An intense positron source based on oriented crystals

The e+BOOST (intense positron source Based On Oriented crySTals) project investigates an innovative positron production scheme exploiting coherent radiation phenomena in oriented crystals. This technique offers a path toward the high-intensity positron beams required by future lepton colliders such as FCC-ee, CLIC, and CepC to achieve their luminosity goals. Traditional positron sources rely on high-energy electrons impinging on amorphous targets, a method limited by the Peak Energy Deposition Density (PEDD) and total energy deposited (Edep), both crucial parameters. For circular colliders like FCC-ee, PEDD is generally manageable in current designs; however, the total energy deposited still imposes significant constraints on the cooling and stability of the target. In linear colliders such as CLIC, both PEDD and Edep represent major limiting factors due to intense beam power and pulsed operation. By contrast, the use of oriented crystals enhances coherent radiation emission, improving electron-positron pair production efficiency while significantly reducing the total energy deposited in the converter material, easing thermal loads and extending target longevity. The proposed crystal-based concept adopts a hybrid target system: a thin oriented crystal radiator followed by a thicker amorphous converter. The radiator generates a high flux of photons, which the converter then transforms into electron-positron pairs. This configuration, first proposed and validated at CERN and KEK, is presently under study within the FCC-ee injector design framework. Recent experimental results confirm a significant increase in radiation yield when the crystal is accurately aligned with the incident beam. These measurements also validate the underlying simulation tools, which now guide the optimization of next-generation positron sources for FCC-ee. This work summarizes the recent achievements of the e+BOOST collaboration, including new experimental data and simulation studies advancing the design of efficient, high-intensity positron sources for future colliders.