Questions & Answers


Talk by Carsten Niebuhr

	Questions & Answers

Q (M. Capeans): Could it be a small leak at the bottom of the detector?

A (C. N.): The whole volume around the tracker is filled with N2. We measure both the leak rate and the fraction of N2 in the gas coming from the chamber. >From both measurements we conclude that the leaks are rather small. Also we don't see how the N2 would lead to aging only in the lower region of CJC2.

Q (F. Grancagnolo): Did you analyse the gas coming from different regions of the chamber? i.e. is there the possibility of having stratification of the gas in the active volume?

A (C. N.): This is indeed one of the suspicions we had. However when we encountered the problem in 1996/97 all 6 gas outlets from the chamber were connected to a single gas ring. Therefore no separate analysis was possible but this is planned for the future.

Q (F. Sauli): You mentioned a temperature gradient in the detector. How large is it, and could it be correlated to the aging asymmetry Top-Bottom?

A (C. N.): We do have several temperature sensors which are placed on the inner face of the CJC endwall. Here we measured temperatures ranging from ~30 to ~47 deg Celsius depending on the position of the probe. Given the observed linear dependence of the aging effect on the height in the chamber and therefore the correlation also with temperature we could imagine a process in which condensation around 30 deg Celsius might play a role.

Q (J. Va'vra): Did you vary H2O amount to see if it would start helping at some point (before switching to ethanol)?

A (C. N.): No we did not try this.

Q (J. Va'vra): Malter can occur at much lower current level than what you have observed (1-2muA). Did you have a sensitivity at much lower level (10-100 nA)?

A (C. N.): In principle we have a sensitivity of 10nA, but during a luminosity fill the current per CJC cell drops from typically 3 to 1 microAmp with fluctuation due to varying background conditions of +/- 100nA. Therefore we can not differentiate between any excess current of this size caused by early Malter effect and these fluctuations.

Q (A. Romaniouk): Is the ageing effect correlated with gas gain difference?

A (C. N.): Yes, but not in the way one might expect as the aging effect developed in a region of CJC2 which from the start had slightly lower gain and lower currents compared to the upper part of the chamber.