1. Chicago, January 8, 2002P. Colas - micromegas TPC1 A micromegas TPC prototype in a magnetic field Principle and advantages of a micromegas TPCPrinciple and advantages of a micromegas TPC Goals and projectsGoals and projects F. Bieser 1, R. Cizeron 2, P. Colas 3, Y. Giomataris 3, J. Jeanjean 2, V. Lepeltier 2, Ph. Rebourgeard 3, M. Ronan 1 (+ many others not mentionned) 1) LBL, 2) LAL Orsay, 3) DAPNIA Saclay

2. Chicago, January 8, 2002P. Colas - micromegas TPC2 Principle of operation VeryVery Drift space

3. Chicago, January 8, 2002P. Colas - micromegas TPC3 Field lines VeryVery « funnel effect » : S1/S2 ~ E amplif / E drift Due to diffusion, when S1/S2 is large, ions are unlikely to follow back the field lines to the drift space. Ions return to the grid: ion feed-back and related space charge effects are suppressed

4. Chicago, January 8, 2002P. Colas - micromegas TPC4 Stationnarity of the gain VeryVery The gain is stationnary (maximal) as a function of the gap around 100  m This gives a micromegas TPC a good potential for dE/dx

5. Chicago, January 8, 2002P. Colas - micromegas TPC5 ADVANTAGES OF MICROMEGAS Very thin amplification gap (50 to 100  m) => fast signalVery thin amplification gap (50 to 100  m) => fast signal Funnel effect => efficient ion collection ( see V. Lepeltier’s talk )Funnel effect => efficient ion collection ( see V. Lepeltier’s talk ) large gains (10 3 -10 4 )large gains (10 3 -10 4 ) gain independent of the gap to first order => promising dE/dxgain independent of the gap to first order => promising dE/dx easy to build, dead zones potentially very smalleasy to build, dead zones potentially very small potential robustness to agingpotential robustness to aging

6. Chicago, January 8, 2002P. Colas - micromegas TPC6 ACHIEVEMENTS Construction of a small TPC (30 channels, 16cm drift length), HV tests and observation of mesh signals with 55 Fe and 90 Sr sources Measurements of drift velocities with a laser (see case of Ar-CF 4 ) (P.C., A. Delbart, J. Derré, I. Giomataris, F. Jeanneau, V. Lepeltier, I. Papadopoulos, Ph. Rebourgeard, Vienne conf., Jan 2001) Measurement of ion current Measurement of aging with Ar-CF4 in progress Several ideas to improve the point resolution

7. Chicago, January 8, 2002P. Colas - micromegas TPC7 STAR ELECTRONICS STAR is a 140 000 channel TPC at RHIC. Started data taking at RHIC in june 2000. Records currently 5000-track eventsSTAR is a 140 000 channel TPC at RHIC. Started data taking at RHIC in june 2000. Records currently 5000-track events A front-end board bears 32 channels with a low- noise amplifier, a shaper, a 5 to 20 MHz Switched Capacitor Array with a depth of 512 buckets and a 10-bit ADCA front-end board bears 32 channels with a low- noise amplifier, a shaper, a 5 to 20 MHz Switched Capacitor Array with a depth of 512 buckets and a 10-bit ADC This is perfectly adapted to the test we have in mind (except polarity)This is perfectly adapted to the test we have in mind (except polarity)

8. Chicago, January 8, 2002P. Colas - micromegas TPC8 STAR ELECTRONICS Mike Ronan helped us to install in Saclay a complete data- taking chain including 20 cards of 32 channels (640 channels) extendable to 1152 channels, in September 2000 and March and September 2001. FEE MOTHER BOARD DET FIB. OPT VME Pulse generator

9. Chicago, January 8, 2002P. Colas - micromegas TPC9 STAR ELECTRONICS With advice from F. Bieser, we have modified a card to adapt it to both positive and negative polarities, so that we can use it for both a micromegas and a wire TPC.

10. Chicago, January 8, 2002P. Colas - micromegas TPC10 IN PROGRESS Construction of a large TPC (L=0.5m,  =0.45m, 1000 channels) in a 2T magnetic field to work with cosmics. Will be modular (removable endplate, reconnectible electronics) in order to test several schemes. Maybe a smaller chamber to be installed in a test beam to study high rate aspects We have a few 100 channels of FEE available, the DELPHI TPC HV supply, low voltage supplies from DELPHI. Gas and detector HV supplies have been ordered.

11. Chicago, January 8, 2002P. Colas - micromegas TPC11 Layout

12. Chicago, January 8, 2002P. Colas - micromegas TPC12 endplate ssss

13. Chicago, January 8, 2002P. Colas - micromegas TPC13 FEE card support

14. Chicago, January 8, 2002P. Colas - micromegas TPC14 CONCLUSION We plan to take cosmics in a high magnetic field (2T) in a few months from now. This is necessary to confirm the high potentiality of micromegas as an endplate for a new TPC generation.