The Experts below are selected from a list of 285 Experts worldwide ranked by ideXlab platform
Martin J Laming - One of the best experts on this subject based on the ideXlab platform.
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non wkb models of the first Ionization Potential effect the role of slow mode waves
The Astrophysical Journal, 2012Co-Authors: Martin J LamingAbstract:A model for element abundance fractionation between the solar chromosphere and corona is further developed. The ponderomotive force due to Alfven waves propagating through or reflecting from the chromosphere in solar conditions generally accelerates chromospheric ions, but not neutrals, into the corona. This gives rise to what has become known as the first Ionization Potential effect. We incorporate new physical processes into the model. The chromospheric Ionization balance is improved and the effect of different approximations is discussed. We also treat the parametric generation of slow mode waves by the parallel propagating Alfven waves. This is also an effect of the ponderomotive force, arising from the periodic variation of the magnetic pressure driving an acoustic mode, which adds to the background longitudinal pressure. This can have subtle effects on the fractionation, rendering it quasi-mass independent in the lower regions of the chromosphere. We also briefly discuss the change in the fractionation with Alfven wave frequency, relative to the frequency of the overlying coronal loop resonance.
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non wkb models of the first Ionization Potential effect implications for solar coronal heating and the coronal helium and neon abundances
The Astrophysical Journal, 2009Co-Authors: Martin J LamingAbstract:We revisit in more detail a model for element abundance fractionation in the solar chromosphere that gives rise to the “first Ionization Potential (FIP) effect” in the solar corona and wind. Elements with first Ionization Potential below about 10 eV, i.e., those that are predominantly ionized in the chromosphere, are enriched in the corona by a factor of 3–4. We model the propagation of Alfv´ en waves through the chromosphere using a non-WKB treatment, and evaluate the ponderomotive force associated with these waves. Under solar conditions, this is generally pointed upward in the chromosphere, and enhances the abundance of chromospheric ions in the corona. Our new approach captures the essentials of the solar coronal abundance anomalies, including the depletion of He relative to H, and also the putative depletion of Ne, recently discussed in the literature. We also argue that the FIP effect provides the strongest evidence to date for energy fluxes of Alfv´ en waves sufficient to heat the corona. However, it appears that these waves must also be generated in the corona, in order to preserve the rather regular fractionation pattern without strong variations from loop to loop observed in the solar corona and slow-speed solar wind.
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a unified picture of the first Ionization Potential and inverse first Ionization Potential effects
The Astrophysical Journal, 2004Co-Authors: Martin J LamingAbstract:We discuss models for coronal abundance anomalies observed in the coronae of the sun and other late-type stars following a scenario first introduced by Schwadron, Fisk, & Zurbuchen of the interaction of waves at loop footpoints with the partially neutral gas. Instead of considering wave heating of ions in this location, we explore the effects on the upper chromospheric plasma of the wave pondermotive forces. These can arise when upward-propagating waves from the chromosphere transmit or reflect upon reaching the chromosphere-corona boundary, and are in large part determined by the properties of the coronal loop above. Our scenario has the advantage that for realistic wave energy densities both positive and negative changes in the abundance of ionized species compared to neutrals can result, allowing both first Ionization Potential (FIP) and inverse FIP effects to come out of the model. We discuss how variations in model parameters can account for essentially all of the abundance anomalies observed in solar spectra. Expected variations with stellar spectral type are also qualitatively consistent with observations of the FIP effect in stellar coronae.
Sangkil Son - One of the best experts on this subject based on the ideXlab platform.
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transient Ionization Potential depression in nonthermal dense plasmas at high x ray intensity
Physical Review E, 2021Co-Authors: Rui Jin, Robin Santra, Malik Muhammad Abdullah, Zoltan Jurek, Sangkil SonAbstract:The advent of x-ray free-electron lasers (XFELs), which provide intense ultrashort x-ray pulses, has brought a new way of creating and analyzing hot and warm dense plasmas in the laboratory. Because of the ultrashort pulse duration, the XFEL-produced plasma will be out of equilibrium at the beginning, and even the electronic subsystem may not reach thermal equilibrium while interacting with a femtosecond timescale pulse. In the dense plasma, the Ionization Potential depression (IPD) induced by the plasma environment plays a crucial role for understanding and modeling microscopic dynamical processes. However, all theoretical approaches for IPD have been based on local thermal equilibrium (LTE), and it has been controversial to use LTE IPD models for the nonthermal situation. In this work, we propose a non-LTE (NLTE) approach to calculate the IPD effect by combining a quantum-mechanical electronic-structure calculation and a classical molecular dynamics simulation. This hybrid approach enables us to investigate the time evolution of Ionization Potentials and IPDs during and after the interaction with XFEL pulses, without the limitation of the LTE assumption. In our NLTE approach, the transient IPD values are presented as distributions evolving with time, which cannot be captured by conventional LTE-based models. The time-integrated Ionization Potential values are in good agreement with benchmark experimental data on solid-density aluminum plasma and other theoretical predictions based on LTE. The present work is promising to provide critical insights into nonequilibrium dynamics of dense plasma formation and thermalization induced by XFEL pulses.
