The fundamental limitations of high-rate gaseous detectors

Future high-luminosity experiments make serious demands on detector technologies and have prompted a "chain" of inventions of new high-rate gaseous detectors: Microstrip Gas Counters (MSGC's), Microgap Chambers (MGC's), Compteur A Trou (CAT's), Micromesh Gas Structure (MICROMEGAS), and Gas Electron Multipliers (GEM's). We report results from a systematic study of breakdown mechanisms in these and other gaseous detectors recently chosen or considered as candidates for high-luminosity experiments. It was found that, for all the detectors tested, the maximum achievable gain before breakdown appeared, dropped dramatically with rate, sometimes inversely proportional to it. Further, in the presence of alpha particles, typical of the backgrounds in high-energy experiments, additional gain drops of 1-2 orders of magnitude were observed for some detectors. We discovered that the breakdown in these detectors was through a previously unknown mechanism for which we give a qualitative explanation. We also present possible ways of increasing the value of the maximum achievable detector gain at high rates and have verified these experimentally.