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Ageing of the LHCb outer tracker

Ageing of the LHCb outer tracker. Masters project Mathieu Blom. Research goals. Big Bang: Matter and anti-matter produced in equal amounts. Yet, the observed universe consists out of matter. What is the fundamental difference between matter and anti-matter?.

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Ageing of the LHCb outer tracker

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  1. Ageing of the LHCb outer tracker Masters project Mathieu Blom

  2. Research goals • Big Bang: Matter and anti-matter produced in equal amounts. • Yet, the observed universe consists out of matter. • What is the fundamental difference between matter and anti-matter? Amsterdam Master of Physics Symposium 2009 - Mathieu Blom

  3. How? Collider experiment @ CERN: LHCb Amsterdam Master of Physics Symposium 2009 - Mathieu Blom

  4. LHCb detector Amsterdam Master of Physics Symposium 2009 - Mathieu Blom

  5. Detect proton-proton collisions Amsterdam Master of Physics Symposium 2009 - Mathieu Blom

  6. Outer tracker: 53.760 small detectors Amsterdam Master of Physics Symposium 2009 - Mathieu Blom

  7. Working principle of the outer tracker • The outer tracker is a drift chamber. • Electron multiplication between anode and cathode. • Charge collected on anode wire. • High voltage: 1520 V • Cathode radius (R): 2.45 mm • Anode radius: 12.7 µm • Gas mixture: Argon/CO2 70/30 • Multiplication factor = Gain: ± 40.000 Outer tracker straw tube Amsterdam Master of Physics Symposium 2009 - Mathieu Blom

  8. Ageing (1) Ageing: the value of the gain decreases over time due to radiation. The glue pollutes the gas system. A carbon containing coating forms on the anode wire. Aged wire Clean wire Amsterdam Master of Physics Symposium 2009 - Mathieu Blom

  9. Ageing (2) The ageing of the LHCb outer tracker exhibits unique features: • The ageing rate is large. • No ageing below the source. • No ageing downstream of the radiation source. This is due to ozone. Source position Relative gain after irradiation Amsterdam Master of Physics Symposium 2009 - Mathieu Blom

  10. Problem • The LHCb outer tracker shows signs of severe ageing. • Its ageing is caused by glue used its construction. • The glue can not be removed from the detector. • The detector is designed to be operational for 5 years, but ageing could limit its lifetime. How do we prevent, reduce or reverse ageing? Amsterdam Master of Physics Symposium 2009 - Mathieu Blom

  11. Possible solution • O2 moderates ageing. O2 also lowers the detector response. Do the positive effects of O2 outweigh the negative ones? • HV-training the anode wires reverses and prevents ageing. HV-training may damage the detector. Does HV-training damage the anode? Amsterdam Master of Physics Symposium 2009 - Mathieu Blom

  12. The effects of O2 on the gainpulse height spectra of 55Fe • 55Fe emits monochromatic photons of 5.9 keV. • These induce pulses on the anode wire. • The height of the pulses is a measure for the gain. • Adding O2 to the gas mixture will lower the gain. Current (mA) Time (ns) Amsterdam Master of Physics Symposium 2009 - Mathieu Blom

  13. The effects of O2 on the gainpulse height spectra 0% O2 2.5% O2 4.5% O2 • 2.5 % O2→ 11% gain loss • 4.5 % O2→ 29% gain loss These amounts are acceptable. Overall effect of adding O2 is positive. • Adding 4.5 O2 reduces the gain with 29% Amsterdam Master of Physics Symposium 2009 - Mathieu Blom

  14. Effects of HV-training on anode wire No negative effects observed →HV-training should be save Before HV-training After HV-training Amsterdam Master of Physics Symposium 2009 - Mathieu Blom

  15. Recap + Outlook • The LHCb outer tracker suffers from ageing. • Ageing can be prevented, reduced, reversed by HV-training and adding O2. • The decrease in signal response caused by O2 is acceptable → 2% O2 has been added to gas mixture. • HV-training keeps the anode wire intact. • Next test: very low concentrations of NO2 (1-10 ppm). And if after listening to this presentation… Amsterdam Master of Physics Symposium 2009 - Mathieu Blom

  16. You are interested in the subject… Thank you • You would like to read my thesis, which will be done in 2 weeks… • You have a bright idea… e-mail me: mblom@nikhef.nl You can help us Amsterdam Master of Physics Symposium 2009 - Mathieu Blom

  17. Backup slides

  18. We have tried: H2O2 + Water Ethanol N2O O2 and tested many solutions of a different nature… Heating modules Burning of the coating with strong currents. And will try Very low concentrations NO2 (1-10 ppm) What else? Amsterdam Master of Physics Symposium 2009 - Mathieu Blom

  19. The effects of adding H2O2 to the counting gas 20 hours irradiation Amsterdam Master of Physics Symposium 2009 - Mathieu Blom

  20. The effects of adding H2O2 to the counting gas Adding H2O2 to the outer tracker gas mixture decreases the ageing rate slightly, this effect can however be attributed to formation of O2. H2O2 does not prevent ageing Amsterdam Master of Physics Symposium 2009 - Mathieu Blom

  21. The effects of O2 on the gainpulse height spectra 0% O2 2.5% O2 4.5% O2 Adding 2.5 or 4.5 % O2 to the outer tracker gas mixture reduces the gain with 11 and 29% respectively. Adding Amsterdam Master of Physics Symposium 2009 - Mathieu Blom

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