The Large Hadron Collider (LHC) collides protons at an energy of 13 TeV and is expected to operate until the mid-2030s. Looking beyond, one possible path for particle physics is a high-energy linear electron–positron collider. The Compact Linear Collider (CLIC) project at CERN envisions an initial-energy 380 GeV centre-of-mass facility focused on precision measurements of the Higgs boson and the top quark, which are promising targets to search for deviations from the Standard Model.

The accelerator technology required by CLIC has been under development for around 30 years. During the past decade, this technology has matured to the point where it is being transferred to applications beyond high-energy physics. Specifically, the unique requirements for CLIC have led to a new “X-band” accelerator technology that is attracting the interest of light-source and medical communities, and which would have been difficult for those communities to advance themselves due to their diverse nature.

Perhaps the most significant X-band application is for “X-ray free-electron laser” (XFEL) facilities that produce intense and short X-ray bursts by passing a very low-emittance electron beam through an undulator magnet. CLIC technology, both the high-frequency and high-gradient aspects, has the potential to significantly reduce the cost of such X-ray facilities, allowing them to be funded at the regional scale.

Linear-accelerator technology is also working its way beyond electron linacs, particularly in the treatment of cancer. The most common accelerator-based cancer treatment is X-rays, but protons and heavy ions offer many potential advantages. A new generation of linacs offer the potential for smaller, lower-cost facilities for hadron therapy with additional flexibility.

While CLIC’s primary objective is to provide technology for a particle-physics facility in the multi-TeV range, an application requiring a mere 45 MeV beam finds itself benefiting from the same technology. Called Smart*Light, this small-scale project is developing a compact X-ray source for a wide range of applications including cultural heritage, metallurgy, geology and medical. It aims to make the equipment small and inexpensive enough to be able to integrate it in a museum or university setting.