Feedback and breakdowns in microstrip gas counters

The phenomena of feedback and breakdowns in microstrip gas counters have been studied. Tests have been performed on a wide variety of microstrips of different geometries and substrates in various gas mixtures and at several pressures. In addition, for direct comparison, similar microstrip gas counters without substrates were also investigated. In the case of ''conventional'' microstrip detectors on substrates, it was found that as maximum gains were approached, self-quenched streamers occurred, but that these were present only over a very narrow voltage range after which they rapidly transited to gliding-discharge-type breakdown sparks. For microstrip detectors without substrates, the situation was quite different. At high gains (> similar to 10(4)) they transited from proportional to self-quenched streamer-mode and would operate stably in this mode over a very broad voltage range. When breakdown occurred in these detectors it was through a previously unreported mechanism and at gains, without exception, 5-10 times higher than in their counterparts with substrates. The conclusion of these studies is that the substrate represents the weak link in the chain and should ideally be avoided or at least removed from the high-field regions. In cases where this is not possible, then the multiplication region should be concentrated to the smallest volume around the anodes and maximally suppressed elsewhere. Recipes for achieving this are provided, along with new geometries which permit gas gains in excess of 10(5) to be achieved.