Micromegas TPC prototype results & Electronics Developments

1. Madhu Dixit Carleton University & TRIUMF On behalf of LC TPC collaboration ILC tracking review - Beijing 5 February, 2007 Micromegas TPC prototype results & Electronics Developments

2. Micro-Pattern Gas Detector development for the ILC TPC • ILC tracker goal: r ≤ 100 m including stiff 90° 2 m drift tracks • Anode wire/cathode pad TPC resolution limited by ExB effects • Negligible ExB effects for Micro Pattern Gas Detectors (MPGD) • TESLA TPC TDR : 2 mm x 6 mm pads (1,500,000 channels) with GEMs or Micromegas • LC TPC R&D: 2 mm pads too wide with conventional readout • For the GEM ~ 1 mm wide pads (~3,000,000 channels) • Even narrower pads would be needed for the Micromegas • The new MPGD readout concept of charge dispersion can achieve good resolution with ~ 2 mm x 6 mm pads. • R&D summary - mainly on the Micromegas TPC readout option Madhu Dixit

3. Micromegas - a parallel plate gas avalanche detectorMicromesh supported by ~ 50 m pillars above anode Madhu Dixit

4. Berkeley Orsay Saclay cosmic ray TPC tests 2 T superconducting magnet 1 mm x 10 mm pads 50 cm diameter Micromegas, 50 cm max. drift distance 1024 read out pads, Star TPC 20 MHz 10 bit digitizers Madhu Dixit

5. Madhu Dixit

6. Madhu Dixit

7. 4 Gev/c beam tests at KEK with standard readout (2.3 mm x 6.3 mm pads) Madhu Dixit

8. MP TPC with Micromegas - standard readoutKEK PS 4 Gev/c hadron test beam (2.3 mm x 6.3 mm pads) Resolution limited by pad width at high magnetic fields, worst at short drift distances Madhu Dixit

9. Improving MPGD resolution without using narrower pads • Disperse track charge after gas gain to improve centroid determination with wide pads. • For the GEM, large transverse diffusion in the transfer & induction gaps provides a natural mechanism to disperse the charge. • No such mechanism for Micromegas • The GEM readout will still need ~ 1 mm wide pads to achieve ~ 100 m ILC resolution goal Charge dispersion on a resistive anode - a mechanism to disperse the MPGD avalanche charge. It makes position sensing insensitive to pad width. The technique works for both the GEM and the Micromegas Madhu Dixit

10. Charge dispersion in a MPGD with a resistive anode • Modified MPGD anode with a high resistivity film bonded to a readout plane with an insulating spacer. • 2-dimensional continuous RC network defined by material properties & geometry. • Point charge at r = 0 & t = 0 disperses with time. • Time dependent anode charge density sampled by readout pads. Equation for surface charge density function on the 2-dim. continuous RC network: (r) Q (r,t) integral over pads mm ns M.S.Dixit et.al., Nucl. Instrum. Methods A518 (2004) 721. Madhu Dixit

11. Micromegas resistive anode readout structure Surface resistivity ~1 M/ 25 m Al/Si coated mylar Drift Gap MESH 50 m pillars Amplification Gap Madhu Dixit

12. Cosmic ray TPC tests with MPGD charge dispersion readout • 15 cm drift length with GEM or Micromegas readout • B=0 • Ar+10% CO2 chosen to simulate low transverse diffusion in a magnetic field. • Aleph charge preamps.  Rise= 40 ns,  Fall = 2 s. • 200 MHz FADCs rebinned to digitization effectively at 25 MHz. • 60 tracking pads (2 x 6 mm2) + 2 trigger pads (24 x 6 mm2). The GEM-TPC resolution was first measured with conventional direct charge TPC readout. The resolution was next measured with a charge dispersion resistive anode readout with a double-GEM & with a Micromegas. Madhu Dixit

