Strongly-Mismatched Regime of Self-guided Laser-driven Nonlinear Plasma-Wave based Electron Acceleration.
A strongly mismatched regime of laser-plasma acceleration using a self-guided laser-driven bubble-shaped nonlinear plasma electron wave is introduced and modeled. In this regime the radial envelope of a laser-pulse incident at the plasma entrance is mismatched to the nonlinear electron response excited by it, in contrast to the established understanding. A nonlinear laser envelope equation is derived to show that as the strength of the mismatch is increased, the envelope oscillations steepen and become increasingly asymmetric, exhibiting shorter and tighter radial squeeze phases. The sharply increasing intensity in a shortened squeeze phase results in the slicing of the longitudinal laser envelope, driving a strong optical-shock. The optical shock results in an elongating bubble shape with significantly higher peak plasma fields and a novel self-injection mechanism which produces beams of high transverse qualities. The behavior of peak beam energies from Particle-In-Cell simulations and self-guided multi-GeV experimental data are in good agreement with the predictions of an adjusted-$a_0$ model and significantly exceed the matched regime predictions.
Publisher URL: http://arxiv.org/abs/1711.00356