Operation of Micropattern Gaseous Detectors

This chapter is dedicated to the physic of the operation of micropattern detectors. The authors analyze in more detail what causes discharges in these detectors. The chapter shows that, at low counting rates, the breakdowns appear due to the Raether limit and in some specific cases due to surface streamers. In some particular detectors (e.g. combined with high-efficient photocathodes or operating in very clean noble gases) the discharges may appear via a feedback mechanism. At high counting rates, the maximum achievable gain drops with the counting rate due to avalanches overlapping in space and time, and also due to a contribution from explosive electron emission. Detailed studies of the problems that micropattern detectors, in particular GEM, may experience while operating in cascade mode are presented. A better understanding of these effects has allowed researches to make a further step in the development of micropattern gaseous detectors in recent years.