Персона: Степаненко, Александр Александрович
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Институт лазерных и плазменных технологий
Стратегическая цель Института ЛаПлаз – стать ведущей научной школой и ядром развития инноваций по лазерным, плазменным, радиационным и ускорительным технологиям, с уникальными образовательными программами, востребованными на российском и мировом рынке образовательных услуг.
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Александр Александрович
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- ПубликацияОткрытый доступEquations and improved coefficients for parallel transport in multicomponent collisional plasmas: Method and application for tokamak modeling(2021) Makarov, S. O.; Coster, D. P.; Rozhansky, V. A.; Kaveeva, E. G.; Stepanenko, A. A.; Zhdanov, V. M.; Степаненко, Александр Александрович© 2021 Author(s).New analytical expressions for parallel transport coefficients in multicomponent collisional plasmas are presented in this paper. They are improved versions of the expressions written in Zhdanov [Transport Processes in Multicomponent Plasma, English ed. (Taylor and Francis, London, New York, 2002)], based on Grad's 21N-moment method. Both explicit and approximate approaches for the calculation of transport coefficients are considered. Accurate application of this closure for the Braginskii transport equations is discussed. Viscosity dependence on the heat flux is taken into account. Improved expressions are implemented into the SOLPS-ITER code and tested for deuterium and neon ITER cases. Some typos found in Zhdanov [Transport Processes in Multicomponent Plasma, English ed. (Taylor and Francis, London, New York, 2002)] are corrected.
- ПубликацияТолько метаданныеDimensional effects in analysis of laser-induced-desorption diagnostics data(2024) Stepanenko, A. A.; Gasparyan, Y. M.; Степаненко, Александр Александрович; Гаспарян, Юрий Микаэлович
- ПубликацияОткрытый доступAssessment of laser induced breakdown spectroscopy accuracy for determination of hydrogen accumulation in tungsten(2021) Tsygvintsev, I. P.; Marenkov, E. D.; Gasparyan, Y. M.; Stepanenko, A. A.; Маренков, Евгений Дмитриевич; Гаспарян, Юрий Микаэлович; Степаненко, Александр Александрович© 2021 The Author(s)Laser-induced breakdown spectroscopy (LIBS) is an in situ method of determining hydrogen (H) content in plasma-facing materials in tokamak fusion reactors. Observing radiation from the plasma plume produced by a powerful laser pulse during the target exposition characterizes the sample composition. This is typically accomplished using the Saha-Boltzmann (SB) plot technique under local thermodynamic equilibrium (LTE) conditions. Despite many experimental studies dedicated to applying LIBS to determine H isotope retention in fusion reactor materials, the current understanding of this method's intrinsic accuracy remains inadequate. In this report, we use numerical calculations to estimate the relative error of determining H content in a sample using LIBS. As an example. we consider LIBS to study a W sample loaded with H in a vacuum. Under typical LIBS pulse parameters (109 W/cm2 and 12 ns duration), the error can be quite large, approximately 70%. We demonstrate that the error tends to decrease as the laser pulse intensity increases. Various factors contributing to the relative error are examined and their dependence on the LIBS plasma parameters is discussed. The SB plot remains a straight line even when LTE conditions are violated, making it difficult to anticipate the experimental results’ error.
- ПубликацияТолько метаданныеSeparation of a Gas Mixture in Nanosize Porous Membranes. Effect of Adsorption and Surface Diffusion(2021) Zhdanov, V. M.; Stepanenko, A. A.; Степаненко, Александр Александрович© 2021, Springer Science+Business Media, LLC, part of Springer Nature.The authors have studied the influence of the adsorption and surface diffusion of one component of a binary gas mixture on pore walls on the effect of separation of the gas mixture during its flow through a nanosize porous membrane in a free molecular regime. A capillary porous-medium model obtained by the momentum-balance method was taken as a basis for analysis. Expressions have been determined for the separation factor and the concentration jump of the adsorbed component for an assigned pressure difference on the membrane, which make it possible to analyze the influence of the initial concentration of the adsorbable component and of the temperature on the separation effect. Calculations have been performed of the concentration jump for a number of commercial gas mixtures (CO2/H2, CO/H2, CH4/H2, and N2/He). It has been shown that taking account of surface diffusion may lead to appreciable variations (of several tens of percent) of the obtained values from Knudsen values of the effect in the absence of adsorption.
- ПубликацияОткрытый доступRelaxation Phenomena in Thermal Molecular Plasmas(2020) Stepanenko, A. A.; Zhdanov, V. M.; Степаненко, Александр АлександровичWe present the results of analysis of relaxation phenomena in thermal molecular plasmas. The physical assumptions and the general scalar moment equations, obtained in the 17-moment approximation of the Grad method, are given. By using these equations, we derive the expressions for the relaxation pressure and bulk viscosity coefficients associated with heavy plasma components (atoms, molecules and their ions) and electrons. To gain a deeper understanding of how the physical parameters of particles and inter-particle interactions influence on the plasma relaxation properties, we also employ the semi-qualitative model of energy relaxation for plasma components. Within this model, the expressions for the partial relaxation pressures and bulk viscosity coefficients are derived and analyzed. It is demonstrated that depending on the plasma degree of ionization and the ratio of the characteristic timescales of energy exchange between particles, the partial relaxation pressures and bulk viscosity coefficients can not only vary but also change their signs.
