Development of a double-phase Xenon cell using micromegas charge readout for applications in dark matter physics

A Micromegas micro pattern charge readout device has been operated at room temperature in Argon and Xenon from 1 to 3.5 atm and also within the saturated vapour phase of a double-phase Xenon target. The dependence of the gain on the amplification field, the pressure and the proportion of quencher has been evaluated. From a fit to the Townsend relation alpha = APexp(-BP/E) the gas parameters A and B were derived and compared with existing data. For the first time Micromegas was operated in double-phase Xenon charge produced within the liquid extracted across the phase boundary prior to amplification in the gas. A 2% concentration of Methane, selected as a quencher to suppress UV photon feedback effects in the gas phase whilst allowing scintillation within the liquid, was blended with Xenon. A maximum gain of 529 was inferred from the measurement of the charge collected at the anode in saturated vapour at 1450 Torr. Operation in double phase however was limited to periods up to 30 min due to condensation of Xenon within the Micromegas and the corresponding collapse of the amplification field. This situation was partially alleviated by heating the anode. Possible improvements to the readout configuration are discussed in the context of operation in double-phase Xenon-based dark matter detectors as a replacement for photomultiplier optical readout. (c) 2005 Elsevier B.V. All rights reserved.