A global simulation for laser driven MeV electrons in $50\mu m$-diameter fast ignition targets

摘要

The results from 2.5-dimensional Particle-in-Cell simulations for theinteraction of a picosecond-long ignition laser pulse with a plasma pellet of50-$\mu m$ diameter and 40 critical density are presented. The high densitypellet is surrounded by an underdense corona and is isolated by a vacuum regionfrom the simulation box boundary. The laser pulse is shown to filament andcreate density channels on the laser-plasma interface. The density channelsincrease the laser absorption efficiency and help generate an energeticelectron distribution with a large angular spread. The combined distribution ofthe forward-going energetic electrons and the induced return electrons ismarginally unstable to the current filament instability. The ions play animportant role in neutralizing the space charges induced by the the temperaturedisparity between different electron groups. No global coalescing of thecurrent filaments resulted from the instability is observed, consistent withthe observed large angular spread of the energetic electrons.