  In this study we investigate the stability limits of Micromegas detectors
upon irradiation with alpha particles. The results are obtained with meshes
with different optical transparency and geometry of wires. The measurements are
performed in Ar- and Ne- based mixtures with different CO$_2$ content. We
observe that the breakdown limit strongly depends on the gas and that a higher
amount of quencher in the mixture does not necessarily correlate with higher
stability. In addition, we observe discharge probability scaling with the wire
pitch. This suggests that a Micromegas mesh cell can be treated as an
independent amplification unit, similar to a hole in a GEM foil. The outcome of
these studies provides valuable input for further optimization of MPGD
detectors, multi-layer stacks in particular.
