The Mu2e calorimeter employs 1348 CsI crystals readout by SiPM and fast FE and DAQ electronics assembled in two annular disks positioned downstream the aluminum target along the beamline.
The operational conditions (radiation levels, 1 tesla magnetic field and 10^-4 Torr vacuum) have posed tight design constraints. The support structure of the two 674 crystals matrices employs two aluminum hollow rings and structural carbon fiber parts. The SiPM and FE electronics associated to each crystal are assembled in a unit inserted in a copper holder and Faraday cage. The 674 units are supported by a machined plastic plate. The plate integrates the cooling system made of a network of copper lines flowing a rad-hard fluid to maintain the SiPM temperature at 0 C. The DAQ electronics is hosted in aluminum crates positioned on the external surfaces of the two disks. The crates also integrate a cooling system. We will review the design and construction progress of the detector mechanical parts.