Grain boundary segregation of solutes is a powerful tool for stabilizing nanocrystalline materials. However, previous studies developed an approach to calculate stabilization only in binary systems. In this work, we derive a spectral segregation model for an arbitrary number of solutes in the dilute limit (neglecting solute–solute interactions) and demonstrate that multicomponent segregation substantially expands the range of nanocrystalline alloys thermodynamically stable against both grain growth and phase separation.

Solute segregation at grain boundaries is emerging as a promising tool for the stabilization of polycrystals against grain growth. Modern approaches to segregation modeling are based on employing atomistic grain boundary segregation spectra. Currently, there is no spectral model that accounts for solute-solute interactions beyond the random mixing approximation. The paper shows that such interactions are crucial for the Ag(Ni) system, which is the focus of this study. We derive the Gibbs free energy for a spectral model of grain boundary segregation that properly captures solute-solute interactions strong enough to violate the random mixing assumption. Strong attractive interactions have been shown to be independent of solute concentration and can be directly incorporated into the segregation spectrum. Moreover, at zero temperature, all types of solute-solute interactions can be incorporated into the segregation spectrum, allowing the calculation of zero-temperature stability scores with regard to solute-solute interactions. This may enhance the reliability of screening for stable nanocrystalline alloys. Finally, the model incorporating solute-solute interactions into the segregation spectrum has been shown to provide a reliable approximation for systems exhibiting strong solute-solute interactions, even at moderate temperatures.

The paper is devoted to the Thomson scattering (TS) diagnostics recently developed for the Globus-M2 spherical tokamak and prototyping the ITER divertor TS diagnostics. The distinctive features of the system are the use of spectrometers, acquisition system and lasers that meet the base requirements for ITER TS diagnostics. The paper describes the diagnostic system that allows precise measurements of TS signals, as well as the results of the first measurements of electron temperature and density in both central region of the plasma column and scrape-off layer. The system provides measurements of electron temperature $T_{e}$ in the range of 5 eV to 5 keV and density $n_{e}$ in the range of $5{\cdot}10^{17}{\div}3.25{\cdot}10^{20} m^{-3}$. The use of two ITER-grade probing lasers of different wavelengths (Nd:YAG 1064.5 nm and Nd:YLF 1047.3 nm) allows reliable measurement of $T_{e}$ in multi-colour mode, i.e., assuming that spectral calibration is unknown.

A diagnostic system for Thomson scattering of the central, edge and divertor plasma regions of a tokamak with reactor technologies is discussed. The rationale and choice of technical solutions are given, the composition of the Thomson scattering diagnostic complex is discussed, as well as an estimate of the accuracy of measuring the electron temperature and plasma density in the central edge and divertor regions of the TRT tokamak. Particular attention is paid to ensuring the functionality of the proposed diagnostics in the reactor mode of the tokamak operation and the results of testing diagnostic equipment in experiments on the Globus-M2 tokamak.

Thomson scattering of the core edge and divertor plasma regions of a tokamak with reactor technologies is discussed. The rationale and choice of technical solutions are given, the composition of the Thomson scattering diagnostic complex is discussed, as well as an estimate of the accuracy of measuring both electron temperature and density. Particular attention is paid to ensuring the functionality of the proposed diagnostics in the reactor mode of the tokamak operation and the results of testing diagnostic equipment in the experiments on Globus-M2 tokamak.

Options for implementing the IR thermography diagnostic system in a TRT facility are considered. Two variants of the optical scheme for measuring the temperature of the first wall and divertor targets are proposed: a wide-angle system combined with two divertor channels and a four-channel viewing system. The optical resolution of both systems and the levels of the collected signal are numerically simulated. On the basis of the calculations performed, conclusions are drawn about the compliance of the systems with the requirements for measuring the temperature of TRT plasma-facing elements. The sources of the temperature measurement error are considered, and the error caused by the reflection of radiation from structural plasma-facing elements by the surface under study is estimated. Calibration issues for IR thermography diagnostics are also discussed.

