AnIntegratedSingle ElectronReadout Systemfor theTESLA TPC
Ton BoerkampAlessandro FornainiWim GotinkHarry van der GraafDimitri JohnJoop RovekampJan TimmermansDavid San Segundo BelloJan Visschers(NIKHEF)
LC WorkshopAmsterdam, April 2, 2003
Essentials for TPCs:
Geometry length, inner & outer diameter:
momentum resolutionmaximum drift time
B-field momentum resolutiondiffusion
(gas) ionisation: primary electronsdE/dX-rays
drifting electrons: drift velocity, diffusion
Gas Amplification: gain, preamp noise, discharges,
space charge
read-out preamp noisebandwidth
Aleph TPC: well optimised, but now there is something new….
1995 Giomataris & Charpak: MicroMegas
1996: F. Sauli: Gas Electron Multiplier (GEM)
ProblemReadout of wires: (ion)induced charge on pads, thuswide charge distribution. High spatial precision fromcentre-of-gravity:
wireavalanche
Cathode pads
GEMMicromegas
Solutions: - Controlled ‘charge leakage’ between pads using resistive layers- ‘Chevron’ pads- (very) many (small) pads: pixels!
At NIKHEF:
MediPix 2 pixel sensor: Jan Visschers et al.
Cathode foil
GEM foils
base plate
MediPix 2
Drift Space
Triple GEM: Cu/Kapton/Cu 5/50/5 mPitch/Metal Hole/Centre 140/85/85 mGDD-F. Sauli, CERN
Aluminium base plate
MediPix chip
3 mm brass block
printed circuit board
O-ring gas sealFixation bar
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 > 90 %- signal rise time (100 - 200 ns) OK for Medipix.
?
Surface charge ?
Proof-of-Principle is ongoing...
-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)
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?
Suggestion of Jan Visschers:‘integrate GEM/Micromegas and pixel sensor’
‘GEM + TimePix’ ‘Micromegas + TimePix’
TimePix + GasGainGrid
- by ‘post-wafer’ processing?- glue Micromegas on TimePix?
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.
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