Strong enhancement of electron-impact-ionization processes in hot dense plasma by transient spatial localization (original) (raw)
Related papers
International Journal of Molecular Sciences
Recent experiments have observed much higher electron–ion collisional ionization cross sections and rates in dense plasmas than predicted by the current standard atomic collision theory, including the plasma screening effect. We suggest that the use of (distorted) plane waves for incident and scattered electrons is not adequate to describe the dissipation that occurs during the ionization event. Random collisions with free electrons and ions in plasma cause electron matter waves to lose their phase, which results in the partial decoherence of incident and scattered electrons. Such a plasma-induced transient spatial localization of the continuum electron states significantly modifies the wave functions of continuum electrons, resulting in a strong enhancement of the electron–ion collisional ionization of ions in plasma compared to isolated ions. Here, we develop a theoretical formulation to calculate the differential and integral cross sections by incorporating the effects of plasma ...
Communications Physics, 2018
Continuum atomic processes initiated by photons and electrons occurring in a plasma are fundamental in plasma physics, playing a key role in the determination of ionization balance, equation of state, and opacity. Here we propose the notion of a transient space localization of electrons produced during the ionization of atoms immersed in a hot dense plasma, which can significantly modify the fundamental properties of ionization processes. A theoretical formalism is developed to study the wavefunctions of the continuum electrons that takes into consideration the quantum de-coherence caused by coupling with the plasma environment. The method is applied to the photoionization of Fe16+ embedded in hot dense plasmas. We find that the cross section is considerably enhanced compared with the predictions of the existing isolated-atom model, and thereby partly explains the big difference between the measured opacity of Fe plasma and the existing standard models for short wavelengths.
Plasma density effects on electron impact ionization
Physical Review E
We present new results on ionization by electron impacts in a dense plasma. We are interested in the density effect known as ionization potential depression and its role in atomic structure. Rather than using the wellknown Stewart-Pyatt or Ecker-Kröll formulas for the ionization potential depression, we consider a distribution function of the ionization energy, which involves the plasma fluctuations due to ion dynamics. This distribution is calculated within classical molecular dynamics. The removal of the noise yields a new distribution which is composed of a small set of Gaussian peaks among which one peak is selected by considering the signal-to-noise ratio. This approach provides an ionization potential depression in good agreement with experimental results obtained at the Linac Coherent Light Source facility. Our results are also compared with other calculations. In a second part, we investigate the effects of the ionization potential depression and the fluctuations on ionization by electron impacts. We propose an expression of the cross section that is based on an average over the ionization energy distribution. This cross section can be calculated analytically. The main strength of our work is to account for the fluctuations due to ion dynamics.
Strong Evidence of Plasma-like Behavior for Ion-Solid Collisions
Charge state distributions of various projectile ions passing through thin carbon foils have been studied in the energy range of 0.7-3.0 MeV/u using x-ray spectroscopy. This technique is found to be appropriate to segregate the charge state distribution in the bulk from that of the surface by measuring the charge changing phenomena right at the interaction zone i.e. at t=0. This observation has been confirmed by different theoretical approaches. Surprisingly, it is found that the charge state distribution measured in the bulk, exhibits Lorentzian profile which is an important characteristic of any plasma. The occurrence of such behaviour suggests that ion-solid collisions constitute tenuous plasma in the bulk of the solid target. Thus, this work is expected to have practical implications in various fields, in particular, plasma physics and astrophysics.
A strong ionization model in plasma physics
2009
Fluid limit for partially ionized plasmas Glow discharge interacting with an ion beam Strong ionization model Inelastic collisions Saha plasma Diffusion limit a b s t r a c t
Enhancement of electron-impact ionization induced by warm dense environments
Physical Review E
Studies have shown significant discrepancies between the recent experiment [Berg et al., Phys. Rev. Lett. 120, 055002 (2018)] and current theoretical calculations on the electron-impact ionization cross section of ions in warm dense magnesium. Here, we present a systematic study the effects of the ionic correlations and freeelectron screening on the electron-impact ionization of ions in warm dense matter. The ionic correlation and the free-electron screening effects yield additional Hermitian terms to the calculation of the ionic central-force-field potential, which significantly change the electronic structure compared with that of the isolated ion. In calculating the electron-impact ionization, we describe the impact and ionized electrons using a damped-distorted wave function, which considers the momentum relaxation of free electrons due to collisions with other free electrons and ions. We reproduce the electron-impact ionization process for Mg 7+ in the solid-density plasma and increase the ionization cross section by one order of magnitude compared with that of the isolated ion, which excellently agrees with the experimental result of Berg et al.
