  This paper presents an 8 GeV Rapid Cycling Synchrotron (RCS) option for
Project X. It has several advantages over an 8 GeV SC linac. In particular, the
cost could be lower. With a 2 GeV 10 mA pulsed linac as injector, the RCS would
be able to deliver 4 MW beam power for a muon collider. If, instead, a 2 GeV 1
mA CW linac is used, the RCS would still be able to meet the Project X
requirements but it would be difficult for it to serve a muon collider due to
the very long injection time.
