Helical channels for longitudinal compression of muon beams

Transverse cooling of muon beams can be achieved through ionization cooling. However, longitudinal emittance growth occurs as a by-product of this method; at the muon energy of choice, low energy muons suffer enhanced energy loss. Even a small amount of longitudinal cooling would be advantageous for a neutrino factory, while longitudinal cooling by a factor of 100 is required for a muon collider. We consider 6D cooling using a helical wiggler channel inside a uniform solenoid field, which results in radial dispersion, which is combined with wedge-shaped absorbers to correct the energy spread and transfer longitudinal emittance into the transverse degrees of freedom. These systems are challenging because of the large dispersions required, and because the muon beams have large energy spread and non-zero transverse emittance. We describe scenarios which, in simulations, yield significant reduction of energy spread for unbunched beams. We explore the demands and performance of such channels, as well as the feasibility of longitudinal compression for bunched beams.