Studies on discharges in Micro Pattern Gaseous Detectors, towards a spark resistant THGEM detector

The problem afflicting any of MPGDs is the phenomenon of discharging which might be destructive in some highly energetic cases, at least being responsible of a slow aging of the detector. So far one solution has been cascading several gain elements (GEM, THGEM detectors) reducing the gain of each one; this method, spreading the charges along their path, reduce effectively the likelihood of a discharge but introduce more material due to the multiple stages of amplification. Our goal is developing a single stage THGEM detector which could withstand discharges, not reducing the gain, hence being still able to amplify low level ionizing particles while implementing some methodologies to reduce the damages due to discharge induced by high rate of particles’ flux and/or highly ionizing particles. This report describes the test bench set up to study discharges between simple structures, which are actually models of the bigger detector. The idea behind this approach is to reduce the complexity of the whole phenomenon, in order to focus directly on a single point to point discharge. Once understood that repetitive discharges modify the electrical behavior of the system, we implemented solutions deduced from the previous findings on prototypes of THGEMs, made and then tested in the TE-MPE-EM fine pitch workshop. Results of these tests are reported and compared. A solution with a new insulator, instead of the common FR4, showed better performances (100 times more resistant) and endurance against sparks. Eventually the efforts made in defining technological process for 3 new standard dimensions THGEM elements are described; the experience gained with the tests suggests that in order to increase the endurance of THGEM detectors against discharges new materials and even new structures have to be tested.