A Geant4-based study on the origin of the sparks in a Micromegas detector and estimate of the spark probability with hadron beams

A Geant4 simulation of a Micromegas detector in hadron beams is presented. Very large energy deposits are observed, resulting from the production of highly ionizing particles in nuclear interactions of incoming hadrons with different parts of the detector. Assuming a spark is induced by a local, large energy deposit, we find that the spark rate grows as a power law with the gain of the detector, as observed experimentally. Using measurements with alpha particles, or alternatively the well known Raether limit, our simulation gives a correct estimate of the spark rate observed in hadron beams. A few experimental tests are proposed to check the validity of this simulation.