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Micromegas Performance and Ageing Studies at CERN

This summary presents the results of performance and ageing studies on the Micromegas detector at CERN, focusing on gain measurements, energy resolution, ion feedback, and ageing effects.

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Micromegas Performance and Ageing Studies at CERN

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  1. Micromegas Performance and Ageing studies David Attié MPGD. Towards an R&D Collaboration, CERN – 10 September 2007 MPGD. R&D Collaboration, CERN – September 10, 2007

  2. Summary • Gain measurements • Energy resolution • Ion feedback • Ageing • Conclusion MPGD. R&D Collaboration, CERN – September 10, 2007

  3. Gain measurements • Goals: • find a gas mixture with comfortable gain margin • know as much as possible the maximum gain (to avoid spark) • Description: • “Standard” 50 mm mesh of • 10 cm x 10 cm size • Gas mixing system with • triple mixture available MPGD. R&D Collaboration, CERN – September 10, 2007

  4. Mixtures of gases containing argon: gain curves iC4H10 CO2, CH4 C2H6 Micromegas Mesh : 50 mm gap of 10x10 cm² size MPGD. R&D Collaboration, CERN – September 10, 2007

  5. Ar/CH4: simulation vs. measurements Good agreement: measurements are consistent with simulations MPGD. R&D Collaboration, CERN – September 10, 2007

  6. Ar/iC4H10: simulation vs. measurements : Agreement with the slope at low fields but not with the absolute gain and the photons effects UV photons ? Penning effect MPGD. R&D Collaboration, CERN – September 10, 2007

  7. Energy resolution vs. gain Argon/Isobutane • Best RMS for a gain • between 3.103 & 6.103 • Degradation increase in inverse • proportion to the quencher MPGD. R&D Collaboration, CERN – September 10, 2007

  8. Energy resolution • Micromegas standard 10 cm x 10 cm • 55Fe source in Argon/iC4H10 (95:5) • Escape line at 3 keV • Kα at 5.9 keV • Kβ at 6.4 keV • Obtain easily a monochromatic source by filtering the Kβ line at 6,4 keV • 10 μm of Chromium foil (Center for X-Ray Optics) • Chromium K-edge (Center for X-Ray Optics) σE/E = 7.0 % FWHM = 16.6 % 2/ndf = 19 σE/E = 8.0 % FWHM = 18.8 % 2/ndf = 112 Pressure = 1 atm, thickness = 10 μm Transmission (%) Photon energy (keV) MPGD. R&D Collaboration, CERN – September 10, 2007

  9. Energy resolution Cr foil source Drift cathode mesh MPGD. R&D Collaboration, CERN – September 10, 2007

  10. Energy resolution • Energy resolution using a « microbulk » • Argon/Isobutane (95:5) • Chromium foil σE/E = 5.7 % FWHM = 13.5 % 2/ndf = 1.36 55Fe MPGD. R&D Collaboration, CERN – September 10, 2007

  11. Energy resolution • Energy resolution using an Ingrid (gap: 50 μm; picth: 32 μm; Ø: 14 μm) • Argon/Methane (90:10) • Chromium foil σE/E = 5.0 % FWHM = 11.7 % 2/ndf = 1.35 55Fe MPGD. R&D Collaboration, CERN – September 10, 2007

  12. Ion feedback • Measurement concept: X-rays generator Idrift I0 • I0: primary current • Idrift: cathode current • Imesh: amplification current -500 V Imesh -300 V MPGD. R&D Collaboration, CERN – September 10, 2007

  13. Ion feedback • Pitch: 58 μm; Ø: 31 μm • Pitch: 20 μm; Ø: 10 μm MPGD. R&D Collaboration, CERN – September 10, 2007

  14. Ageing • X-rays gun (40 kV, 20 mA) • Micromegas “Bulk” (T2K-like) • Gas mixture: • Argon/Isobutane (95:5) • Argon/CF4/Isobutane (95:3:2) MPGD. R&D Collaboration, CERN – September 10, 2007

  15. Ageing Normalized unit • Mesh current Ar/CF4/Iso (95:3:2) 16,1 C / cm² ~ 20 LHC years Time (d) MPGD. R&D Collaboration, CERN – September 10, 2007

  16. Ageing Normalized unit • Mesh current • Temperature • Pressure Time (d) MPGD. R&D Collaboration, CERN – September 10, 2007

  17. Ageing 11 cm 11 cm • Gain ~4000 • Mesh current ~ 5 μA during 5 days inside 10 cm² • New measurement procedure with an other bulk: Hole 2cm x 5cm Absorber 200 mm of Al 2cm x 2cm MPGD. R&D Collaboration, CERN – September 10, 2007

  18. Ageing Current (mA) • Mesh current Ar/Iso (95:5) 0,17 C/cm² ~ 2 LHC years Time (d) MPGD. R&D Collaboration, CERN – September 10, 2007

  19. Ageing MPGD. R&D Collaboration, CERN – September 10, 2007

  20. Conclusion • The choice of the gas mixture could be adapted to the needs • The energy resolution can easily reach 5 % RMS (11,7 % FWHM) • The ion feedback is depending of the geometry and achieve 10-3 • Until now, no ageing has been observed clearly • The studies continue following the technology developments… MPGD. R&D Collaboration, CERN – September 10, 2007

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