Aging studies of CMS muon chamber prototypes

Radiation Damage and Long-Term Aging in Gas Detectors

“…While no anode deposits, due to the polymerization of gas mixture components, have been observed on Au/W-wires after exposure in Ar/CF 4 /CO 2 , a bulk of data indicate the changes of consistency and appearance of fluorine-containing (often accompanied by Si) films on non-gold plated cathodes [14,35,40,46,47]. Since the resultant insulating layers may lead to increased dark current, spurious noise counts and finally trigger the self-sustained Malter discharge, the use of the more robust electrode materials to CF 4 is recommended (e.g.…”

“…However, the aging performance in Ar(Xe)/CO 2 and Ar(Xe)/CO 2 /O 2 is sensitive to hydrocarbon contamination and even to minor traces of silicon pollutants in arXiv:physics/0403055 v1 9 March 2004 the detector (e.g. straw material may contain a few atomic Si mono-layers) and in the gas-system components (Si-based lubricant residues) [14][15][16]57]. In case of a weak external silicon source in the gaseous detector, several studies revealed appearance of aging effects at the beginning (in terms of gas flow) of the irradiated area (all Si-molecules are quickly eaten up by the avalanche process and produce deposits) and sometimes even right before the irradiated area (due to the upstream diffusion of active species at low gas flows).…”

Using an 80% CF4+20% CO2 gas mixture to recover aged anode wires in proportional chambers

“…The most dangerous chemical element which is systematically detected in the analysis of wire deposits is silicon. The Si-compounds are found in gas-system components [2], sealant room temperature vulcanizing silicone rubber [3], silicon-based lubricant etc. Usually Si-deposits appear at accumulated charges much below 1 1C/cm per wire.…”

“…These mixtures demonstrate no observable drop in gas gain due to polymerization of gas components and a small presence of CF 4 actually cleans Si-aged wires. The ATLAS Transition Radiation Tracker (TRT), for instance, has included the use of CF 4 to etch aged wires as a long-term strategy to survive at LHC [2][3][4]. However, Ar(Xe)/CO 2 /CF 4 mixtures at accumulated doses above 1 1C/cm per wire suffer from aging effects not related to polymerization.…”

“…It has been found that oxygen and other active radicals produced in avalanches penetrate through the pores and micro-cracks in the gold-plating and react with tungsten [3]. The products of these reactions have much lower densities than tungsten (r¼19.3 g/cm 3 ) and explode the gold layer.…”