Plasma–liquid interactions represent a growing interdisciplinary area of research involving plasma science, fluid dynamics, heat and mass transfer, photolysis, multiphase chemistry and aerosol science. This review provides an assessment of the state-of-the-art of this multidisciplinary area and identifies the key research challenges. The developments in diagnostics, modeling and further extensions of cross section and reaction rate databases that are necessary to address these challenges are discussed. The review focusses on non-equilibrium plasmas.

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Plasma-liquid interactions: A review and roadmap

The THEMIS plasma instrument is designed to measure the ion and electron distribution functions over the energy range from a few eV up to 30 keV for electrons and 25 keV for ions. The instrument consists of a pair of “top hat” electrostatic analyzers with common 180°×6° fields-of-view that sweep out 4π steradians each 3 s spin period. Particles are detected by microchannel plate detectors and binned into six distributions whose energy, angle, and time resolution depend upon instrument mode. On-board moments are calculated, and processing includes corrections for spacecraft potential. This paper focuses on the ground and in-flight calibrations of the 10 sensors on five spacecraft. Cross-calibrations were facilitated by having all the plasma measurements available with the same resolution and format, along with spacecraft potential and magnetic field measurements in the same data set. Lessons learned from this effort should be useful for future multi-satellite missions.

The THEMIS ESA Plasma Instrument and In-flight Calibration

It is shown that under the usual conditions of zero‐electron‐kinetic‐energy, pulsed field ionization (ZEKE–PFI) spectroscopy the lifetimes of very high‐lying Rydberg states are increased by at least approximately the factor n (in addition to the expected factor of n3), the principal quantum number, due to strong l mixing by the Stark effect. Additional factors may increase lifetimes by still another factor of approximately n. Pulsed field ionization under typical conditions is shown as likely to be predominantly diabatic and the effect on resolution is assessed. Factors affecting rotational line intensities are also discussed.

Factors affecting lifetimes and resolution of Rydberg states observed in zero-electron-kinetic-energy spectroscopy

Purpose: TheGEANT4 general-purpose Monte Carlo simulation toolkit is able to simulate physical interaction processes of electrons, hydrogen and helium atoms with charge states ( H 0 , H + ) and ( He 0 , He + , He 2 + ), respectively, in liquid water, the main component of biological systems, down to the electron volt regime and the submicrometer scale, providing GEANT4 users with the so-called “GEANT4-DNA” physics models suitable for microdosimetry simulation applications. The corresponding software has been recently re-engineered in order to provide GEANT4 users with a coherent and unique approach to the simulation of electromagnetic interactions within the GEANT4 toolkit framework (since GEANT4 version 9.3 beta). This work presents a quantitative comparison of these physics models with a collection of experimental data in water collected from the literature. Methods: An evaluation of the closeness between the total and differential cross section models available in theGEANT4 toolkit for microdosimetry and experimental reference data is performed using a dedicated statistical toolkit that includes the Kolmogorov–Smirnov statistical test. The authors used experimental data acquired in water vapor as direct measurements in the liquid phase are not yet available in the literature. Comparisons with several recommendations are also presented. Results: The authors have assessed the compatibility of experimental data withGEANT4microdosimetry models by means of quantitative methods. The results show that microdosimetric measurements in liquid water are necessary to assess quantitatively the validity of the software implementation for the liquid water phase. Nevertheless, a comparison with existing experimental data in water vapor provides a qualitative appreciation of the plausibility of the simulation models. The existing reference data themselves should undergo a critical interpretation and selection, as some of the series exhibit significant deviations from each other. Conclusions: TheGEANT4-DNA physics models available in the GEANT4 toolkit have been compared in this article to available experimental data in the water vapor phase as well as to several published recommendations on the mass stopping power. These models represent a first step in the extension of the GEANT4 Monte Carlo toolkit to the simulation of biological effects of ionizing radiation.

Comparison of GEANT4 very low energy cross section models with experimental data in water.

Nonthermal secondary electrons with initial kinetic energies below 100 eV are an abundant transient species created in irradiated cells and thermalize within picoseconds through successive multiple energy loss events. Here we show that below 15 eV such low-energy electrons induce single (SSB) and double (DSB) strand breaks in plasmid DNA exclusively via formation and decay of molecular resonances involving DNA components (base, sugar, hydration water, etc.). Furthermore, the strand break quantum yields (per incident electron) due to resonances occur with intensities similar to those that appear between 25 and 100 eV electron energy, where nonresonant mechanisms related to excitation/ionizations/dissociations are shown to dominate the yields, although with some contribution from multiple scattering electron energy loss events. We also present the first measurements of the electron energy dependence of multiple double strand breaks (MDSB) induced in DNA by electrons with energies below 100 eV. Unlike the SSB and DSB yields, which remain relatively constant above 25 eV, the MDSB yields show a strong monotonic increase above 30 eV, however with intensities at least 1 order of magnitude smaller than the combined SSB and DSB yields. The observation of MDSB above 30 eV is attributed to strand break clusters (nano-tracks) involving multiple successive interactions of one single electron at sites that are distant in primary sequence along the DNA double strand, but are in close contact; such regions exist in supercoiled DNA (as well as cellular DNA) where the double helix crosses itself or is in close proximity to another part of the same DNA molecule.

