Influence of Electron-Impact Multiple Ionization on Equilibrium and Dynamic Charge State Distributions: A Case Study Using Iron

Hahn, Michael; Savin, D. W.

doi:10.1088/0004-637x/800/1/68

Cited by 18 publications

(16 citation statements)

References 58 publications

(118 reference statements)

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“…Electron impact multiple ionization (EIMI) is a process in which a single electron-ion collision causes two or more bound electrons to be removed from the ion. Hahn & Savin (2015) tabulated cross section data for EIMI of Fe, which can be used in CSD calculations.…”

Section: Influence Of Electron Impact Multiple Ionization On the Csdmentioning

confidence: 99%

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A Simple Method for Modeling Collision Processes in Plasmas With a Kappa Energy Distribution

Hahn

Savin

2015

ApJ

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We demonstrate that a nonthermal distribution of particles described by a kappa distribution can be accurately approximated by a weighted sum of Maxwell-Boltzmann distributions. We apply this method to modeling collision processes in kappa-distribution plasmas, with a particular focus on atomic processes important for solar physics. The relevant collision process rate coefficients are generated by summing appropriately weighted Maxwellian rate coefficients.This method reproduces the rate coefficients for a kappa distribution to an estimated accuracy of better than 3%. This is equal to or better than the accuracy of rate coefficients generated using "reverse engineering" methods, which attempt to extract the needed cross sections from the published Maxwellian rate coefficient data and then reconvolve the extracted cross sections with the desired kappa distribution. Our approach of summing Maxwellian rate coefficients is easy to implement using existing spectral analysis software. Moreover, the weights in the sum of the Maxwell-Boltzmann distribution rate coefficients can be found for any value of the parameter κ, thereby enabling one to model plasmas with a timevarying κ. Tabulated Maxwellian fitting parameters are given for specific values of κ from 1.7 to 100. We also provide polynomial fits to these parameters over this entire range. Several applications of our technique are presented, including the plasma equilibrium charge state distribution (CSD), predicting line ratios, modeling the influence of electron impact multiple ionization on the equilibrium CSD of kappa-distribution plasmas, and calculating the time-varying CSD of plasmas during a solar flare.

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Section: Influence Of Electron Impact Multiple Ionization On the Csdmentioning

confidence: 99%

“…EIMI significantly modifies the CSD at these temperatures, because the kappa distribution contains enough high energy electrons to ionize from the L shell. The resulting L-shell hole leads to autoionization of an M-shell electron, ending in a net double ionization (Hahn & Savin 2015).…”

Section: Influence Of Electron Impact Multiple Ionization On the Csdmentioning

confidence: 99%

A Simple Method for Modeling Collision Processes in Plasmas With a Kappa Energy Distribution

Hahn

Savin

2015

ApJ

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“…The single ionization (SI) is the strongest process among the ionization processes. On the other hand, multiple ionization can be important in the dynamic environments where high-energy electrons can suddenly appear on the scene (Müller 1986;Hahn & Savin 2015).…”

Section: Introductionmentioning

confidence: 99%

Electron-impact double ionization of the carbon atom

Jonauskas

2018

A&A

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Electron-impact single- and double-ionization cross sections and Maxwellian rate coefficients are presented for the carbon atom. Scaling factors are introduced for the electron-impact excitation and ionization cross sections obtained in the distorted wave (DW) approximation. It is shown that the scaled DW cross sections provide good agreement with measurements for the single ionization of the C atom and C1+ ion. The direct double-ionization (DDI) process is studied using a multi-step approach. Ionization–ionization, excitation–ionization–ionization, and ionization–excitation–ionization branches are analyzed. It is demonstrated that the three-step processes contribute ≼40% of the total DDI cross sections for the case where one of the electrons takes all of the excess energy after the first ionization process.

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“…This is especially true for line emission: the collisional excitation cross section has many resonances in the cross sections, and accurately modeling a new electron distribution would require reintegrating the original energy dependent cross sections with the new distribution; in most cases these energy resolved files no longer exist and their regeneration would be impractical. Therefore, we adopt the decomposition approach of Hahn & Savin (2015) to create spectra using AtomDB, by adding Maxwellian spectra.…”

Section: Methodsmentioning

confidence: 99%

“…If we can decompose an electron distribution into a linear combination of Maxwellian components, the rate coefficient for any process is simply the sum of the rates for these individual Maxwellian components. This Maxwellian decomposition method has regularly been used to approximate κ-distributions with a sum of Maxwellians (Ko et al 1996, Kaastra et al 2009, Hahn & Savin 2015. Hahn & Savin (2015) approximated the κ-distribution for a wide range of values using a formula…”

Section: Processesmentioning

confidence: 99%

X-Ray Spectra from Plasmas with High-energy Electrons: κ-distributions and e⁻–e⁻ Bremsstrahlung

Cui

Foster

Yuasa

2019

ApJ

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Shocks, turbulence and winds all influence the electron velocity distribution in hot plasmas, exciting lower-energy electrons and generating a high-energy (typically power-law) tail. This effect, typically described as a κ distribution can affect both the line and continuum X-ray spectrum emitted by the plasma. Hahn & Savin (2015) proposed a "Maxwellian decomposition" to generate the rate coefficients of κ distributions. Using their method and the AtomDB atomic database, we have developed a general model to calculate the emission from a plasma with a κ distribution. We compare our κ results for the charge state distribution and spectra of oxygen to those from KAPPA package with the ion data available within the CHIANTI atomic database. Sufficiently energetic electrons, created either in a κ distribution or merely a very hot Maxwellian plasma, can also emit via electron-electron (ee) bremsstrahlung, a process not previously included in AtomDB. We have added this process to AtomDB and apply it to calculate the temperature gradients, as well as the total spectra from the post-shock regions of an accreting magnetic cataclysmic variable (CV). We find the contribution of e-e bremsstrahlung to the total spectra exceeds 10% at KT∼ 100 keV, with the total emissivity in the post-shock accretion stream differing by more than 10% at energies above 60 keV.

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Influence of Electron-Impact Multiple Ionization on Equilibrium and Dynamic Charge State Distributions: A Case Study Using Iron

Cited by 18 publications

References 58 publications

A Simple Method for Modeling Collision Processes in Plasmas With a Kappa Energy Distribution

A Simple Method for Modeling Collision Processes in Plasmas With a Kappa Energy Distribution

Electron-impact double ionization of the carbon atom

X-Ray Spectra from Plasmas with High-energy Electrons: κ-distributions and e⁻–e⁻ Bremsstrahlung

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Influence of Electron-Impact Multiple Ionization on Equilibrium and Dynamic Charge State Distributions: A Case Study Using Iron

Cited by 18 publications

References 58 publications

A Simple Method for Modeling Collision Processes in Plasmas With a Kappa Energy Distribution

A Simple Method for Modeling Collision Processes in Plasmas With a Kappa Energy Distribution

Electron-impact double ionization of the carbon atom

X-Ray Spectra from Plasmas with High-energy Electrons: κ-distributions and e−–e− Bremsstrahlung

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Product

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X-Ray Spectra from Plasmas with High-energy Electrons: κ-distributions and e⁻–e⁻ Bremsstrahlung