13. Charge dispersion pulses & pad response function (PRF) • Non-standard variable pulse shape; both the rise time & pulse amplitude depend on track position. • The PRF is a measure of signal size as a function of track position relative to the pad. • We use pulse shape information to optimize the PRF. • The PRF can, in principle, be determined from simulation. • However, system RC non-uniformities & geometrical effects introduce bias in absolute position determination. • The position bias can be corrected by calibration. • PRF and bias determined empirically using a subset of data used for calibration. Remaining data used for resolution studies. Madhu Dixit

14. GEM & Micromegas track Pad Response Functions Ar+10%CO2 2x6 mm2 pads The pad response function (PRF) amplitude for longer drift distances is lower due to Z dependent normalization. GEM PRFs Micromegas PRFs Micromegas PRF narrower due to higher resistivity anode & smaller diffusion than in GEM after avalanche gain. Madhu Dixit

15. Track PRFs with GEM & Micromegas readout The PRFs are not Gaussian. The PRF depends on track position relative to the pad. PRF = PRF(x,z) PRF can be characterized by FWHM (z) & base width (z). PRFs determined from the data parameterized by a ratio of two symmetric 4th order polynomials. a2 a4 b2 & b4 can be written down in terms of  and  & two scale parameters a & b. Madhu Dixit

16. 6 mm 2 mm Track fit using the the PRF Track at: xtrack= x0+ tan() yrow Determine x0 &by minimizing2 for the entire event • Definitions: • - residual: xrow-xtrack • bias: mean of xrow-xtrack = f(xtrack) • resolution: standard deviation of residuals Madhu Dixit 16

17. Bias corrections for the GEM & for Micromegas Initial bias Initial bias Remaining bias after correction Remaining bias after correction 2x6 mm2 pads 2x6 mm2 pads Micromegas GEM Madhu Dixit

18. Transverse resolution (B=0) - Cosmic Rays Ar+10%CO2 R.K.Carnegie et.al., NIM A538 (2005) 372 K. Boudjemline et.al., NIM A - in press A. Bellerive et al, LCWS 2005, Stanford Compared to conventional readout, charge dispersion gives better resolution for the GEM and the Micromegas. Madhu Dixit

19. Track display -Ar+5%iC4H10KEK 4 GeV/c hadrons Micromegas2 mm x 6 mm pads B = 1 T main pulse Zdrift = 15.3 cm Madhu Dixit

20. Pad Response Function / Ar+5%iC4H10Micromegas+Carleton TPC 2 x 6 mm2 pads, B = 1 T 30 z regions / 0.5 cm step 0 < z < 0.5 cm 0 .5 < z < 1 cm 1 < z < 1.5 cm 1.5 < z < 2 cm 2 < z < 2.5 cm 2.5 < z < 3 cm 3 < z < 3.5 cm 3.5 < z < 4 cm 4 < z < 4.5 cm 4.5 < z < 5 cm 5 < z < 5.5 cm 5.5 < z < 6 cm normalized amplitude 6 < z < 6.5 cm 6.5 < z < 7 cm 7 < z < 7.5 cm 7.5 < z < 8 cm 8 < z < 8.5 cm 8.5 < z < 9 cm Madhu Dixit xtrack – xpad / mm 4 pads / ±4 mm

21. Pad Response Function Ar+5%iC4H10 9 < z < 9.5 cm 9.5 < z < 10 cm 10 < z < 10.5 cm 10.5 < z < 11 cm 11 < z < 11.5 cm 11.5 < z < 12 cm normalized amplitude 12 < z < 12.5 cm 12.5 < z < 13 cm 13 < z < 13.5 cm 13.5 < z < 14 cm 14 < z < 14.5 cm 14.5 < z < 15 cm xtrack – xpad / mm 4 pads / ±4 mm PRF parameters • a = b = 0 •  = base width = 7.3 mm •  = FWHM = f(z) The parameters depend on TPC gas & operational details Madhu Dixit

