Discharge behaviour of resistive Micromegas

As other gaseous detectors with planar geometry, resistive Micromegas suffer of possible discharges between the cathode (mesh) and the anode planes. As the probability of appearance may depend on the mesh structure and the gas mixture, a systematic study is on-going to test meshes of different wire diameter, weft opening and production technique. The mesh with the best performance has been additionally tested in different gas mixtures, changing the percentages of Ar and CO$_2$ in the mixture and/or adding small quantities of additional quenchers. In this paper we present the preliminary results obtained on the present small, but growing, sets of meshes and gas mixtures, which seem to favour meshes with small openings and the addition of isobutane.