1. 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

2. Essentials for TPCs: Geometrylength, inner & outer diameter: momentum resolution maximum drift time B-fieldmomentum resolution diffusion (gas) ionisation:primary electrons dE/dX  -rays drifting electrons:drift velocity, diffusion Gas Amplification:gain, preamp noise, discharges, space charge read-outpreamp noise bandwidth

3. Aleph TPC: well optimised, but now there is something new….

4. 1995Giomataris & Charpak:MicroMegas

5. 1996: F. Sauli: Gas Electron Multiplier (GEM)

6. Problem Readout of wires: (ion)induced charge on pads, thus wide charge distribution. High spatial precision from centre-of-gravity: wire avalanche Cathode pads GEM Micromegas Solutions:- Controlled ‘charge leakage’ between pads using resistive layers - ‘Chevron’ pads - (very) many (small) pads: pixels!

7. At NIKHEF: MediPix 2 pixel sensor: Jan Visschers et al. Cathode foil GEM foils base plate MediPix 2 Drift Space

8. Triple GEM: Cu/Kapton/Cu 5/50/5  m Pitch/Metal Hole/Centre 140/85/85  m GDD-F. Sauli, CERN

10. Aluminium base plate MediPix chip 3 mm brass block printed circuit board O-ring gas seal Fixation bar

12. 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.

13. ? 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)

14. 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?

15. Suggestion of Jan Visschers: ‘integrate GEM/Micromegas and pixel sensor’ ‘GEM + TimePix’‘Micromegas + TimePix’ TimePix + GasGainGrid - by ‘post-wafer’ processing? - glue Micromegas on TimePix?

16. If it works…: - Effordable: 340 kE/m 2 (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 (10 9 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.

17. 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