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 screening and transient spatial localization. The approach is then used to investigate the electron-impact ionization of ions in solid-density magnesium plasma, yielding results that are consistent with experiments. In dense plasma, the correlation of continuum electron energies is modified, and the integral cross sections and rates increase considerably. For the ionization of Mg9+e+1s22s2S→1s21S+2e, the ionization cross sections increase several-fold, and the rates increase by one order of magnitude. Our findings provide new insight into collisional ionization and three-body recombination and may aid investigations of the transport properties and nonequilibrium evolution of dense plasma.
Abstract
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 Fe
16+
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.
The electron impact excitation process is important to investigate the ionization balance, the dynamical evolution of non-equilibrium plasmas, and the physical properties of plasmas. In dense ...plasmas, previous theories show that the electron impact excitation cross section is generally decreased compared with that in the case of isolated atoms or ions which applies to a dilute system. Investigations show that such decrease is caused by plasma screening. In this study, we propose a mechanism which increases the electron impact excitation cross section in dense plasmas. Due to the random collisions of the scattering electrons with other free electrons and ions in the plasma, the wavefunction of the scattering electrons can no longer be described by employing a plane wave distorted only by the scattering potential. The momentum of the scattering electrons is no longer a constant but changes with their distribution in a certain range, resulting in a phenomenon of transient spatial localization. The momentum broadening of the scattering electron is proposed to quantitatively describe such a localization. A theoretical formalism is developed to consider the transient spatial localization effect in the atomic collision theory and is applied to investigate the electron impact excitation processes of 1s21S0→1s2p1P1o and 1s21S0→1s3p1P1o of Si12+ embedded in dense plasmas. The results show that the calculated cross sections and rate coefficients are decreased by plasma screening, whereas their quantities are significantly increased in the dense plasmas by the transient spatial localization compared with those obtained by the isolated-atom model. These research findings provide new insight into the microscopic atomic process of the electron impact excitation and macroscopic physical properties such as the electron conductive opacity and the thermal conductivity.
•Mechanism of localization which enhances excitation processes by electron is proposed.•Plasma screening and localization effects on excitation of Si XIII in dense plasma are studied.•Increase of excitation cross sections and rates in dense plasma by localization are demonstrated.
Both coherent pumping and energy relaxation play important roles in understanding physical processes of ultra-intense coherent light-matter interactions. Here, using a large-scale quantum master ...equation approach, we describe dynamical processes of practical open quantum systems driven by both coherent and stochastic interactions. As examples, two typical cases of light-matter interactions are studied. First, we investigate coherent dynamics of inner-shell electrons of a neon gas irradiated by a high-intensity X-ray laser along with vast number of decaying channels. In these single-photon dominated processes, we find that, due to coherence-induced Rabi oscillations and power broadening effects, the photon absorptions of a neon gas can be suppressed resulting in differences in ionization processes and final ion-stage distributions. Second, we take helium as an example of multiphoton and multichannel interference dominated electron dynamics, by investigating the transient absorption of an isolated attosecond pulse in the presence of a femtosecond infrared laser pulse.
A collisional-radiative model based on the approach of detailed relativistic configurations is developed, where the complete set of atomic data including photo-excitation, photoionization, electron ...impact excitation, electron impact ionization and autoionization is calculated, and the data of the inverse processes are obtained by detailed balance. The population distribution is obtained by solving the rate equation under the steady-state condition. The present model is applied to calculate the charge state distribution and M band emission spectra of gold plasmas in non-local thermodynamic equilibrium under a variety of plasma conditions. Comparisons between the present work and experimental results were made and good agreement is found. For the strong transition lines, the intensities predicted by the present model agree with those of experimental spectra within 50%. The present work is useful in analyzing and interpreting experiments as well as in diagnosing the electron temperature in experiments.
The L-shell radiative opacity of lowly charged Cu plasmas is investigated using a detailed level accounting method. The transmission spectra are compared with a recent experiment at ∼16 eV and 0.005 ...g/cm3, and good agreement is observed. For a systematic study, radiative opacities caused by 2p → 3d transitions at temperatures of 10–35 eV and densities of 0.001–0.1 g/cm3 are calculated. The dominant ionization stages are lowly charged ones with an open M-shell at such plasma conditions. The result shows that charge state distribution and radiative opacities are very sensitive to temperature. The two strongest absorption peaks of 2p3/2 → 3d5/2 and 2p1/2 → 3d3/2 caused by relativistic orbital splitting are well separated at temperatures lower than 25 eV, whereas they are mixed together to form a broadband structure at higher temperatures.
Single and double Auger decay processes of Ar
+
2
p
−1
hole levels belonging to the configurations of 2
p
5
3
s
2
3
p
5
and 2
p
5
3
s
3
p
6
are investigated in the framework of perturbation theory ...implemented by the distorted wave approximation. The single Auger decay channels and rates are determined and the predicted total rates can differ by more than an order of magnitude for the levels of 2
p
5
3
s
2
3
p
5
, yet they are very close for levels belonging to 2
p
5
3
s
3
p
6
. By combining the double photoionization cross sections of the neutral species, our theoretical Auger spectra of the single Auger decay process nicely interpreted a recent experiment S.M. Huttula et al., Phys. Rev. Lett.
110
, 113002 (2013). A configuration averaged branching ratio of 6.5% and 7.3% are predicted for the direct double Auger decay to the total probability for 2
p
5
3
s
2
3
p
5
and 2
p
5
3
s
3
p
6
, respectively, which is smaller than that of Ar 2
p
−1
hole states.
ABSTRACT
Electron impact excitation and ionization with atoms and ions within a dense plasma are fundamental microscopic processes that determine the ionization balance, physical properties (such as ...electron conductive opacity and thermal conductivity) and plasma formation and dynamics. While collision cross-sections and rates are well studied in dilute systems, similar investigations are scarce for dense plasmas under stellar interior conditions using an appropriate plasma-screening potential. Here we investigate the plasma-screening effect on the electron impact excitation and ionization cross-sections, effective collision strengths, and rate coefficients within plasmas under stellar interior conditions in a mass density range of 1–15.748 g cm−3 and a temperature range of 200–1000 eV. These investigations were carried out using our recently developed plasma-screening model, taking Fe16+ as an example. The results show that the cross-sections of the electron impact excitation are generally decreased, whereas they are always significantly increased for the collision ionization due to the plasma screening. In a plasma at a temperature of 200 eV and density of 15.748 g cm−3, the plasma screening causes a decrease in the excitation cross-section of 36 per cent for the dipole-allowed transition $2\mathrm{ s}^22\mathrm{ p}^6~^1\mathrm{ S}_0 \rightarrow 2\mathrm{ s}^22\mathrm{ p}^53\mathrm{ d}~^1\mathrm{ P}^o_1$ and of 50 per cent for the dipole-forbidden transition $2\mathrm{ s}^22\mathrm{ p}^6~^1\mathrm{ S}_0 \rightarrow 2\mathrm{ s}^22\mathrm{ p}^53\mathrm{ d}~^3\mathrm{ D}^o_1$. However, the collision ionization cross-section of a 2p electron from the ground level of Fe16+ is increased by 500 per cent and 100 per cent under an incident electron energy of 1500 and 10 000 eV, respectively. This results in the rate coefficient increasing by a factor of 18.5 at a temperature of 200 eV and density of 15.748 g cm−3.
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