Near-GeV-Energy Laser-Wakefield Acceleration of Self-Injected Electrons in a Centimeter-Scale Plasma Channel

The first three-dimensional, particle-in-cell (PIC) simulations of laser-wakefield acceleration of self-injected electrons in a 0.84 cm long plasma channel are reported. The frequency evolution of the initially 50 fs (FWHM) long laser pulse by photon interaction with the wake followed by plasma dispersion enhances the wake which eventually leads to self-injection of electrons from the channel wall. This first bunch of electrons remains spatially highly localized. Its phase space rotation due to slippage with respect to the wake leads to a monoenergetic bunch of electrons with a central energy of 0.26 GeV after 0.55 cm propagation. At later times, spatial bunching of the laser enhances the acceleration of a second bunch of electrons to energies up to 0.84 GeV before the laser pulse intensity is significantly reduced.

Figure 1

(a) Maximum electron energy, $E_{\mathrm{M}\mathrm{A}\mathrm{X}}$, as a function of laser propagation distance in the plasma channel. (b) The accelerated electron distribution functions at two distances in the channel in 3D simulations $(E>10\mathrm{M}\mathrm{e}\mathrm{V})$. The beam propagates in vacuum for 0.04 cm after exiting the plasma.

Figure 2

(a) The distribution of radial position at which the electrons shown in Fig. 1b originated. (b) The longitudinal component of the wakefield taken after the laser enters the channel (0.1 cm) and when electrons are self-injected (0.25 cm).

Figure 3

(a), (b) The vector potential and (c) the electric field both normalized to their initial values in the plasma channel. The dotted lines are the initial envelope of the laser. The horizontal scale is $x(c/{\omega }_p)$ in (a), (b), and (c).

Figure 4

Electron density contour showing the wake structure at three different locations in the channel in $(z\mathrm{v}\mathrm{s}x)$ and out $(y\mathrm{v}\mathrm{s}x)$ of the plane of the electric field of the laser. 1 and 2 are the locations of the first and second self-injected electron bunch, respectively.

Figure 5

End on view of the transverse distribution of high energy particles at (a) $x=0.5\mathrm{c}\mathrm{m}$ and (b) at $x=0.84\mathrm{c}\mathrm{m}$. The circle denotes the ring of peak density of the original plasma channel.