Complete Muon Collider Cooling Channel Design and Simulations

Considerable progress has been made in developing promising subsystems for muon beam cooling channels to provide the great reduction of emittances required for an Energy-Frontier Muon Collider; but an end-to-end design is lacking. Meanwhile, the recent discovery of a Higgs-like boson has created interest in the high-energy physics community for a Higgs Factory to investigate whether its properties verify Standard Model predictions or represent new physics. This project is developing principles and tools to match beam phase space distributions between and within muon beam cooling subsystems that may have different characteristics. The Helical Cooling Channel (HCC), with combined helical dipole and solenoid fields, allows a general analytic approach to guide designs of transitions from one set of cooling channel parameters to another. These principles and tools are being applied to design complete cooling channels for a Higgs Factory and an Energy Frontier Muon Collider. Transverse and longitudinal phase space matching techniques were developed in Phase I and applied to previously designed segments that presented the greatest matching challenge. Simulation results demonstrated even better performance in half the length of the original! Theoretical considerations of space charge effects started. Improvements in the G4beamline simulation program and its use on FermiGrid facilitated the computations and associated successes. Studies of early segments in a particular promising cooling channel indicate a need to optimize its design further in Phase II. Armed with the demonstrated matching techniques and further enabled by the computing power of NERSC, where G4beamline will be installed, the entire cooling channel will be revisited and designed, considering space charge effects. Analytic fields used in the Phase I design work will be replaced by realistic fields generated by coil elements. Commercial Applications and Other Benefits: Our ulterior motive is to enable the DOE to hire US companies to construct Muon Colliders, the next multi-billion dollar scientific instruments to investigate the smallest things in the universe. The cold muon beams developed in the project also have important potential applications for homeland security, medicine, and other basic and applied scientific research.