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1. Derivation of the ion equation

   Grenier, E (March 2020, Quarterly of applied mathematics)

   We consider the classical Euler-Poisson system for electrons and ions, interacting through an electrostatic field. The mass ratio of an electron and an ion is small and we establish an asymptotic expansion of solutions, where the main term is obtained from a solution to a self-consistent equation involving only the ion variables. Moreover, on R^3, the validity of such an expansion is established even with \ill-prepared" Cauchy data, by including an additional initial layer correction. 

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2. Ion emission from niobium nanosecond laser plasma

   https://doi.org/10.1016/j.vacuum.2025.114048  

   Islam, Md Obidul; Mahmood, Rawdah; Elsayed-Ali, Hani E (April 2025, Vacuum)

   A niobium laser multicharged ion source was developed using laser ablation with 10-ns, 1064-nm pulses and a laser fluence of 10–83 Jcm-2. Three distinct groups of Nb ions were detected: ultrafast, fast, and thermal. The ions were accelerated and allowed to drift in a transport line containing an electrostatic ion energy analyzer, a retarding field analyzer, and a Faraday cup. Analysis of the ion energy and charge (z) showed that each group of ions experienced different acceleration potentials during plasma expansion. Time-of-flight (TOF) signal of the thermal ions showed overlap of the signals from Nb1+ and Nb2+. For the fast ion group, z up to Nb7+ was observed and the ion acceleration potential during plasma expansion increased with z, over the charge states from Nb1+ to Nb7+. The TOF signal indicated that the ultrafast ions were composed of higher-charge ions. 

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3. Benchmark experiments of the power law parametrization of the effective ion collecting area of a planar Langmuir probe in low temperature plasmas

   https://doi.org/10.1088/1361-6595/ac4d03  

   Lim, Yegeon; Severn, Greg; Yip, Chi-Shung; Ghim, Y-c (February 2022, Plasma Sources Science and Technology)

   Abstract For unmagnetized low temperature Ar plasmas with plasma density ranging from 3 × 10 8 to 10 10 cm −3 and an electron temperature of ∼1 eV, the expansion of the ion collecting area of a double-sided planar Langmuir probe with respect to probe bias is experimentally investigated, through a systematic scan of plasma parameters. In accordance with many existing numerical studies, the ion collecting area is found to follow a power law for a sufficiently negative probe bias. Within our experimental conditions, the power law coefficient and exponent have been parameterized as a function of the normalized probe radius and compared with numerical results where qualitatively comparable features are identified. However, numerical results underestimate the power law coefficient while the exponent is overestimated. Our experimental measurements also confirm that ion–neutral collisions play a role in determining the expanded ion collecting area, thus changing values of the power law coefficient and exponent. This work suggests that a power law fit to the ion collecting area must be performed solely based on experimentally obtained data rather than using empirical formulae from simulation results since material and cleanness of the probe, type of working gas, and neutral pressure may also affect the expansion of the ion collecting area, factors which are difficult to model in a numerical simulation. A proper scheme of analyzing an I – V characteristic of a Langmuir probe based on a power law fit is also presented. 

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4. Analytical Model of Foreshock Ion Interaction With a Discontinuity: A Statistical Study

   https://doi.org/10.1029/2022JA031162  

   Liu, Terry Z.; Vu, Andrew; Angelopoulos, Vassilis; Zhang, Hui (April 2023, Journal of Geophysical Research: Space Physics)

   Abstract When a solar wind discontinuity interacts with foreshock ions, foreshock transients such as hot flow anomalies and foreshock bubbles can form. These create significant dynamic pressure perturbations disturbing the bow shock, magnetopause, and magnetosphere‐ionosphere system. However, presently these phenomena are not predictable. In the accompanying paper, we derived analytical equations of foreshock ion partial gyration around a discontinuity and the resultant current density. In this study, we utilize the derived current density strength to model the energy conversion from the foreshock ions, which drives the outward motion or expansion of the solar wind plasma away from the discontinuity. We show that the model expansion speeds match those from local hybrid simulations for varying foreshock ion parameters. Using MMS, we conduct a statistical study showing that the model expansion speeds are moderately correlated with the magnetic field strength variations and the dynamic pressure decreases around discontinuities with correlation coefficients larger than 0.5. We use conjunctions between ARTEMIS and MMS to show that the model expansion speeds are typically large for those already‐formed foreshock transients. Our results show that our model can be reasonably successful in predicting significant dynamic pressure disturbances caused by foreshock ion‐discontinuity interactions. We discuss ways to improve the model in the future. 

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5. Mott insulating low thermal expansion perovskite ${\mathrm{TiF}}_3$

   https://doi.org/10.1103/PhysRevB.108.235140  

   Sheets, Donal; Lyszak, Kaitlin; Jain, Menka; Fernando, Gayanath W.; Sochnikov, Ilya; Franklin, Jacob; Hancock, Jason N.; Geilhufe, R. Matthias (December 2023, Physical Review B)

   We characterize perovskite TiF3, a material which is reported to display significant negative thermal expansion at elevated temperatures above its cubic-to-rhombohedral structural phase transition at 330 K. We find the optical response favors an insulating state in both structural phases, which we show can be produced in density functional theory calculations only through the introduction of an on-site Coulomb repulsion. Analysis of the magnetic susceptibility data gives a S = 21 local moment per Ti+3 ion and an antiferromagnetic exchange coupling. Together, these results show that TiF3 is a strongly correlated electron system, a fact which constrains possible mechanisms of strong negative thermal expansion in the Sc1−x Tix F3 system. We consider the relative strength of the Jahn-Teller and electric dipole interactions in driving the structural transition. 

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