Stacked magnets for a muon accelerator

A proposed muon-muon collider uses a final accelerator which is separate from the collider ring. To minimize acceleration time and hence loss of muons by decay, a possible design for this accelerator consists of two, long, parallel linacs having a large energy gain per pass and semi-circular arcs of fixed-field magnets at each end. The muons would make 10 to 20 passes around the final accelerator ring, with an input energy of 250 GeV and output energy of 2 TeV; the present design assumes 16 passes. The recirculator magnets, described here for the end arcs, consist of an array of 16 apertures arranged in four adjacent, vertical stacks having four, 50 mm apertures in a stack, each stack having an iron yoke in common. This type of configuration reduces cost by taking advantage of coupling between apertures, but results in some undesirable skew harmonics. The highest dipole field is 7 Tesla, and there is an 0.406 T difference between adjacent apertures in a stack. A similar quadrupole stack having a maximum gradient of 175 T/m is also presented.