Outgassing studies on Triple GEMs for CMS GE2/1 and ME0 R&D.

Fiorina D., Fallavollita F., Merlin J.A.

I - Fisica nucleare e subnucleare
Aula 32C-3 - Mercoledì 19 h 09:00 - 13:00
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After several years of successful R&D with Gas Electron Multipliers (GEM) based detectors, the CMS GEM collaboration is going to install the innermost region of the forward muon spectrometer of the CMS experiment with the triple-GEM technology. This region is characterized by a harsh radiation environment, primarily composed by neutrons and photons. Aging phenomena constitute one of the most complex and potential serious problems which could limit, or severely impair, the use of gaseous detectors in unprecedented harsh radiation environments. As for all gaseous detectors, the Triple-GEM technology might be subject to classical aging, i.e. the degradation of their detection performance due to the presence of contaminants in the gas volume when operating in a particle high-rate environment. Most of the contaminants usually come from the outgassing of some materials used in the assembly of the detectors. The past experience on aging studies has demonstrated the outgassing behavior of some of these materials and related classical aging issues under heavy X-rays and $\gamma$-rays irradiation. Despite the replacement of some critical materials with new ones without outgassing issues, the experimental data from different gas-based detectors actually installed in the CMS muon system seem to make us think of some aging effects not expected in laboratory tests. For this reason, a new outgassing test on a $10 \times 10$ cm${}^{2}$ triple-GEM prototype is in progress at CMS - GEM QA/QC lab, in order to better understand if there are new, ever studied, outgassing issues and to comprehend if particles, with different specific ionization, may induce aging effects which were not present in the previous X-rays and $\gamma$-rays studies. The prototype is irradiated in two different regions at the same time with two different types of source: a 5.5 MeV alpha emitter (${}^{241}$$Am) and 5.9 keV X-ray source (${}^{55}$Fe) to investigate if different behaviors in the two areas develop. The contaminants are released in the gas by fluxing it in a heated box containing the material under test. Also, a Single Wire Proportional Chamber with polluted gas is irradiated with a X-rays source in order to monitor the effects of polymerization. Preliminary results on outgassing studies will be presented.

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