Geant Simulation of Six-Dimensional Cooling of Muon Beams in Ring Coolers

The reduction of the phase-space volume of the beam (cooling) is essential for both muon colliders and neutrino factories. In a muon collider in particular, the six-dimensional (6D) emittance must be reduced by six orders of magnitude. Cooling the beam in all phase space dimensions can be done through emittance exchange, in which the beam loses energy by traversing wedge-shaped absorbers in a dispersive magnetic field, designed in a way such that more energetic muons go through more absorber material than less energetic ones, thus losing more energy. The longitudinal momentum is then regained using RF cavities. We simulate ring coolers, in which the beam undergoes 6-dimensional cooling through emittance exchange while rotating several times in the ring. The simulation software is a Geant3-based package, specially designed for this purpose, with changing electric fields in RF cavities treated correctly. Magnetic fields are read from external maps. Two ring cooler designs and cooling simulation results are presented here.