Chapter 4: High-gradient plasma and laser accelerators

Novel high-gradient accelerators have demonstrated acceleration of electrons and positrons with electric field strengths of 1 to > 100 GeV/m. This is about 10 to 1000 times higher than achieved in RF-based accelerators, and as such they have the potential to overcome the limitations associated with RF cavities. Plasma-based accelerators have produced multi-GeV bunches with parameters approaching those suitable for a linear collider. These accelerators offer the prospect of near term, compact and cost-effective particle physics experiments that provide new physics possibilities supporting precision studies and the search for new particles. The expert panel has defined a long term R&D; roadmap towards a compact collider with attractive intermediate experiments and studies. A delivery plan for the required R&D; has been developed and includes work packages, deliverables, a minimal plan, connections to ongoing projects and an aspirational plan.