22. Bias for central rows / Ar+5%iC4H10 B = 1 T correction bias before bias after row 4 Residual / mm (± 0.15 mm) ± 20 mm row 5 row 6 xtrack / mm (± 14 mm) Madhu Dixit

23. KEK beam test - Transverse resolution Ar+5%iC4H10 E=70V/cm DTr = 125 µm/cm (Magboltz) @ B= 1T Micromegas TPC 2 x 6 mm2 pads • Transverse diffusion strongly suppressed at high B fields. Examples (4 T): DTr~ 25 m/cm (Ar/CH4 91/9) Aleph TPC gas ~ 20 m/cm (Ar/CF4 97/3) 4 GeV/c + beam ~ 0°,  ~ 0° Extrapolate to B = 4T Use DTr = 25 µm/cm Resolution (2x6 mm2 pads) Tr  100 m (2.5 m drift) 0= (52±1) mm Neff = 220 (stat.) Madhu Dixit

24. Preliminary 5 T cosmic tests of charge dispersion at DESYCOSMo (Carleton, Orsay, Saclay, Montreal) Micromegas TPC DTr= 19m/cm, 2 x 6 mm2 pads ~ 50 m av. resolution over 15 cm (diffusion negligible) 100 m over 2 meters appears feasible Nov-Dec, 2006 Madhu Dixit

25. The effect of lower gain on resolution Gain ~ 2300 Gain ~ 4700 1 3 4 2 Sample cosmic ray tracks - data taken at high & at low gains (B = 0.5 T) Madhu Dixit

26. COSMo TPC transverse resolution - Cosmic rays DESY magnet Gain ~ 4700 B=0.5 T Gain ~ 2300 B=0.5 T The resolution and 0 still good at low gain Madhu Dixit

27. Gain dependence on B field for Ar+5%C4H10 Micromegas gain constant to within ~ 0.5% up to 5 Tesla Madhu Dixit

28. Micromegas gain with a resistive anode Argon/Isobutane 90/10 Resistive anode suppresses sparking & improves Micromegas HV stability Madhu Dixit

29. Simulating the charge dispersion phenomenon M.S.Dixit and A. Rankin, Nucl. Instrum. Methods A566 (2006) 281. • The charge dispersion equation describe the time evolution of a point like charge deposited on the MPGD resistive anode at t = 0. • No standard pulse shape. For improved understanding & to compare to experiment, one must include the effects of: • Longitudinal & transverse diffusion in the gas. • Intrinsic rise time Trise of the detector charge pulse. • The effect of preamplifier rise and fall times tr & tf. • And for particle tracks, the effects of primary ionization clustering. Madhu Dixit

30. Charge dispersion signals for the GEM readoutSimulation vs. measurement for Ar+10%CO2 (2 x 6 mm2 pads) Collimated ~ 50 m 4.5 keV x-ray spot on pad centre. Difference = induced signals (MPGD '99, Orsay & LCWS 2000) were not included in simulation). Primary pulse normalization used for the simulated secondary pulse Simulated primary pulse is normalized to the data. Madhu Dixit

31. GEM TPC charge dispersion simulation (B=0) Cosmic ray track, Z = 67 mm Ar+10%CO2 2x6 mm2 pads Simulation Data Centre pulse used for normalization - no other free parameters. Madhu Dixit

32. Micromegas gas gain measurements at Saclay (David Attie, EUDET Meeting, Munich 18 October, 2006) Mixtures of gases containing argon Mesh : 50 mm gap of 10x10 size iC4H10 Gaz froids: CO2, CH4 C2H6 Madhu Dixit

33. New development: Bulk Micromegas (2004) I. Giomataris et al., CERN-Saclay collaboration, NIM A 560 (2006). Bulk Micromegas obtained by lamination of a woven grid on an anode with two photo-imageable films. The pillars hold the mesh on the whole surface: no frame needed. Madhu Dixit

