With the discovery of the Higgs boson at the LHC, the last particle of the Standard Model of particle physics has been found. However, many important questions remain unanswered; the difference between matter and anti-matter, the interpretation of the number of species of matter particles, the nature of dark matter, can the fundamental forces be unified? Particle colliders are the main tool for the study of fundamental particles – their intense beams allow rare physics processes to be studied in controlled laboratory environments. Which type of machine is desired to continue to high-energy physics is heavily debated in the particle physics community, with a decision on the next machine possible coming at the next update of the European strategy, expected in the 2nd half of the 2020s.
Should one pursue precision physics with a lepton collider, or aim for a hadron collider with much higher energy than the LHC? Proposals for both linear electron-positron colliders and circular proton-proton colliders exist. A common element of these proposals is the large size of the respective machines. 10-100 km long underground tunnels would be needed, and consequently the machines would be expensive to fund within the available budgets. A way forward for continuing physics at the energy frontier is to develop novel accelerator technology that may drastically reduce the size and cost of future colliders. This project’s overall objective is to identify paths to compact and affordable multi-TeV colliders by studying two novel acceleration methods: plasma wakefield acceleration technology, where very strong electric fields generated in plasmas may allow particles to be accelerated to TeV energies in short space, and fast muon acceleration, allowing for a compact muon ring collider at the multi-TeV energies.
The development of accelerator technology done for particle physics has benefitted society in diverse fields, from cancer treatment to materiel science.
Challenge: collider studies at the multi-TeV frontier are essential to address open particle physics questions. However, it is unclear which accelerator technology is best suited to reach this goal. While RF technology is a good option for a "Higgs Factory" collider, plasma-based accelerators give promise for significantly shorter and more cost effective multi-TeV colliders. As of today, however, no concepts of plasma linacs have been completed to the level that a comparison to RF linacs can be done. This impedes further work towards plasma colliders.
Opportunity: This project will resolve this by combing experiment and design to establish the performance of a plasma linac, and thus open novel tracks to multi-TeV collisions using plasma. We consider the plasma linac for muon colliders, as well as for a gamma-gamma collider. The latter option bypasses the positron plasma acceleration problem, proven to be particularly challenging. For all plasma-based linacs, an urgent question that will be addressed concerns the impact of transverse instabilities on acceleration efficiency and linac design.
Team: The project manager is an expert on plasma-based acceleration and the PI of plasma instability experiments at FACET-II. He has lead the CERN linear collider novel technology working group, which has studied collider upgrade possibilities with plasmas, as well as the physics case for gamma-gamma colliders. The project will pull expertise from both collider- and plasma communities and is uniquely positioned to study the opportunities and challenges of plasma-based colliders, and to assess their advantages.
Approach: Complete experimental studies of beam-plasma transverse instabilities vs efficiency at FACET-II. Refine models of plasma acceleration stages taking into account experiment results. Use the models to design plasma-based linacs for a gamma-gamma collider, and to investigate a plasma-based muon linac. Compare the performance of plasma-based linacs to RF linacs.