Ionisation cooling in FFAG neutrino factories

Japanʹs unique scenario for a neutrino factory is at present the only one that does not rely on ionisation cooling of the muon beam. This is made possible by the large intrinsic acceptances of the fixed field alternating gradient (FFAG) accelerators replacing the linacs and recirculators of the other scenarios. Nevertheless, it is shown, using basic cooling theory, that moderate cooling in the first FFAG could be beneficial for the overall muon yield. Moreover, a solution using Be windows in the radio-frequency accelerating cavities would improve their performance. Simulation results obtained with the ACCSIM code essentially corroborate the theoretical cooling predictions, although showing a yet unexplained emittance exchange mechanism between the transverse phase spaces.