IPME RAS Research Articles

РЕЗУЛЬТАТЫ РАСЧЕТА БЕНЧМАРК-МОДЕЛЕЙ ПО РАДИАЦИОННОЙ ЗАЩИТЕ, ПРЕДНАЗНАЧЕННЫХ ДЛЯ ИССЛЕДОВАНИЯ ПРОХОЖДЕНИЯ ИОНИЗИРУЮЩЕГО ИЗЛУЧЕНИЯ ЧЕРЕЗ ВОДУ И СТАЛЬНЫЕ РЕШЕТКИ

The work is devoted to evaluating the accuracy of using the BNAB-RF system of constants together with the discrete ordinate method and the KATRIN-2.5 and CASCAD codes (IPM RAS) for studying the passage of neutrons and photons through water and steel gratings. The results of calculating the benchmark models for radiation protection from the SINBAD database are presented, namely, the ASPIS Neutron / Gamma-Ray Transport Through Waiter / Steel Arrays, NESDIP-2 Benchmark Experiment and NESDIP-3 Benchmark Experiment models, which were located in experimental channel of the NESTOR reactor. As a neutron source, a disk made of an alloy of uranium and aluminum irradiated with a stream of thermal neutrons leaving the NESTOR reactor was used. Protective compositions consisted of steel containers with water and plates of various steels (stainless steel and mild steel). Measurements of the passage of ionizing radiation were carried out using foils placed between steel plates or immersed in water at different distances from the neutron source. The calculations of neutron and photon reactions were carried out using the discrete ordinate method in 3D and 2D geometries KATRIN-2.5 and CASCADE, respectively. The constant systems BNAB-93 and BNAB-RF were used as group libraries. We can especially note the calculated estimates for the passage of gamma radiation presented here, obtained from the reaction (n-gamma) in the materials of the ASPIS installation. The results of calculations showed a good agreement of the calculated values with the experimental data. Based on the obtained numerical results, the BNAB-RF constant system was verified as applied to the calculation of radiation protection from ionizing radiation passing through water and steel gratings.

Diffraction limited X-ray optics: technology, metrology, applications

Progress in the fabrication technology of normal incidence multilayer interference mirrors permits the traditional optical methods of microscopy, astronomy, and lithography to be transferred to the vacuum ultraviolet (VUV, wavelength: 10–200 nm) and the long-wavelength part of the soft X-ray (SXR, wavelength: 2–10 nm) ranges. Due to the short wavelength and properties of interaction with the substance, the radiation of these ranges provides unique opportunities in nanophysics, nanotechnology, and nanodiagnostics of matter. To use the potential of a short wavelength in full, diffraction-limited optical elements are required. Compared to traditional optical elements, their accuracy must be at least two orders of magnitude higher. The article provides an analysis of the real capabilities of traditional methods of making and studying precision optical elements and reports on the methods of fabrication and characterization of diffraction-limited optics for the VUV and SXR ranges developed at IPM RAS. Examples of the use of these optical elements for the tasks of extraterrestrial astronomy, X-ray microscopy, and lithography are given.

Artificial intelligence based neurofeedback

A new approach to the design of neurofeedback systems based on using Artificial Intelligence (AI) tools is proposed. The concept of control models of biological neural networks, and the set-up including equipment and software tools developed in IPME RAS in order to implement the proposed concept is described. as well as the AI methods and programs proposed for use.

Laboratory reflectometer for the investigation of optical elements in a wavelength range of 5–50 nm: description and testing results

We describe a laboratory reflectometer developed at the IPM RAS for precision measurements of spectral and angular dependences of the reflection and transmission coefficients of optical elements in a wavelength range of 5–50 nm. The radiation is monochromatised using a high-resolution Czerny–Turner spectrometer with a plane diffraction grating and two spherical collimating mirrors. A toroidal mirror focuses the probe monochromatic beam on a sample. The X-ray source is a highly ionised plasma produced in the interaction of a high-power laser beam with a solid target at an intensity of 1011–1012 W cm–2. To stabilise the emission characteristics, the target executes translatory and rotary motions in such a way that every pulse irradiates a new spot. The short-focus lens is protected from contamination by erosion products with the use of a specially designed electromagnetic system. The samples under study are mounted on a goniometer is accommodated in a dedicated chamber, which provides five degrees of freedom for samples up to 500 mm in diameter and two degrees of freedom for a detector. The sample mass may range up to 10 kg. The X-ray radiation is recorded with a detector composed of a CsI photocathode and two microchannel plates. A similar detector monitors the probe beam intensity. The spectral reflectometer resolution is equal to 0.030 nm with the use of ruled gratings with a density of 900 lines mm–1 (spectral range: 5–20 nm) and to 0.067 nm for holographic gratings with a density of 400 lines mm–1 (spectral range: 10–50 nm). We analyse the contribution of higher diffraction orders to the probe signal intensity and the ways of taking it into account in the measurements. Examples are given which serve to illustrate the reflectometer application to the study of multilayer mirrors and filters.

