CLIC looks towards 2025

The CLIC collaboration is moving towards its technical design report.



CLIC is being optimised in preparation of a 2025 Readiness Report.

The CLIC collaboration is looking towards the next European Strategy for Particle Physics (ESPP) update around 2025-26. The current plan is to submit a Project Readiness Report (PRR) at that time, as a step toward a Technical Design Report. During the first week of December the collaboration met to discuss the progress towards the PRR.

The starting point is that the CLIC 380 GeV Higgs and top factory project studies, covering the accelerator and detector & physics performances, are already very mature. The CLIC collaboration submitted an extended set of documents for the European strategy process in 2018-19. Nevertheless, improvements are possible in several areas. In 2022 a number of more recent studies, with updated parameters for parts of the accelerator complex, were included in a white paper for the Snowmass process [1].

Among the changes included were increased luminosity numbers for the initial stage of 380 GeV and reduced power consumption. The luminosity results are based on extensive beam-dynamics studies, folding in dynamics and static effects that can perturb the CLIC nanobeams, and the hardware needed to create, measure and correct the beams from the injectors, through the damping rings, main linacs and beam-delivery systems. Issues such as effective damping, alignment, stray fields, thermal and mechanical stability, ground vibrations, instrumentation, focusing, field qualities and correctors, as well as feedback and steering algorithms, are included in these studies [2]. Further work will consolidate these studies and also go deeper into the robustness and redundancies of the systems and algorithms.

The power and energy optimization studies have also produced impressive results, to a level that annual running of CLIC at 380 GeV will be as low as 50% of CERN’s energy consumptions today. These studies are discussed in [3], and include design changes, technical improvements, most notably klystrons efficiency improvements, and optimized operation models making use of the ability of a linear collider to adjust its power consumption quickly. Future studies of power, energy and sustainability in general will include these improvements also for the 1.5 and 3 TeV possible upgrade stages, as well as the benefits of additional technical developments, e.g. permanent magnets (designed and successfully prototyped but currently not included in the power estimates).  The carbon footprint and rare earth material estimates will also be addressed. While operation of future accelerators will benefit strongly from future carbon neutral energy, the carbon footprints related to the construction, as civil engineering, components and raw materials, will remain important and need to be estimated.   

Another important development is that the X-band RF technology has successfully been exported into very many compact beamline systems being designed for numerous potential applications in medicine, research and industry. This development was initiated already 6-7 years ago with the Horizon 2020 CompactLight Design Study for a compact Free Electron Laser (FEL) facility based on X-band technology [4]. The impact on industrial readiness for CLIC is important, as much more is invested in constructing relevant equipment and components than what the Particle Physics community can provide. Collaboration with, and support for, these projects remain crucial, not least to make sure the parameters needed for CLIC are being pursued. These developments are evolving quickly and the state of the art will be summarized in the CLIC PRR.

CLIC is very dependent on RF performance and optimization of the RF complex. As a part of the PRR the injector complex will be re-examined, the damping ring RF revisited (this is already partly done to reduce power), the X-band structures optimized for large-scale production, and more long-term R&D, e.g. related to cool copper with HTS coating, for gradient and power efficiency, pursued. This work covers all aspects from RF design to construction of components, and testing in the X-band test-stands at CERN and elsewhere. The results are expected to provide a more optimized accelerator design also more suitable for large scale component production. Module studies and assemblies are also being pursued to make sure the accelerator can be constructed and installed in modular manner.

Comparative studies will be carried out for a klystron-based implementation, optimized for luminosity at reduced power. Similar studies were made in 2016 but all the progress in components and klystrons would make it interesting to repeat, and re-optimize for both (primarily) reduced power and (secondarily) cost. In 2016 the optimization was done primarily for cost.

A cost update for CLIC will be included in the PRR. A detailed cost estimate was made in 2018 based on a detailed work breakdown structure, including civil engineering and infrastructure. The recent inflation related to energy, civil engineering and material prices necessitates an update. It is likely the carbon footprint and rare earth studies will also drive changes that in detail differ from the choices made some years back, and might impact costs.

Related to CLIC but under the larger heading of Linear Collider studies several studies are in common with or related to similar studies for the International Linear Collider (ILC). While ILC-specific studies will not be included in the CLIC PRR, the progress and situation of ILC will be important in relation to future projects at CERN in general and CLIC in particular. ILC can be implemented relatively quickly in Japan but if the hosting issue is not settled soon it is natural to consider the possibility of an ILC implementation at CERN so as to have a comparison of its relative merits and opportunities with respect to CLIC. For a given energy ILC is a larger facility, and has a smaller range of energy expandability than CLIC, but with a technology and design that are very mature and well established in laboratories and industries worldwide as they are being used in relevant large FEL linacs in Europe, US and Asia. The feasibility of running one arm of ILC in continuous wave mode to collide its electrons with LHC protons, unique to CERN, should also be considered in this perspective.

For both CLIC and ILC complementary physics opportunities with electron beams, in addition to operating in collider mode, also need to be studied and documented further. Additional considerations of upgrading an initial LC facility implementation so as to utilize potentially improved future RF technologies are also needed.

The issues discussed above will be main focus of forthcoming CLIC studies and meetings in 2023-25.