1. Amsterdam, April 2,2003P. Colas - Micromegas TPC1 Micromegas TPC: New Results and Prospects New tests in magnetic fieldNew tests in magnetic field FeedbackFeedback Cosmic setupCosmic setup F. Bieser 1, R. Cizeron 2, P. Colas 3, C. Coquelet 3, E. Delagnes 3, P. Desaunnais 2 A. Giganon 3, Y. Giomataris 3, G. Guilhem 2, J. Jeanjean 2, V. Lepeltier 2, V. Puill 2, Ph. Rebourgeard 3, J.-P Robert 3, M. Ronan 1 (and many others, not mentionned) 1) LBL, 2) LAL Orsay, 3) DAPNIA Saclay workshop ECFA-DESY workshop

2. Amsterdam, April 2,2003P. Colas - Micromegas TPC2 Measurements in a magnetic field 2T magnet in operation since March 2002 in Saclay. 2 data taking periods until now: June 2002: ion feedback measurements in a 1cm-drift MWPC TPC and a Micromegas TPC February 2003: measurement of the gain and of the ion feedback with a 15cm-drift Micromegas TPC Future: take cosmic tracks in a 50 cm, 1000 channel Micromegas TPC

3. Amsterdam, April 2,2003P. Colas - Micromegas TPC3 Measurements in a magnetic field The 2T, 530mm bore magnet is now in its final location. It provides a 1% homogeneous field over +- 25cm. (An 8 T, 150mm bore magnet could be used in the future)

4. Amsterdam, April 2,2003P. Colas - Micromegas TPC4 The 15 cm drift TPC Gains up to 7000 for Ar+3%CF 4 at 75 kV/cm over 50  m 64000 for Ar+10% isobutane at 84 kV/cm over 50  m were measured in Orsay (january 2003). In the following measurements, the gain was about 1300 and the gas was Ar+10%CH 4 THE RUNNING CONDITIONS ARE REALISTIC: Long drift : 15cm drift field : 240 V/cm Moderate gain

5. Amsterdam, April 2,2003P. Colas - Micromegas TPC5 Measurements in a magnetic field Measure the iron 55 peak position and width as a function of the magnetic field B=1 tesla

6. Amsterdam, April 2,2003P. Colas - Micromegas TPC6 Measurements in a magnetic field

7. Amsterdam, April 2,2003P. Colas - Micromegas TPC7 Ion feed-back: the micromegas funnel effect S1/S2 ~ E amplif / E drift ~80 000 / 200 Due to electron diffusion, most ions are created outside the funnel tube : when S1/S2 is large and  comparable to the pitch (S2 small wrt avalanche cloud size), the ions are unlikely to follow back the field lines to the drift space. The ions return to the grid: ion feed-back and related space charge effects are suppressed S1 S2 L 

8. Amsterdam, April 2,2003P. Colas - Micromegas TPC8 l  Calculations : add the contribution of each hole to the electron yield -> get the fraction in the funnel tube 2D 3D Ion feedback theory The two important quantities are  : the dispersion after 50 microns and l, the grid pitch 

9. Amsterdam, April 2,2003P. Colas - Micromegas TPC9 Results 1500 lpi (sigma/l=0.75)1000 lpi (sigma/l=0.5)500 lpi (sigma/l=0.25) Ion feedback theory

10. Amsterdam, April 2,2003P. Colas - Micromegas TPC10 ion feedback Conclusion: the ion feedback is close to its optimum of 1/field ratio if  /l > 0.5 (i.e. >1000 l.p.i. meshes for usual gases)

11. Amsterdam, April 2,2003P. Colas - Micromegas TPC11 ION FEEDBACK MEASUREMENTS V mesh V drift I 2 (mesh) I 1 ( pA-meter ) X-ray source Primaries + feedback I 1 +I 2 ~ G x primaries Obtain primaries from G=1 (V mesh small) Eliminate G between the 2 equations to obtain the feedback fraction Typically 25 pA Typically 350 pA Typically 35 nA

12. Amsterdam, April 2,2003P. Colas - Micromegas TPC12 The feedback does not depend significantly on the magnetic field It is in agreement with prediction for Ar-CH 4 (90:10) and for a 500 lpi grid (data from June 2002) Optimal case (reached for a 1000 lpi grid)

13. Amsterdam, April 2,2003P. Colas - Micromegas TPC13 In the February 2003 data taking, the field ratio was 334, corresponding to an optimal feedback of 0.3%. The observed feedback, 0.9%, is what is expected for a 500 lpi grid. -> We have a good understanding of the feedback in a micromegas TPC. It is insensitive to magnetic fields up to at least 2T.

14. Amsterdam, April 2,2003P. Colas - Micromegas TPC14 TPC for the cosmic test Field cage Detector Front end electronics

15. Amsterdam, April 2,2003P. Colas - Micromegas TPC15 2x10 mm 2 pads 1024 pads 1x10 mm2 pads

16. Amsterdam, April 2,2003P. Colas - Micromegas TPC16 Front-end electronics STAR readout. 32 channels per card, 10-bit ADC, up to 512 50ns time buckets. 16 cards have been modified to raise the pedestal, to gain sensitivity to negative signals, and protection diodes have been added

17. Amsterdam, April 2,2003P. Colas - Micromegas TPC17 Tests of front-end electronics 1000 channels being tested. Noise <4counts per channel 3cards to be repared 2% of the channels have pbs

18. Amsterdam, April 2,2003P. Colas - Micromegas TPC18 Status of the cosmic test Magnet operational, in final position Endplate fully wired Mesh manufactured last week, to be tested Cosmic trigger being installed New high purity gas system being ordered Field cage under construction

19. Amsterdam, April 2,2003P. Colas - Micromegas TPC19 CONCLUSION New measurements have shown that the behaviour of a micromegas TPC in a magnetic field is not deteriorated. Gain, transparency, ion feedback have been shown not to be affected by a 2T magnetic field. Collaboration with Carleton showed charge spreading on a micromegas with the anode coated with a resistive foil These results, together with aging tests and other measurements and simulations already presented, show the adequation of micromegas technology to the readout of the LC TPC A cosmic test is in preparation, with 1000 pads.