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Description
The final cooling section of a muon collider accelerator complex requires low emittance
muon beams in order to achieve the high luminosities needed at the interaction point
in the collider ring. The objective of the final cooling stage is to minimize the trans-
verse emittance while limiting the growth of the longitudinal emittance. As the beam
propagates through the final cooling channel, the bunch length increases significantly,
requiring very low RF frequencies to efficiently re-accelerate the muons after energy loss
in hydrogen absorbers. Induction LINAC concepts have previously been proposed for
this purpose. However, their relatively low accelerating gradients result in longer ac-
celeration times and consequently increased muon losses due to decay. In this work,
we present a multi-harmonic RF acceleration scheme that enables the use of higher
RF frequencies while maintaining compatibility with long muon bunches. The higher
achievable accelerating gradients reduce the acceleration time and mitigate decay losses.
We describe the concept of multi-harmonic acceleration and present a complete lattice design for the last final cooling cell.