Radiation background studies for the Phase II inner tracker upgrade.

Radiation background simulations have been performed using PYTHIA8 and FLUKA for the ATLAS Phase II tracker upgrade at the HL-LHC. A detailed geometry and material description of the proposed LoI inner tracker has been implemented in FLUKA. Fluence and dose predictions in the silicon pixel and strip detector regions are reported. Studies comparing PHOJET and GEANT4 with the baseline simulations are discussed. Previous radiation background studies for the ATLAS inner detector at the LHC show good agreement between measurement and simulation, giving increased confidence in the upgrade predictions.