Basic principles are discussed for a first mirrors unit (FMU) design for International Thermonuclear Experimental Reactor (ITER) optical diagnostics, equipped with an RF capacitive coupled discharge cleaning subsystem. A nontunable RF prematcher device is shown to be desirable in the proximity to the discharge load to avoid excessive heating of an in-vessel RF feeder part. A possibility of satisfactory RF prematching with a simple nontunable L-shaped circuit is demonstrated for the experimentally measured RF discharge impedance variation. The structure of an FMU RF power distribution circuit is suggested, consisting of an RF prematcher, an RF power meter, and, when required, an RF decoupler of a DC-grounded water-cooled mirror. Planar implementation of an RF prematching device is recognized as the most feasible and universal, as a result of analysis of various base element types. Three options of RF-decoupled mirror cooling manifolds are discussed, revealing an optimal selection of their electric and dimensional parameters. A structural implementation of a planar RF prematcher ceramic parts fastening is suggested, taking into account their integrity under inertial, neutron, and thermal loads expected during ITER operation. Successful pilot tests of the RF prematcher performance and structural integrity demonstrate the promise of the described design approach.

A conceptual design for diagnosing erosion of the first wall and divertor plates of a tokamak with reactor technologies TRT is proposed. The principles of constructing a diagnostic complex based on the following systems are developed: laser radar, dual-wavelength digital holographic interferometry and active laser IR thermography. An optical scheme is developed for combining the optical paths to input laser radiation and collect scattered light from diagnostic systems. To view the maximum area of the first wall, a scheme for optical scanning of the surface of the first wall and divertor is proposed. Based on optical simulation, the spatial distribution of the power density and phase of interferometry laser radiation in the illuminated region of the first wall is constructed, and the dimensions of the light fields and power density for IR thermography and laser radar diagnostics are determined. An image formation scheme is proposed and the spatial resolution is determined for interferometry and IR thermography methods. The light scattering function on models of the ITER divertor cladding is studied experimentally. The energy of the collected signal is calculated on the basis on the experimental data for all three diagnostic methods and the requirements for the diagnostic equipment are formulated.

diagnostics of the plasma electron component by the metho d of Thomson scattering Te(R, t) of laser radiation makes it possible to reliably measure the spatial distributions of the electron temperature and density. One of the obstacles to the implementation of TS diagnostics in thermonuclear reactors is the distortion of the spectral characteristics of the optical system due to radiation-induced absorption and contamination of optical elements with erosion products of the first wall. As a consequence, the reliability of measurements by the TS method will decrease over time. The paper describes the method of multi-laser Thomson scattering, which will solve this problem. The results of the first experiments on the Globus-M2 tokamak are also presented.

Piezoelectric motors designed for operation in the ITER tokamak-reactor must be tested for stability under severe radiation conditions. Properties of lead zirconate-titanate that is the most common type of piezoelectric materials were analyzed from the point of view on influence of radiation. It is shown that, at the expected in ITER level of radiation, this piezoceramics has a good potential for resistance to radiation induced amorphization and depolarization.

Leucosapphire (c-LS) structure and transmission in visible after surface treatment in 90%H2-10%N2 RF discharge are studied. According to AFM, the number of scratches of the mechanically polished surface decreased significantly after removal of about a 300 nm layer (exposure time of 12 h) under unchanged rms of roughness. According to TEM, a two-layer structure formed in the near-surface region consists of an outer 10 nm amorphous layer followed by a crystalline layer of 40-50 nm with a high defect density. The c-LS transmission in the angle of 400-1000 nm either slightly increased or remained unchanged. The demonstrated transmission stability during exposure in 90%H2-10%N2 RF discharge allows us to consider the plasma sputtering as a promising technique for cleaning contaminated windows protecting first mirror of divertor Thomson scattering being developed for ITER divertor Keywords: Leucosapphire, RF discharge, hydrogen, nitrogen, AFM, TEM, surface layer structure, visible transmission.

