  Planned upgrades of the LHC over the next decade should allow the machine to
operate at a center of mass energy of 14 TeV with instantaneous luminosities in
the range 5--7e34 cm^-2 s^-1. With these parameters, ATLAS could collect 3,000
fb^-1 of data in approximately 10 years. However, the conditions under which
this data would be acquired are much harsher than those currently encountered
at the LHC. For example, the number of proton-proton interactions per bunch
crossing will rise from the level of 20--30 per 50 ns crossing observed in 2012
to 140--200 every 25 ns. In order to deepen our understanding of the newly
discovered Higgs boson and to extend our searches for physics beyond that new
particle, the ATLAS detector, trigger, and readout will have to undergo
significant upgrades. In this whitepaper we describe R&D necessary for ATLAS to
continue to run effectively at the highest luminosities foreseen from the LHC.
Emphasis is placed on those R&D efforts in which US institutions are playing a
leading role.
