arXiv subjects

R. Florido

Publications and source records attributed to R. Florido.

8 recordsLinked to original sources

arXiv2025

Computer simulations of the Stark effect in the helium-beta complex of krypton in ICF conditions

There is an ongoing interest in using spectroscopy in inertial confinement fusion (ICF) experiments, where dopants such as krypton can provide vital information about the temperature and density of the imploding plasma. While the most advanced tools for calculating Stark profiles are computer simulation models (CSMs), their application to complex lineshapes under the extreme conditions of ICF experiments is computationally challenging. In this manuscript, we present results of several CSM realizations applied to the Stark shape of the krypton He-beta line and its satellites at ICF-relevant conditions (ne = 1e24 to 1e25 cm-3, Te = 3keV). We demonstrate that codes with the same underlying physics but different numerical approaches yield identical results and analyze the differences in the line profile caused by various physical effects.

physics.plasm-ph↗

arXiv2025

Tracking electron capture processes in classical molecular dynamics simulations for spectral line broadening in plasmas

Plasma spectroscopy is a fundamental tool for diagnosing laboratory and astrophysical plasmas. Accurate interpretation of spectra depends upon precise modeling and comprehension of Stark broadening and other mechanisms affecting spectral lines. In this context, computer simulations have emerged as valuable tools, offering idealized experiments with well-defined conditions. Molecular dynamics simulations, in particular, excel at replicating the particle interactions within the plasma and their impact on the state of a radiating atom or ion. However, these simulations present challenges in tracking electron capture processes, since setting an unambiguous criterion to distinguish between bound and free electrons is not trivial. In this paper we introduce a new algorithm that, within a classical framework, precisely identifies the scenario in which an electron is captured by an ion and then follows a stable orbit around it. The algorithm's applicability extends to emitters with charges Z >= 1. The procedure enables the correct identification of valid time-histories of the electric microfield perturbing the emitting ion, which will be used for subsequent line shape calculations. The ionization balance results obtained from the application of this algorithm are compared with an additional method based on the potential energy of the particles in the simulations and with atomic kinetic simulations. For both methods, we find good agreement, therefore validating the use of this approach.

physics.plasm-ph↗

arXiv2024

Classical molecular dynamics simulations of hydrogen plasmas and development of an analytical statistical model for computational validity assessment

Classical molecular dynamics simulations of hydrogen plasmas have been performed with emphasis on the analysis of equilibration process. Theoretical basis of simulation model as well as numerically relevant aspects -- such as the proper choice and definition of simulation units -- are discussed in detail, thus proving a thorough implementation of the computer simulation technique. Because of lack of experimental data, molecular dynamics simulations are often considered as "idealized computational experiments" for benchmarking of theoretical models. However, these simulations are certainly challenging and consequently a validation procedure is also demanded. In this work we develop an analytical statistical equilibrium model for computational validity assessment of plasma particle dynamics simulations. Remarkable agreement between model and molecular dynamics results including a classical treatment of ionization-recombination mechanism is obtained for a wide range of plasma coupling parameter. Furthermore, the analytical model provides guidance to securely terminate simulation runs once the equilibrium stage has been reached, which in turn gives confidence on the statistics that potentially may be extracted from time-histories of simulated physical quantities.

physics.plasm-ph↗

arXiv2022

X-ray imaging and radiation transport effects on cylindrical implosions

Magnetization of inertial confinement implosions is a promising means of improving their performance, owing to the potential reduction of energy losses within the target and mitigation of hydrodynamic instabilities. In particular, cylindrical implosions are useful for studying the influence of a magnetic field thanks to their axial symmetry. Here we present experimental results from cylindrical implosions on the OMEGA-60 laser using a 40-beam, 14.5 kJ, 1.5 ns drive and an initial seed magnetic field of B0=24 T along the axis of the targets, compared with reference results without an imposed B-field. Implosions were characterized using time-resolved X-ray imaging from two orthogonal lines of sight. We found that the data agree well with magnetohydrodynamic simulations once radiation transport within the imploding plasma is considered. We show that for a correct interpretation of the data in this type of experiments, explicit radiation transport must be taken into account.

physics.plasm-ph↗

arXiv2022

A cylindrical implosion platform for the study of highly magnetized plasmas at LMJ

Investigating the potential benefits of the use of magnetic fields in Inertial Confinement Fusion (ICF) experiments has given rise to new experimental platforms like the Magnetized Liner Inertial Fusion (MagLIF) approach at the Z-machine (Sandia National Laboratories), or its laser-driven equivalent at OMEGA (Laboratory for Laser Energetics). Implementing these platforms at MJ-scale laser facilities, such as the Laser MegaJoule (LMJ) or the National Ignition Facility (NIF), is crucial to reaching self-sustained nuclear fusion and enlarges the level of magnetization that can be achieved through a higher compression. In this paper, we present a complete design of an experimental platform for magnetized implosions using cylindrical targets at LMJ. A seed magnetic field is generated along the axis of the cylinder using laser-driven coil targets, minimizing debris and increasing diagnostic access compared with pulsed power field generators. We present a comprehensive simulation study of the initial B-field generated with these coil targets, as well as 2-dimensional extended magneto-hydrodynamics (MHD) simulations showing that a 5T initial B-field is compressed up to 25kT during the implosion. Under these circumstances, the electrons become magnetized, which severely modifies the plasma conditions at stagnation. In particular, in the hot spot the electron temperature is increased (from 1keV to 5keV) while the density is reduced (from 40gcc to 7gcc). We discuss how these changes can be diagnosed using X-ray imaging and spectroscopy, and particle diagnostics. We propose the simultaneous use of two dopants in the fuel (Ar and Kr) to act as spectroscopic tracers. We show that this introduces an effective spatial resolution in the plasma which permits an unambiguous observation of the B-field effects. Additionally, we present a plan for future experiments of this kind at LMJ.

physics.plasm-ph↗

arXiv2017

Laser-driven strong magnetostatic fields with applications to charged beam transport and magnetized high energy-density physics

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 $I_{\mathrm{las}}λ_{\mathrm{las}}^2$. 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 $60 \,\mathrm{μm}$ 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.

physics.plasm-ph↗

arXiv2014

Direct asymmetry measurement of temperature and density spatial distributions in inertial confinement fusion plasmas from pinhole space-resolved spectra

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 space-resolved 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.

physics.plasm-ph↗

arXiv2002

Locating Pollicott-Ruelle resonances in chaotic dynamical systems: A class of numerical schemes

A class of numerical methods to determine Pollicott-Ruelle resonances in chaotic dynamical systems is proposed. This is achieved by relating some existing procedures which make use of Pade approximants and interpolating exponentials to both the memory function techniques used in the theory of relaxation and the filter diagonalization method used in the harmonic inversion of time correlation functions. This relationship leads to a theoretical framework in which all these methods become equivalent and which allows for new and improved numerical schemes.

nlin.CD↗