Breakdown Limit Studies in High Rate Gaseous Detectors

We report results from a systematic study of breakdown limits for novel high rate gaseous detectors: MICROMEGAS, CAT and GEM, together with more conventional devices such as thin-gap parallel-mesh chambers and high-rate wire chambers. It was found that for all these detectors, the maximum achievable gain, before breakdown appears, drops dramatically with incident flux, and is 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 many detectors. It was found that breakdowns at high rates occur through what we have termed an "accumulative" mechanism, which does not seem to have been previously reported in the literature. Results of these studies may help in choosing the optimum detector for given experimental conditions

Breakdown limit studies in high-rate gaseous detectors

We report results from a systematic study of breakdown limits for novel high-rate gaseous detectors: MICROMEGAS, CAT and GEM, together with more conventional devices such as thin-gap parallel-mesh chambers and high-rate wire chambers. It was found that for all these detectors, the maximum achievable gain, before breakdown appears, drops dramatically with incident flux, and is sometimes inversely proportional to it. Further, in the presence of alpha particles, typical of the breakgrounds in high-energy experiments, additional gain drops of 1-2 orders of magnitude were observed for many detectors. It was found that breakdowns at high rates occur through what we have termed an "accumulative" mechanism, which does not seem to have been previously reported in the literature. Results of these studies may help in choosing the optimum detector for given experimental conditions.http://www.sciencedirect.com/science/article/B6TJM-3VR1CVW-25/1/9bfb8c65132c9b4b8673fa6d100f916

The distribution of laser light for the calibration and monitoring system of the ATLAS hadronic calorimeter

In this paper we describe the design and preliminary results of a system to distribute light from a laser to 10,000 photomultiplier tubes (PMTs) in the ATLAS hadronic calorimeter. This system uses optical devices, plastic optical fibers and fibers connectors, specially designed for this application. The uniformity of distribution is reasonable and the light losses are acceptable within the light budget available and the range required. (3 refs)

The silicon shower maximum detector for the STIC

The structure of a shashlik calorimeter allows the insertion of tracking detectors within the longitudinal sampling to improve the accuracy in the determination of the direction of the showering particle and the e\u3c0 separation ability. The new forward calorimeter of the DELPHI detector has been equipped with two planes of silicon pad detectors respectively after 4 and 7.4 radiation lengths. The novelty of these silicon detectors is that to cope with the shashlik readout fibers, they had to incorporate 1.4 mm holes every cm2. The detector consists of circular strips with a radial pitch of 1.7 mm and an angular granularity of 22.5\ub0, read out by means of the MX4 preamplifier. The preamplifier is located at 35 cm from the silicon detector and the signal is carried by Kapton cables bonded to the detector. The matching to the MX4 input pitch of 44 \u3bcm was made by a specially developed fanin hybrid

The Small Angle Tile Calorimeter project in DELPHI

The new Small Angle TIIe Calorimeter (STIC) covers the forward regions in DELPHI. The main motivation for its construction was to achieve a systematic error of 0.1% on the luminosity determination. This detector consists of a \u201cshashlik\u201d type calorimeter, equipped with two planes of silicon pad detectors placed respectively after 4 and 7.4 radiation lengths. A veto counter, composed of two scintillator planes, covers the front of the calorimeter to allow \u3f1 12 \u3b3 separation and to provide a neutral energy trigger. The physics motivations for this project, results from extensive testbeam measurements and the performance during the 1994 LEP run are reported here