Surface-Magnetic-Field and Fast-Electron Current-Layer Formation by Ultraintense Laser Irradiation

Abstract

Multi-MeV electron generation by ultraintense laser pulses plays a major role in fast ignition laser fusion and related high energy density science. This Letter discloses a unique feature of relativistic electron motion and self-induced electromagnetic fields which depend upon laser incident angle and intensity. When the incident angle is larger than the critical value (theta> or =thetacr), despite an MeV electron being injected obliquely into the target, the high energy electron is decoupled from the bulk of the plasma and transported along the surface by the structured electron motion guided by the surface quasistatic electromagnetic field. The surface electromagnetic field and fast-electron density and current profiles are sustained as a quasisteady state by the intense laser irradiation. The analytical structures of the field and electron density agree reasonably well with 2D particle in cell simulation results.

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

“…In the same figure, one can also observe packets of electrons heated symmetrically in both positive and negative p y directions. To interpret this result, one can notice that the phase space, although more diffuse in our case, is very similar to what has been already observed 30,31 at higher laser intensities and denser plasmas due to the self-generation of large quasistatic magnetic fields [32][33][34] at the plasma surface. In our case, the magnetic field component at the surface is dominated by the resonant oscillating magnetic field of the surface wave.…”

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.…”

“…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. A significant fraction of fast electrons injected into the plasma are deflected to the vacuum by the magnetic field, and pulled back again from the vacuum region by the charge separation field around the surface.…”

“…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].…”

Investigations of Field Dynamics in Laser Plasmas with Proton Imaging

“…Electrons which can not escape are trapped by the rising electric potential and create the electron sheath. This electron cloud spreads over the target surface while cold electrons of the target foil built up a return current [95,117]. The resulting electric field ionizes the contamination layer at the target surface and accelerates the ions.…”