Micropattern gas detectors: the CMS MSGC project and gaseous pixel detector applications

Abstract

We report recent results from the development and testing of two types of micropattern gas detectors—micro-strip gas chambers and GEM-based devices with two types of pixel read-out. Thirty-two micro-strip gas chambers were tested in a high intensity hadron beam as a milestone for CERN's Compact Muon Solenoid (CMS) experiment. The detectors were operated with voltage settings corresponding to 98% hit detection efficiency at CMS for a total high intensity exposure period of 493 h. All of the requirements expected by the milestone—gain stability, number of lost strips, spark rate, etc.—were met, with wide margins. In a separate investigation, we have coupled PCB pixel read-out planes to GEM foils. In one case, 2 mm×2 mm pixels were fanned out to individual discriminators and scalers to provide very fast (2 MHz/pixel) read-out; this system has been used as an imaging device to provide diagnostic information in fusion experiments. The second type of device used smaller pixels (200 μm squares) and a Flash-ADC read-out system to reconstruct individual photoelectron tracks. The angular distribution of the tracks allows the polarisation direction of polarised X-ray sources to be identified, with possible applications for future space experiments studying celestial X-ray emissions.