  The acceleration gradients generated in a laser- or beam-driven plasma
wakefield accelerator are typically three orders of magnitude greater than
those produced by a conventional accelerator, and hence plasma accelerators can
open a route to a new generation of very compact machines. In addition,
plasma-based accelerators can generate beams with unique properties, such as
tens of kiloamp peak currents, attosecond bunch duration, ultrahigh brightness
and intrinsic particle beam-laser pulse synchronization.
  In this roadmap we review the status of plasma accelerator research in the
UK. We outline potential applications, describe the research and development
required to enable those applications, and discuss synergies with related areas
of research. We also set-out the resources required to realise these ambitions
and provide a timeline for advances in the key areas.
