Questions & Answers


Talk by Anatoli Krivchitch

	Questions & Answers

Q (F. Sauli): What is the source of oxygen? CO₂, H₂0, 0₂?

A (A. K.): My feeling is that it is from CO₂. But I cannot for sure exclude an influence of H₂0 or another admixture. That is why I am talking now only about the phenomenon of the wire swelling. We should perform a further study of this effect with gas mixtures such as Ar/CF₄ and Ar/CO₂.

Q (I. Tichomirov): Can increasing the gold thickness improve the situation with the anode wire swelling?

A (A. K.): I think an increasing of the gold thickness must be the second step. The first one should be a correct device for the wire manufacturing technology. The tungsten wire coating should be done using a gold melting technology.

Q (M. Titov): What is the possible difference between your results and the results for the CMS muon chamber prototypes?

A (A. K.): Many differences. Because the wire diameter for CMS chamber is 50 um. We observed a small peak of oxygen in the center of the irradiated zone and some cracks in the gold surface for 10% CF₄. Maybe this was the start.

Q (M. Hohlmann): What was the wire tension in your straw tubes?

A (A. K.): The wire tensions were 60g.

Q (D. Khazins): Do you plan to do a swelling test with a pure W-wire without gold plating ? I think such a test might clarify the phenomenon.

A (A. K.): Not now. First we should investigate the gas mixtures with and without CO₂/CF₄.

Q (G. Bohm): A remark: F-radicals shoud not only be aggressive against Au, but also with W, desorbing as WF₆ gas. This could explain the W-deposit on the wire. Remember also the influence of H₂0 (ed. in the results reported by A. Schreiner at this workshop), buffering the fluorine.

A (A. K.): I agree that this reaction can take place in context with the wire swelling effect. We already mentioned this in our preprint (PNPI); ~2406 (2001).

Q (R. Henderson):

1) Have you tested with no CO₂?

2) Our results with CF₄/Isobutane (80:20) went to 5 C/cm and we saw no changes in the wire.

A (A. K.):

1) In the near future we are going to study aging with Ar/CF₄ and Ar/CO₂ gas mixtures.

2) For me it is very difficult to make a comment on such a question. At least, I would need to know exactly the gas gain in the center of the irradiated zone.

Q (J. Va'vra):

1) Did you do a "control" test by removing CF₄ from the mix?

2) To see what role F plays in the problem?

A (A. K.):

1) We are going to perform the aging test at least for the following gas mixtures: Ar/CF₄, Ar/CO₂.

2) I am sure F plays an important role in the problem. The traces of F have been observed in some of our XEM results. In the near future we are going to perform a Nuclear Reaction Analysis for F.

Q (H. Kolanoski):

1) What was the water concentration in your setup?

2) Did you also observe wire swelling at low water concentration for Xe/CO₂/CF₄ (in contrast to the ATLAS observations) ?

3) Did you observe wires breaking after the relatively large accumulated charge?

A (A. K.):

1) <100ppm.

2) <100ppm.

3) Never.