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Gas Pixel Detector for X-ray Observation

This presentation discusses the gas pixel detector for x-ray observation, including the TimePix readout chip, micro-pattern gaseous detector TPC, and integrated Micromegas. It also explores its application for x-ray observations and the measurement of primary statistics in gas.

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Gas Pixel Detector for X-ray Observation

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  1. Gas pixel detector for x-ray observation David Attié1 M. Campbell3, M. Chefdeville1,2, P. Colas1, E. Delagnes1, Y. Giomataris1, H. van der Graaf2, X. Llopart3, J. Timmermans2, J. Visschers2, 1. 2. 3. Astrophysics Detector Workshop – Nice – November 18th, 2008

  2. Outline Introduction: motivations for a gas pixel detector • The TimePix readout chip • Description • TimePix Syncronization Logic • Micro Pattern Gaseous Detector TPC • Description of Micromegas • Integrated Micromegas: InGrid • Micro-TPC • Application for x-ray observations • Measurement of primary statistics in gas • TPC-based polarimeter Conclusion Astrophysics Detector Workshop – Nice – November 18th, 2008

  3. Motivations for pixelized gaseous detector • Gaseous detector advantages: • 2D/3D imaging • Low occupancy and low radiation length X0  mean free path could be important • Spatial resolution: • σxy limited by the pad size (pitch/√12) • narrow charge distribution (RMS ~15 μm) • High granularity: • δ-ray recognition/suppression in TPC • possibility to count primary clusters & electrons • direction & energy of tracks: low-energy e- for X-ray polarimetry ALICE TPC simulations Bellazzini et al. NIMA 560, 2006, 425  Digital TPC as a x-ray polarimeter for astrophysics observations Astrophysics Detector Workshop – Nice – November 18th, 2008

  4. Astronomical x-ray polarimetry • Interpretations based on spectral and timing data are often ambiguous; polarization measurements will resolve the ambiguities. • Polarization of astrophysical sources may give signature of: • Emission processes: cyclotron, synchrotron, non thermal bremmstrahlung(Westfold, 1959; Gnedin & Sunyaev, 1974; Rees, 1975) • Scattering on aspherical accreting plasmas: disks, blobs, columns • (Rees, 1975; Sunyaev & Titarchuk, 1985; Mészáros, P. et al. 1988) • Vacuum polarization and birefringence through extreme magnetic fields • (Gnedin et al., 1978; Ventura, 1979; Mészáros & Ventura, 1979) • Geometry of x-ray sources and physical properties of emission sites • magnetic field strength and direction in compacts objects • environment (disk or spherical) in supermassive black holes (AGN) • accretion geometry • Cosmic ray acceleration in supernova remnants Astrophysics Detector Workshop – Nice – November 18th, 2008

  5. Description of the TimePix chip 55 mm m μ 14080 m (pixel array) 55 4 4 16120 m 55 mm 2 2 3 3 1 1 5 5 55 μ m 14111 m • Chip (CMOS ASIC) upgraded in the EUDET framework for high energy physics from the Medipix2 chip developed first for medical applications • IBM technology 0.25 μm on 6 layers • Characteristics: • surface: 1.4 x 1.6 cm2 • matrix of 256 x 256 • pixel size: 55 x 55 μm2 • For each pixel: • preamp/shaper • threshold discriminator • register for configuration • TimePix synchronization logic • 14-bit counter • Noise: ~ 650 e- • 70 e- per pixel, Cin ~ 15 fF Pixel Synchronization Logic Interface 1 2 3 4 5 Configuration latches Preamp/shaper Counter THL disc. Llopart et al., NIMA 581 (2007) 361 Astrophysics Detector Workshop – Nice – November 18th, 2008

  6. TimePix Synchronization Logic Control Medipix Mode Timepix Mode TOT Mode 10 ns not detected detected Summed charge • Each pixel can be configured independently in 5 different modes • Internal clock up to 100 MHz 100 MHz Internal Shutter Shutter Internal Clock Digital Signal Analog Signal Astrophysics Detector Workshop – Nice – November 18th, 2008