Simple electron-impact excitation cross-sections including plasma density effects
High Energy Density Physics, 2021
The modeling of non-local-thermodynamic-equilibrium plasmas is crucial for many aspects of high-energy-density physics. It often requires collisional-radiative models coupled with radiativehydrodynamics simulations. Therefore, there is a strong need for fast and as accurate as possible calculations of the cross-sections and rates of the different collisional and radiative processes. We present an analytical approach for the computation of the electron-impact excitation (EIE) cross-sections in the Plane Wave Born (PWB) approximation. The formalism relies on the screened hydrogenic model. The EIE cross-section is expressed in terms of integrals, involving spherical Bessel functions, which can be calculated analytically. In order to remedy the fact that the PWB approximation is not correct at low energy (near threshold), we consider different correcting factors (Elwert-Sommerfeld, Cowan-Robb, Kilcrease-Brookes). We also investigate the role of plasma density effects such as Coulomb screening and quantum degeneracy on the EIE rate. This requires to integrate the collision strength multiplied by the Fermi-Dirac Distribution and the Pauli blocking factor. We show that, using an analytical fit often used in collisional-radiative models, the EIE rate can be calculated accurately without any numerical integration, and compare our expression with a correction factor presented in a recent work.
Ionization by electron impacts and ionization potential depression
Journal of Physics B: Atomic, Molecular and Optical Physics
We calculate the cross-section of ionization by free-electron impacts in high or moderate density plasmas. We show that the so-called ionization potential depression (IPD) strongly affects the magnitude of the cross-section in the high-density domain. We use the well-known IPD formulas of Stewart–Pyatt and Ecker–Kröll. A more recent approach based on classical molecular dynamics simulation is also investigated. The latter provides an alternative way to calculate IPD values. At near-solid densities the effects of the free-electron degeneracy should be investigated. The rates are then calculated within the Fermi–Dirac statistics. We first use the semi-empirical formula of Lotz for ionization cross-section. The results may differ significantly from measured cross-sections or calculations with reliable atomic codes. Then, in a second step, we propose a new formula that combines the Lotz formula and a polynomial expansion in terms of the ratio of the energy of the incident electron and t...
Characterization of electron states in dense plasmas and its use in atomic kinetics modeling
Journal of Quantitative Spectroscopy and Radiative Transfer, 2003
We describe a self-consistent statistical approach to account for plasma density e ects in collisional-radiative kinetics. The approach is based on the characterization of three distinct types of electron states, namely, bound, collectivized, and free, and on the formalism of the e ective statistical weights (ESW) of the bound states. The present approach accounts for individual and collective e ects of the surrounding electrons and ions on atomic (ionic) electron states. High-accuracy expressions for the ESWs of bound states have been derived. The notions of ionization stage population, free electron density, and rate coe cient are redeÿned in accordance with the present characterization scheme. The modiÿed expressions for the probabilities of electron-impact induced transitions as well as spontaneous and induced radiative transitions are then obtained. The in uence of collectivized states on a dense plasma ionization composition is demonstrated to be strong. Examples of calculated ESWs and populations of ionic quantum states for steady state and transient plasmas are given. ?
Electron-ion collisions in intensely illuminated plasmas
Physics of Plasmas, 1997
In the presence of a high-frequency intense uniform electric field, the collisions of electrons with ions can be made more frequent or less frequent, depending on the polarization of the hf field, the direction and magnitude of particle velocity, and the ratio of the plasma Debye length to the size of the electron oscillation in the hf field. The stimulated bremsstrahlung emission is calculated for both circularly and linearly polarized fields.