The ATLAS liquid argon calorimeter: upgrade plans for the HL-LHC

The ATLAS detector was designed and built to study proton-proton collisions produced at the LHC at centre-of-mass energies up to 14 TeV and instantaneous luminosities up to 10$^{34}$ cm$^{-2}$s$^{-1}$. Liquid argon (LAr) sampling calorimeters are employed for electromagnetic and hadronic calorimetry. The LAr has to withstand a High Luminosity LHC (HL-LHC) operation of the collider and associated detectors at luminosities of up to (5-7)$\times$10$^{34}$ cm$^{-2}$s$^{-1}$, with the goal of accumulating an integrated luminosity of 3000 fb$^{-1}$. This is well beyond the values for which the detectors were designed. The electromagnetic and hadronic calorimeters will be able to tolerate the increased particle flux, but the performance of the forward calorimeter (FCal) will be affected. Two possible solutions for keeping the current performance are being discussed. The electronics readout will also need to withstand a 3-5 times larger radiation environment. In the hadronic endcap calorimeter (HEC) cold GaAs preamplifiers are located inside the endcap cryostats. The properties of these devices have been investigated in recent proton and neutron irradiation tests to determine whether they must be replaced. In addition, the entire front-end readout system is not expected to survive the integrated luminosity at the HL-LHC and will be replaced. The description of the new read-out system is described here.