NNC RK Bulletin. 2021; 4(88):10–15Page 14, at the end of the text prior to the section «REFERENCES»should be added: «This research was funded by the Ministry of Energy of the Republic of Kazakhstan (BR09158585).»The original article can be found at https://doi.org/10.52676/1729-7885-2021-4-10-15.

The paper presents the results of spectroscopic measurements of plasma discharges at the KTM tokamak. The measurements were carried out during the June 2021 campaign, which plasma discharges were obtained with a plasma current from 120 kA to 150 kA and a duration of ~250 ms.In connection with the design changes inside the vacuum chamber of the tokamak, special attention is paid to the study of the elemental composition of the plasma and the analysis of impurities and the ways of their entry is carried out. Impurities in plasma directly affect radiation losses. Optical spectroscopy (OS) is one of the main methods for studying the penetration of impurities into plasma.An Avaspec-ULS2048CL-EVO-RS-BB spectrometer was used to determine the emission spectrum of the KTM tokamak plasma. The time evolution of the hydrogen lines was measured using the diagnostics of a Hα-Dα monitor equipped with narrow-band interference filters (FWHM 1 nm).Based on the measured emission spectrum, it was found that in the hydrogen plasma of the KTM tokamak, in addition to the presence of a working gas, there were also impurities of carbon, oxygen, nitrogen and argon (C, O, N, Ar) in various ionization states.

The formation in the T-15 Upgrade tokamak of plasma filaments with a smaller volume than in the base discharge scenario, keeping the total plasma current constant, has been studied by numerical simulation. The purpose of such operating regimes is to raise the specific power of additional plasma heating. These regimes are of interest for attaining highest possible temperatures under limited additional heating power, e.g., for attaining AT (Advanced Tokamak) regimes. Additionally, these operating regimes can be investigated in the early stage of the T-15 Upgrade experiments when the total available heating power is low. Calculations with the Tokameq code have produced stationary equilibrium configurations for reduced plasma volume regimes. Three variants of plasma-volume reduction have been considered: displacing the plasma filament to the strong magnetic field region near the inner chamber wall while maintaining the filament center in the equatorial plane, and also displacing the plasma filament up or down. Numerical calculations have shown that such regimes may reduce the plasma-filament volume by a factor of 2 to 5, thus significantly raising the specific power of additional heating.

Studies were performed on the possibility of using the coaxial plasma jet accelerator to facilitate breakdown and the plasma current start-up in the Globus-M2 and KTM tokamaks. The results of experiments on the jet injection into the Globus-M2 tokamak with a magnetic field of 0.7 T showed that the discharge current rise began 1–2 ms earlier than it did in experiments using gas puffing and inductive breakdown of the working gas. In this case, the breakdown voltage decreased approximately 2 times. The results of experiments on plasma jet injection through the equatorial diagnostic duct into the KTM tokamak with a magnetic field of 0.9 T showed that the gas breakdown occurred up to 6 ms earlier than the breakdown initiated using the inductive method. In this case, the loop voltage decreases approximately 1.5 times. In almost all shots using the accelerator, the gas breakdown occurred, while in its absence, sometimes the gas breakdown could not be obtained.

The paper describes a new system of integrated modelling SIEMNED (Software and Information Environment for Modelling and Numerical support of Experiments on complex Devices) designed for numerical support of experiments on tokamak installations. Also discussed are the results of its application to the modelling of discharge scenarios at the T-15 MD installation, which is currently being prepared for the physical launch.

The paper describes a new open access computing resource nfusion.cs.msu.ru. The resource includes modules for calculating equilibrium, vertical stability, plasma evolution, simulation systems for magnetic diagnostics, as well as a new algorithm for constructing three-dimensional tetrahedral meshes in areas of complex structure. The modules are integrated into a unified software environment designed for numerical support of experiments on tokamak installations. The possibility of accessing the calculation modules on the server via the Internet, data exchange and the issuance of calculation results in the form of files, figures, and tables has been implemented. The resource supports the simultaneous operation of several users and has an information support system in Russian and English.

The paper describes the main experimental results of testing the method of thermographic measurements on a test bench with a plasma-beam facility. The developed method is intended to improve the accuracy of surface temperature measurements of candidate materials of the first wall of future thermonuclear reactors during investigations on the KTM tokamak. The method is based on the use of an external infrared radiation to directly determine the changes in the body reflectivity and a corresponding increase in the accuracy of the temperature measurement by a thermographic camera by recalculating and correcting the value of the emissivity. Resulting curves of changes in reflectivity (emissivity) obtained from the measurements are close to the real values within the inaccuracy of the method. The results of the test demonstrated the efficiency of the proposed method.

The article presents and discusses works on achieving ohmic breakdown at the KTM tokamak. The vacuum chamber of the KTM tokamak has a number of design features that significantly distinguish it from other installations - massive low-resistance vacuum chamber with unevenly distributed elements. The first experiments showed that the presence of massive asymmetrically distributed conductive elements of the KTM vacuum chamber leads to the complexity and inaccuracy of modeling the induced eddy currents and, accordingly, to the inaccuracy of calculating the field null configuration. Due to the limited value of the toroidal electric field of about 1.6 V / m and the toroidal magnetic field of 1 T, there are high requirements for the value of the stray poloidal magnetic field in the breakdown region for its implementation. So, it was required to carry out comprehensive work to achieve a breakdown at the KTM tokamak.

The article describes the characteristics of optical diagnostics of the tokamak KTM and the results of measuring the plasma parameters of the tokamak KTM obtained with their help. The measurements of the parameters of the plasma discharge were carried out as part of the work at the second stage of the physical start-up of the tokamak KTM. Based on the obtained experimental data the elemental composition of the plasma was estimated by measuring line radiation in the visible range (380–700 nm), the moment of plasma breakdown was determined and the position and shape of the plasma column was estimated.

