Speaker
Description
The CMS Collaboration is preparing to build replacement endcap calorimeters for the High Luminosity LHC (HL-LHC) era. The new High-Granularity Calorimeter (HGCal) is a highly granular sampling calorimeter with approximately six million silicon channels and about four hundred thousand scintillator tile-readout with on-tile silicon multipliers. The calorimeter is designed to operate in the harsh radiation environment at the HL-LHC, where pile-up is expected to exceed 140. The silicon part of the calorimeter will be made of about 26000 silicon modules, which will be built in six Module Assembly Centers (MACs) around the world. To reduce tooling needs through assembly, curing time and then cost, a hybrid approach has been used for the assembly of silicon modules choosing a combination of epoxy and tape which need to be validated for the absorbed dose expected where the HGCal detector will be installed. During the last two years, in a joint effort between University of California Santa Barbara and National Taiwan University, several modules with different sensor thicknesses, silicon cell density, and baseplate materials (Ti for the hadronic and Cu-W for the electromagnetic part) were assembled and irradiated in the RBI Co-60 facility in Croatia up to 150 MRad absorbed dose. To explore the robustness of the hybrid assembly procedure and materials, modules have been studied before and after irradiation, at room and cold temperatures, measuring characteristics like IV and noise behavior, flatness, and checking for delamination at different stages of the thermal cycling campaign. Results will be shown for a first set of low density silicon Ti baseplate modules irradiated up to 50 MRad absorbed dose, and for a second set of low density and high density Cu-W baseplate modules irradiated respectively at 50 MRad and 150 MRad absorbed doses. Lastly, because the transfer tape is expected to fail at 200 MRad absorbed dose, a final set of modules have been assembled with epoxy only and similarly tested to mimic failure of the transfer tape and to further validate the hybrid assembly method.