Surface Acceleration of Fast Electrons with Relativistic Self-Focusing in Preformed Plasma

Abstract

We report an observation of surface acceleration of fast electrons in intense laser-plasma interactions. When a preformed plasma is presented in front of a solid target with a higher laser intensity, the emission direction of fast electrons is changed to the target surface direction from the laser and specular directions. This feature could be caused by the formation of a strong static magnetic field along the target surface which traps and holds fast electrons on the surface. In our experiment, the increase in the laser intensity due to relativistic self-focusing in plasma plays an important role for the formation. The strength of the magnetic field is calculated from the bent angle of the electrons, resulting in tens of percent of laser magnetic field, which agrees well with a two-dimensional particle-in-cell calculation. The strong surface current explains the high conversion efficiency on the cone-guided fast ignitor experiments.

Fast electron generation in cones with ultraintense laser pulses

“…Other groups have measured beamed electrons in vacuum and suggested that this is due to surface transport. 14,16,17 However, the total number of electrons escaping into vacuum in these experiments is very small and the correlation of those electrons to the internal distribution is weak at best. 18 A simple argument sets the physical limits.…”

Strongly Enhanced Laser Absorption and Electron Acceleration via Resonant Excitation of Surface Plasma Waves

“…[37][38][39][40] It is thus of interest, for comparison with experimental results, to calculate the electron energy distribution function for different angles with respect to the vacuum-plasma interface. In …”

Enhanced surface acceleration of fast electrons by using subwavelength grating targets

“…Due to the self-consistently enhanced quasi-static magnetic field and sheath electric field around the surface, the fraction of surface accelerated fast electrons can be enhanced by increasing the total number of the fast electrons generated in the laser-target interaction [10][11][12][13][14][15]. As shown in ref.…”

“…Surface acceleration of fast electrons was observed when the intense short pulse laser beam irradiated the planar target at large incident angle [13][14][15]. PIC simulations and analytical theory [10][11][12] show that a quasi-static surface magnetic field is induced by the fast electrons generated in the interaction via J B × heating or vacuum heating.…”

“…The physical process of guiding and confining of fast electrons along the cone wall was explored individually by using planar target [10][11][12][13][14][15] or inverse cone target [16].…”