  Gas detector are very light instrument used in high energy physics to measure
the particle properties: position and momentum. Through high electric field is
possible to use the Gas Electron Multiplier (GEM) technology to detect the
particles and to exploit the its properties to construct a large area detector,
such as the new IT for BESIII. The state of the art in the GEM production allow
to create very large area GEM foils (up to 50x100 cm2) and thanks to the small
thickness of these foil is it possible to shape it to the desired form: a
Cylindrical Gas Electron Multiplier (CGEM) is then proposed. The innovative
construction technique based on Rohacell, a PMI foam, will give solidity to
cathode and anode with a very low impact on material budget. The entire
detector is sustained by permaglass rings glued at the edges. These rings are
use to assembly the CGEM together with a dedicated Vertical Insertion System
and moreover there is placed the On-Detector electronic. The anode has been
improved w.r.t. the state of the art through a jagged readout that minimize the
inter-strip capacitance. The mechanical challenge of this detector requires a
precision of the entire geometry within few hundreds of microns in the whole
area. In this presentation will be presented an overview of the construction
technique and the validation of this technique through the realization of a
CGEM and its first tests. These activities are performed within the framework
of the BESIIICGEM Project (645664), funded by the European Commission in the
action H2020-RISE-MSCA-2014.
