A CALCULATION OF SEMI-EMPIRICAL ONE-ELECTRON WAVE FUNCTIONS FOR MULTI-ELECTRON ATOMS USED FOR ELEMENTARY PROCESS SIMULATION IN NONLOCAL PLASMA

Subject of Research. The paper deals with development outcomes for creation method of one-electron wave functions of complex atoms, relatively simple, symmetrical for all atom electrons and free from hard computations. The accuracy and resource intensity of the approach are focused on systematic calculations of cross sections and rate constants of elementary processes of inelastic collisions of atoms or molecules with electrons (ionization, excitation, excitation transfer, and others). Method. The method is based on a set of two iterative processes. At the first iteration step the Schrödinger equation was solved numerically for the radial parts of the electron wave functions in the potential of the atomic core self-consistent field. At the second iteration step the new approximationfor the atomic core field is created that uses found solutions for all one-electron wave functions. The solution optimization for described multiparameter problem is achieved by the use of genetic algorithm. The suitability of the developed method was verified by comparing the calculation results with numerous data on the energies of atoms in the ground and excited states. Main Results. We have created the run-time version of the program for creation of sets of one-electron wave functions and calculation of the cross sections and constants of collisional transition rates in the first Born approximation. The priori available information about binding energies of the electrons for any many-particle system for creation of semi-empirical refined solutions for the one-electron wave functions can be considered at any step of this procedure. Practical Relevance. The proposed solution enables a simple and rapid preparation of input data for the numerical simulation of nonlocal gas discharge plasma. The approach is focused on the calculation of discharges in complex gas mixtures requiring inclusion in the model of a large number of elementary collisional and radiation processes involving heavy particles in different quantum states

PHYSICAL OBJECT-ORIENTED MODELING IN DEVELOPMENT OF INDIVIDUALIZED TEACHING AND ORGANIZATION OF MINI-RESEARCH IN MECHANICS COURSES

Subject of Research. The paper presents a relatively simple method to develop interactive computer models of physical systems without computer programming skills or automatic generation of the numerical computer code for the complex physical systems. Developed computer models are available over the Internet for educational purposes and can be edited by users in an unlimited number of possibilities. An applicability of computer simulations for the massive open individualized teaching and an organization of undergraduate research are also discussed. Method. The presented approach employs an original physical object-oriented modeling method, which is an extension of object-oriented programming ideas to tasks of developing simulations of the complex physical systems. In this framework, a computer model of the physical system is constructed as a set of interconnected computer objects simulating the system components: particles and fields. Interactions between the system components are described by self-adapting algorithms that are specified during the model initiation stage and are set according to either the classical or relativistic approach. The utilized technique requires neither a priori knowledge regarding an evolution of the physical system nor a formulation of differential equations describing the physical system. Main Results. Testing of the numerical implementation and an accuracy of the algorithms was performed with the use of benchmarks with the known analytical solutions. The developed method - a physical reality constructor - has provided an opportunity to assemble a series of computer models to demonstrate physical phenomena studied in the high school and university mechanic courses. More than 150 original interactive models were included into the collections of multi-level multimedia resources to support teaching of the mechanics. The physical reality constructor was successfully tested to serve as a test bed for the independent research by students on physical properties of complex mechanical systems, the analysis of which is beyond the scope of the standard physics and mathematics curriculum. The heuristic capabilities of models created by the physical reality constructor were also demonstrated. The capability to investigate dynamics of the complex systems, an a priori analysis of which is not evident or with a difficult or impossible-to-calculate evolution, was also demonstrated. Practical Relevance. The developed computer program for automated development of interactive educational simulations provides a solution to standing problems in accompanying massive open individualized learning multi-level courses in physics as well as an opportunity to develop creative forms of training in physics with elements of research

SIMULATION OF PULSED BREAKDOWN IN HELIUM BY ADAPTIVE METHODS

The paper deals with the processes occurring during electrical breakdown in gases as well as numerical simulation of these processes using adaptive mesh refinement methods. Discharge between needle electrodes in helium at atmospheric pressure is selected for the test simulation. Physical model of the accompanying breakdown processes is based on self- consistent system of continuity equations for streams of charged particles (electrons and positive ions) and Poisson equation for electric potential. Sharp plasma heterogeneity in the area of streamers requires the usage of adaptive algorithms for constructing of computational grids for modeling. The method for grid adaptive construction together with justification of its effectiveness for significantly unsteady gas breakdown simulation at atmospheric pressure is described. Upgraded version of Gerris package is used for numerical simulation of electrical gas breakdown. Software package, originally focused on solution of nonlinear problems in fluid dynamics, appears to be suitable for processes modeling in non-stationary plasma described by continuity equations. The usage of adaptive grids makes it possible to get an adequate numerical model for the breakdown development in the system of needle electrodes. Breakdown dynamics is illustrated by contour plots of electron densities and electric field intensity obtained in the course of solving. Breakdown mechanism of positive and negative (orientated to anode) streamers formation is demonstrated and analyzed. Correspondence between adaptive building of computational grid and generated plasma gradients is shown. Obtained results can be used as a basis for full-scale numerical experiments on electric breakdown in gases