  7. Detectors using TimePix chip + - + + - - Solid detector Gas detector x, y, F(x, y)  2D x, y, z(t), E(x,y)  3D Drift cathode grid X-ray source Ionizing particle Gas volume Semiconductor sensor Flip-chip bump bonding connections Amplification System (MPGD) TimePix chip Medipix2/TimePix chip Astrophysics Detector Workshop – Nice – November 18th, 2008

  8. InGrid: Integrated Micromegas Grid • Micromegas is a Micro Pattern Gaseous Detector formed by a metallic micromesh (hole pitch 70 μm) sustained by 50 μm pillars above the anode (pads) • Multiplication between anode and mesh • Gain is a function of the electric field and the gap up to 105 • Integrate Micromegas detector directly on a CMOS chip by post-processing but need resistive layer protection: ~20 μm of amorphous silicon (a-Si:H) e- ~ 1 kV/cm NIKHEF(MESA+, Univ. Twente) CERN ~ 80 kV/cm Resistive layer for protection of a-Si:H IMT Neuchatel pad PCB Astrophysics Detector Workshop – Nice – November 18th, 2008

  9. InGrid: energy resolution • Energy resolution depends on the grid geometry • Grids can be very flat • best energy resolution achieved:  13.6 % with 55Fe source in P10 • removal of Kβ 6.5 keV line:  11.7 % @ 5.9 keV in P10 • Hole pitch down to 14 μm with various diameters • Different gaps (35-75 μm) • Until now: grid is 1 μm of Al but can also be increased to 5 μm by electrolysis to be more robust Escape peak Kα 13.6 % FWHM Escape peak Kβ Gap: 50 μm; Hole picth: 32 μm,Ø: 14 μm 11.7% FWHM Kβ-filtered spectrum with Cr foil Astrophysics Detector Workshop – Nice – November 18th, 2008

  10. Micro-TPC using TimePix/Micromegas • Micro-TPC with a 6 cm height field cage • Size : 4 cm × 5 cm × 8 cm Windows for X-ray sources Cover Windows for β sources 6 cm Field cage Micromegas mesh • Gas mixture at atmospheric pressure TimePix chip Astrophysics Detector Workshop – Nice – November 18th, 2008

  11. Micro-TPC TimePix/Micromegas • TimePix chip + SiProt 20 μm + Micromegas • 55Fe source • Ar/Iso (95:5) • Time mode • z = 25 mm • Vmesh = -340 V • tshutter = 283 μs Astrophysics Detector Workshop – Nice – November 18th, 2008

  12. Measurements of primary statistics in gases • Diffusion σt should be big enough to separate electrons: e- per pixel ~ 1 • Study of primary electrons and Fano factor F using RMS • Spectrum of number of electrons for 2000 events: • F: Fano factor • √b: single e- gain distribution rms (%) • ε: detection efficiency • N: number of primary e- • Sensitive to Kα & Kβ lines • FWHM = 9,5 % • 5.9 keV line at ~ 226 e- TimePix+Ingrid+ 15 μm SiProt Argon + 5% Isobutane Astrophysics Detector Workshop – Nice – November 18th, 2008

  13. Polarimetry using photoelectric absorption • Ideal polarimeter is a track imager with: resolution elements < mean free path of photoelectron E • Differential photoelectron cross-section emitted from the atomic s-orbital in non relativist limit: • θ polar angle, φ azimutal angle • Emission angles are modulated by the polarization P X-ray Photoelectron θ Auger electron φ maximum in the plane x-ray direction Nmax Nmin Astrophysics Detector Workshop – Nice – November 18th, 2008

  14. Prototype TPC polarimeter using TimePix/Micromegas • TimePix chip + SiProt 20 μm + Micromegas • 55Fe source • Ne/Iso (90:10) • TOT mode • z < 5 mm • Vmesh = -450 V • tshutter = 0.2 s Astrophysics Detector Workshop – Nice – November 18th, 2008

  15. Prototype TPC polarimeter using TimePix/Micromegas Photoelection + eauger track in Neon+10 Isobutane • Identify the cluster • TimePix chip + SiProt 20 μm + Micromegas • 55Fe source • Ne/Iso (90:10) • TOT mode • z < 5 mm • Vmesh = -450 V • tshutter = 0.2 s • Determination of the polarization • Barycentre • Principal axis Reconstructed absorption point Reconstructed photoemission direction with identification of the absorption point and the removal of the final part of the track φ φ photoemission angle • Low Ek-edge of Neon  eauger are • isotropically emitted with a small • fraction of the photon energy • In low Z gas mixture tracks are • longer so angular reconstruction is easier Astrophysics Detector Workshop – Nice – November 18th, 2008

