Muon beam ionization cooling in a linear quadrupole channel

In a scenario for either a Neutrino Factory or Muon Collider, the anticipated transverse beam emittance subsequent to capture and phase rotation is so large that it permits a relaxation of the requirements on beam spot size in the early stages relative to the final stages of ionization cooling. Staging the cooling process according to initial emittances, coupled with modest cooling factors, permits more optimal and efficient cooling channel designs and avoids much of the difficulty encountered with channels which attempt to maintain strong focusing (large, 300–500 mrad, divergences) across ultra-large momentum ranges (⩾±20% δ p / p ). Relaxation of spot size at the absorber, especially in the “precooling” stage, allowed development of an efficient transverse cooling channel based simply on a quadrupole FODO cell. This work describes the design of such a cooling channel and its application as an upstream stage of beam cooling. Being a linear channel with no bends, it serves to reduce the large transverse beam size delivered from muon-beam capture and bunching before entering more restricted optical structures such as transverse plus longitudinal cooling channels or accelerators.