Self-injected laser wakefield acceleration in tapered plasma densities

Extremely strong electric fields generated by relativistic plasma waves can be used to accelerate electrons to high energy. This can be done either by external injection or self-injection of plasma electrons. In this paper, we report that plasma electrons by the self-injected laser wakefield acceleration using a sharp density transition can gain significantly higher energies when the trapped particles are accelerated in a tapered plasma density. Two-dimensional (2-D) simulation studies show that significantly higher energies can be obtained with an increasing plasma density although space-charge effect of the trapped electrons deforms and deteriorates the laser wakefield severely.