The e+BOOST project was conceived in the context of high-energy lepton colliders, such as FCC-ee, in which the positron source is the most critical component. The baseline FCC-ee concept relies on a conventional scheme in which a high-energy primary electron beam impinges on an amorphous tungsten target, producing bremsstrahlung photons that convert into e+e- pairs. At very high intensities (e.g., for linear colliders), the energy deposition in the target can lead to excessive heating. In particular, the Peak Energy Deposition Density (PEDD) may generate strong thermal gradients and associated mechanical stresses, potentially resulting in target damage or failure.
To address these limitations, e+BOOST aims at developing an innovative crystal-based positron source. By exploiting coherent electromagnetic interactions in oriented single crystals (such as tungsten or diamond), the yield of soft bremsstrahlung photons can be significantly enhanced with respect to conventional amorphous targets. The reference concept adopts a hybrid configuration, where a thin aligned crystal acts as a radiator, followed by a thicker amorphous converter. The enhanced soft-photon flux generated in the radiator, once converted, translates into an increased yield of secondary positrons.
The e+BOOST project has demonstrated the feasibility of a crystal-based positron source for the FCC-ee injector. Simulation-driven optimisation, supported by Geant4 and RF-Track tools, identified hybrid and single-crystal tungsten designs that increase positron yield at the damping ring while keeping PEDD within the FCC-ee limits. Beamtests on the CERN T9 Proton Synchrotron beamline validated the underlying coherent-crystal mechanisms and confirmed reproducible performance gains with industrial-grade oriented crystals. These results provide a solid basis for the forthcoming validation at PSI on the FCC-ee injector demonstrator and indicate a scalable pathway toward more efficient and sustainable positron-source technologies, with potential impact across the broader collider program and future high-intensity facilities.
To address these limitations, e+BOOST aims at developing an innovative crystal-based positron source. By exploiting coherent electromagnetic interactions in oriented single crystals (such as tungsten or diamond), the yield of soft bremsstrahlung photons can be significantly enhanced with respect to conventional amorphous targets. The reference concept adopts a hybrid configuration, where a thin aligned crystal acts as a radiator, followed by a thicker amorphous converter. The enhanced soft-photon flux generated in the radiator, once converted, translates into an increased yield of secondary positrons.
The e+BOOST project has demonstrated the feasibility of a crystal-based positron source for the FCC-ee injector. Simulation-driven optimisation, supported by Geant4 and RF-Track tools, identified hybrid and single-crystal tungsten designs that increase positron yield at the damping ring while keeping PEDD within the FCC-ee limits. Beamtests on the CERN T9 Proton Synchrotron beamline validated the underlying coherent-crystal mechanisms and confirmed reproducible performance gains with industrial-grade oriented crystals. These results provide a solid basis for the forthcoming validation at PSI on the FCC-ee injector demonstrator and indicate a scalable pathway toward more efficient and sustainable positron-source technologies, with potential impact across the broader collider program and future high-intensity facilities.