Final Cooling for a High-Energy High-Luminosity Lepton Collider

TL;DR

This paper discusses various methods for final cooling in high-energy muon colliders, comparing baseline and alternative approaches to achieve significant transverse emittance reduction while managing longitudinal emittance.

Contribution

It introduces and evaluates alternative final cooling techniques, including emittance exchange and novel focusing systems, expanding beyond the traditional high-field solenoid approach.

Findings

Baseline approach has low-energy transverse cooling with longitudinal heating.

Wedge-based emittance exchange can achieve significant transverse cooling.

Li-lens and quadrupole systems are promising for final cooling.

Abstract

A high-energy muon collider scenario require a "final cooling" system that reduces transverse emittance by a factor of ~10 while allowing longitudinal emittance increase. The baseline approach has low-energy transverse cooling within high-field solenoids, with strong longitudinal heating. This approach and its recent simulation are discussed. Alternative approaches which more explicitly include emittance exchange are also presented. Round-to-flat beam transform, transverse slicing, and longitudinal bunch coalescence are possible components of an alternative approach. Wedge-based emittance exchange could provide much of the required transverse cooling with longitudinal heating. Li-lens and quadrupole focusing systems could also provide much of the required final cooling.