Abstract
The Gas Electron Multiplier (GEM) manufacturing technique has recently evolved to allow the production of large area GEMs. A novel approach based on single mask photolithography eliminates the mask alignment issue, which limits the dimensions in the traditional double mask process. Moreover, a splicing technique overcomes the limited width of the raw material. Stretching and handling issues in large area GEMs have also been addressed. Using the new improvements it was possible to build a prototype triple-GEM detector of ∼ 2000 cm 2 active area, aimed at an application for the TOTEM T1 upgrade. Further refinements of the single mask technique allow great control over the shape of the GEM holes and the size of the rims, which can be tuned as needed. In this framework, simulation studies can help to understand the GEM behavior depending on the hole shape.
Highlights
Gas Electron Multipliers (GEMs) are gaseous charge amplification structures invented in 1997 by F
The raw material is usually 50 μm thick kapton, with 5 μm copper cladding on both sides. This substrate gets laminated on the two sides with solid photoresist of 15 μm in thickness, on which the GEM hole pattern is transferred by UV exposure from flexible masks
Etching the bottom copper layer In single mask photolithography the GEM bottom electrode is pierced by immersing the foil into an acid solution
Summary
Gas Electron Multipliers (GEMs) are gaseous charge amplification structures invented in 1997 by F. They are currently widely used for a variety of different applications, not limited to high energy physics. Standard GEM foils larger than ∼ 40 cm are not available, since the manufacturing process becomes difficult when applied to large areas. Given the increasing demand for large area GEMs, an effort has been started aimed at finding a new GEM production technique that can be scaled up to square meter size. The manufacturing steps have been analyzed and four main bottlenecks have been identified. These are namely the alignment of the two photolithographic masks, the limited size of the raw material and the GEM stretching and handling.
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