Preliminary design of FCC-ee pre-injector complex

The design of a 100 km circular $e^+ e^−$ collider with extremely high luminosity is an important component of the global Future Circular Collider (FCC) study hosted by CERN. FCC-ee is being designed to serve as Z, W, H and top factory, covering beam energies from 45.6 to 175 GeV. For the injectors, the Z-operation is the most challenging mode, due to the high total charge and low equilibrium emittance in the collider at this energy. Thus, fulfilling the Z-mode will also meet the demands for all other modes of FCC-ee. This goal can be achieved by using a 6 GeV NC linac with an S-band RF frequency of 2.856 GHz and a repetition rate of 100 Hz. This linac will accelerate two bunches per RF pulse, each with a charge of 6.5 nC. Positrons will be generated by sending 4.46 GeV $e^−$ onto a hybrid target so that the $e^+$ created can still be accelerated to 1.54 GeV in the remaining part of the same linac. The emittance of the e (+) beam will then shrink to the nm level in a 1.54 GeV damping ring. After damping, the $e^+$ will be reinjected into the linac and accelerated to 6 GeV. The $e^−$ and $e^+$ will then be accelerated alternately to 45.6 GeV in the booster, before they are injected into the collider.