- ПубликацияТолько метаданныеEnhanced particle flux due to localized divertor MHD instability in DIII-D tokamak(2020) Wang, H. Q.; Watkins, J. G.; Guo, H. Y.; Leonard, A. W.; Stepanenko, A. A.; Степаненко, Александр Александрович© 2020 Author(s).An MHD mode with a frequency of <10 kHz has been identified near the inner strike point from various diagnostics, i.e., divertor Langmuir probes, magnetics sensors, and interferometers, but does not appear in the upstream and core diagnostics. This MHD mode is associated with magnetic oscillations of ≳5 G, has a long wavelength in the toroidal direction with toroidal mode number n = 1, but is localized in a narrow radial region of a few cm. The mode appears when the outer strike point remains attached and the inner strike point nearly detaches, grows with increasing density, and eventually weakens and vanishes as the outer strike point detaches. This mode results in particle flux with an order of magnitude higher than the background plasmas near the inner strike point. The mode characteristics are consistent with the Current-Convective-Instability theory prediction. Initial simulations based on experimental input have found oscillations with similar frequencies but weaker amplitude.
- ПубликацияТолько метаданныеImpact of electromagnetic effects on macroscopic dynamics of blobs in hot low-beta edge plasma of fusion devices(2020) Stepanenko, A. A.; Степаненко, Александр АлександровичThe impact of electromagnetic effects on macroscopic dynamics of blobs in hot low-beta ( beta < m e / m i) edge plasma of fusion devices is analyzed. The physical model governing filament dynamics is presented. The qualitative analysis of the blob motion in electrostatic and electromagnetic regimes is performed. The scalings for the plasma potential and filament advection velocity are obtained along with the estimates of plasma parameters, for which the physics of Alfven waves and skin effect can have an impact on the filament motion. It is shown that required edge/scrape-off layer conditions can be found in modern tokamaks. Analytical expressions for the distributions of the parallel current and electrostatic potential in a blob, containing electrostatic and electromagnetic contributions, are derived. It is demonstrated that in sufficiently hot, weakly resistive plasma the electromagnetic effects can lead to noticeable variations of the potential along the magnetic field lines distorting the blob propagation pattern in contrast to the electrostatic case. Results of the theoretical analysis are compared with results of 3D BOUT++ modeling, which show that in the electromagnetic limit, the macroscopic motion of blobs can exhibit ballooning features due to the emission of Alfven waves, absent in electrostatic simulations. It is concluded that, at least in the near scrape-off layer region of fusion devices, electromagnetic models of plasma dynamics may be appropriate for the analysis of blob motion instead of electrostatic ones.
- ПубликацияТолько метаданныеSpatial–Temporal Properties of Current-Convective Turbulence in Divertor Plasma under DIII-D-Like Detached Conditions(2019) Wang, H. Q.; Stepanenko, A. A.; Степаненко, Александр Александрович© 2019, Pleiades Publishing, Ltd.Abstract: Recent experimental observations of divertor plasma turbulence at the ASDEX Upgrade tokamak have demonstrated the onset of strong fluctuations of plasma radiation intensity in the near X-point region within the inner divertor leg, when the machine was operating with the pronounced asymmetry in detachment of plasma between the inner and outer divertors. As been recently shown, one of the possible mechanisms responsible for these fluctuations can be related to the current-convective instability (CCI). In this contribution, we assess whether the CCI can drive turbulence with spatial and temporal parameters similar to those observed lately in DIII-D experiments. It is demonstrated that the CCI drives saturated plasma fluctuations, dominated by low-frequency modes with toroidal wavelengths on the order of the machine circumference in the inner divertor region—features that are similar to turbulence characteristics found in experiments.
- ПубликацияТолько метаданныеBoundary slip phenomena in multicomponent gas mixtures(2019) Zaznoba, V. A.; Stepanenko, A. A.; Zhdanov, V. M.; Степаненко, Александр Александрович© 2019 Author(s).The slip phenomena in multicomponent gas mixtures are studied. The moment equations, derived from the linearized Boltzmann equation by using the 13-moment approximation of the Grad's method, are used to obtain the full (containing the contribution from the Knudsen layer) and asymptotic (valid far from the plane physical boundary of the domain) expressions for the nonequilibrium macroscopic parameters of the mixture species. The latter relations are employed to deduce the expressions for the mixture slip velocity and the viscous, thermal, and diffusion slip coefficients by using the modified Maxwell method and the diffuse-specular model of molecule scattering on the wall. The derived relations for the slip coefficients are given in the convenient form expressed in terms of basic transport coefficients, such as partial viscosity and thermal conductivity coefficients, diffusion and thermal diffusion coefficients, and coefficients of molecule momentum accommodation at the wall. The expressions found are used to calculate the slip coefficients for binary (He-Ar) and ternary (He-Ar-Xe) gas mixtures. The numerical results are in good agreement with the data calculated by using other methods.
- ПубликацияОткрытый доступImpact of divertor plasma parameters on characteristics of current-convective turbulence under DIII-D-like detached conditions(2019) Wang, H. Q.; Krasheninnikov, S. I.; Stepanenko, A. A.; Степаненко, Александр Александрович© 2019 Author(s).Recent observations of turbulence in plasma of a DIII-D inner divertor revealed the formation of poloidally localized fluctuations with frequencies in the low-kilohertz range, when the machine was operating in the fluctuating state of detachment. This phenomenon can be related to the onset of the current-convective instability (CCI). In this contribution, we use the basic physical model of the instability to simulate the saturated current-convective turbulence under the DIII-D-like detached conditions. Parameter scans of turbulence characteristics are performed. The spatial and temporal spectra of fluctuations are obtained and compared with the available experimental data. It is demonstrated that simulations are able to qualitatively reproduce most of the distinct features of turbulence found in the experiments, indicating that the CCI can be a plausible mechanism responsible for plasma activity recently observed in DIII-D.
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