Gas pixel detector for x-ray observation David Attié P. Colas, E. Delagnes, Y. Giomataris, M. Campbell, X. Llopart, M. Chefdeville, H. van der Graaf, J. Timmermans, J. Visschers I’m here to present a TPC review David.Attie@cea.fr NDIP08 – Aix-les-Bains – June 19th, 2008

NDIP08 – Aix-les-Bains – June 19th, 2008 Outline Introduction: motivations for a gas pixel detector The TimePix readout chip Description Architecture and schematic Micro Pattern Gaseous Detector TPC Description of Micromegas Micro-TPC Application for x-ray observations Measurement of primary statistics in gas TPC based polarimeter Conclusion David.Attie@cea.fr NDIP08 – Aix-les-Bains – June 19th, 2008

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 2 e- from double beta decay, nuclear recoils in WIMP or neutrino interactions for dark matter search ALICE TPC simulations  Digital TPC as a tracking detector with very high spatial resolution for astrophysics & high energy physics experiments David.Attie@cea.fr NDIP08 – Aix-les-Bains – June 19th, 2008

Description of the TimePix chip Chip (CMOS ASIC) upgraded in the EUDET framework 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 1 2 3 4 5 55 μ m 14111 m 16120 m 14080 m (pixel array) 55 mm Synchronization Logic Interface 1 2 3 4 5 Preamp/shaper Configuration latches Counter THL disc. Llopart et al., NIMA 581 (2007) 361 David.Attie@cea.fr NDIP08 – Aix-les-Bains – June 19th, 2008

TimePix Synchronization Logic Control Each pixel can be configured independently in 5 different modes Internal clock up to 100 MHz Timepix Mode TOT Mode Medipix Mode 100 MHz Internal Shutter Shutter DACs values Mask P1 P0 Mode Masked 1 Medipix TOT Timepix-1hit Timepix Internal Clock 10 ns not detected detected Digital Signal Analog Signal Summed charge David.Attie@cea.fr NDIP08 – Aix-les-Bains – June 19th, 2008

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) Medipix2/TimePix chip TimePix chip David.Attie@cea.fr NDIP08 – Aix-les-Bains – June 19th, 2008

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 Multiplication between anode and mesh Gain up to 105 ~ 1 kV/cm ~ 80 kV/cm pad PCB Integrate Micromegas detector directly on a CMOS chip by post-processing Resistive layer for protection of a-Si:H IMT Neuchatel NIKHEF (MESA+, Univ. Twente) David.Attie@cea.fr NDIP08 – Aix-les-Bains – June 19th, 2008

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 David.Attie@cea.fr NDIP08 – Aix-les-Bains – June 19th, 2008

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 David.Attie@cea.fr NDIP08 – Aix-les-Bains – June 19th, 2008

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 David.Attie@cea.fr NDIP08 – Aix-les-Bains – June 19th, 2008

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 David.Attie@cea.fr NDIP08 – Aix-les-Bains – June 19th, 2008

Polarimetry using photoelectric absorption Ideal polarimeter is a track imager with: resolution elements < mean free path of photoelectron E X-ray Photoelectron 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 θ Auger electron φ maximum in the plane γ direction Nmax Nmin David.Attie@cea.fr NDIP08 – Aix-les-Bains – June 19th, 2008

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 David.Attie@cea.fr NDIP08 – Aix-les-Bains – June 19th, 2008

Prototype TPC polarimeter using TimePix/Micromegas Identify the cluster Photoelection + eauger track in Neon+10 Isobutane 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 David.Attie@cea.fr NDIP08 – Aix-les-Bains – June 19th, 2008

Example of TPC for x-ray polarimeter Drift Electrode GEM like Readout Strips 130 μm pitch Black et al. NIMA 581, 2007, 755 Gas mixture: Neon/DME 50:50 at 0,6 atm Photoelectron y e- Drift x(t) x y z Digitized Waveforms Differentiated Waveforms Image X-ray Trigger Polarized 6.4 keV photons 2O mm Uniform response Modulation (P ~50 %) No false modulation An encouraging start Counts Unpolarized 5.9 keV photons 0o 45o 90o Photoemission electron angle (degree) David.Attie@cea.fr NDIP08 – Aix-les-Bains – June 19th, 2008

NDIP08 – Aix-les-Bains – June 19th, 2008 Conclusions TimePix chip/Micromegas + SiProt: demonstrator for the digital TPC  useful tool for x-ray observations Ultimate resolution for a TPC thanks to the single electron sensibility Micro-TPC is an excellent tool to characterize photon absorption in gas mixtures statistics of primary electrons and clusters Fano factor (gain fluctuation) Identification of the photoelectron angle by imaging the photoelectron track is very promising for soft x-ray polarimetry ( 2 keV < Eγ < 50 keV) 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 David.Attie@cea.fr NDIP08 – Aix-les-Bains – June 19th, 2008

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 FREIBURG A. Bamberger K. Desch U. Renz M. Titov N. Vlasov A. Zwerger P. Wienemann CERN Erik Heijne Xavier Llopart Medipix Consortium domo arigato gazaimase = merci beaucoup Ijo desus = c’est fini ! β- from 90Sr source in He/Isobutane 80:20 Thank you for your attention David.Attie@cea.fr NDIP08 – Aix-les-Bains – June 19th, 2008

NDIP08 – Aix-les-Bains – June 19th, 2008 Backup slides David.Attie@cea.fr NDIP08 – Aix-les-Bains – June 19th, 2008

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: ~5 fps@20MHz http://www.utef.cvut.cz/medipix/usb/usb.html Mosaic achitecture: David.Attie@cea.fr NDIP08 – Aix-les-Bains – June 19th, 2008

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 David.Attie@cea.fr NDIP08 – Aix-les-Bains – June 19th, 2008

TimePix chip schematic Previous Pixel For each pixel Ref_Clkb Clk_Read Mux 4 bits thr Adj Mask Mux Input Preamp Disc 14 bits Shift Register THR Shutter Timepix Synchronization Logic Shutter_int Ctest P0 Conf Testbit Polarity P1 8 bits configuration Test Input Ovf Control Ref_Clk Clk_Read Next Pixel Analogic part Digital part David.Attie@cea.fr NDIP08 – Aix-les-Bains – June 19th, 2008

First TimePix Quad 3 2 1 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 David.Attie@cea.fr NDIP08 – Aix-les-Bains – June 19th, 2008

NDIP08 – Aix-les-Bains – June 19th, 2008 TimePix & GEMs Freiburg (+Bonn) Ar CO2 70/30 Cartes de 181x181 en mode Time & et en TOT Fournit les informations charge & temps en même temps Fort potentiel pour la séparation de traces He CO2 70/30 David.Attie@cea.fr NDIP08 – Aix-les-Bains – June 19th, 2008

TimePix using Micromegas Timepix chip + Micromegas on frame: Moiré effects + pillars Timepix chip + SiProt + Ingrid: “Uniform” MESA+ Resistive layer for protection IMT Neuchatel “counting” mode David.Attie@cea.fr NDIP08 – Aix-les-Bains – June 19th, 2008

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 ! David.Attie@cea.fr NDIP08 – Aix-les-Bains – June 19th, 2008

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 David.Attie@cea.fr NDIP08 – Aix-les-Bains – June 19th, 2008

Gas mixture containing Neon http://www-cxro.lbl.gov David.Attie@cea.fr NDIP08 – Aix-les-Bains – June 19th, 2008

Simulated quality factor Bellazzini et al., NIMA 572 (2007) 167 David.Attie@cea.fr NDIP08 – Aix-les-Bains – June 19th, 2008