High rate behavior and discharge limits in micro-pattern detectors

Abstract

We present and discuss a set of systematic measurements, carried out with gaseous proportional micro-pattern detectors, in order to assess their maximum gain when irradiated with high-rate soft X-rays and heavily ionizing alpha particles. The inventory of detectors tested includes: microstrips, micromegas, micro-dot, gas electron multiplier, CAT (compteur à trous), trench (or groove), micro-CAT (or WELL) detectors, as well as systems with two elements of gaseous amplification in cascade. W e confirm the general trend of all single-stage detectors to follow Raether's criterion, i.e. a spontaneous transition from avalanche to streamer, followed by a discharge, when the avalanche size reaches a value of a few 10 7 ; a noticeable exception is the micro-dot counter holding more than 10 8 . In multiple structures, where the gain is shared between two devices i n cascade, the maximum overall gain under irradiation is increased by at least one order of magnitude; we speculate this to be a consequence of a voltage dependence of Raether's limit, larger for low operating potentials. Our conclusion is that only multiple devices can guarantee a sufficient margin of reliability for operation in harsh LHC running conditions.

The GEM photomultiplier operated with noble gas mixtures

“…Indeed, recent observations on GEM coupling to other ampli"cation elements [20,21] suggested that the distance between the elements should not be less than 0.3}0.6 mm, or else the two ampli"cation elements are equivalent, in terms of the maximum gain, to a single one.…”

GEM tracker for high-luminosity experiments at the JLab Hall A

“…hit spatial resolution at the level of 70 µm, The first and second requirements, taking into account the moderately large area (and therefore costs), are well fulfilled by the recent GEM technology; in particular the high particle flux which corresponds to a hits rate on the tracker entrance at the level of 500 kHz/cm 2 (from simulation, the reduction is due to the low efficiency of the gamma photon detection) is well below the stable gain limit ≥ 10 MHz/cm 2 reported in literature [6]. In fact, the front tracker is based on 6 high resolution, large GEM detectors (chambers), for a total tracker length of about 50 cm.…”

Gas detectors: achievements and trends

“…All devices permit to reach gains above 10 4 . However, a systematic study of their behavior reveals the similarity of values for the maximum sustainable gain, several thousand, when exposed to alpha particles [20]. As an example, Fig.…”

“…Fig. 3 illustrates the basic problem [20]. As a function of voltage, it provides the proportional gain, measured in laboratory conditions (low rate soft X-rays); the efficiency plateau for minimum ionizing particles is also shown, for a typical configuration and making use of currently available high-density electronics.…”

“…Double and triple GEM detectors have been extensively tested in particle beams [30,38,39], and fourstage GEMs are under development for single photoelectron detection [40]. With a double GEM, gains in excess of 10 4 can be obtained at very high rates and in presence of heavily ionizing tracks [20]. In Fig.…”