Sparks in MSGC and GEM detectors and a robust alternative

Abstract Sparks in MSGCs can be induced by strongly ionizing particles that damage the anodes. In MSGCs combined with GEMs, the MSGC gain can be reduced below the sparking threshold. However, occasionally discharges in the GEM can produce large secondary sparks at the MSGC. We discuss the dependence of the spark rate on geometrical and electrical parameters of the detectors. Different gas mixtures are compared. The most efficient way to avoid secondary sparks is to reduce the electric field between GEM and MSGC to below 6.6 kV/cm. We present first results from a robust alternative to MSGCs, the groove detector.