  16. Prototype TPC polarimeter using TimePix/Micromegas • Double structure operated for the first time (He/Iso, 80:20, 55Fe, 30 mm gap) • No protection layer  chip survived ~5 hours, protection layer still necessary • Recent test of silicon nitride (Si3N4) protection layer of 7.5 μm very promising 450V 100V NIKHEF(MESA+, Univ. Twente) 55Fe in He/Iso in TOT mode 210Po in He/Iso in TOT mode Astrophysics Detector Workshop – Nice – November 18th, 2008

  17. Example of TPC for x-ray polarimeter y x Photoelectron z Readout Strips 130 μm pitch Drift Electrode GEM like Black et al. NIMA 581, 2007, 755 Gas mixture: Neon/DME 50:50 at 0,6 atm y e- Drift x(t) Differentiated Waveforms Digitized Waveforms Image X-ray Trigger Polarized 6.4 keV photons 2O mm • Uniform response • Modulation (P ~50 %) • No false modulation • An encouraging start • Quantum efficiency ~ 6% Counts Unpolarized 5.9 keV photons 0o 45o 90o Photoemission electron angle (degree) Astrophysics Detector Workshop – Nice – November 18th, 2008

  18. Conclusions • TimePix chip/Micromegas + SiProt: demonstrator for the digital TPC  useful tool for x-ray observations (polarimeter for space telescope: IXO?) • Identification of the photoelectron angle by imaging the photoelectron trackis very promising for soft x-ray polarimetry ( 2 keV < Eγ < 50 keV) with a quantum efficiency up to a few percent. • Need a polarized source and a biggest “Polarimeter/Timepix” collaboration • Ultimate resolution for a TPC thanks to the single electron sensibility: Micro-TPC is an excellent tool to characterize photon absorption in gases • Still some technologic issues: • Self triggering capability • How to improve the readout of the chips (speed and larger surface) ? - through Si connectivity: avoiding bonding wires - fast readout technology (~5 Gb/s) • Sealed detector Astrophysics Detector Workshop – Nice – November 18th, 2008

  19. The TimePix collaboration • NIKHEF Harry van der Graaf • Martin Fransen • Jan Timmermans • Jan Visschers • Sipho van der Putten • Arno Aarts • Saclay CEA/DAPNIA David Attié • Paul Colas • Esther Ferrer-Ribas • Arnaud Giganon • Yannis Giomataris • Marc Riallot • Univ. Twente/Mesa+ Jurriaan Schmitz • Victor Blanco Carballo • Cora Salm • Sander Smits • FREIBURGA. Bamberger • K. Desch • U. Renz • M. Titov • N. Vlasov • A. Zwerger • P. Wienemann • CERN Erik Heijne • Xavier Llopart • Medipix Consortium β- from 90Sr source in He/Isobutane 80:20 Thank you for your attention Astrophysics Detector Workshop – Nice – November 18th, 2008

  20. Backup slides Astrophysics Detector Workshop – Nice – November 18th, 2008

  21. Micromegas & GEMs (MPGD) 50 µm 40 kV/cm ~1000 µm 1 kV/cm ~50 µm 80 kV/cm Technology choice for TPC readout: Micro Pattern Gaseous Detector • better ageing properties • easier to manufacture • more robust than wires • no E×B effect • fast signal & high gain • low ion backdrift GEM Micromegas • MICROMEsh GAseous Structure(Y. Giomataris et al., 1996) • metallic micromesh (typical pitch 50μm) • sustained by 50μm pillars, multiplication between anode and mesh, high gain • Gas Electron Multiplier (F. Sauli, 1997) • 2 copper foils separated by kapton • multiplication takes place in holes • low gain • Gas Electron Multiplier (F. Sauli, 1997) • 2 copper foils separated by kapton • multiplication takes place in holes • use of 2 or 3 stages Avalanche Astrophysics Detector Workshop – Nice – November 18th, 2008

