Rapid cycling synchrotrons are limited in duty cycle from ramped magnetic fields, with 50-60Hz the current or practical technical state of the art. To achieve a higher cycling rate requires fixed magnetic fields. A strong-focusing proton synchrotron with fixed magnetic fields and swept-frequency RF (53 MHz at extraction) has been proposed to replace the present 8 GeV Fermilab Booster synchrotron to accommodate the high current and increased energy in the PIP II era and plan for the PIP III phase at Fermilab. A conceptual fixed-field synchrotron design is presented using a nonlinear gradient, nonscaling FFA approach. The radial field profile will be optimized to provide strong-focusing, constant synchrotron tunes over the acceleration range from 2-8 GeV in a 24-sector machine with 24 10-meter straight sections to accommodate injection and ferrite RF cavities. The extraction radius is constrained to 513 meters in circumference to match to the Fermilab Main Injector which accelerates 8 GeV protons to 120 GeV.
*Work supported by Fermi Research Alliance, LLC under contract no. DE-AC02-07CH11359