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Micromegas TPC: New Results and Prospects

Micromegas TPC: New Results and Prospects. Amsterdam. ECFA-DESY workshop. 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 ,

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Micromegas TPC: New Results and Prospects

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  1. Micromegas TPC: New Results and Prospects Amsterdam ECFA-DESY workshop F. Bieser1, R. Cizeron2, P. Colas3, C. Coquelet3, E. Delagnes3, P. Desaunnais2 A. Giganon3, Y. Giomataris3, G. Guilhem2, J. Jeanjean2, V. Lepeltier2, V. Puill2, Ph. Rebourgeard3, J.-P Robert3, M. Ronan1 (and many others, not mentionned) 1) LBL, 2) LAL Orsay, 3) DAPNIA Saclay • New tests in magnetic field • Feedback • Cosmic setup P. Colas - Micromegas TPC

  2. 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 NEW P. Colas - Micromegas TPC

  3. 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) P. Colas - Micromegas TPC

  4. The 15 cm drift TPC • Gains up to • 7000 for Ar+3%CF4 at 75 kV/cm over 50 mm • 64000 for Ar+10% isobutane at 84 kV/cm over 50 mm • were measured in Orsay (january 2003). • In the following measurements, the gain was about 1300 and the gas was Ar+10%CH4 • THE RUNNING CONDITIONS ARE REALISTIC: • Long drift : 15cm • drift field : 240 V/cm • Moderate gain P. Colas - Micromegas TPC

  5. Measurements in a magnetic field Measure the iron 55 peak position and width as a function of the magnetic field B=1 tesla P. Colas - Micromegas TPC

  6. Measurements in a magnetic field P. Colas - Micromegas TPC

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

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

  9. 500 lpi (sigma/l=0.25) 1000 lpi (sigma/l=0.5) 1500 lpi (sigma/l=0.75) Ion feedback theory Results P. Colas - Micromegas TPC

  10. ion feedback Conclusion: the ion feedback is close to its optimum of 1/field ratio if s/l > 0.5 (i.e. >1000 l.p.i. meshes for usual gases) P. Colas - Micromegas TPC

  11. ION FEEDBACK MEASUREMENTS X-ray source Primaries + feedback I1 (pA-meter) Typically 25 pA Vdrift Typically 350 pA Typically 35 nA I1+I2 ~ G x primaries I2 (mesh) Vmesh Obtain primaries from G=1 (Vmesh small) Eliminate G between the 2 equations to obtain the feedback fraction P. Colas - Micromegas TPC

  12. Optimal case (reached for a 1000 lpi grid) The feedback does not depend significantly on the magnetic field It is in agreement with prediction for Ar-CH4 (90:10) and for a 500 lpi grid (data from June 2002) P. Colas - Micromegas TPC

  13. 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. P. Colas - Micromegas TPC

  14. TPC for the cosmic test Field cage Detector Front end electronics P. Colas - Micromegas TPC

  15. 1024 pads 2x10 mm2 pads 1x10 mm2 pads P. Colas - Micromegas TPC

  16. 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 P. Colas - Micromegas TPC

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

  18. 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 P. Colas - Micromegas TPC

  19. 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. P. Colas - Micromegas TPC

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