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 gain  Operation stability / chamber performance using ArCO 2  Temperature gradient along the modules... but report is not taking important measurements sufficiently into account

Wire breaking in CF 4 gases  repeatedly observed breaking anode wires in irradiated regions when using ArCO 2 CF 4  Wires irraddiated in CF 4 showed indications for wire etching  Never observed wire breaking in ArCO 2 Serious argument against usage of CF 4 Not even commented by reviewers

CF 4 admixture and anode deposits Common believe: CF 4 always prevents deposits 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 prevent deposits in all cases  Effect depends on irradiation rate Difficult to predict the behavior of CF 4 for the real detector

Simultanous aging studies for ArCO 2 and ArCO 2 CF 4 Relative gas gain mC/cm Irradition spot ~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 the magic cleaning property of CF 4 mixtures but all kind a dangerous effects  Aging tests at much higher intensities than for LHC do not prove that the seen effect will be present at LHC but they also do not prove the opposite Potential risk of CF 4 is large compared to the moderate gain in physics performace

Gain Uniformity Scan along 5m module

Gas Properties