Dynamic programming method in extremal constrained routing problems

The problem of routing movements in a finite system of sets is considered. The problem is constrained by precedence conditions and by necessity of executing several (internal) jobs on the sets. The cost of execution of these jobs is summed up with the cost of performing (external) movements from set to set. The contents of the paper correspond to the presentation made by the author at the Conference on Control of Dynamical Systems (IPM RAS, Moscow, 2009)

Numerical simulation of flows in a high-frequency induction plasmatron and of heat transfer in underexpanded air jets

Some results of numerical simulation of flows in the discharge channel of the IPG-4 induction plasmatron installed at the Institute for Problems in Mechanics of the Russian Academy of Sciences (IPM RAS) and in underexpanded jets of dissociated and partially ionized air from sonic nozzles are discussed. These results are in good agreement with experimental data on heat fluxes and on the pressure at the stagnation point of a blunt cylindrical body. These experimental data were obtained at the IPM RAS Laboratory for Interaction of Plasma and Radiation with Materials.

Control of wave motion in the chain of pendulums

The problem of controlled excitation of oscillations in a chain of N coupled pendulums is considered. Such a problem may arise when studying different physical and mechanical systems and is also of interest for design of prospective laboratory equipment for control education. The simulation results for the chain of 50 pendulums are given. The multi-pendulum mechatronic setup from 50 computer-controlled coupled pendulums, developed in the IPME RAS, Saint Petersburg, is presented.

Flow and heat transfer in underexpanded air jets issuing from the sonic nozzle of a plasma generator

We present the results of an experimental investigation and numerical simulation of the gasdynamic structure of underexpanded dissociated-air jets and the heat transfer in these strongly nonequilibrium flows under the test conditions realized in the 100-kW electrodeless VGU-4 plasma generator of the Institute for Problems in Mechanics of the Russian Academy of Sciences (IPM RAS). The flow and heat transfer analysis is carried out on the basis of measurements of the static pressure in the plenum chamber, at the sonic nozzle exit, and on the low-pressure chamber wall, the stagnation pressure on the jet axis using a Pitot tube, and the heat transfer at the stagnation points of water-cooled models placed along the jet axis. The numerical simulation, based on complete Navier-Stokes equations, includes the calculation of (1) equilibrium air plasma flows in the discharge channel of the VGU-4 plasma generator; (2) underexpanded nonequilibrium dissociated-air jet outflow into the ambient space; and (3) axisymmetric jet flow past cylindrical models.

Investigation of the Influence of Different Heterogeneous Recombination Mechanisms on the Heat Fluxes to a Catalytic Surface in Dissociated Carbon Dioxide

A kinetic model of heterogeneous recombination in dissociated carbon dioxide on high-temperature heat-shield coatings is developed; the model takes into account the nonequilibrium adsorption-desorption reactions of oxygen atoms and their recombination in the Eley-Rideal and Langmuir-Hinshelwood reactions. On the basis of a comparison of the calculated heat fluxes in dissociated carbon dioxide with those measured in the VGU-3 plasma generator of the Institute for Problems in Mechanics of the Russian Academy of Sciences (IPM RAS) and the available literature data, the parameters of the catalysis model are chosen for the glassy coating of the Buran orbiter tile heat shield based on the SiO2–B2O3–SiB4 system. The effects of heterogeneous recombination proceeding in accordance with the Langmuir-Hinshelwood mechanism, as well as the processes involving carbon atoms and those involving physically adsorbed oxygen atoms, on the heat fluxes to the glassy coating are analyzed on the surface temperature range from 300 to 2000 K.