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Resistive anode to improve the resolution of MPGD TPCs

Resistive anode to improve the resolution of MPGD TPCs. Madhu Dixit Carleton University & TRIUMF. 3rd Symposium on Large TPCs for Low Energy Rare Event Detection. Paris 12 December 2006. The large TPC challenge: How to reduce complexity and achieve good resolution at an affordable costs.

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Resistive anode to improve the resolution of MPGD TPCs

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  1. Resistive anode to improve the resolution of MPGD TPCs Madhu Dixit Carleton University & TRIUMF 3rd Symposium on Large TPCs for Low Energy Rare Event Detection Paris 12 December 2006

  2. The large TPC challenge:How to reduce complexity and achieve good resolution at an affordable costs • Several large MPGD-TPCs proposed for HEP and for rare event detection; e.g. • ILC TPC: 1,500,000 channels (2 mm x 6 mm pads) • T2K TPC: 100,000 channels (7 mm x 9 mm pads) • ILC challenge: Tr ~ 100 m for all tracks (2 m drft) • ILC MPGD-TPC prototype R&D indicates 2 mm wide pads too wide, need 1 mm or narrower pads • New MPGD readout concept of charge dispersion developed to achieve good resolution with wide pads. • The proof of concept and ILC-TPC prototype test results • Possible application to T2K TPC - improving resolution without resorting to narrower pads TPC Rare Event Symposium - Paris

  3. The physics limit of TPC resolution comes from transverse diffusion: Neff = effective no. of electrons contributing to position determination. • For best resolution, choose a gas with smallest diffusion The rule applies to the wire TPCs. They use induced cathode pad signals for position determination. But ExB & track angle systematic effects degrade wire TPC resolution. ExB effect does not limit the MPGD-TPC. But there are no comparable induced cathode pad signals. The MPGD-TPC resolution is limited by pad width w. The resolution gets worse for wide pads in absence of diffusion. Limits to the TPC position resolution TPC Rare Event Symposium - Paris

  4. Proportionalwire Micro PatternGas Detector Anode pads Cathode pads width w width w Direct signal on the MPGD anode pad Induced cathode signal determined by geometry Pad width limits the MPGD-TPC resolutionExB angle effects limit the wire/pad TPC resolution For small diffusion, less precise centroid for wide pads Accurate centroid determination possible with wide pads TPC Rare Event Symposium - Paris

  5. How to get good MPGD resolution with wide pads? • Find a mechanism similar to proportional wire induced cathode pad signals • Charge dispersion - a new geometrical pad signal induction mechanism for the MPGD readout that makes position determination insensitive to pad width. TPC Rare Event Symposium - Paris

  6. Position sensing from charge dispersion in a MPGD with a resistive anode Position sensing on a resistive anode proportional wire from charge division Telegraph equation (1-D): Deposit point charge at t=0 Solution for charge density (L ~ 0) Generalize 1 D proportional wire charge division to a 2 D RC network Position sensing from charge dispersion in MPGDs with a resistive anode Equivalent to Telegraph equation in 2-D Solution for charge density in 2-D TPC Rare Event Symposium - Paris

  7. 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 TPC Rare Event Symposium - Paris

  8. Al-Si Cermet on mylar Drift Gap MESH Amplification Gap 50 m pillars Resistive anode Micromegas 530 k/ Carbon loaded Kapton resistive anode was used with GEM. This was replaced with higher resistivity 1 M/ Cermet for tests with Micromegas. TPC Rare Event Symposium - Paris

  9. The proof of concept - GEM charge dispersion x ray tests M.S.Dixit et.al., Nucl. Instrum. Methods A518 (2004) 721. TPC Rare Event Symposium - Paris

  10. Point resolution for GEM Charge dispersion readout (Ar+10%CO2) Collimated ~ 4.5 keV x rays, Spot size ~ 50 m 2x6 mm2 pads GEM resolution ~ 70 m. Similar resolution measured for a Micromegas with a resistive anode readout using 2 mm x 6 mm pads TPC Rare Event Symposium - Paris

  11. Learning to track with charge dispersion Cosmic ray tests – no magnetic field 15 cm drift length with GEM or Micromegas readout B=0 Ar+10% CO2chosen 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 endcap. TPC Rare Event Symposium - Paris

  12. 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 is narrower due to the use of higher resistivity anode & smaller diffusion than GEM after avalanche gain TPC Rare Event Symposium - Paris

  13. Transverse resolution (B=0) for cosmic rays Ar+10%CO2 R.K.Carnegie et.al., NIM A538 (2005) 372 K. Boudjemline et.al., submitted to NIM To be published Compared to conventional readout, charge dispersion gives better resolution for the GEM and the Micromegas. TPC Rare Event Symposium - Paris

