Bright muon beams needed for high luminosity colliders are difficult to achieve because muons are produced in a tertiary process that leaves a large phase space volume filled with short lived particles. Practical beam cooling schemes involve ionization cooling, where the muons pass through a low-Z absorber and lose momentum in all three dimensions but only have the longitudinal component regenerated by RF cavities. In this report we describe new techniques based on ionization cooling that hold the promise of muon beams that are as small as the electron and proton beams normally found in synchrotrons and colliders. For example, we describe a six-dimensional (6D) cooling channel* based on helical magnets surrounding RF cavities filled with dense hydrogen gas** and show analytically and by simulations that it can be used to achieve the small transverse emittances demanded by a high-luminosity muon collider. Simulations verify the analytic predictions and have shown a 6D emittance reduction of over 3 orders of magnitude in a 100 m channel segment. Using three such sequential segments, where the RF frequencies are increased and transverse dimensions reduced as the beams become cooler, implies a 6D emittance reduction of almost six orders of magnitude. After this, two new post-cooling ideas can be employed to reduce invariant transverse emittances to one or two mm-mr, which allows high luminosity with fewer muons than previously imagined. In this report we discuss the status of and the plans for a 6D cooling demonstration experiment and other simulation and engineering efforts. We also describe the new post-cooling ideas and comment on the prospects for a Higgs factory or energy frontier muon collider using existing laboratory infrastructure.
Talk Slides: (Slides when available)