Data Needs for Modeling Low-Temperature Non-Equilibrium Plasmas: The LXCat Project, History, Perspectives and a Tutorial

Condensed Matter Systems Exposed to Radiation: Multiscale Theory, Simulations, and Experiment

This roadmap reviews the new, highly interdisciplinary research field studying the behavior of condensed matter systems exposed to radiation. The Review highlights several recent advances in the field and provides a roadmap for the development of the field over the next decade. Condensed matter systems exposed to radiation can be inorganic, organic, or biological, finite or infinite, composed of different molecular species or materials, exist in different phases, and operate under different thermodynamic conditions. Many of the key phenomena related to the behavior of irradiated systems are very similar and can be understood based on the same fundamental theoretical principles and computational approaches. The multiscale nature of such phenomena requires the quantitative description of the radiation-induced effects occurring at different spatial and temporal scales, ranging from the atomic to the macroscopic, and the interlinks between such descriptions. The multiscale nature of the effects and the similarity of their manifestation in systems of different origins necessarily bring together different disciplines, such as physics, chemistry, biology, materials science, nanoscience, and biomedical research, demonstrating the numerous interlinks and commonalities between them. This research field is highly relevant to many novel and emerging technologies and medical applications.

Non-thermal plasma mitigation of low concentration of air pollutants: removal of isopropyl alcohol using transition metal-oxide integration

The present work studied the decomposition of isopropyl alcohol (IPA), widely used in chemical industries and households, in a packed-bed dielectric barrier discharge (DBD) plasma reactor. Metal oxide (MOx) coated on γ-Al2O3 (M = Cu, Mn, Co) was utilized for packing. The plasma-packed mode was a likely alternative to the conventional removal techniques, as it aids the conversion of dilute concentrations of IPA to CO and CO2 at ambient conditions (room temperature and atmospheric pressure). The mean electron energy calculations suggest that electrons with higher energy are generated when the discharge zone is packed with catalysts. When comparing IPA conversion (input concentration of 25 ppm) for no packing mode and MOx/γ-Al2O3 coupled plasma mode, the latter method enhances conversion to greater than 90% at an applied voltage of 18 kV. Also, MOx/γ-Al2O3 showed the highest selectivity to CO2 (70%) compared to plasma-only mode (45%). The metal-oxide layer provides the necessary catalytic surface facilitating the oxidation of IPA to COx through active oxygen species or the interaction of surface hydroxyl groups. The use of MOx/γ-Al2O3 resulted in about 90% carbon balance and reduced ozone generation, demonstrating the significance of integrating metal oxide to achieve efficient conversion and maximal selectivity towards the desired products.

Semi-empirical analysis of leptons in gases in crossed electric and magnetic fields. Part II. Transverse compression of muon beams

This article employs fluid equations to analyze muon beams in gases subject to crossed electric and magnetic fields, focusing, in particular, on a scheme proposed by Taqqu [Phys. Rev. Lett. 97, 194801 (2006)], whereby transverse compression of the beam is achieved by creating a density gradient in the gas. A general criterion for maximizing beam compression, derived from first principles, is then applied to determine optimal experimental conditions for μ+ in helium gas. Although the calculations require the input of transport data for (μ+, He), which are generally unavailable, this issue is circumvented by "aliasing" (μ+, He) with (H+, He), for which transport coefficient data are available.

Kinetic Study for Plasma Assisted Cracking of NH3: Approaches and Challenges

Ammonia is considered as one of the promising hydrogen carriers toward a sustainable world. Plasma assisted decomposition of NH₃ could provide cost- and energy-effective, low-temperature, on-demand (partial) cracking of NH₃ into H₂. Here, we presented a temperature-dependent plasma-chemical kinetic study to investigate the role of both electron-induced reactions and thermally induced reactions on the decomposition of NH₃. We employed a plasma-chemical kinetic model (KAUSTKin), developed a plasma-chemical reaction mechanism for the numerical analysis, and introduced a temperature-controlled dielectric barrier discharge reactor for the experimental investigation using 1 mol % NH₃ diluted in N₂. As a result, we observed the plasma significantly lowered the cracking temperature and found that the plasma-chemical mechanism should be further improved to better predict the experiment. The commonly used rates for the key NH₃ pyrolysis reaction (NH₃ + M ↔ NH₂ + H + M) significantly overpredicted the recombination rate at temperatures below 600 K. Furthermore, the other identified shortcomings in the available data are (i) thermal hydrazine chemistry, (ii) electron-scattering cross-section data of N_xH_y, (iii) electron-impact dissociation of N₂, and (iv) dissociative quenching of excited states of N₂. We believe that the present study will spark fundamental interest to address these shortcomings and contribute to technical advancements in plasma assisted NH₃ cracking technology.

