Full characterization tests of Micromegas with elongated pillars

Transcription

1 University of Würzburg Full characterization tests of Micromegas with elongated pillars B. Alvarez1 Gonzalez, L. Barak1, J. Bortfeldt1, F. Dubinin3, G. Glonti1, F. Kuger1,2, P. Iengo1, E. Oliveri1, J. Samarati1, G. Sekhniaidze4, O. Sidiropoulou1,2, J. Wotschack1 1 CERN, 2University of Würzburg, Germany, 3Russian Academy of Sciences, 4INFN and University of Naples IPRD 2016 Siena 3-6 October

2 Resistive Bulk Micromegas Micromegas are parallel-plate chamber : thin amplification region separated by metallic micromesh from conversion region Amplification region : defined by micro-mesh and Conversion & drift space (few mm) Mesh anode structure, 0.1 mm width ensured by regularly spaced insulating pillars. Results from a long R&D phase to develop Micromegas suitable for large experiments Copper readout strips are covered by a 50um thick Kapton foil carrying resistive strips ( 0.5-1ΜΩ/ ) to limit discharge currents Signals picked-up by readout strips Hit position from charge-weighted mean 2

3 Pillar Structure Circular pillars every few mm DuPontTM Pyralux coverlay, pattern creation using photo lithography, resistivity according to specs: 3.4x1016 Ohm cm pillar height = 128 um (coverlay is 64um thick and the pillars of 128um are obtained laminating 2 layers) pillar diameter 300 um Small prototypes ( e.g. 10x10 cm2 ) Large detectors (>1x1 m2) for large area applications - bulk technology mechanically floating mesh - produced in specialized workshops at - technology transfer for mass production in industries* CERN or in research institutes - production in industry necessary due to number of boards and cost - pillars well attached to anode structure - enormous problem with pillar attachment untolerable inhomogeneity in amplification region * F. Kuger and P. Iengo on behalf of ATLAS coll. proceeding of MPGD2015 Conference to be published in EPJ ( contribid=52&sessionid=8&resid=0&materialid=paper&confid=8839) 3

4 Pillar influence on Position Reconstruction Track 25 um above Track 400 um above the micro-mesh the micro-mesh electron drift and amplification in Argon:Isobutane 90:10 vol.% mixture amplification gap 128 um pitch 63 um E_ampl = 8.6 kv/cm E_drift = 0.2 kv/cm Brown line: electron drift line Blue circle: excitation Red dot: ionization - negligible effect on detection efficiency - small effect on position reconstruction if pillar small P. Bhattacharya et al., Nucl. Instrum. Meth. A793, (2015) 4

5 Large area applications readout structure production in industry mandatory avoid pillar attachment problems by increasing pillar surface limit distortion of electric fields in direction perpendicular to strips exploiting the field line distortion to limit the impact on performance elongated pillars (few mm x 200um) Small bulk prototype 10x10 cm2 (TLP) Two different patterns: - 2mm x 0.2mm with 4.8mm pitch - 100mm x 0.2mm with 4.8 spacing 358 strips strip width 0.08mm strip pitch 0.4mm amplification gap 128um drift gap 5mm 5

6 Detector characterization: Setup Ar:CO2 93:7 vol.% 55 trigger from signal on micro-mesh mesh grounded via Keithley Picoamperometer Fe source, 12 MBq measure current between anode and mesh scaler to measure the trigger rate Multi Channel Analyzer to acquire pulse height spectrum measure the absolute gas gain Source position APV-25 front-end electronics on 2 mm wide pillars strips to determine absolute charge calibration 100 mm wide pillars Source position 6

7 Detector characterization: Gas gain in ArCO 2 93:7 vol.% G= Mean N N e= Mean histo I f n e q e p Gaus Np = where : 5900 W Ar 93 % W CO 7 % = W Ar = 26, W CO = 33 2 I = fit w / o source + fit with source 7

