Conveners: Oliver Brüning and Yannis Papaphilippou.
Indico web page for meetings: https://indico.cern.ch/category/17311/.
The working group 5 for developing a sustainable LHeC and FCC-eh collider programme has as main objective to adress key aspects of accelerator design and technology, such as ERL optimisation, IR design, the refinement and optimisation of power and cost estimates, and the overall beam optimisation for the establishement of coherent collider parameters including a physics run timeline and associated luminosity performance ramp-up.
The ERL lattice design and dynamics was thoroughly studied in the PhD thesis of Kevin Andre (2022) . Some further design options and optimization to be undertaken include a separate FFAG arc design and impact on emittance preservation, lattice and robustness studies with respect to imperfections with improved simulation framework (X-suite) but also impact of Coherent Synchrotron Radiation and micro-bunching instability handling. It would be indeed important to continue building ERL expertise through collaboration with Orsay PERLE and bERLinPRO for gaining operational experience
A clear synergy with FCCee injector design exists with the option to consider a recirculating LINAC (RLI) based on LHeC/FCCeh ERL. The objective would be to produce a coherent set of parameters for RLI to replace LINAC pre-injectors + Booster, including positron production. An additional synergy with FCCee is regarding the SRF pre-series production while building CERN SRF expertise and industrial validation. In this respect, some additional studies need to be done for the impact on cryogenic system towards reduced power and cost. Finally, one could finally revie the idea of TLEP option based on ERL (Z, W, H-factory in the LHC tunnel).
For the interaction region (optics and magnets) for LHeC and FCCeh, the design study was pursued by the PhD work of TizianaVon Witzleben (to be finalised in 2025, see IPAC 2023 paper, FCC week 2023 talk and Synergy workshop 2024 talk). This design will surve as input for the design asymmetric magnets of the IR (magnets groups) using HL short model coils.
Further progress was made on Machine-detector interface, (see the talk by Laurent Forthomme during the Synergy workshop 2024), regarding SR radiation handling/shielding in IR for machine and detector protection but also optics variants for forward and backward detectors.
All this work will lead to the establishement of coherent collider parameters and operational scenario, including the update of power and cost, whcih were already done for 50 GeV energy, 100 MW power and ERL various circumferences. Some further work and parameter optimization is required for 140MW wall-plague power limit (magnets, RF design), the injection/dump energy choice and consideration for dedicated vs parasitic running (increased e-current, BBU limit in ERL). Finally, sustainability and life-cycle analysis was initiated, namley CE optimization based on CO2 emission, but also considerations for High-Temperature SRF @ 4.5 K and fast re-active tuners.