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quantum mechanical calculation of Ionization Potential lowering in dense plasmas
Physical Review X, 2014Co-Authors: Sangkil Son, R Thiele, Z Jurek, B Ziaja, Robin SantraAbstract:Dense plasmas, found in stellar interiors, are composed of atoms with decreased Ionization Potentials compared with isolated atoms. Researchers have developed a new model to explain the Ionization Potential data, successfully reproducing the results that previous models could not.
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quantum mechanical calculation of Ionization Potential lowering in dense plasmas
arXiv: Plasma Physics, 2014Co-Authors: Sangkil Son, R Thiele, Z Jurek, B Ziaja, Robin SantraAbstract:The charged environment within a dense plasma leads to the phenomenon of Ionization Potential depression (IPD) for ions embedded in the plasma. Accurate predictions of the IPD effect are of crucial importance for modeling atomic processes occurring within dense plasmas. Several theoretical models have been developed to describe the IPD effect, with frequently discrepant predictions. Only recently, first experiments on IPD in Al plasma have been performed with an x-ray free-electron laser (XFEL), where their results were found to be in disagreement with the widely-used IPD model by Stewart and Pyatt. Another experiment on Al, at the Orion laser, showed disagreement with the model by Ecker and Kr\"oll. This controversy shows a strong need for a rigorous and consistent theoretical approach to calculate the IPD effect. Here we propose such an approach: a two-step Hartree-Fock-Slater model. With this parameter-free model we can accurately and efficiently describe the experimental Al data and validate the accuracy of standard IPD models. Our model can be a useful tool for calculating atomic properties within dense plasmas with wide-ranging applications to studies on warm dense matter, shock experiments, planetary science, inertial confinement fusion and studies of non-equilibrium plasmas created with XFELs.
Bernard Talin - One of the best experts on this subject based on the ideXlab platform.
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Ionization Potential depression for non equilibrated aluminum plasmas
Journal of Physics B: Atomic Molecular and Optical Physics, 2015Co-Authors: Annette Calisti, Sandrine Ferri, Bernard TalinAbstract:A classical molecular dynamics simulation model, designed to simulate neutral plasmas with various charge states of a given atom together with electrons, is used to investigate the Ionization Potential depression (IPD) in dense plasmas. The IPD is discussed for aluminum plasma at and out of equilibrium. The simulation results are compared with those of earlier theoretical models and with experimental data obtained in the framework of x-ray free-electron laser experiments. The model proposed in this work appears as an important tool to provide data for further discussion on IPD models.
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Ionization Potential Depression in Hot Dense Plasmas Through a Pure Classical Model.
Contributions to Plasma Physics, 2015Co-Authors: Annette Calisti, Sandrine Ferri, Bernard TalinAbstract:The Ionization Potential of an ion embedded in a plasma, lowered due to the whole of the charged particles (ions and electrons) interacting with this ion, is the so-called plasma effect. A numerical plasma model based on classical molecular dynamics has been developed recently. It is capable to describe a neutral plasma at equilibrium involving ions of various charge states of the same atom together with electrons. This code is used here to investigate the Ionization Potential depression (IPD). The study of the IPD is illustrated and discussed for aluminum plasmas at mid and solid density and electron temperatures varying from 50eV to 190eV. The method relies on a sampling of the total Potential energy of the electron located at an ion being ionized. The Potential energy of such electron results from all of the interacting charged particles interacting with it.
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Ionization Potential depression in hot dense plasmas through a pure classical model
2014Co-Authors: Annette Calisti, Sandrine Ferri, Bernard TalinAbstract:The Ionization Potential of an ion embedded in a plasma is lowered due to the whole charged particles (ions and electrons) interacting with that ion. It is the so called plasma effect. The numerical plasma model developed years ago, based on classical molecular dynamics, capable to describe a neutral plasma at equilibrium involving ions of various charge states of the same atom together with electrons, is used to investigate the Ionization Potential depression (IPD). The study of the IPD is illustrated and discussed for aluminum plasmas at mid and solid density and electron temperatures varying from 50eV to 190eV. The method relies on a sampling of the total Potential energy of the electron located at an ion being ionized. The Potential energy of such electron results from the whole interacting charged particles interacting with it.
Robin Santra - One of the best experts on this subject based on the ideXlab platform.
