Russian University Proposes Rapid Simulation Method for Plasma Ion Parameters

Researchers from the HSE University and the Moscow Institute of Physics and Technology have developed a simple analytical method for calculating the behavior of heavy ions in helium under strong electric fields. The findings have been published in Physica Scripta.

Plasma is a gas composed of charged particles such as electrons, negative ions, and positive ions, typically quasi-neutral and highly conductive. In addition to fluorescent lamps and welding arcs, plasma also exists in controlled nuclear fusion devices such as tokamaks. Atmospheric plasma jets can also be used for wound disinfection, work surface cleaning, and improving crop seed performance.

In plasma jet research, scientists typically need to predetermine jet parameters through computer modeling. Key data required for modeling include the characteristics of charged particles, mobility, and reaction rate constants, which vary with electric field strength. Traditionally, such data have been primarily calculated using the Monte Carlo method. This method offers high accuracy but is computationally expensive: determining the mobility and reaction rate constants of a single ion at one electric field strength may take hours, or even days in complex cases.

In this study, Alexander Ponomarev, Associate Professor at the HSE University Faculty of Physics, and Nikolai Alexandrov, Professor at the Moscow Institute of Physics and Technology, proposed simple analytical formulas that can estimate ion mobility and reaction rate constants within seconds. The researchers improved and combined classical methods to develop multiple calculation schemes. Among them, the simplest method is applicable to high reduced electric fields, i.e., above 60 Td, while the improved method covers a wider range, including low electric fields.

The research team also developed methods for estimating reaction rates, enabling the calculation of the rates of negative ion decay and electron loss. Such parameters are important for simulating changes in plasma composition.

To verify the reliability of the new method, the researchers compared its calculation results with data obtained via the Monte Carlo method. The study focused on oxygen negative ions, tetraoxygen negative ions, and nitric oxide negative ions, which are important in atmospheric plasma. The results showed that under strong electric fields, the deviation of the simplest method in calculating ion mobility was up to about 10%, while the improved method showed deviations between 2% and 7%, depending on the ion type. The study also confirmed that the method is applicable to ultra-strong electric fields of up to 250 Td.

Regarding ion reaction rate constants, the deviation between the new method and Monte Carlo calculations did not exceed a factor of two. The researchers believe that, since the reaction rate constants of charged particles can vary by two to three orders of magnitude with electric field strength, reducing calculation time from hours to seconds holds practical value in plasma modeling.

Alexander Ponomarev noted that the method reduces the complexity of ion characterization calculations to a level close to what an ordinary calculator can handle. The research team believes that faster computational capabilities could drive further research into plasma interactions with living tissue and plasma treatment of seeds.