First experience with the prototype Atlas MDT gas circulation system at GIF

In addition to being the largest detector subsystem in size, the MDT part of the Atlas Muon Spectrometer also comprises a significant active gas volume of roughly 800 cubic meters. Although the chosen MDT operating gas, Argon:CO2 in relation 93:7, is made up of fairly inexpensive and inert standard gases, financial and technical constraints still necessitate that the detector gas is circulated through the Atlas MDT system with only a small percentage being replaced each cycle. A first test system, using the final Atlas MDT gas circulator, has been built and is at present under study at the CERN Gamma Irradiation Facility GIF together with a BIS type MDT chamber. This note describes the test setup, the goals of the measurement program and summarises first experiences with the system.