Multi-dimensional collective effects in high-current relativistic beams relevant to High Density Laboratory Plasmas

[摘要] In summary, an analytical model describing the self-pinching of a relativistic charge-neutralized electron beam undergoing the collisionless Weibel instability in an overdense plasma has been developed. The model accurately predicts the final temperature and size of the self-focused filament. It is found that the final temperature is primarily defined by the total beam???s current, while the filament???s radius is shown to be smaller than the collisionless skin depth in the plasma and primarily determined by the beam???s initial size. The model also accurately predicts the repartitioning ratio of the initial energy of the beam???s forward motion into the magnetic field energy and the kinetic energy of the surrounding plasma. The density profile of the final filament is shown to be a superposition of the standard Bennett pinch profile and a wide halo surrounding the pinch, which contains a significant fraction of the beam???s electrons. PIC simulations confirm the key assumption of the analytic theory: the collisionless merger of multiple current filaments in the course of the Weibel Instability provides the mechanism for Maxwellization of the beam???s distribution function. Deviations from the Maxwell-Boltzmann distribution are explained by incomplete thermalization of the deeply trapped and halo electrons. It is conjectured that the simple expression derived here can be used for understanding collsionless shock acceleration and magnetic field amplification in astrophysical plasmas.

[发布日期] 2014-05-09

[学科分类] 原子、分子光学和等离子物理

[关键词] Weibel instability;electron beams