  There are conflicting requirements on the value of the momentum compaction
factor during energy ramping in a synchrotron: at low energies it should be
positive and sufficiently large to make the slippage factor small so that it is
possible to work closer to the RF voltage crest and ensure sufficient RF bucket
area, whereas at higher energies it should be small or negative to avoid
transition crossing. In the present report we propose a lattice with a variable
momentum compaction factor and consider the possibility of using it in a high
repetition rate proton driver for a muon collider and neutrino factory.