On the anomalous low spontaneous emission rates for p-series of sodium due to the effect of natural Förster resonance

International audienceWe are concerned here with a possibility of dipole matrix element strong blockade for excited atoms in the vicinity of Förster resonance. The latter occurs when the difference Deltadelta = deltal' - deltal between the quantum defects of l- and (l' = ± l1)-adjacent series becomes equal to 0.5. The comparison between lifetimes of Rydberg p-states in alkaline atoms indicates anomaly large (fivefold) values in the case of sodium. We explain this fact with the configuration of p- and s-series in Na which practically meets the Förster resonance realization requirement. Important specific futures of the Förster resonance discussed here and related to radiative kinetics of Rydberg states are of interest for interpretation of fluorescence spectra observed in astrophysics

Particularities of optical pumping effects in cold and ultra-slow beams of Na and Cs in the case of cyclic transitions

The time-dependent population dynamics of hyperfine (HF) levels of n2p3/2 states is examined for cyclic transitions in alkali atoms. We study a slow and cold atomic beam of Na (n = 3) and Cs (n = 6), taking into account the long interaction time of light with atoms (~200 μs) inside the resonant laser beam. Simple analytical expressions for the populations of the excited states and for the intensities of the absorption lines are derived for a three-level system model. We show that at moderate pump laser power the mixing of HF levels is sufficient to form a flow of population from a cyclic transition to partially open transitions. We discuss various phenomena associated with the evolution of optical pumping that cannot be explained by general analysis of two-level system model

Диагностика атмосферных плазменных струй барьерного разряда в потоке аргона и гелия в цилиндрическом СВЧ-резонаторе

Introduction. Technologies related to the use of low-temperature atmospheric plasmas are developing at a rapid pace. Creation of new low-temperature plasma sources for specific applications requires monitoring of dynamic processes in such discharges with a high time resolution. Electron concentration is one the most important plasma characteristics, which can be very low for a low-temperature atmospheric pressure plasma. However, the methods currently available for diagnostics of gas-discharge plasmas are either characterized by insufficient sensitivity or unable to monitor dynamic processes in non-stationary discharges. In this regard, the development of new diagnostic approaches to low-temperature atmospheric plasma seems to be a relevant research direction.Aim. To develop a diagnostic method for an atmospheric plasma with a low gas temperature and a low electron concentration in a cylindrical microwave resonator.Materials and methods. The proposed diagnostic method is based on the well-known principle of measuring the frequency shift and the Q-factor of the eigenmodes of the microwave resonator, inside which the plasma under study is located.Results. Measurements of the atmospheric barrier discharge plasma jets in a helium and argon stream in a cylindrical microwave resonator were performed. The proposed geometry made it possible to significantly increase the sensitivity of measurements. It became possible to exclude the effect of polarization degeneracy in a round cylindrical resonator. The developed system was also tested on test objects with a known value of permittivity.Conclusion. A method for microwave diagnostics of stationary and non-stationary cold atmospheric plasma jets in a cylindrical resonator, inside which transmitting and receiving antennas are installed, as well as an orthogonal thin conductor preventing the excitation of undesirable modes, was developed.Введение. В настоящее время активно развиваются технологии, связанные с использованием атмосферной плазмы с низкой газовой температурой. При создании новых источников низкотемпературной плазмы для конкретных приложений возникает необходимость в измерении динамических процессов в нестационарных разрядах с высоким временным разрешением. Одной из наиболее важных характеристик плазмы является концентрация электронов, которая для плазмы атмосферного давления с низкой температурой газа может быть очень небольшой. Однако доступные в настоящее время методы диагностики газоразрядной плазмы либо обладают недостаточной чувствительностью, либо не позволяют отслеживать динамические процессы в нестационарных разрядах. В этой связи представляет интерес разработка новых средств, позволяющих проводить диагностику атмосферной низкотемпературной плазмы.Цель работы. Разработка метода диагностики атмосферной плазмы с низкой температурой газа и низкой электронной концентрацией в цилиндрическом СВЧ-резонаторе.Материалы и методы. Предлагаемый метод диагностики основан на известном способе измерения сдвига частоты и добротности собственных мод СВЧ-резонатора, внутри которого находится исследуемая плазма.Результаты. Выполнена диагностика атмосферных плазменных струй барьерного разряда в потоке гелия и аргона в цилиндрическом СВЧ-резонаторе. Предложенная геометрия позволила существенно увеличить чувствительность измерений. Удалось исключить влияние эффекта поляризационного вырождения мод в круглом цилиндрическом резонаторе. Разработанная система была также апробирована на тестовых объектах с известным значением диэлектрической проницаемости.Заключение. Разработан метод СВЧ-диагностики стационарных и нестационарных холодных атмосферных плазменных струй в цилиндрическом резонаторе, внутри которого установлены передающая и приемная антенны, а также ортогональный тонкий проводник, обеспечивающий подавление нежелательных мод