  The completion of the PIP-II project and its superconducting linear
accelerator will provide up to 1.2 MW of beam power to the LBNF/DUNE facility
for neutrino physics. It will also be able to produce high-power beams directly
from the linac that can be used for lower-energy particle physics experiments
as well, such as directing beam toward the Muon Campus at Fermilab for example.
Any further significant upgrade of the beam power to DUNE, however, will be
impeded by the limitations of the present Booster synchrotron at the facility.
To increase the power to DUNE by a factor of two would require a new
accelerator arrangement to feed the Main Injector that does not include the
Booster. In what follows, a path toward upgrading the Fermilab accelerator
complex to bring the beam power for DUNE to 2.4 MW is presented, using a new
rapid-cycling synchrotron plus an energy upgrade to the PIP-II linac. The path
includes the ability to instigate a new lower-energy, very high-power beam
delivery system for experiments that can address much of the science program
presented by the Booster Replacement Science Working Group. It also allows for
the future possibility to go beyond 2.4 MW up to roughly 4 MW from the Main
Injector.
