The upgrade of the ATLAS Luminosity detector (LUCID) for HL-HLC

Throughout ATLAS Run-2, the LUCID detector, that is located close to the beampipe on both side of the interaction point, has been the reference luminosity detector, providing the on-line and off-line luminosity measurement with high stability and a preliminary uncertainty of about 1.7\%. For the high-luminosity LHC, new beampipe equipment and more demanding luminosity precision requirements and LHC beam conditions are expected. The detector will therefore be completely redesigned, exploiting both new and tried-and-tested technologies. Prototype detectors for the new running conditions and technologies have been developed and installed and will be tested during the upcoming LHC Run-3. These consist of a PMT-based detector, which uses the quartz window as Cherenkov medium and is positioned further from the beampipe, a low-rate PMT detector, located in the shadow of one of the ATLAS shieldings, and the fiber detector, in which fiber bundles are used as Cherenkov-light emitter and transmitter and that are calibrated with an innovative hybrid LED and radioactive-source system. In these prototypes, the behaviour of new Hamamatsu R1635 and R7459 PMT’s will be evaluated. In this contribution, the motivations for the detector redesign and a description of the LUCID upgrade are illustrated, as well as a detailed account of the preliminary tests performed with the prototypes, including PMT characterization and a study of the fiber degradation under irradiation