8 Detector characterization: Drift field Dependence A B Below 600 V/cm: electrons lost due to attachment to gas during drift Above 600 V/cm: electrons lost due to decreasing electron mesh transparency 8

9 CERN Gamma Irradiation Facility (GIF++) A dedicated irradiation facility with photon flux up to 10 8 cm-2s-1, energy of 662 kev : ( ~14 Tbq ) muon beam with ~2kHz rate and 100GeV/c momentum Investigation & characterization of particle detectors in high-rate photon background possible ( as encountered in most LHC experiments ) Filter system permits attenuating the photon flux in several steps to reach attenuation factors of several orders of magnitude ( ) 9

10 Tm m 4 TL P MM SW Tm m 7 Tm m 1 August Test GIF++: Set up beam 137 Cs Test August, preliminary results Reference detectors : resistive strips Micromegas with two dimensional strip readout structure (Tmm) 2D position resolution O(60um) MMSW: Micromegas quadruplet with mechanically floating mesh Amplification and drift scans with and w/o source Attenuation filters : 4.6, 10, 46 Muon beam 100GeV/c 10

11 Track reconstruction in High-Rate Background To identify muons from photons an iterative Kalman filter based track reconstruction * is performed The used Kalman filter performs a least-squares fit of the data in a track candidate and is based on a matrix multiplication in the 3D space The detector system is aligned using tracks, correcting for translation and relative rotations of the detectors around the beam-axis * J. Bortfeldt et al., Low material budget floating strip Micromegas for ion transmission radiography, NIMA 2016, in press 11

12 Determination of Spatial resolution ( A ) Spatial resolution of reference detectors (Tmms) has been determined using the geometric mean method *: σ SR σ inc σ exc i σ inc : i * Carnegie et al., Resolution studies of cosmic-ray tracks i in a TPC with GEM readout, NIMA 538, 2005 The width of the gaussian residual distribution between measured and predicted hits when the detector i i is included in the fit σ exc : The width of the gaussian residual distribution between measured and predicted hits when the detector i i is excluded from the fit ( B ) Use track extrapolation method: The track is measured from the reference detectors and is extrapolated to the TLP σ SR = σ SR σ track 2 TLP 2 i σsr,ref Δx σtrack σ track : accuracy of hit position prediction in the detector under test using the resolution of the reference detectors σsr,ref Tmms Tmm TLP 12

13 Spatial resolution under Irradiation: Preliminary results Atten. filter 0 = No source Atten. Filter 1 = 130 khz/cm2 Blue: reference detectors (Tmms) Green: detector under study (TLP) Spatial resolution in two different pillar regions is the same Spatial resolution is equivalent to those of similar detectors with circular pillars from data w/o source Increase of spatial resolution for high rate. Tracking algorithm has been optimized for low rate (no background) analysis and will be adapted for the high rate case (time information will be exploited for a pre-selection of the hits and clusters) Best track accuracy minimal track uncertainty can be obtained ~ z= -450 mm 13

14 Conclusions Characterization done using an 55 Fe source Gain Electron transparency observed, expected drift field behavior The detector has been irradiated with a more intense source and with a muon beam in GIF++ Iterative Kalman filter tracking based algorithm is used to identify muons from photons Spatial resolution: 65um without irrdiation, as expected from similar detectors with circular pillars 85um with highest rate Tracking algorithm to be adapted for high rate case ongoing. Analysis of pulse height behavior, tracking efficiency and photon detection efficiency ongoing Elongated thin pillars do not show any limitation in the tracking performance Can be used in industrial production of Micromegas readout structures for large area applications Thank you!!! 14

15 BACK-UP

16 Detector characterization: Drift field Dependence tio a l u m i S n Fraction of non-attached electrons after 5mm drift in ArCO 2 93:7 with different levels of O2 contamination Sim on i t ula Electron transparency of different mesh geometries, labeled with aperture width [μm] - wire diameter [μm] : open area

17 Kalman filter based track finding algorithm