser (single electron) beam
• - Development of TimePix CMOS sensor