FCC-ee positron source from conventional to crystal-based

The high-luminosity requirement in future lepton colliders imposes a need for a high-intensity positron source. In the conventional scheme, positron beams are obtained by the conversion of bremsstrahlung photons into electron–positron pairs through the interaction between a high-energy electron beam and a high-Z amorphous target. One method to enhance the number of produced positrons is by boosting the incident electron beam power. However, the maximum heat load and thermo-mechanical stresses bearable by the target severely limit the beam power of the incident electrons. To overcome these limitations, an innovative approach using lattice coherent effects in oriented crystals appears promising. This approach uses a single thick crystal that serves as a radiator and a converter. In this paper, we investigate the application of this scheme as an alternative to the conventional positron source at the Future Circular Collider (FCC-ee). Simulations were carried out from the positron production stage to the entrance of the damping ring to estimate the accepted positron yield. The results demonstrate the advantages of the crystal-based positron source: it requires thinner targets than the conventional scheme, resulting in a 14% reduction in the deposited power while achieving a 10% increase in accepted positron yield.