Development of a Micromegas micro pattern charge readout device for use in two phase xenon dark matter detectors

A Micromegas micro pattern charge readout device has been operated at room temperature in xenon from 1 to 2.5 atmospheres (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. For the first time Micromegas has been 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 1.9 atm. Operation in double phase however was limited to periods up to 30 minutes 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.