Single, double, and multiple double strand breaks induced in DNA by 3-100 eV electrons.

Energetic neutral atom (ENA) detectors have been successfully flown on missions such as the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) and are now an important tool for probing the geospace environment. Interpretation of ENA data, however, requires knowledge of a number of key charge transfer cross sections. Here we present a critical review of the published experimental measurements and recommend a set of parameterized cross sections. The processes considered are charge transfer of H + and O + with H, O, N 2 , and O 2 for collision energies from 10 eV to 100 keV. The limitations of the measurement techniques and the probable reliability of the recommended cross sections are addressed.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2005JA011298

Charge transfer cross sections for energetic neutral atom data analysis

Accurate values of the electron-impact ionization cross sections for the rare gases are needed in a variety of contexts. However, despite numerous investigations over many decades, uncertainty as to the correct values has persisted. The pioneering total-cross-section measurements of Rapp and Englander-Golden are generally regarded as the most reliable but no comprehensive study has independently verified their correctness. In this paper, measurements of electron-impact ionization cross sections of helium, neon, argon, krypton, and xenon are reported for energies ranging from the first ionization threshold to 1000 eV. These data confirm the essential correctness of Rapp and Englander-Golden's total measurements and at the same time provide a complete set of consistent absolute partial cross sections.

Determination of the absolute partial and total cross sections for electron-impact ionization of the rare gases

Absolute partial cross sections from threshold to 1000 eV are reported for electron-impact ionization of ${\mathrm{H}}_{2}$, ${\mathrm{N}}_{2}$, and ${\mathrm{O}}_{2}$. Data are presented for the production of ${\mathrm{H}}_{2}^{\mathrm{}+}$ and ${\mathrm{H}}^{+}$ from ${\mathrm{H}}_{2}$; the production of ${\mathrm{N}}_{2}^{\mathrm{}+}$, ${\mathrm{N}}^{+}$+${\mathrm{N}}_{2}^{\mathrm{}2+}$, and ${\mathrm{N}}^{2+}$ from ${\mathrm{N}}_{2}$; and the production of ${\mathrm{O}}_{2}^{\mathrm{}+}$, ${\mathrm{O}}^{+}$+${\mathrm{O}}_{2}^{\mathrm{}2+}$, and ${\mathrm{O}}^{2+}$ from ${\mathrm{O}}_{2}$. The product ions are mass analyzed with a time-of-flight mass spectrometer and detected with a position-sensitive detector whose output provides clear evidence that all energetic fragment ions are collected. The overall uncertainty in the absolute cross-section values for singly charged parent ions is \ifmmode\pm\else\textpm\fi{}3.5% and is marginally higher for fragment ions. Previous cross-section measurements are compared to the present results. \textcopyright{} 1996 The American Physical Society.

Absolute partial cross sections for electron-impact ionization of H2, N2, and O2 from threshold to 1000 eV

Absolute partial cross sections from threshold to 1000 eV are reported for the production of ${\mathrm{Ar}}^{\mathit{n}+}$ (n=1--4) by electron-impact ionization of argon. The total cross sections, obtained from an appropriately weighted sum of the partial cross sections, are also reported. These results are obtained with an apparatus incorporating a time-of-flight mass spectrometer with position-sensitive detection of the product ions. The simple apparatus design embodies recent developments in pressure measurement and particle detection and is believed to yield more reliable results than those previously reported. For singly charged ions, the overall uncertainty in the absolute cross section values reported here is \ifmmode\pm\else\textpm\fi{}3.5%. Previous measurements of absolute partial and total cross sections are reviewed and compared with the present results.

Absolute partial and total cross sections for electron-impact ionization of argon from threshold to 1000 eV.

Absolute partial cross sections for electron-impact ionization of H2O and D2O are reported for electron energies from threshold to 1000 eV. Data are presented for the production of H2O++OH++O+, O2+, H2+, and H+ from H2O and for the production of D2O+, OD+, O+, O2+, D2+, and D+ from D2O. The product ions are mass analyzed using a time-of-flight mass spectrometer and detected with a position-sensitive detector whose output demonstrates that all product ions are completely collected. The overall uncertainty in the absolute cross section values is ±4.5% for singly charged parent ions and is slightly greater for fragment ions. The cross sections for H2O and D2O are found to be the same to within experimental uncertainties except for the H2+ cross section which is approximately a factor of 2 greater than the D2+ cross section. Previous results are compared to the present measurements.

B. G. Lindsay

Papers

Charge transfer cross sections for energetic neutral atom data analysis

Determination of the absolute partial and total cross sections for electron-impact ionization of the rare gases

Absolute partial cross sections for electron-impact ionization of H2, N2, and O2 from threshold to 1000 eV

Absolute partial and total cross sections for electron-impact ionization of argon from threshold to 1000 eV.

Absolute partial cross sections for electron-impact ionization of H2O and D2O from threshold to 1000 eV