• Ya.Derbenev, A. Bogacz, G. Krafft, R. Li, L. Merminga, B. Yunn, Y. Zhang
  Jefferson Laboratory, USA
  

  A CEBAF accelerator based electron-light ion collider of c.m. energy from 20 to 65 GeV and luminosity from 10³³ to10³⁵ cm^-2 s^-1 with both beams polarized is envisioned as a future upgrade to CEBAF. The concept of luminosity of ELIC has been established based on high energy electron cooling (HEEC), short ion bunches, very strong focus at interaction point, use of crab-crossing as a way to achieve very high bunch collision rate, and stacking an intense polarized ion beam while overcoming the space charge at injection to booster. Two steps upgrade scenario is under study: CEBAF accelerator-ring - ring scheme as the first step, and a multi-turn ERL - ring as the second step, to attain a better electron emittance and maximum luminosity. The spin polarization of both beams and HEEC schemes will be discussed and illustrated, and numerical examples will be presented.

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• Ya.Derbenev, R.P.Johnson
  Jefferson Laboratory USA, Muon Inc., USA

A six-dimensional (6D) ionization cooling channel based on helical magnets surrounding RF cavities filled with dense hydrogen gas is the basis for the latest plans for muon colliders. The helical cooling channel (HCC) has solenoidal, helical dipole, helical quadrupole, and helical sextupole magnetic fields, where emittance exchange is achieved by using a continuous homogeneous absorber. Momentum-dependent path length differences in the dense hydrogen energy absorber provide the required correlation between momentum and ionization loss to accomplish longitudinal cooling. Recent studies of 800 MHz RF cavities pressurized with hydrogen, as would be used in this application, show that their maximum gradient is not limited by the required external magnetic field, unlike vacuum cavities. Two new cooling ideas, Parametric-resonance Ionization Cooling and Reverse Emittance Exchange, will be employed to further reduce transverse emittances to a few mm-mr, which allows high luminosity with fewer muons than previously imagined. We describe these new ideas as well as a new precooling idea based on a HCC with z dependent fields that is being developed for an exceptional 6D cooling demonstration experiment. The status of the designs, simulations, and tests of the cooling components for a high luminosity, low emittance muon collider will be reviewed.

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