  Fast muon beam six dimensional (6D) phase space cooling is essential for muon
colliders. The Helical Cooling Channel (HCC) uses hydrogen-pressurized RF
cavities imbedded in a magnet system with solenoid, helical dipole, and helical
quadrupole components that provide the continuous dispersion needed for
emittance exchange and effective 6D beam cooling. A series of HCC segments,
each with sequentially smaller aperture, higher magnetic field, and higher RF
frequency to match the beam size as it is cooled, has been optimized by
numerical simulation to achieve a factor of 105 emittance reduction in a 300 m
long channel with only a 40% loss of beam. Conceptual designs of the hardware
required for this HCC system and the status of the RF studies and HTS helical
solenoid magnet prototypes are described.
