ATLAS TRT straw tube ageing tests at PNPI

In 1998-1999 ageing investigations of ATLAS TRT straws have been performed at the ATS. The tests were carried out with a Xe(70%)+CO2(10%)+CF4(20%) gas mixture. It was obtained a noticeable gain drop in the irradiated zone wich started from the accumulated charge Q ~ 4 C/cm. As a result of the ageing, the destruction of the gold-plated tungsten anode wire surface was observed and the wire diameter was found to increase from 35 mm to 42 mm.

An analysis of the aged wire in the irradiated zone by the nuclear reaction method showed that the oxygen concentration in the irradiated surface was significantly increased.

  • The data of the ATLAS TRT ageing test run have been presented in PNPI preprints N2328 and N2331

    • The set-up


    The scheme of the ageing tests perfomance is presented in the figure. The test set-up consisted of 2 straws blown through with Xe(70%)+CO2(10%)+CF4(20%) gas mixture. A stroncium-90 b-source with intencity 18 kHz have been used for straw irradiation. The irradiation zone diameter was 25 mm.

    The straws used in the tests had a diameter of 4 mm. Gold plated tungsten anode wires had a diameter of 35 mm. The applied high voltage provides the gas gain 3x104.


    Ageing results

    The results of the SEM/XEM analysis indicated the evident damage of the irradiation zone. As one can see in SEM micrograph the gold coating is broken and wire diameter has increased by 20% (from 35 mm to 42 mm). The absence of deposits in the irradiated zone have to be emphasized. Then it should be another reason for explanation of the diameter increase. Moreover, using the nuclear reaction method, the significant increase of the oxigen concentration in the the gold coating has been found.


    The following plot shows the distribution of the oxygen concentration inside of the wire with depth. It is clear seen the dependence of the amount of oxygen from the irradiation level. The biggest concentration of oxygen is in the center of the irradiated zone. The discussion of the mechanism of wire diameter increase (swelling) is presented in PNPI preprint N2328. The detailed study of the factors causing such a kind of wire damage is in progress.


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