Simulation of ultrashort electron pulse generation from optical injection into wake-field plasma waves

Abstract

A laser-plasma-based source of relativistic electrons is described in detail, and analyzed in two dimensions using theoretical and numeric techniques. Two laser beams are focused in a plasma, one exciting a wake-field electron plasma wave while another locally alters some electron trajectories in such a way that they can be trapped and accelerated by the wave. Previous analyses dealt only with one-dimensional models. In this paper two-dimensional particle-in-cell simulations and analysis of single particle trajectories show that the radial wake field plays an important role. The simulation results are interpreted to evaluate the accelerated electron beam's properties and compared with existing devices.

Electron Trapping from Interactions between Laser-Driven Relativistic Plasma Waves

“…Electrons in group II originate directly on the axis of the drive pulse, and to the side of the injector pulse (yellow trajectory). These electrons first experience the interaction with the drive pulse, and then kicked and injected into the drive wakefield by the combination of the injector pulse's ponderomotive force and its wakefield [19,44,45]. This group is injected via ponderomotive drift and, partially, due to stochastic heating in the beatwave.…”

Imaging Laser wake fields by Thomson Scattering a Co-Propagating Pulse

“…As the wake fields propagated forward, more and more electrons with energy above the trapping threshold were captured until the largest amplitude formation of the plasma wave. [24,25] As described in Ref. [2], wave breaking is not always catastrophic and a part of the electrons in the wave can escape, reducing its amplitude, while maintaining the wave structure.…”

“…Since the ponderomotive force is proportional to the laser intensity gradient, these pushed electrons were directed primarily in the longitudinal direction because the laser pulse length (𝑐𝜏 = 9 µm) is much shorter than its focal spot size in our experiment. [24] On the other hand, the ions do not respond to the ponderomotive force because their mass is much larger than electrons. Under the restoring force (backward and centripetal) due to the electric field of the space charge separation, the electrons would be dragged back towards their original position.…”

Simulation studies of laser wakefield acceleration based on typical 100 TW laser facilities

“…2) How can we capture enough electrons? There are several ways to "inject" the electrons into the plasma wave, such as wave-breaking injection [1,10], blow-out/bubble injection [11,12], external injection [13], optical injection [14], density transition injection [15], etc. Optical injection and density transition injection are complicated for an experimental setup and with regard to the technique today it is hard to externally inject the charged particles into a plasma wave with the wavelength of only several millimeters.…”