Köln 2004 – scientific programme

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HK: Physik der Hadronen und Kerne

HK 12: Poster Session: Instrumentation and Applications

HK 12.37: Poster

Tuesday, March 9, 2004, 13:30–15:30, Foyer

Effects of N₂ in the ALICE TRD and TPC gases — •Chilo Garabatos — Gesellschaft für Schwerionenforschung, Darmstadt, Germany

It is inevitable that nitrogen impurities build up in detectors operated in a closed-loop gas circulation mode. Therefore, we have studied the effect of N₂ contamination on the drift and amplification properties of mixtures with noble gases and CO₂.

For the Xe-CO₂ [85-15] mixture foreseen for the ALICE Transition Radiation Detector (TRD), the admixture of up to 20 % N₂ marginally affects the drift velocity at the operating drift field of 700 V/cm, whereas the gain slightly decreases.

On the other hand, for the Ne-CO₂ [90-10] drift gas of the ALICE Time Projection Chamber (TPC), the addition of 5 % N₂ results in a decrease of the drift velocity of only 5 % at 400 V/cm, but substantially extends the efficiency plateau of the Readout Chambers. Measurements and simulations of drift velocities and gains in these mixtures will be shown, and a picture describing the detector stability involving Penning effects in the avalanche will be discussed.