Assembling of GEM Detectors for the TOTEM experiment

The TOTEM T2 telescope has 40 gaseous electron multipliers (GEM) installed inside the plugs of the CMS HF calorimeter on both sides of the intersection point at a distance 13.56 m. The GEM design is based on the utilisation of three semi-circular GEM foils. The readout board contains 256 concentric strips measuring the radial coordinates of traversing particles and a matrix of 1560 pads delivering the trigger information. The assembling of GEM detectors started during the autumn 2005 in Helsinki. The production is almost entirely carried out in clean rooms, where a special production line for large gaseous detectors has been assembled. A special attention is paid on quality control of the GEM foils and readout boards as the most critical components of the detectors. The design, assembling, quality control and some test results of the GEM detectors are described.