Recovery of HADES drift chambers suffering from Malter-like effects

The central tracking system of the HADES detector, installed at the SIS-18 synchrotron at GSI/Darmstadt (Germany), employs large-area, low-mass drift chambers, featuring Aluminum potential wires and small cell sizes. The chambers in front of the magnetic field, closest to the interaction point, have...

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Bibliographic Details
Published inarXiv.org
Main Authors Wendisch, Christian, Muentz, Christian, Lopes, Luis, Schwab, Erwin, Stroth, Joachim
Format Paper
LanguageEnglish
Published Ithaca Cornell University Library, arXiv.org 18.03.2024
Subjects
Carbon dioxide
Chambers
Discharge
Drift
Gas flow
Gas mixtures
Heavy ions
Reaction products
Tracking systems
Visual effects
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Summary:The central tracking system of the HADES detector, installed at the SIS-18 synchrotron at GSI/Darmstadt (Germany), employs large-area, low-mass drift chambers, featuring Aluminum potential wires and small cell sizes. The chambers in front of the magnetic field, closest to the interaction point, have developed significant self-sustained currents and discharges during operation, most probably triggered by isobutane-based gas mixtures. Only both, (i) replacing isobutane by CO2 and (ii) adding 1000 to 3500 ppmv of water into the Ar/CO2 counting gas mixture, individually optimized for a given chamber, allowed to recover the chambers, enabling stable operation in several production runs since then, e.g. with high-intensity heavy-ion induced reactions. The origin of the instability was found to be deposits on the cathode wires, provoking the Malter-like effects, by visual inspection and energy-dispersive X-ray spectroscopy. The charge on the wires accumulated during their lifetime does not point to so-called classical aging, but presumably the interaction of isobutane with materials in the gas flow, residual impurities, and reaction products formed in plasma, e.g., built by discharges.
ISSN:2331-8422