Speaker
Description
The BESIII (Beijing Spectrometer III) collaboration aims to replace the spectrometer’s aging inner MDC (Multilayer Drift Chamber) with a new inner tracker based on CGEM (Cylindrical Gas Electron Multiplier) technology during the 2024 long shutdown. The new Cylindrical GEM Inner Tracker (CGEM-IT) will consist of three independent tracking layers, each with three GEM multiplication stages. Stringent overall size constraints and a limited radiation length budget require the use of advanced lightweight materials such as honeycomb, Rohacell®, Kapton® and laminated carbon fiber or fiberglass meshes for realizing the structural elements supporting cathodes and anodes of the detector. The thin GEM foils are instead floating and constitute the main point of mechanical fragility in the design.
Two out of the three layers have already been built and are collecting data in a cosmic ray telescope setup at the Institute of High Energy Physics in Beijing. The CGEM electrodes of the third and outermost layer, with their relatively large radii, suffered from mechanical issues due to buckling that prevented the detector from functioning properly.
A possible solution was found in the introduction of PEEK spacer grids in the small gaps that separate the thin GEM electrodes. This talk describes an extensive test campaign aimed at validating the effectiveness of the grids under stresses compatible with ordinary handling. A representative mockup of the detector reinforced with PEEK grids was built, equipped with accelerometers, and subjected to a series of drop tests, each followed by a full CT scan. The contribution aims to provide both a detailed case-study and a proven methodology to investigate similar mechanical issues in analog lightweight detectors.
