Design and modeling of a liquid-lead dump concept for beamstrahlung radiation absorption in the CERN Future Circular e$^+$e$^-$ Collider

TL;DR

The paper analyzes two flowing-liquid-lead beamstrahlung dumps for FCC-ee to absorb ~370 kW of BS power with mean photon energy ~62 MeV. It combines Fluka photon-transport simulations with ANSYS Fluent CFD for two-phase Pb–Ar flow, enabling optimization of absorber geometry under a practical max flow of about 300 kg/s. The slope-based (L- and S-slope) and compact upstream curtain plus pool (CUSP) concepts are found to be thermally robust and integrable, with S-slope delivering more uniform heating and CUSP achieving comparable absorption in a much shorter footprint. Radiation protection and engineering integration are addressed, demonstrating the viability of circulating liquid lead as a baseline BS absorber technology for FCC-ee, while highlighting areas for experimental validation and radiological assessment.

Abstract

The electron-positron Future Circular Collider (FCC-ee) being developed at CERN will generate intense beamstrahlung radiation, thus requiring photon absorbers downstream of the interaction points. This work presents the conceptual design of flowing-liquid-lead absorbers capable of dissipating around 370 kW of photon power, with a mean photon energy of 62 MeV. Two configurations are investigated: an inclined-flow geometry, developed to increase the photon interaction length to maximize absorption, and a compact upstream slope with an additional pool, in which a free-surface lead flow intercepts the power peak before a downstream pool dissipates the remaining load. Photon-matter interactions are modeled using Monte Carlo simulations in fluka, while conjugate heat-transfer and free-surface dynamics are analyzed through computational-fluid-dynamics simulations using ansys fluent. Design refinements are introduced based on the simulated thermal and hydraulic performance and to mitigate secondary effects such as photon backscattering. Both configurations demonstrate stable operation within the 300 kg/s flow limit and maintain liquid-lead and structural temperatures within the operational range of 450--500 $^{\circ}$C. The results establish circulating liquid lead as a feasible and thermally robust baseline technology for beamstrahlung absorption in FCC-ee.

Figures (24)

• Figure 1: Diagram presenting the layout of FCC-ee, showing the four collision points (left) Benedikt:2928793 and a schematic illustrating the position of the BS dump relative to each IP (right) Frasca2024.
• Figure 2: Schematics for the two main concepts of liquid lead flow for the BS dump: (a) slope concept; (b) upstream curtain/pool concept.
• Figure 3: Schematics of the two slope designs for the liquid-lead flow in the BS dump, showing the (a) linear (L-slope) and (b) optimized curved (S-slope) shapes.
• Figure 4: Free-surface profiles for the (a) L-slope and (b) S-slope with the corresponding effective thickness predicted by the analytical and CFD models. Definitions: n., numerical results; a., analytical calculations.
• Figure 5: Power deposition of the photon beam on the (a) L-slope and (b) S-slope.