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

Essentials for TPCs:

Geometry B-field (gas) ionisation: drifting electrons: Gas Amplification: read-out length, inner & outer diameter: momentum resolution maximum drift time momentum resolution diffusion primary electrons dE/dX  -rays drift velocity, diffusion gain, preamp noise, discharges, space charge preamp noise bandwidth

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

1995 Giomataris & Charpak: MicroMegas

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

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!

At NIKHEF: MediPix 2 pixel sensor: Jan Visschers et al.

Cathode foil Drift Space GEM foils base plate MediPix 2

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

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

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 ?

-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...

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/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.

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