Particle accelerators for particle physics and light sources are large and expensive. There are a number of advanced accelerator schemes that aim at significantly increasing the accelerating gradient to reduce the size of these accelerators. Among them, the beam-driven, plasma-based accelerator, know as the plasma wakefield accelerator or PWFA. In the PWFA a relativistic particle bunch drives large amplitude wakefield in a plasma. The accelerating field can reach 10GV/m, while the focusing strength is in the MT/m range for plasma densities around 1017 cm3.
Thanks to this large gradient and strong focusing, trailing electrons gained 42 GeV along only 85 cm of plasma in a PWFA at the SLAC National Accelerator Laboratory [I. Blumenfeld et al., Nature 445, 741 (2007)]. These experiments also produced a wealth of beam and plasma physics results, both with electron and positron bunches.
At the same time, PWFA experiments at the Brookhaven National Laboratory using a low energy electron beam aim at demonstrating resonant excitation of plasma wakefields. The electron beam is tailored using a masking technique [P. Muggli et al., Phys. Rev. Lett. 101, 054801 (2008)] to reach large transformer ratios and to test ideas that will be applied future high-energy PWFA experiments at the SLAC FACET facility. These results have triggered a renewed interest in the PWFA, and new experiments are planned at CERN. The goal is to use the large energy of LHC-like proton bunches (>10kJ/bunch) to accelerate a trailing electron bunch to the TeV energy range in a single PWFA section.
The remarkable recent progress of the PWFA makes it one of the leading advanced acceleration schemes for a future collider or a linac-based light source. I will give an overview of the experimental results obtained to date, and describe future experiments and challenges to make the PWFA a new accelerator technology.