Contribution Contributed Oral
A new technique for assembling large-size GEM detectors and its experimental results
GEM detectors have been successfully used in modern nuclear and particle physics experiments. The key to the GEM application at large-scale experiments is cost-effective realization of large-size detectors, in which development of GEM detector assembly techniques plays a key role. The detector group at the University of Science and Technology of China (USTC) has been conducting intensive R&D on large-size GEM detectors, particularly on assembly techniques of GEM detectors, since 2013. The main aim is to build up technology for constructing the tracking detector at the SoLID experiment proposed for the 12-GeV upgrade program at JLab.
We started large-size GEM R&D by implementing the self-stretching GEM assembly technique developed at CERN for the CMS Muon GEM upgrade project, and gained a great deal of experience with the self-stretching technique through large-size GEM detector prototyping.
From our implementation and practice of the self-stretching technique, we found a major disadvantage of the technique in application for very large GEM detectors with size larger than 1m. When GEM foil size reaches over 1m, the overall foil extension of a triple-GEM under tension of ~ 5N/cm can be as large as ~2.5mm. This was precisely measured by a dedicated GEM stretching test station. The screws used to stretch foils would then be pulled by the inner frames and tilted towards the GEM stretching direction, and finally exceed the tolerance of the screw hole size and get blocked. This would result in partial application of stretching force to the foils and improper setting of O rings in the screw holes which could further cause gas leakage. In view of these problems, we have developed a new GEM stretching technique called “sliding self-stretching” based upon the original self-stretching technique. In this new technique, the nuts are fixed by the main frame which forces the stretching screws to keep vertical to the side-plane of the mainframe, and the GEM foils can move freely up to 5mm with respect to the main frame. With this sliding self-stretching technique, GEM foils as large as ~1m can still be stretched very uniformly while gas tightness is ensured. A large-size GEM prototype (1m×0.5m) has been successfully built with this new technique, demonstrating the advantage of the sliding self-stretching technique over the original one in large-size GEM assembly. The GEM prototype was thoroughly tested in terms of uniformity and effective gain. In order to test the spatial resolution of the prototype, we have built a GEM readout system based on APV25. As the first step, we tested a 30 cm×30 cm GEM detector with the readout system, and obtained a good result.
This report presents the details of the sliding self-stretching technique for large-size GEM assembly and test results of a large-size GEM prototypes built with the technique. The performance of the GEM prototypes is also compared to that of large-size GEM detectors built with other techniques.
We have developed a new technique for assembling large-size GEM detectors based upon the self-stretching technique. With this new technique, we can build GEM detectors at scale close to or larger than 1m. The GEM foils are stretched very uniformly and gas tightness is well ensured in GEM detectors built with the new technique. This report presents the details of the new self-stretching technique for large-size GEM assembly and test results of a large-size GEM prototypes built with the technique.