  This whitepaper summarizes and the state of the field of high-power
cyclotrons and FFAs as discussed by international experts during a three-day
workshop of the same name. The workshop was held online from Sep 7 to Sep 9,
2021 as part of the US Snowmass'21 Community Exercise, specifically the
Accelerator Frontier (AF) and the subpanel Accelerators for Neutrinos (AF02).
Thus, we put emphasis on the application of high-power cyclotrons in particle
physics, specifically neutrino physics, and as drivers for muon production. In
the introduction, we discuss the role of cyclotrons for particle physics, and
later we highlight existing and planned experiments in the corresponding
sections. However, as these same accelerators have important applications in
the fields of isotope production - both for research and medicine - and
possibly even in energy research, by providing beam to demonstrator experiments
in the areas of Accelerator Driven Systems (ADS), we include these far-reaching
topics to provide a full picture of the status and applications of high-power
cyclotrons. Furthermore, Fixed Field Alternating Gradient accelerators (FFAs)
have recently seen renewed interest. They are in many respects (basic operating
principles) similar to cyclotrons and have thus been included in this workshop
and whitepaper as well. We are discussing current projects and whether FFAs
have the prospect of becoming high-intensity machines.
