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Ageing Phenomena in the LHCb Outer Tracker

1 November 2007 IEEE2007 Niels Tuning On behalf of the LHCb Outer Tracker Collaboration. Ageing Phenomena in the LHCb Outer Tracker. Introduction Ageing Phenomenon Cause Treatments. pp with s =14 TeV L = 2.10 32 cm -2 s -1 10 12 b-hadrons per year. LHCb in a nutshell. s. b. μ.

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Ageing Phenomena in the LHCb Outer Tracker

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  1. 1 November 2007 IEEE2007 Niels Tuning On behalf of the LHCb Outer Tracker Collaboration Ageing Phenomena in the LHCb Outer Tracker • Introduction • Ageing Phenomenon • Cause • Treatments IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning

  2. pp with s =14 TeV L = 2.1032 cm-2s-1 1012 b-hadrons per year LHCb in a nutshell s b μ μ s b b s Aim: look for new physics by measuring CP violation and rare decays IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning

  3. The LHCb Tracking System Tracking Detectors Trigger Tracker Inner Tracker Si strip detector Vertex Locator n-on-n Si strip detector 8mm from LHC beam  Impact parameter  B-lifetime • Outer Tracker • Straw tube technology • Gaseous • Momentum • B-mass IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning

  4. Outer Tracker 340 mm • One large straw tube module: • 34 x 490 cm2 • 4 x 64 = 256 straw tubes 5m • Total nr of channels: 53.760 • Gas: Ar/CO2 70/30 • Anode: 25µm W/Au • Cathode:Kapton XC/Al IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning

  5. Final Module Check:radioactive source scan Example of uniform response • Check detector response: • Current from 90Srβ-source • Pulse height from monochromatic 55Feγ-source • Full scan of the entire module • Every cm2 of the OT is checked Good Example: Bad Example: # Wire  Current (nA) 5 meter +20%  Position Wire locators IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning

  6. Ageing Phenomenon (I) Ratio Plot: Iafter/Ibefore Irradiate with 2 mCi 90Sr source Gas flow 150nA • Gain loss “in the neighborhood” • of the irradiation point: Croissant? Bean? Kidney? • Only at moderate intensity • Upstream of gas flow A real surprise – this was not seen in the aging tests performed over the last years with test modules IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning

  7. Intermezzo:Ageing Studies in R&D phase • Ageing Studies in R&D phase with test module: • 12 MeV proton beam • Hadronic environment (in situ HERA-B) • 9 keV X-ray tube: Accumulated 3 C/cm in 120 days No effects seen • IEEE 2004 NSS-MIC conference(Oct 2004, Rome) by Sebastian Bachmann • Session N39: Radiation Damage Effects II - Aging of Gaseous Detectors • Title:Ageing Studies for the Straw Tube Detectors for the LHCb Outer Tracking System IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning

  8. Ageing Phenomenon (II) • Gain loss “in the neighborhood” of the irradiation point: • Only at moderate intensity • Upstream of gas flow Gas flow Relative gain IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning

  9. Wire Inspection SEM-EDX: Deposit on the surface? Non-irradiated wire Irradiated wire Optical: Carbon IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning

  10. Philosophy: Create module without glue Add component by component, until it ages Find the Culprit(s) Test module (straws): 480 hrs, 20mCi Normal F-module: 20 hrs, 20mCi Test module IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning

  11. Find the Culprit Test module: 17 hrs, 2 mCi Put fresh glue at straw entrance  Ageing Glue: Araldite AW103, HY991 In parallel, new test modules are built with different glue  Confirm malicious effect of glue IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning

  12. Ageing: Treatments (I) No heating: 20 hrs2mCi 90Sr • Beneficial effects: • Heating (2 weeks at 45 oC) • Flushing • HV training With heating: 325 hrs2mCi 90Sr IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning

  13. Ageing: Treatments (I) No heating: 20 hrs2mCi 90Sr  Gain loss (%)  Flushing Time (weeks) • Beneficial effects: • Heating (2 weeks at 45 oC) • Flushing • HV training With heating: 325 hrs2mCi 90Sr ½ year Detector is installed, and flushing since 1 year IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning

  14. Ageing: Treatments (II)  Relative Gain  Irradiation Time (hours) 1st HV training 2nd HV training 3rd HV training • Beneficial effects: • Heating • Flushing • HV training (24 hrs, 1900V, G~700k) • Dark current ~ 10µA / wire • Wire inspection promising; no carbon deposits despite large currents • Other beneficial effects: • Lower gas flow during operation • Addition of O2 to counting gas IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning

  15. Ageing: Treatments (III) • Other beneficial effects: • Lower gas flow during operation • Addition of O2 to counting gas Ar/CO2 70/30, 22hrs, 20 l/hr Ar/CO2/O2 70/27.5/2.5, 46hrs, 10 l/hr IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning

  16. Summary • Observed serious gain loss with modest irradiation • No gain loss at highest intensity • No gain loss downstream the source • Outgassing glue is found to be the cause • Various treatments have been identified • Flushing • Heating • HV training • Lower gas flow • Addition of O2 IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning

  17. What science we’ll know in 2050 • The December 1999 issue of Scientific American, cited eight questions to which science is likely to have found the answers by the year 2050: Can physics be unified? Can aging be postponed? How was the Universe born? How does the mind work? What secrets do genes hold? Can robots be intelligent? Is there life in outer space? How much do we change the climate? IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning

  18. Backup slides IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning

  19. Consequence for LHCb? • Difficult to predict consequence: • Relate source to LHCb Source LHCb nA/straw/cm nA/straw/cm IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning

  20. Consequence for LHCb? • Difficult to predict consequence: • Relate source to LHCb • Add all beneficial effects • Multiplicative? • Extrapolate damage to 108 s • Linearly? • Exponentially? NB All numbers are for the region of maximum damage (“hot spot”) E.g. 10 cm (in Y) away from that, numbers have to be scaled down by a factor 23 IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning

  21. Consequence for LHCb? • Difficult to predict consequence: • Relate source to LHCb • Add all beneficial effects • Multiplicative? • Extrapolate damage to 108 s • Linearly? • Exponentially? • Low gas gain  cell efficiency • Gain drop of 50% is roughly equivalent to a HV step of ~70 V • Assume an initial operational voltage of 1520 V • Gain drop of 50% ~ effective HV reduction of 70V • ~15% lower drift-cell efficiency IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning

  22. Consequence for LHCb? Nominal • Difficult to predict consequence: • Relate source to LHCb • Add all beneficial effects • Multiplicative? • Extrapolate damage to 108 s • Linearly? • Exponentially? • Low gas gain  cell efficiency • Cell eff  track efficiency Tracking efficiency CAVEAT This study is purely illustrational! • tracking is not optimized to handle significant reductions of cell efficiencies • the gain loss and thus the reduction of cell efficiency is far from being uniform! OT-cell efficiency An OT-cell efficiency 15% lower than nominal over the entire detector surface induces a 8% reduction of the tracking efficiency IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning

  23. IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning

  24. Reverse gas flow Gas flow • Only ageing close to input • Polution not caused at curing time •  Classical outgassing after all Close to output Gas flow Close to input (12 Jun 07, #24) IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning

  25. Reverse gas flow, check other output now Gas flow • Only ageing close to input • Polution not caused at curing time •  Classical outgassing after all Gas flow Close to input (14 Jun 07) IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning

  26. Confirm Gain Loss with 55Fe pulse height • Gain loss measured with • Current from 90Sr • Pulse height from 55Fe IEEE NSS (N48-3) - Ageing in the LHCb Outer Tracker - N. Tuning

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