High field – low energy muon ionization cooling channel

Abstract

Muon beams are generated with large transverse and longitudinal emittances. In order to achieve the low emittances required by a muon collider, within the short lifetime of the muons, ionization cooling is required. Cooling schemes have been developed to reduce the muon beam 6D emittances to $\ensuremath{\approx}300\text{ }\text{ }\ensuremath{\mu}\mathrm{m}\text{\ensuremath{-}}\mathrm{rad}$ in transverse and $\ensuremath{\approx}1--1.5\text{ }\text{ }\mathrm{mm}$ in longitudinal dimensions. The transverse emittance has to be further reduced to $\ensuremath{\approx}50--25\text{ }\text{ }\ensuremath{\mu}\mathrm{m}\text{\ensuremath{-}}\mathrm{rad}$ with an upper limit on the longitudinal emittance of $\ensuremath{\approx}76\text{ }\text{ }\mathrm{mm}$ in order to meet the high-energy muon collider luminosity requirements. Earlier studies of the transverse cooling of low energy muon beams in high field magnets showed a promising performance, but did not include transverse or longitudinal matching between the stages. In this study we present the first complete design of the high field-low energy ionization cooling channel with transverse and longitudinal matching. The channel design was based on strong focusing solenoids with fields of 25--30 T and low momentum muon beam starting at $135\text{ }\mathrm{MeV}/\mathrm{c}$ and gradually decreasing. The cooling channel design presented here is the first to reach $\ensuremath{\approx}50$ micron scale emittance beam. We present the channel's optimized design parameters including the focusing solenoid fields, absorber parameters and the transverse and longitudinal matching.