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transient Ionization Potential depression in nonthermal dense plasmas at high x ray intensity
Physical Review E, 2021Co-Authors: Rui Jin, Robin Santra, Malik Muhammad Abdullah, Zoltan Jurek, Sangkil SonAbstract:The advent of x-ray free-electron lasers (XFELs), which provide intense ultrashort x-ray pulses, has brought a new way of creating and analyzing hot and warm dense plasmas in the laboratory. Because of the ultrashort pulse duration, the XFEL-produced plasma will be out of equilibrium at the beginning, and even the electronic subsystem may not reach thermal equilibrium while interacting with a femtosecond timescale pulse. In the dense plasma, the Ionization Potential depression (IPD) induced by the plasma environment plays a crucial role for understanding and modeling microscopic dynamical processes. However, all theoretical approaches for IPD have been based on local thermal equilibrium (LTE), and it has been controversial to use LTE IPD models for the nonthermal situation. In this work, we propose a non-LTE (NLTE) approach to calculate the IPD effect by combining a quantum-mechanical electronic-structure calculation and a classical molecular dynamics simulation. This hybrid approach enables us to investigate the time evolution of Ionization Potentials and IPDs during and after the interaction with XFEL pulses, without the limitation of the LTE assumption. In our NLTE approach, the transient IPD values are presented as distributions evolving with time, which cannot be captured by conventional LTE-based models. The time-integrated Ionization Potential values are in good agreement with benchmark experimental data on solid-density aluminum plasma and other theoretical predictions based on LTE. The present work is promising to provide critical insights into nonequilibrium dynamics of dense plasma formation and thermalization induced by XFEL pulses.
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quantum mechanical calculation of Ionization Potential lowering in dense plasmas
Physical Review X, 2014Co-Authors: Sangkil Son, R Thiele, Z Jurek, B Ziaja, Robin SantraAbstract:Dense plasmas, found in stellar interiors, are composed of atoms with decreased Ionization Potentials compared with isolated atoms. Researchers have developed a new model to explain the Ionization Potential data, successfully reproducing the results that previous models could not.
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quantum mechanical calculation of Ionization Potential lowering in dense plasmas
arXiv: Plasma Physics, 2014Co-Authors: Sangkil Son, R Thiele, Z Jurek, B Ziaja, Robin SantraAbstract:The charged environment within a dense plasma leads to the phenomenon of Ionization Potential depression (IPD) for ions embedded in the plasma. Accurate predictions of the IPD effect are of crucial importance for modeling atomic processes occurring within dense plasmas. Several theoretical models have been developed to describe the IPD effect, with frequently discrepant predictions. Only recently, first experiments on IPD in Al plasma have been performed with an x-ray free-electron laser (XFEL), where their results were found to be in disagreement with the widely-used IPD model by Stewart and Pyatt. Another experiment on Al, at the Orion laser, showed disagreement with the model by Ecker and Kr\"oll. This controversy shows a strong need for a rigorous and consistent theoretical approach to calculate the IPD effect. Here we propose such an approach: a two-step Hartree-Fock-Slater model. With this parameter-free model we can accurately and efficiently describe the experimental Al data and validate the accuracy of standard IPD models. Our model can be a useful tool for calculating atomic properties within dense plasmas with wide-ranging applications to studies on warm dense matter, shock experiments, planetary science, inertial confinement fusion and studies of non-equilibrium plasmas created with XFELs.
H Reinholz - One of the best experts on this subject based on the ideXlab platform.
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Ionization Potential depression and pauli blocking in degenerate plasmas at extreme densities
Physical Review E, 2019Co-Authors: Chengliang Lin, G Ropke, D Blaschke, T Doppner, W D Kraeft, R Redmer, H ReinholzAbstract:New facilities explore warm dense matter (WDM) at conditions with extreme densities (exceeding ten times condensed matter densities) so that electrons are degenerate even at temperatures of $10--100$ eV. Whereas in the nondegenerate region correlation effects such as Debye screening are relevant for the Ionization Potential depression (IPD), new effects have to be considered in degenerate plasmas. In addition to the Fock shift of the self-energies, the bound-state Pauli blocking becomes important with increasing density. Standard approaches to IPD such as Stewart-Pyatt and widely used opacity tables (e.g., OPAL) do not contain Pauli blocking effects for bound states. The consideration of degeneracy effects leads to a reduction of the Ionization Potential and to a higher degree of Ionization. As an example, we present calculations for the Ionization degree of carbon plasmas at $T$ = 100 eV and extreme densities up to 40 $\mathrm{g}/{\mathrm{cm}}^{3}$, which are relevant to experiments that are currently scheduled at the National Ignition Facility.
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Ionization Potential depression and dynamical structure factor in dense plasmas
Physical Review E, 2017Co-Authors: Chengliang Lin, G Ropke, Wolf Dietrich Kraeft, H ReinholzAbstract:The properties of a bound electron system immersed in a plasma environment are strongly modified by the surrounding plasma. The modification of an essential quantity, the Ionization energy, is described by the electronic and ionic self-energies, including dynamical screening within the framework of the quantum statistical theory. Introducing the ionic dynamical structure factor as the indicator for the ionic microfield, we demonstrate that ionic correlations and fluctuations play a critical role in determining the Ionization Potential depression. This is, in particular, true for mixtures of different ions with large mass and charge asymmetry. The Ionization Potential depression is calculated for dense aluminum plasmas as well as for a CH plasma and compared to the experimental data and more phenomenological approaches used so far.