  22. Micromegas & GEMs (MPGD) Technology choice for TPC readout: Micro Pattern Gaseous Detector • better ageing properties • easier to manufacture • more robust than wires • no E×B effect • fast signal & high gain • low ion backdrift GEM Micromegas • simplicity • single stage of amplification • natural ion feedback suppression • discharges non destructive • 2- or 3- stage amplification • easy operation • low field above the electronics • low discharge probability Astrophysics Detector Workshop – Nice – November 18th, 2008

  23. Mixtures of gases containing argon: gain curves iC4H10 CO2, CH4 C2H6 Micromegas Mesh : 50 mm gap of 10x10 cm² size Astrophysics Detector Workshop – Nice – November 18th, 2008

  24. Readout system for Medipix2/TimePix chip • MUROSv2.1: • Serial readout • VHDCI cable of length <3m • read 8 chips in mosaic • tunable clock [30-200MHz] • ~40fps @160MHz http://www.nikhef.nl/pub/experiments/medipix/muros.html • USB: • Serial readout • ~5 fps@20MHz http://www.utef.cvut.cz/medipix/usb/usb.html • Mosaic achitecture: Astrophysics Detector Workshop – Nice – November 18th, 2008

  25. TimePix chip schematic Previous Pixel For each pixel Ref_Clkb Clk_Read Mux 4 bits thr Adj Mask Mux Preamp Input Disc 14 bits Shift Register Shutter THR Timepix Synchronization Logic Shutter_int Ctest P0 Conf Testbit Polarity P1 8 bits configuration Test Input Ovf Control Ref_Clk Clk_Read Next Pixel Digital part Analogic part Astrophysics Detector Workshop – Nice – November 18th, 2008

  26. TimePix chip architecture • 36×106 transistors on 6 layers (~550 transistors/pixel  13.5 μW) • Reference clock per pixel up to 100 MHz • Characteristics: • analog power: 440 mW • digital power (Ref_Clk = 80 MHz): 450 mW • serial readout (@ 100 MHz): 9.17 ms • parallel readout (@ 100 MHz): 287 μs • Pixel modes: • masked • counting mode (Medipix, Timepix-1h) • Time-Over-Threshold  “charge” info • Common stop  “time” info Astrophysics Detector Workshop – Nice – November 18th, 2008

  27. First TimePix Quad 1 2 3 • First Timepix quad • + 300 μm Si crystal • Medipix mode counting • 55Fe source • tshutter =40 s • Time mode • 90Sr source • tshutter = 237 μs • Time-Over-Threshold mode • 241Am source • tshutter = 5 s Llopart & Campbell, CERN Astrophysics Detector Workshop – Nice – November 18th, 2008

  28. TimePix & GEMs • Cartes de 181x181 en mode Time & et en TOT • Fournit les informations charge & temps en même temps • Fort potentiel pour la séparation de traces Freiburg (+Bonn) Ar CO2 70/30 He CO2 70/30 Astrophysics Detector Workshop – Nice – November 18th, 2008

  29. TimePix using Micromegas • Timepix chip + Micromegas on frame: Moiré effects + pillars • Timepix chip + SiProt + Ingrid: “Uniform” Resistive layer for protection MESA+ IMT Neuchatel “counting” mode Astrophysics Detector Workshop – Nice – November 18th, 2008

  30. Micro-TPC TimePix/Micromegas • TimePix chip + SiProt 20 μm + Micromegas • 90Sr source • Ar  He • Time mode • z ~ 40 mm • Vmesh = -340 V • tshutter = 180 μs spark-proof ! Astrophysics Detector Workshop – Nice – November 18th, 2008

  31. Micro-TPC TimePix/Micromegas • TimePix chip + SiProt 20 μm + Micromegas • 90Sr source • Ar/Iso (95:5) • Time mode • z ~ 40 mm • Vmesh = -340 V • tshutter = 180 μs Astrophysics Detector Workshop – Nice – November 18th, 2008

  32. Gas mixture containing Neon http://www-cxro.lbl.gov Astrophysics Detector Workshop – Nice – November 18th, 2008

  33. Simulated quality factor Bellazzini et al., NIMA 572 (2007) 167 Astrophysics Detector Workshop – Nice – November 18th, 2008

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