  Plasma wakefield acceleration (PWFA) holds much promise for advancing the
energy frontier because it can potentially provide a 1000-fold or more increase
in acceleration gradient with excellent power efficiency in respect with
standard technologies. Most of the advances in beam-driven plasma wakefield
acceleration were obtained by a UCLA/USC/SLAC collaboration working at the SLAC
FFTB[ ]. These experiments have shown that plasmas can accelerate and focus
both electron and positron high energy beams, and an accelerating gradient in
excess of 50 GeV/m can be sustained in an 85 cm-long plasma. The FFTB
experiments were essentially proof-of-principle experiments that showed the
great potential of plasma accelerators.
  The FACET[ ] test facility at SLAC will in the period 2012-2016 further study
several issues that are directly related to the applicability of PWFA to a
high-energy collider, in particular two-beam acceleration where the witness
beam experiences high beam loading (required for high efficiency), small energy
spread and small emittance dilution (required to achieve luminosity).
  The PWFA-LC concept presented in this document is an attempt to find the best
design that takes advantage of the PWFA, identify the critical parameters to be
achieved and eventually the necessary R&D to address their feasibility. It best
benefits from the extensive R&D that has been performed for conventional rf
linear colliders during the last twenty years, especially ILC[ ] and CLIC[ ],
with a potential for a comparably lower power consumption and cost.
