Focusing a high-power femtosecond laser pulse into plasma produces
an electrostatic wake which can be harnessed to accelerate electrons
to GeV energies in several centimetres. A ponderomotive force
(red arrows in the figure) arising from the light pressure pushes
aside the plasma electrons to generate the wake. The electrostatic
fields associated with this wake is utilised to produce accelerating
fields which are 3-4 orders of magnitude larger than is possible
in the RF cavity of a conventional accelerator.
The excitation of a plasma wakefield is analogous to the wave
behind a motorboat on a lake. If a short bunch of electrons
is injected at an appropriate phase into the electrostatic wave,
it can be accelerated by the Coulomb force associated with the
wakefield (black arrows). In our analogy, a surfer riding the
wave behind the motorboat would gain energy from the wave. Ultra-short,
ultra-intense laser pulses from commercially available table-top
terawatt femtosecond lasers are suitable drivers of plasma wakes.
Eventually, using several Joules of laser energy, we expect
to produce electron bunches with a mean energy above 1 GeV,
an energy spread of about 1% and a peak current exceeding 1
kA . However, to demonstrate the technology, the energy will
initially be restricted to ~100 MeV.