Numerical and theoretical studies on basic issues for fast ignition: from fast particle generation to beam driven ignition

Abstract

ABSTRACT In all recently proposed schemes for laser-driven Fast Ignition (Fl) of Inertial Confinement Fusion (ICF) targets,two key elements are the conversion of the energy of a Petawatt laser pulse into a beam of strongly relativisticelectrons and its transport through a dense plasma or a solid target. The electron beam may either drive ignitiondirectly or be exploited to accelerate a proton beam which in turn is used to ignite the target. Both approaches to FT involve a number of physical processes that are challenging for theory and simulation. In this paper, theoretical and numerical investigations are presented concerning several fundamental issues of relevance to Fl,including electron beam instabilities, electron transport in solid-density materials, and requirements for protonbeam driven ignition.Keywords: Fast Ignition, energy conversion, electron and ion beam transport, proton beam driven ignition. 1. INTRODUCTION An essential element of Fast Ignition (Fl) of ICF targets is the conversion of the energy of a Petawatt laser pulseinto a beam of strongly relativistic electrons. In the original proposal,' the electron beam is generated by directinteraction of the laser pulse with the coronal plasma and reaches the precompressed fuel core after propagatingin the dense plasma region. The electron beam is expected to carry a current of several MegaAmperes, and itstransport properties are thus affected by the self-generated electric and magnetic fields, by beam instabilities andby inefficient charge neutralization due to low conductivity of the background electrons. Efficient energy transportis also a key factor in alternative FT schemes.2 Electric field generation by relativistic electrons penetrating in