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Divergence of laser-driven relativistic electron beams
A Debayle1, J J Honrubia, E d'Humières
1ETSI Aeronáuticos, Universidad Politécnica de Madrid, Madrid, Spain.
Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics
|January 15, 2011
Summary
Fast electron beams from ultrahigh intensity lasers diverge due to radial deviation and angular dispersion. Preplasma effects significantly alter beam divergence, impacting transport calculations and magnetic field penetration in targets.
Area of Science:
- Plasma Physics
- Laser-Plasma Interactions
- Computational Physics
Background:
- Investigating electron acceleration by ultrahigh intensity lasers is crucial for applications in inertial confinement fusion and high-energy particle sources.
- Understanding fast electron beam divergence is key to controlling energy transport in laser-produced plasmas.
- Previous models often simplified beam divergence, potentially miscalculating energy transport and magnetic field effects.
Purpose of the Study:
- To investigate the physical mechanisms governing the divergence of fast electron beams generated by ultrahigh intensity lasers.
- To analyze the role of preplasma and magnetic fields in electron beam collimation and transport.
- To improve the accuracy of fast electron transport calculations in laser-plasma interactions.
Main Methods:
- Utilized two-dimensional planar particle-in-cell (PIC) simulations to model electron acceleration.
- Employed a two-dimensional cylindrically-symmetric hybrid code incorporating electron radial velocity.
- Analyzed the interplay between radial beam deviation and angular dispersion under varying preplasma conditions.
Main Results:
- Identified two primary contributors to electron beam divergence: regular radial deviation and angular dispersion.
- Demonstrated that preplasma significantly influences radial deviation via the laser ponderomotive force and electron acceleration.
- Showed that small-scale magnetic fields from Weibel instability cause angular dispersion, and preplasma effects can become comparable.
- Simulations revealed reduced azimuthal magnetic field strength and penetration in solid targets when electron radial velocity is considered.
Conclusions:
- The divergence of fast electron beams is a complex interplay of radial deviation and angular dispersion, significantly affected by preplasma.
- Neglecting preplasma-induced radial deviation leads to overestimation of beam collimation by resistive magnetic fields.
- Accounting for electron radial velocity is essential for accurate modeling of magnetic field dynamics in laser-driven electron acceleration.
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