Challenges in the Design of FCC-ee High Energy Booster

• Ahmad Mash'al (Iranian Light Source Facility and School of Particles and Accelerators, IPM)

The Future Circular Collider (FCC) is a particle accelerator proposed as a new research infrastructure for high-energy physics in the post-LHC era. The first stage of the FCC integrated project is an e+e− collider, called FCC-ee, which would serve as Higgs factory, electroweak, and top factory at the highest luminosities, and run at four different center-of-mass energies, namely on the Z pole, at the WW threshold, at the ZH production peak, and at the ttbar threshold. The main aim of the FCC-ee High-Energy Booster (HEB) is to accelerate particles from about 20 GeV to collision energy for the four modes (Z, W, H, and ttbar). The HEB will be located in the same tunnel as the collider rings. There are several criteria and limitations that must be met in order to design the HEB magnetic lattice. The limited filling time of both colliders, which is 20 minutes, as well as the short beam lifetime, cause the need for top-up injection and all its associated considerations. Moreover, the emittance of the extracted beam from HEB must be lower than the collider emittance. The final emittance of HEB depends on many factors such as final energy, lattice optics, the emittance of the injected beam, the ramp time, and the ramp structure. It is therefore necessary to have two different optics for HEB magnetic lattice, one dedicated to the lower energies (modes Z and W) and the other for the higher energies (modes H and ttbar). Besides beam properties, there are other factors affecting the lattice layout. These include the geometry of the site, the optimization of the tunnel size, maintenance requirements, the installation process, etc. These are some of the challenges in the design of the HEB that must be overcome.