Powerful laser-plasma processes are explored to generate discharge currents of a few 100 kA in coil targets, yielding magnetostatic fields (B-fields) in excess of 0.5 kT. The quasi-static currents are provided from hot electron ejection from the laser-irradiated surface. According to our model, describing qualitatively the evolution of the discharge current, the major control parameter is the laser irradiance I las λ 2 las . The space-time evolution of the B-fields is experimentally characterized by high-frequency bandwidth B-dot probes and by proton-deflectometry measurements. The magnetic pulses, of ns-scale, are long enough to magnetize secondary targets through resistive diffusion. We applied it in experiments of laser-generated relativistic electron transport into solid dielectric targets, yielding an unprecedented 5-fold enhancement of the energy-density flux at 60 µm depth, compared to unmagnetized transport conditions. These studies pave the ground for magnetized high-energy density physics investigations, related to laser-generated secondary sources of radiation and/or high-energy particles and their transport, to high-gain fusion energy schemes and to laboratory astrophysics.
We discuss the modeling of population kinetics of nonequilibrium steady-state plasmas using a collisional-radiative model and code based on analytical rates (ABAKO). ABAKO can be applied to low-to-high Z ions for a wide range of laboratory plasma conditions: coronal, local thermodynamic equilibrium or nonlocal thermodynamic equilibrium, and optically thin or thick plasmas. ABAKO combines a set of analytical approximations to atomic rates, which yield substantial savings in computer running time, still comparing well with more elaborate codes and experimental data. A simple approximation to calculate the electron capture cross section in terms of the collisional excitation cross section has been adapted to work in a detailed-configuration-accounting approach, thus allowing autoionizing states to be explicitly included in the kinetics in a fast and efficient way. Radiation transport effects in the atomic kinetics due to line trapping in the plasma are taken into account via geometry-dependent escape factors. Since the kinetics problem often involves very large sparse matrices, an iterative method is used to perform the matrix inversion. In order to illustrate the capabilities of the model, we present a number of results which show that the ABAKO compares well with customized models and simulations of ion population distribution. The utility of ABAKO for plasma spectroscopic applications is also outlined.
We review the critical results of the 4th Non-LTE Code Comparison Workshop held in December 2005. To test the NLTE population kinetics codes, both steady-state and time-dependent cases for C, Ar, Fe, Sn, Xe, and Au plasmas were selected for detailed comparisons. Additional features such as the effects of non-Maxwellian free electrons, the influence of a Planckian radiation field, and the emission spectra were required in specific cases. The scope of problems was expanded from the previous workshops to include two problems outside the dense plasma physics, namely, the EUV lithography sources and the astrophysical photoionized plasmas. We briefly outline the technical organization of the workshop, present motivations for the chosen cases, and discuss some representative results. Ó 2007 Published by Elsevier B.V.
The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters. CitationFrenje, J.A., et al., "Experimental validation of low-Z ion-stopping formalisms around the Bragg peak in high-energy-density plasmas." Physical review letters
We discuss the processing of data recorded with multimonochromatic x-ray imagers (MMI) in inertial confinement fusion experiments. The MMI records hundreds of gated, spectrally resolved images that can be used to unravel the spatial structure of the implosion core. In particular, we present a new method to determine the centers in all the array of images, a better reconstruction technique of narrowband implosion core images, two algorithms to determine the shape and size of the implosion core volume based on reconstructed broadband images recorded along three-quasiorthogonal lines of sight, and the removal of artifacts from the space-integrated spectra.
Radiative properties are fundamental for plasma diagnostics and hydro-simulations. For this reason, there is a high interest in their determination and they are a current topic of investigation both in astrophysics and inertial fusion confinement research. In this work a flexible computation package for calculating radiative properties for low and high Z optically thin and thick plasmas, both under local thermodynamic equilibrium and non-local thermodynamic equilibrium conditions, named RAPCAL is presented. This code has been developed with the aim of providing accurate radiative properties for low and medium Z plasmas within the context of detailed level accounting approach and for heavy elements under the detailed configuration accounting approach. In order to show the capabilities of the code, there are presented calculations of some radiative properties for carbon, aluminum, krypton and xenon plasmas under local thermodynamic and non-local thermodynamic equilibrium conditions.
Two-dimensional space-resolved temperature and density images of an inertial confinement fusion (ICF) implosion core have been diagnosed for the first time. Argon-doped, direct-drive ICF experiments were performed at the Omega Laser Facility and a collection of two-dimensional spaceresolved spectra were obtained from an array of gated, spectrally resolved pinhole images recorded by a multi-monochromatic x-ray imager. Detailed spectral analysis revealed asymmetries of the core not just in shape and size but in the temperature and density spatial distributions, thus characterizing the core with an unprecedented level of detail.Inertial confinement fusion (ICF) is an approach that utilizes laser produced ablation pressure to compress a millimeter-sized spherical shell capsule containing fuel (e.g., deuterium and tritium) and drive the fuel temperature and density to conditions suitable for ignition [1]. The key is a spherically symmetric and stable compression. While state-of-the-art hydrodynamics simulations have been used to design ignition implosions, the challenge of achieving a symmetric implosion experimentally has thus far prevented ICF from reaching the conditions required for successful ignition [2]. Hence, measuring the spatial asymmetry in the temperature and density distributions in the implosion core is crucial for understanding how to make it more symmetric.Several diagnostics were developed in the last few decades in order to investigate implosion core conditions. K-shell line emission spectroscopy using Ar as a tracer has proved to be a powerful tool to extract spaceaveraged electron temperature, T e , and density, n e [3-5]. However, two-dimensional (2-D) space-resolved spectra have never been extracted to study the asymmetries of T e and n e structures in the implosion core. X-ray pinhole imaging of ICF implosion cores has been used to study the shape and size of the core and, in particular, to characterize deviations from spherical symmetry [6,7]. Nevertheless, these images do not reveal the implosion asymmetries in T e and n e distributions.This Letter describes a new spectroscopic method that combines the ideas of Ar tracer spectroscopy and pinhole imaging to extract implosion core images in T e and n e without making symmetry assumptions. These pinhole images are extracted by analyzing a collection of 2-D space-resolved spectra obtained from an array of spectrally resolved core images. The direct measurement of temperature and density asymmetries in the core provides stringent constraints on what actually happens in implosion experiments and can be used to benchmark hydrodynamic simulations. The discussion here focuses on the application to ICF implosion core conditions; nevertheless, the ideas are general. The extraction and analysis of space-resolved spectra from spectrally resolved pinhole images opens up new possibilities for x-ray spectroscopy of high-energy density plasmas.The spectroscopic data were recorded in a series of Ar-doped ICF implosion experiments performed at the Omega Laser ...
Detailed analysis of x-ray narrow-band images from argon-doped deuterium-filled inertial confinement fusion implosion experiments yields information about the temperature spatial structure in the core at the collapse of the implosion. We discuss the analysis of direct-drive implosion experiments at OMEGA, in which multiple narrow-band images were recorded with a multimonochromatic x-ray imaging instrument. The temperature spatial structure is investigated by using the sensitivity of the Ly beta/He beta line emissivity ratio to the temperature. Three analysis methods that consider the argon He beta and Ly beta image data are discussed and the results compared. The methods are based on a ratio of image intensities, ratio of Abel-inverted emissivities, and a search and reconstruction technique driven by a Pareto genetic algorithm.
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