Development of Spectral and Atomic Models for Diagnosing Energetic Particle Characteristics in Fast Ignition Experiments

In the fast ignition concept for inertial fusion energy, high-intensity short-pulse lasers are used to create energetic particles (protons and relativistic electrons) that propagate to the fuel within a compressed capsule. The efficient transport of these energetic particles to the fuel is a key issue in fast ignition research. A combination of well-diagnosed experiments and well-tested simulation tools are needed in order to understand energetic particle transport through dense plasmas, a prerequisite for fast ignition to become a viable option for inertial fusion. This project will develop and apply spectral and atomic physics models, used in concert with a particle-in-cell (PIC) code, to simulate diagnostic signatures associated with energetic particle transport in short-pulse laser experiments. The developed models will be applied to fast-ignition-related short-pulse-laser experiments to characterize the properties of energetic electrons and protons. Phase I developed and benchmarked cross section models for energetic protons and relativistic electrons, and utilized them in a collisional-radiative code; developed an interface for post-processing simulation results; developed and initiated a plan to utilize more accurate ionization modeling in PIC code simulations; and performed proof-of-principal simulations relevant to short-pulse laser experiments. Phase II will: (1) develop diagnostics for characterizing energetic particle distributions based on polarization spectroscopy; (2) develop atomic physics modules for use within PIC codes; (3) implement high-fidelity, Stark-broadened line profiles in a multi-dimensional spectral analysis code, in order to provide accurate spectral diagnostics based on inner-shell transitions; and (4) benchmark the new models by comparison with well-diagnosed short-pulse laser experiments. Commercial Applications and other Benefits as described by the awardee: Beyond the application to fast ignition concepts for inertial fusion energy, powerful, user-friendly computational tools, capable of simulating the spectroscopic and atomic properties of laser-produced plasmas, should be applicable to radiation sources for EUV and x-ray lithography, plasma radiation sources used in defense research, magnetic fusion energy plasma diagnostics, materials plasma processing, and radiation sources developed for medical physics research and instrumentation.