Propagation of a laser-driven relativistic electron beam inside a solid dielectric

Area of Science:

• Plasma physics
• Laser-matter interactions
• Relativistic electron beams

Background:

• Understanding ionization wave dynamics is crucial for laser-driven particle acceleration and inertial confinement fusion.
• Characterizing the behavior of relativistic electron beams interacting with solid targets provides insights into energy deposition and plasma generation.

Purpose of the Study:

• To comprehensively characterize the ionization wave dynamics within a glass target induced by a laser-driven, relativistic electron beam.
• To investigate the electron density distribution, propagation speed, and associated electromagnetic fields during this process.

Main Methods:

• Utilized laser probe diagnostics including shadowgraphy, interferometry, and polarimetry for detailed analysis.
• Employed the 50-TW Leopard laser system at the University of Nevada, Reno for experimental setup.
• Performed two-dimensional particle-in-cell (PIC) computer simulations to model electron beam dynamics.

Main Results:

• Observed a hemispherical ionization wave propagating at approximately c/3 for 10 picoseconds at a laser flux of ~2 × 10^18 W/cm².
• Measured a maximum free-electron density of ~2 × 10^19 cm⁻³, corresponding to ~0.1% ionization.
• Identified a
• fountain effect
• characterized by radial electron spreading and return to the target surface, supported by PIC simulations.
• Determined maximum magnetic and electric fields of ~15 kG and ~1 MV/cm, respectively, with a hot, ringlike electron temperature structure (~0.7 eV).

Conclusions:

• The study elucidates the complex dynamics of laser-induced ionization waves in glass, revealing key parameters of propagation and electron behavior.
• PIC simulations confirmed the role of self-consistent electrostatic fields in the radial spreading of fast electrons.
• The rapid recombination on a sub-picosecond timescale suggests efficient energy loss mechanisms post-laser pulse.