A large area GEM detector

A prototype triple GEM detector has been constructed with an area of ̃2000 cm², based on foils of 66 cm x 66 cm. GEMS of such dimensions have not been made before, and innova-tions to the existing technology were made to build this detector. A single-mask technique overcomes the cumbersome practice of alignment of two masks, which limits the achievable lateral size. Refinement of this technique results in foils with performance similar to traditional GEMS, while lowering cost and complexity of production. In a splicing procedure, foils are glued over a narrow seam, thus obtaining a larger foil. This procedure was shown not to affect the performance of the GEMS. The seam can be as narrow as 2 mm, mechanically strong enough to withstand the necessary stretching tension, and sufficiently flat to maintain homogeneous electric fields in the gas volumes above and below the foil. These innovations should make the manufacture of GEM foils of 1 m² and beyond possible. With the planned high luminosity upgrade of LHC, a considerable demand for such large area MPGDS is expected for replacement of wire-based trackers. Other possible fields of applications are in large area photodetectors, and high granularity calorimeters using particle flow algorithms.