  14. First tests in a magnetic field (Oct, 2005)Micromegas TPC - charge dispersion readout 4 GeV/c KEK PS 2 hadron test beam Super conducting 1.2 T magnet Inner diameter : 850 mm Effective length: 1 m Canada, France, Germany, Japan (Carleton, Montreal, Saclay, Orsay, MPI (Munich), KEK, Kinnki, Kogakuin, Saga, Tsukuba and TUAT) TPC Rare Event Symposium - Paris

  15. Transverse spatial resolution Ar+5%iC4H10 E=70V/cm DTr = 125 µm/cm (Magboltz) @ B= 1T Micromegas TPC 2 x 6 mm2 pads 4 GeV/c + beam ~ 0°,  ~ 0° • Strong suppression of transverse diffusion at 4 T. Examples: DTr~ 25 m/cm (Ar/CH4 91/9) Aleph TPC gas ~ 20 m/cm (Ar/CF4 97/3) Extrapolate to B = 4T Use DTr = 25 µm/cm Resolution (2x6 mm2 pads) Tr  100 m (2.5 m drift) s0= (52±1) mm Neff = 220 (stat.) TPC Rare Event Symposium - Paris

  16. Tests in the 5 T magnet test facility at DESY (Nov-Dec, 2006) (Carleton-Orsay-Saclay-Montreal) COSMo TPC track display TPC Rare Event Symposium - Paris

  17. COSMo TPC - Transverse ResolutionB= 5 T DT= 19 m/cm Micromegas resistive readout 2 mm x 6 mm pads Cosmic ray tracks Preliminary ~ 50 m average TPC Rare Event Symposium - Paris

  18. COSMo TPC - Transverse ResolutionB= 5 T Ar/C4H10 95/5 DT= 27 m/cm Micromegas resistive readout 2 mm x 6 mm pads Cosmic ray tracks Preliminary ~ 50 m average TPC Rare Event Symposium - Paris

  19. 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. • To compare to experiment, one needs to 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. TPC Rare Event Symposium - Paris

  20. Simulation for a single charge cluster(tracks can be simulated by superposition) The charge density function for a point charge in Cartesian coordinates: Physics effects included in simulation in two parts: 1) as effects which depend on spatial coordinates x & y, or; 2) as effects which depend on time. 1) The spatial effects function includes charge dispersion phenomena & transverse size w of the charge cluster due to transverse diffusion. Qpad(t) is the pad signal from charge dispersion when a charge Nqe of size w is deposited on the anode at t = 0; (1) xhigh, xlow, yhigh, ylow define the pad boundaries & TPC Rare Event Symposium - Paris

  21. (2) I(t) incorporates intrinsic rise time, longitudinal diffusion & electronics shaping times as time dependent effects. (1) and (2) are convoluted numerically for the model simulation. TPC Rare Event Symposium - Paris

  22. Charge dispersion spot x-ray signal for GEM Simulation versus measurement (Ar+10%CO2)(2 x 6 mm2 pads) Collimated ~ 50 m 4.5 keV x-ray spot on pad centre. Difference = induced signal (not included in simulation) studied previously:MPGD '99 (Orsay), LCWS 2004 Paris Primary pulse normalization used for the simulated secondary pulse Simulated primary pulse is normalized to the data. TPC Rare Event Symposium - Paris

  23. 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 simulation normalization - no other free parameters. TPC Rare Event Symposium - Paris

  24. Application to T2K TPC 7x9 mm2 pads 10% p/p (1 GeV/c) Good enough Requirement limited by Fermi motion (from a talk by F.Sánchez (Universitat Autònoma de Barcelona) But better momentum resolution would be useful: Better background rejection = More channels => $$? Can one do it with the presently chosen pad dimensions? TPC Rare Event Symposium - Paris

  25. T2K simulation for 8 x 8 mm2 padsTrack crosses no pad row or column boundariesAr+10% CO2 , vDrift = 28 m/ns (E = 300 V/cm) Aleph preamp tRise = 40 ns, tFall = 2 s Anode surface resistivity 150 K/, dielectric gap = 75 m, K = 2 Track at z = 175 mm, x = 0,  = 0 (uniform ionization) (ns) (ns) TPC Rare Event Symposium - Paris

  26. Pad response function Relative amplitude -20 -10 0 10 20 Micromegas TPC with resistive readout - Simulated PRF8 x 8 mm2 pads, Ar+10% CO2@ 300 V/cm, 175 mm drift distance (mm) TPC Rare Event Symposium - Paris

  27. Summary • Traditional MPGD-TPC has difficulty achieving good resolution with wide pads • With charge dispersion, the charge can be dispersed in a controlled way such that wide pads can be used without sacrificing resolution. We have achieved excellent resolution with wide pads 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. • The ILC-TPC resolution goal, ~100 m for all tracks,appears feasible.Good control of systematics will be needed. • For T2K, it appears possible to achieve better resolution than design goal if charge dispersion readout is used. • Good understanding of charge dispersion. The simulation can be used to optimize charge dispersion TPC readout. TPC Rare Event Symposium - Paris

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