Upgrade Plans for ATLAS Forward Calorimetry for the HL-LHC

Although LHC data-taking is expected to continue for a number or years, plans are already being developed for operation of the LHC and associated detectors at a increased instantaneous luminosity about 5 times the original design value of 10^34 cm^-2 s^-1. The increased particle flux at this high luminosity (HL) will have an impact on many sub-systems of the ATLAS detector. In particular, in the LAr forward calorimeter (FCal), which was designed for operation at LHC luminosities, the associated increase in the ionization load at HL-LHC luminosities poses a number of problems that can degrade its performance, related to beam heating, space charge effects in the LAr gaps and HV losses due to increased current draws over the HV current-limiting resistors. One solution to these problems, which would require the opening of both endcap cryostats, is the construction and installation of a new FCal, with cooling loops, narrower LAr gaps, and lower value protection resistors. A second proposed solution, which does not involve opening the cryostats, is the installation of a small warm calorimeter in front of the FCal, resulting in a reduction of the particle flux to levels at which the existing device can operate normally. The talk will review the design of the ATLAS forward calorimeter and discuss the effects that are expected to degrade the performance at HL-LHC luminosities as well as the proposed upgrade scenarios.