Analytical Formulas for Approximating Cross Sections of Electron Collisions with Hydrogen, Noble Gases, Alkali and Other Atoms

This paper presents an analysis of data on the cross sections of elastic and inelastic collisions of electrons with noble gases, alkali and other atoms. For the selected sets of experimental and theoretical data, optimal analytical formulas are found, and approximation coefficients are calculated. The obtained semi-empirical formulas reproduce the values of the transport (diffusion), excitation and ionization cross sections for noble gases. Much attention is paid to the ionization cross sections of metal atoms, which are often present as an impurity in gas-discharge plasma. The approximation formulas reproduce the values of the ionization cross sections for hydrogen, metal and other elements in a wide range of energies with accurate orders of errors of the available theoretical and experimental data. For some elements with a two-hump plot of the dependence of the ionization cross section on the collision energy, it is proposed to use a two-term formula that takes into account ionization from both external and internal shells.

Interactions of Si+(2PJ) and Ge+ (2PJ) with rare gas atoms (He-Rn): interaction potentials, spectroscopy, and ion transport coefficients

Accurate interatomic potentials were calculated for the interaction of a singly-charged silicon cation, Si⁺, with a single rare gas atom, RG (RG = Kr-Rn), as well as a singly-charged germanium cation, Ge⁺, with a single rare gas atom, RG (RG = He-Rn). The RCCSD(T) method and basis sets of quadruple-ζ and quintuple-ζ quality were employed; each interaction energy is counterpoise corrected and extrapolated to the basis set limit. The lowest electronic term (²P) of each cation was considered, and the interatomic potentials calculated for the diatomic terms that arise from these: ²Π and ²Σ⁺. Additionally, the interatomic potentials for the respective spin-orbit levels were calculated, and the effect on the spectroscopic parameters was examined. Variations in several spectroscopic parameters with the increasing atomic number of RG were examined. The presence of incipient chemical interaction was also examined via Birge-Sponer-like plots and various population analyses across the series. In the cases of heavier RG, these were consistent with a small amount of electron transfer from the heavier RG atom to the cation, rationalizing the spin-orbit splittings. This was also supported by the observed larger-than-expected spin-orbit splittings for the Si⁺-RG complexes. Finally, each set of RCCSD(T) potentials including spin-orbit coupling was employed to calculate transport coefficients for the cation moving through a bath of the RG. The calculated ion mobilities showed significant differences for the two atomic spin-orbit states, arising from subtle changes in the interaction potentials.

Crossing Frequency Method Applicable to Intermediate Pressure Plasma Diagnostics Using the Cutoff Probe

Although the recently developed cutoff probe is a promising tool to precisely infer plasma electron density by measuring the cutoff frequency (fcutoff) in the S21 spectrum, it is currently only applicable to low-pressure plasma diagnostics below several torr. To improve the cutoff probe, this paper proposes a novel method to measure the crossing frequency (fcross), which is applicable to high-pressure plasma diagnostics where the conventional fcutoff method does not operate. Here, fcross is the frequency where the S21 spectra in vacuum and plasma conditions cross each other. This paper demonstrates the fcross method through three-dimensional electromagnetic wave simulation as well as experiments in a capacitively coupled plasma source. Results demonstrate that the method operates well at high pressure (several tens of torr) as well as low pressure. In addition, through circuit model analysis, a method to estimate electron density from fcross is discussed. It is believed that the proposed method expands the operating range of the cutoff probe and thus contributes to its further development.

Analytical Cross Section Approximation for Electron Impact Ionization of Alkali and Other Metals, Inert Gases and Hydrogen Atoms

The paper presents an analysis of data on the cross sections of electron impact ionization of atoms of alkali metals, hydrogen, noble gases, some transition metals and Al, Fe, Ni, W, Au, Hg, U. For the selected sets of experimental and theoretical data, an optimal analytical formula is found and approximation coefficients are calculated. The obtained semi-empirical formula reproduces the values of the ionization cross sections in a wide range of energies with an accuracy of the order of error of the available theoretical and experimental data.

Toward a complete and comprehensive cross section database for electron scattering from NO using machine learning

We review experimental and theoretical cross sections for electron scattering in nitric oxide (NO) and form a comprehensive set of plausible cross sections. To assess the accuracy and self-consistency of our set, we also review electron swarm transport coefficients in pure NO and admixtures of NO in Ar, for which we perform a multi-term Boltzmann equation analysis. We address observed discrepancies with these experimental measurements by training an artificial neural network to solve the inverse problem of unfolding the underlying electron-NO cross sections while using our initial cross section set as a base for this refinement. In this way, we refine a suitable quasielastic momentum transfer cross section, a dissociative electron attachment cross section, and a neutral dissociation cross section. We confirm that the resulting refined cross section set has an improved agreement with the experimental swarm data over that achieved with our initial set. We also use our refined database to calculate electron transport coefficients in NO, across a large range of density-reduced electric fields from 0.003 to 10 000 Td.