Laser-Plasma Accelerators: A Status Report

In this paper, the status of the Laser-Plasma Accelerator field within the Advanced Accelerator Concepts area of research is reviewed. In particular, I review the status of the Plasma Beat Wave Acceleration (PBWA) scheme, the SelfModulated, Laser-Wake Field Acceleration (SMLWFA) scheme and the Laser-Wake Field Acceleration (LWFA) scheme. In all these three schemes, charged particles are accelerated by a relativistic (phase velocity ~ c), space-charge wave excited in a plasma by a photon beam. The wave potential becomes large enough to trap either the background plasma electrons, in a process known as self-trapping, or electrons (positrons) must be externally injected with a certain minimum energy to be trapped and accelerated by this potential. There is a simple scaling law that gives the accelerating electric field of such waves as Ez(V/cm) ~ E(ne) (cm") where E = n/n0 is the density perturbation associated with the wave and ne is the initial unperturbed plasma density. The maximum energy gain limited by dephasing is given by ~ 2yph (MeV) where yph = (co0/(0p) is the relativistic Lorentz factor associated with the phase velocity of the wave, 0)0 is the laser frequency and (Dp is the plasma frequency.