Bunch self-focusing regime of laser wakefield acceleration with reduced emittance growth.

A new regime of laser wakefield acceleration of an injected electron bunch is described. In this regime, the bunch charge is so high that the bunch wakefields play an important role in the bunch dynamics. In particular, the transverse bunch wakefield induces a strong self-focusing that suppresses the transverse emittance growth arising from misalignment errors. The decelerating longitudinal bunch wakefield, however, is not so strong that it completely cancels the accelerating laser wakefield. In fact, the induced energy spread can be compensated by exploiting phase slippage effects. These features make the new regime interesting for high beam quality laser wakefield acceleration.

Merging of plasma currents.

The merging process of current filaments in a strongly magnetized plasma is described. The evolution is calculated using a contour dynamics method, which accurately tracks piecewise constant distributions of the conserved quantities. In the interaction of two screened currents, both develop dipolar vortical flows, bringing the currents together. This is the manifestation of the Lorentz force between aligned currents. Currents will merge into single filaments. Reconnection of the magnetic field takes place, converting the magnetic topology from a figure eight to a circle.

Generation of fast electrons by breaking of a laser-induced plasma wave.

A one-dimensional model for fast electron generation by an intense, nonevolving laser pulse propagating through an underdense plasma has been developed. Plasma wave breaking is considered to be the dominant mechanism behind this process, and wave breaking both in front of and behind the laser pulse is discussed. Fast electrons emerge as a short bunch, and the electrostatic field of this bunch is shown to limit self-consistently the amount of generated fast electrons.

Simulation of laser wakefield acceleration of an ultrashort electron bunch.

The dynamics of the acceleration of a short electron bunch in a strong plasma wave excited by a laser pulse in a plasma channel is studied both analytically and numerically in slab geometry. In our simulations, a fully nonlinear, relativistic hydrodynamic description for the plasma wave is combined with particle-in-cell methods for the description of the bunch. Collective self-interactions within the bunch are fully taken into account. The existence of adiabatic invariants of motion is shown to have important implications for the final beam quality. Similar to the one-dimensional case, the natural evolution of the bunch is shown to lead, under proper initial conditions, to a minimum in the relative energy spread.