Front End for a neutrino factory or muon collider

Abstract

A neutrino factory or muon collider requires the capture and cooling of a large number of muons. Scenarios for capture, bunching, phase-energy rotation and initial cooling of 's produced from a proton source target have been developed, initially for neutrino factory scenarios. They require a drift section from the target, a bunching section and a -E rotation section leading into the cooling channel. Important concerns are rf limitations within the focusing magnetic fields and large losses in the transport. The currently preferred cooling channel design is an "HFOFO Snake" configuration that cools both μ + and μ -transversely and longitudinally. The status of the design is presented and variations are discussed.

The Future Prospects of Muon Colliders and Neutrino Factories

“…The primary requirement is the number of useful muons produced at the end of the decay channel, which, to good approximation, is proportional to the primary proton beam power, and (within the 5-15 GeV range) only weakly dependent on the proton beam energy. Considering a conversion efficiency of about 0.013 muons per proton-GeV [13] a proton beam in the 1-4 MW power range at an energy of 6.75 GeV provides the number of muons of each kind required for NF or MC applications. • A buncher comprised of an accumulator and a compressor that forms intense and short (~2 ns) proton bunches.…”

“…We use 16 T SC magnets, which are actively and lly being developed for the Future Circular Collider (FCC) project [12]. The required agnets could either be superconducting or normal-conducting -up to 5T peak fields n demonstrated in ~2ms pulsed prototypes [13][14][15][16]. The former are more economical.…”

“…• A pion production target [14], capable of withstanding the high proton beam power, inserted in a high field solenoid to capture the pions and guide them into a decay channel. • A front-end [13,15] comprised of a solenoid decay channel, equipped with RF cavities, that captures the muons longitudinally into a bunch train and then applies a time-dependent acceleration that increases the energy of the slower (low-energy) bunches and decreases the energy of the faster (high-energy) bunches. • An "initial" cooling channel that uses a moderate amount of ionization cooling [16,17,18,19] to reduce the 6D phase space occupied by the beam by a factor 50 (a factor 5 in each transverse plane and a factor 2 in the longitudinal plane), so that it fits within the acceptance of the first acceleration stage.…”

“…In order to achieve the required flux of 5 x 10 20 neutrinos per year at the far detector, 60 bunches of 3.5 x 10 10 muons/bunch are stored in the muon decay ring at a 15 Hz repetition rate. Assuming a reasonable overall muon transmission efficiency, including decay losses, along the NuMAX complex and a production of 0.08 useful muons per 6.75 GeV proton on target [13], the facility requires a high but not unreasonable proton beam power of 2.75MW on target for muon production. A modest amount of 6D cooling by a factor of 50 (5 in each transverse plane and 2 in the longitudinal direction) allows matching of the muon beam emittances to the acceptances of the cost-effective and power-efficient acceleration system.…”

“…Fig. 15 compares neutrino radiation doses for muon bunches with 310 13 particles/s, representative of a proton driver source, and 10 11 particles/s, representative of a positron source, in a ring at 100 m depth (higher dose in straight sections) as from [57] where 8 T dipole fields are considered in the arcs. In the straight sections the dose depends on its length and is assumed to be a factor ten higher.…”