Pulsed Focusing Recirculating Linacs for Muon Acceleration

Neutrino Factories and Muon Colliders require rapid acceleration of short-lived muons to multi-GeV and TeV energies. Recirculating Linear Accelerators (RLA) can provide exceptionally fast and economical acceleration, mainly limited only by the extent of the focusing range of the RLA quadrupols, since each muon must pass several times through each high-gradient cavity. However, the technical feasibility and cost effectiveness if such schemes have not been fully developed, and the ultimate limitations have not been fully analyzed. A new concept of changing the strength of RLA focusing quadrupols as a function of time as the muons gain energy is being developed to increase the number of passes that each muon will make through the RF cavitied, resulting in cost savings. We will develop the optics and technical requirements for RLA designs, using RF cavities capable of simultaneous acceleration of both u + and u- species, with pulsed linac quadrupoles and arc magnets to allow the maximum number of passes. We have found a solution for a 3 to 50 GeV 400 MHz RLA that uses bets function beating to preserve the beam quality for an RLA by varying the quadrupole strength along a bisected linac. A Non-Scaling Fixed Field Alternating Gradient (NS-FFAG) lattice has been designed for the return arcs of that RLA that has attractive properties including very large momentum acceptance. We have explored possibilities for ramped arcs (dipoles and quads) for TeV scale muon RLA. A single-Linac RLA that incorporates pulsed quadrpoles will be designed at 1.3 GHz for use with ILC-type SRF accelerating structures using fast pulsed quadrupoles and droplet arc magnets, including tracking simulations. The design will include the optics for the multi-pass Linac and droplet-shaped multi-pass return arcs based on NS-FFAG optics, including chromatic compensation. Cost-effective options for very high energy arcs will explored. Commercial Applications and other Benefits as described by the awardee: Future large scale facilities such as Neutrino Factories and Muon Colliders will be very expensive national investments; more effective use of RF cavities through the use of pulsed RLA design would save hundreds of millions of dollars.