Final Cooling with Thick Wedges for a Muon Collider

Abstract

A muon collider is a particle accelerator that collides muons rather than protons or electrons. An important component of such a collider is cooling, in which the emittance of the muon beam is reduced to make it suitable for use in a collider. In the last stage of this process, called final 4D cooling, emittance in the transverse axes is reduced while emit-tance in the longitudinal axis is allowed to grow. Final 4D cooling is poorly understood, and previously published cooling channels fail to achieve the required emittances without serious technical challenges, such as the requirement for high-field solenoids. In this study, we developed and optimized a conceptual design for the 4D cooling channel based on single thick wedges. We used G4Beamline to simulate the channel and Python to generate and analyze particle distributions. We characterized the effects of various parameters on the performance of this system, including the initial emittances and Twiss parameters, the length and angle of the wedges, the length of the drift channel, and the length, frequency, gradient, and phase of the RF cavity. We optimized the design parameters of the cooling channel and produced two conceptual designs (corresponding to two possible starting points for the input beam) which achieve transverse cooling by a factor of 3.5. These channels achieve a lower transverse and longitudinal emittance than the best design previously published.