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

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 ArCO 2  Temperature gradient along the modules … but conclusion / recommendations given in the written report are not addressing sufficiently basic results of our aging measurements

Wire breaking in CF 4 gases  repeatedly observed breaking anode wires in irradiated regions when using ArCO 2 CF 4 (75/10/15)  Wires irradiated in CF 4 showed indications for wire etching  Never observed wire breaking in ArCO 2 (70/30) Serious argument against usage of CF 4 Not commented by reviewers

Effect of CF 4 admixtures Believe of reviewers: CF 4 prevents deposits  not using CF 4 is risky Test to see our sensitivity to aging: Irradiation test using ArCH 4 CF 4 Expect to see deposits and gain drop Fe 55 spectra irrad, channel non irrad. cha nA/cm nA/cm nA/cm nA/cm  CF 4 does not always prevent deposits  Effects depend on irradiation intensity Difficult to predict the behavior of CF 4 for the real detector

Aging studies for ArCO 2 and ArCO 2 CF 4 Relative gas gain mC/cm Irradiation spot diameter ~10cm Current density 700 – 1000 nA/cm

No deposits for ArCO 2 Severe deposits for ArCO 2 CF 4  we repeated the test with flipped gas- system channels:  same observations: (no) deposits for (ArCO 2 ) ArCO 2 CF 4  We never observed Si in the deposits Depositions for ArCO 2 CF 4 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 ArCO 2 measurements.

Conclusions  We observed reproducibly wire etching and depositions with ArCO 2 CF 4  Effects depend on irradiation area, intensity and water content  We have not observed aging (gain drop or wire breaking) using ArCO 2 when operating with “reasonable” dry gas (water < 500 ppm) we see no guarantee for the magic cleaning property of CF 4 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 CF 4 admixtures do not lead to any damage at LHC intensities. Potential risk of CF 4 is large compared to the moderate gain in physics performance: Baseline counting gas is ArCO 2

Gain Uniformity Scan along 5m module

Gas Properties