Six-Dimensional Beam Cooling in a Gas Absorber

72180-Future energy-frontier accelerators depend on the development of robust and affordable techniques to quickly reduce the size of a muon beam. Although schemes exist to reduce horizontal and vertical muon beam dimensions, no satisfactory solution exists to quickly shrink the beam bunch length or momentum spread, as required for a Muon Collider or as would be cost-effective for a Neutrino Factory. Recent observations have shown that, in a continuous gaseous absorber, the increased path length from increased momentum could be used to create the needed energy loss to reduce energy spread and achieve six-dimensional cooling. This project will exploit this concept by developing a linear channel of gas-filled, high-gradient radio frequency (RF) cavities in superimposed solenoidal and helical multipole magnetic fields, for cooling in all six dimensions. Phase I extended and developed the analytical treatment for two independent Monte Carlo programs to simulate the proposed helical cooling channels. Comparisons of the two simulation programs with each other and with analytical predictions demonstrated six-dimensional cooling with pressurized RF cavities in a helical channel for the first time. Phase II will develop integrated, six-dimensional helical beam-cooling channel designs using the analytical and simulation programs developed in Phase I. Conceptual designs of muon beam lines, incorporating helical cooling channels with realistic RF cavities and superconducting magnetic coils, will be developed for use in neutrino factories and muon colliders. Commercial Applications and Other Benefits as described by awardee: The use of a continuous gaseous absorber to cool muons in a helical channel with pressurized high-gradient RF cavities would advance accelerator science. The high RF gradient allows the the six-dimensional cooling channel to be compact and efficient, with no space unoccupied by RF. Such a channel will help make Neutrino Factories affordable and Muon Colliders compelling.