34. Advantages of Bulk Micromegas • Large surfaces at low cost (1000 € for a 34cm x 36cm detector) • Almost no dead area • Very robust (robust mesh held everywhere) • Insensitive to dust (the mesh is dust-tight down to 30 µ) • Good/excellent uniformity of the gap • Can be segmented and repaired pillar New bulk development: excellent resolution and stability (KEK test Jan.07, 55Fe with no collimation) Madhu Dixit

35. Bulk Micromegas development for T2K Bulk Micromegas is cut with a 2 mm border Fully engineered project Minimum dead space between panels ~ 8 mm Madhu Dixit

36. Large panel Micromegas for T2K TPCs • T2K will have 3 TPCs • 72 Micromegas modules • Total area ~ 9 m2 • 124416 readout channels Madhu Dixit

37. Electronics • Development for LP TPC based on ALICE TPC ALTRO digitizing electronics. • TPC requirements: highest flexibility in terms of pad geometry and shape of pad panels. • Design for 1 x 4 mm2 pads • Proposal: 32 channels modules, where each channel corresponds to an area of around 4 mm2. • 2000 channels of 40 MHz ALTRO chips available. • Plans to acquire more channels - up to 10,000 for LP TPC tests. Madhu Dixit

38. Front End and Readout Electronics Alice TPC L1: 6.5ms 1 KHz L2: < 100 ms 200 Hz power consumption < 40 mW / channel Front End Card (128 CHANNELS) DETECTOR drift region 88ms Custom Backplane Capton cable 8 CHIPS (16 CH / CHIP) 8 CHIPS (16 CH / CHIP) ALTRO gating grid Digital Circuit PASA RCU ADC RAM anode wire CUSTOM IC (CMOS 0.35mm) pad plane 557 568 PADS CUSTOM IC (CMOS 0.25mm ) (3200 CH / RCU) • LINEARIZATION • BASELINE CORR. • TAIL CANCELL. • ZERO SUPPR. CSA SEMI-GAUSS. SHAPER 1 MIP = 4.8 fC S/N = 30 : 1 DYNAMIC = 30 MIP 10 BIT 10 MHz MULTI-EVENT MEMORY GAIN = 12 mV / fC FWHM = 190 ns

39. PASA PASA designed for wire chamber pulses with long ion tails Wire TPC charge pulse Tail cancellation and shaping Semi-Gaussian output pulse with ~200 ns integrationproduced for the digitizer. (base width ~ 450 ns) 0 2 4 6 8 10 Time (s) Madhu Dixit

40. With 2scharge preamp decay time 0 200 400 600 800 1000 PASA preamplifier-shaper not suitable for MPGD-TPC readout • Charge pulse rise times will be much longer for ILC TPC tracks (dominated by charge collection). • Up to ~ 500 ns to collect the charge due to longitudinal diffusion and track angles. • ILC TPC resolution near statistical limit of diffusion. • Must collect over 90% of electrons for best resolution. • No optimum shaping time to achieve both good single hit and 2-track resolution • Better to digitize charge pulse directly without shaping. GEM charge pulse - point x ray source (ns) Madhu Dixit

41. New preamp design to replace PASA Luciano Musa Madhu Dixit

42. Luciano Musa Programmable peaking & decay times Programmable gain Madhu Dixit

43. Leif Jonsson Eudet meeting - Munich Nov. 2006 Madhu Dixit

44. Summary • MPGD-TPC has difficulty achieving good resolution with wide pads • With charge dispersion, the charge can be dispersed in a controlled way. Wide pads can be used without sacrificing resolution. Charge dispersion works both for the GEM and the Micromegas. • At 5 T, an average ~ 50 m resolution has been demonstrated with 2 x 6 mm2readout pads for drift distances up to 15 cm. • Electronics development on track • The ILC-TPC resolution goal, ~100 m for all tracks,appears feasible. Madhu Dixit