We performed detailed studies to measure the effect of the mesh geometry and gas mixtures on the discharge behavior of resistive Micromegas.
A Micromegas detector has been built at CERN with a special design allowing to easily replacing the mesh. It has 1028 readout strips with a pitch of 400 μm, an active area of 40x50 cm2 and 128 μm high pillar spacers. The resistive strips, screen-printed on an insulating foil, have the same size as the readout ones. Meshes of different geometries have been stretched on iron frames fitting the detector structure.
The test procedure consisted in measuring current, gain and counting rate from 55Fe gamma source, as function of the amplification voltage up to the discharge limit.
The systematic analysis of the data allowed to conclude on the stability interval of the six different types of mesh we tested, consistent with the expectations based on the values for the average and maximum electrical field created by the mesh geometry.
With the same experimental setup, test and analysis procedure we have studied the discharge behavior of different Argon-based gas mixtures; results of the gas study will be also reported.