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Outer Tracker Comments

Ulrich Uwer University of Heidelberg. LHCb Week May 27, 2004. Aging Review Report:. Outer Tracker Comments. Aging Report. Many useful comments:. Safety factor for aging tests Acceleration factor for aging tests Material selection Importance of gas-system validation.

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Outer Tracker Comments

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  1. Ulrich Uwer University of Heidelberg LHCb Week May 27, 2004 Aging Review Report: Outer Tracker Comments

  2. Aging Report Many useful comments: • Safety factor for aging tests • Acceleration factor for aging tests • Material selection • Importance of gas-system validation Many good questions: • Gain uniformity and wire excentricity • Operation gas gain • Operation stability and chamber performance using ArCO2 • Temperature gradient along the modules … but conclusion / recommendations given in the written report are not addressing sufficiently basic results of our aging measurements

  3. Wire breaking in CF4 gases • repeatedly observed breaking anode wires in irradiated regions when using ArCO2CF4 (75/10/15) • Wires irradiated in CF4 showed indications for wire etching • Never observed wire breaking in ArCO2 (70/30) Serious argument against usage of CF4 Not commented by reviewers

  4. Believe of reviewers: CF4 prevents deposits not using CF4 is risky Effect of CF4 admixtures Fe 55 spectra 300 mC/cm @ 200 nA/cm +1 day @ 400 nA/cm Test to see our sensitivity to aging: Irradiation test using ArCH4CF4 Expect to see deposits and gain drop + 1 day @ 200 nA/cm + 1 day @ 400 nA/cm irrad, channel non irrad. cha. • CF4 does not always prevent deposits • Effects depend on irradiation intensity Difficult to predict the behavior of CF4 for the real detector

  5. Aging studies for ArCO2 and ArCO2CF4 Relative gas gain Relative gas gain mC/cm Irradiation spot diameter ~10cm Current density 700 – 1000 nA/cm

  6. No deposits for ArCO2 Severe deposits for ArCO2CF4 • we repeated the test with flipped gas-system channels:  same observations: (no)deposits for (ArCO2) ArCO2CF4 • We never observed Si in the deposits Depositions for ArCO2CF4 are not caused by pollutions of the gas-system as expressed by the reviewers: The system (used for HERA-B MSGC tests) is validated by the ArCO2 measurements.

  7. Conclusions • We observed reproducibly wire etching and depositions with ArCO2CF4 • Effects depend on irradiation area, intensity and water content • We have not observed aging (gain drop or wire breaking) using ArCO2 when operating with “reasonable” dry gas (water < 500 ppm) we see no guarantee for the magic cleaning property of CF4 mixtures but all kind a dangerous effects • Aging tests at much higher intensities than at LHC do not prove that effects seen will be present at LHC but there is also no evidence that CF4 admixtures do not lead to any damage at LHC intensities. Potential risk of CF4 is large compared to the moderate gain in physics performance: Baseline counting gas is ArCO2

  8. Gain Uniformity Scan along 5m module

  9. Gas Properties

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