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