  After the successful LHC operation at the center-of-mass energies of 7 and 8
TeV in 2010-2012, plans are actively advancing for a series of upgrades of the
accelerator, culminating roughly ten years from now in the high-luminosity LHC
(HL-LHC) project, delivering of the order of five times the LHC nominal
instantaneous luminosity along with luminosity leveling. The final goal is to
extend the dataset from about few hundred fb$^{-1}$ to 3000 fb$^{-1}$ by around
2035 for ATLAS and CMS. In parallel, the experiments need to be kept lockstep
with the accelerator to accommodate running beyond the nominal luminosity this
decade. Current planning in ATLAS envisions significant upgrades to the
detector during the consolidation of the LHC to reach full LHC energy and
further upgrades. The challenge of coping with the HL-LHC instantaneous and
integrated luminosity, along with the associated radiation levels, requires
further major changes to the ATLAS detector. The designs are developing rapidly
for a new all-silicon tracker, significant upgrades of the calorimeter and muon
systems, as well as improved triggers and data acquisition. This report
summarizes various improvements to the ATLAS detector required to cope with the
anticipated evolution of the LHC luminosity during this decade and the next.

Instrumentation and Detectors;High Energy Physics - Experiment