Dynamics of a plasma channel created by the wakefield of a short laser pulse

Abstract

A new physical effect of a plasma channel formation by the ponderomotive force of a wakefield excited by a short laser pulse with duration of the order of electron plasma oscillation period ${\omega }_{\text{p0}}^{\text{−1}}$ ${\mathrm{(\omega }}_{\text{p0}}$ is the plasma frequency) is discussed. The hydrodynamic and particle numerical codes, including plasma ion response, are used to simulate the long-term wakefield behavior. It is found that the wakefield creates a channel with a radial profile depending on the laser pulse width. Particularly, for a narrow pulse, wherein the width is less than ${\mathrm{c/\omega }}_{\text{p0}}$ $\mathrm{(c}$ is the speed of light), the channel has an annular form with on-axis density maximum. The depth of the channel increases with the distance from the pulse until fine-scale mixing arises and the wake starts to break. Particle simulations show that wave breaking results in emergence of fast electrons taking an essential part of the wake energy during a few plasma periods. Quasilinear fluid equations describing self-consistently, the laser wakefield generation, and plasma channel formation are derived. The wave-breaking conditions are obtained in the geometrical optics approximation. The results of numerical simulations for high-intensity laser pulses are in good agreement with theoretical predictions. The scaling laws for wave breaking are discussed.