The results of measuring the electron temperature and density spatial distributions in plasma of the Globus-M2 tokamak using the Thomson scattering diagnostics are presented. The diagnostics provides measurements throughout the entire tokamak discharge, starting from time of gas breakdown. The Thomson scattering data were analyzed in order to determine the positions of the last closed flux surface, the plasma magnetic axis, and the radius of inversion during the saw-tooth oscillations. The results of measurements performed during the internal reconnection of magnetic field lines are presents, as well as the dynamics of spatial distributions of electron temperature, density and pressure during the plasma transition to the H-mode. The results of measuring the electron temperature distribution in the scrape-off layer using the Thomson scattering diagnostics are also presented for distances up to 4 cm outside the last closed flux surface.

In ITER, the first mirrors of optical diagnostics will be prone to deposition of the first wall materials which will result in the degradation of the mirror's optical parameters and the parameters of the diagnostic itself. To restore the mirror's reflectivity a cleaning system based on the gas discharge will be employed. The present paper discussed low-frequency power modulation of capacitively-coupled RF discharge utilized to decrease the mean RF power supplied through the in-vessel feeding line. The impact of power modulation on the incident ion flux, distribution of ion energy, and sputtering rates of the first wall materials were studied for the cases of DC-coupled and -decoupled mirrors with/without external magnetic field. The parameters of the plasma were measured depending on modulation frequency (1 Hz - 10 kHz) and duty cycle (10 - 90 %) for He plasma at a pressure of a few Pa. Based on the measurements of ion flux and ion energy the sputtered rates of Be and BeO were estimated. The estimations of the sputtering rate were followed by experiments on BeO sputtering in He plasma. Finally, the recommendations are given for selecting an appropriate RF power required to clean the mirror from Be/BeO deposits in ITER.

Solute segregation at grain boundaries is becoming a promising tool for stabilising a polycrystal against grain growth. The modern approach enables modelling this segregation using the grain boundary segregation spectra. In this paper, considering the spectral model of segregation, we derive the thermodynamic state functions, including Gibbs free energy, and find an equilibrium equation, taking into account a solute-solute interaction and non-zero temperature. The stability criteria against grain growth and competing phase precipitation are also proposed. We show that the sign of a solute-solute interaction is of important difference, since the attractive interaction improves stability and is not negligible even in the dilute limit, while the repulsive interaction weakens stability, but is negligible at low concentrations. The equilibrium segregation concentrations are found to be determined only by temperature, neglecting a solute-solute interaction, otherwise a dependence on the total solute concentration appears.

Absorbed power of the neutral-injection beam in spherical tokamaks Globus-M/M2 is estimated numerically. Deceleration of fast particles is simulated by means of the NUBEAM code. The signal of analyzer of charge-exchange atoms is simulated by means of the FIDASIM code using the distribution function of fast ions calculated by means of the NUBEAM code. Comparison of calculated and experimental signals allowed determining the degree of influence of instabilities on confinement of fast particles along with absorbed beam power.

An important part of high-temperature plasma study is the determination of the electron temperature dynamics in the tokamak plasma. At spherical tokamaks, one can use Thomson scattering diagnostics as well as soft X-ray emission diagnostics (SXR). The capabilities of electron temperature measurement by the first diagnostics are limited by the repetition rate of laser pulses and their number in one tokamak discharge. Data of the second diagnostics are continuous in time and are determined by the time resolution of the detectors; however, obtaining the electron temperature using these data encounters a number of difficulties considered in this study. A method of combined processing of results of these diagnostics using machine learning algorithms was developed for overcoming these difficulties and applying the adVoprosy Atomnoi Nauki i Tekhniki, Seriya: Termoyadernyi Sintezages of both diagnostics. Training data include soft X-ray diagnostic data, hard X-ray diagnostic data, and CIII line emissivity diagnostic data. Thomson local scattering measurements were used as labels for supervised machine learning. The developed technique provides significant extension of the possibilities of determining the electron temperature at the Globus-M2 tokamak.