О ВОЗМОЖНОСТИ ПОВЫШЕНИЯ ТОЧНОСТИ ТЕПЛОВИЗИОННЫХ ИЗМЕРЕНИЙ КАНДИДАТНЫХ МАТЕРИАЛОВ ПЕРВОЙ СТЕНКИ ТЕРМОЯДЕРНЫХ РЕАКТОРОВ НА ТОКАМАКЕ КТМБ.Ж.Чектыбаев 1 , Э

Main experimental work results of obtaining plasma discharge at KTM tokamak are outlined in the paper. Results of initial prebreakdown magnetic field configuration scenario calculations by Plasmaless Tokscen numerical code and results of measuring parameters of selected scenario by diagnostic set of KTM are shown. All KTM electromagnetic system power supplies have been used during experiments on KTM tokamak. However, power supplies of central solenoid and toroidal magnetic field coils have been used only on its half project power, because of incompleteness of commissioning works.

The paper deals with a complex of OHF diagnostics of tokamak KTM, designed to measure the electron density of the plasma. The composition of the OHF diagnostics, their technical features of execution and placement are discussed, and the first experimental results on the measurement of the electron density of the KTM plasma using them are presented. Special attention is paid to the principle of operation of OHF devices and the location of diagnostics on the tokamak.

The article presents the calculated variants of current scenarios for the realization of ohmic breakdown of the hydrogen gas in the KTM tokamak. The magnetic configuration of the fields at the time of the breakdown and the main parameters of the breakdown in the vacuum chamber are given, taking into account the basic conditions and limitations for the KTM tokamak. Current scenarios are prepared using the Plasmaless Tokscen calculation code. Based on the calculated estimates of the feasibility of the breakdown, optimal values of the necessary parameters for starting work on the KTM tokamak were selected.

Nowadays, several hundred of numerical codes have been created and successfully operated within the framework of research program of Controlled Fusion, simulating all the most important processes in the plasma. The most important problem today is the creation of an integrated software environment on their basis capable of designing of Tokamak installations and supporting of experiments on them. The creation of such an environment implies the development of software that is equally convenient for calculators, experimenters and engineers. The development of such software includes the construction of developed informational and computational portals that allow using locally stored numerical codes and simulation systems remotely via a standard Web-browser. Recently appeared Web-programming systems, Internet technologies and new computer protocols provide the necessary basic tools for creating such informational-computational portals. We’ve developed a new open access computing resource nfusion.cs.msu.ru, which includes modules for calculating the equilibrium, vertical stability, evolution and transport of plasma, as well as simulation systems for magnetic plasma diagnostics [1-5]. These modules are integrated into a unified software environment that allows the numerical support on tokamak installations. The resource allows you to access the calculation modules stored on the server via the Internet, perform an automated data exchange between the modules, and print out the results of calculations in the form of files, pictures, graphs and tables. The resource supports the work of several users located in different places simultaneously and has a system of information support in two languages (Russian, English). This work was carried out with the support from the RFBR (grants No. 17-07-00544-a, 17-07-00883-a). References [1]. Sadykov A.D., Sychugov D.Yu., Shapovalov G.V., Chektybaev B.Zh., Skakov M.K. and Gasilov N.A. 2015 Nuclear Fusion, 55, N. 4, 55043017.

Currently, all of the main elements of the T-15 design have acquired their specifics, and, therefore, it is possible to conduct a sufficiently detailed analysis of future experiments. In this paper, we simulated the stage of current increase and the beginning of transition to a configuration with a divertor. We were interested in the degree of correlation between the scenario calculations, which were carried out using various numerical codes, the existence or absence of the problem with vertical plasma instability at this stage, and the accuracy of restoration of the plasma boundary, which depends on the error of magnetic sensors. As a result of calculations, it was possible to show that the stage of discharge, which was considered by us, is quite real from the point of view of its realization.

Building T-15 tokamak highlights the problem of clarifying the discharge scenarios foreseen for this installation. An analysis of the transition to the divertor configuration (0.7-1.2 sec.) and the stationary phase was performed in the works [1-3]. It has been shown that in these stages the vertical plasma instability is suppressed by the feedback system, and that the system of magnetic diagnostics restores the plasma boundary to the specified accuracy if the sensors measurement error does not exceed 1-3 percent. Calculations have shown a good degree of compliance with the results obtained using the DINA and TOKSCEN codes that indicates the study reliability of these stages of the discharge. Thus, the most urgent task today is to study the initial stage of the discharge, from the current breakdown before the start of the process of forming the divertor configuration (approximately 0.7 sec.). The study means: 1) the clarification of the time dependence of the current magnitude in the coils of the poloidal magnetic system, 2) the comparison of the results of calculations on the various codes, 3) the clarification of the restoration accuracy of the plasma boundary in the initial stage of the discharge. The aim of the work was to conduct such an analysis. The calculations use numerical codes DINA [4], TOKSCEN [5] and RPB (restoration of the plasma boundary) [6]. The calculations could find a realistic scenario of an initial stage of the discharge. This work was supported by grant from Russian Scientific Foundation (project 14-22-00193).

Experimental technique of measurement of magnetic field null region inside of the KTM tokamak vacuum chamber has been developed. Square matrix of 36 2D Hall sensors, which used in the technique, allows carrying out direct measurements of poloidal magnetic field dynamics in the vacuum chamber. To better measuring accuracy, Hall sensor’s matrix was calibrated with commercial Helmholtz coils and in situ measurement of defined magnetic field from poloidal and toroidal coils. Standard KTM Data-Acquisition System has been used to collect data from Hall sensors. Experimental results of measurement of magnetic field null in the vacuum chamber of KTM are shown in the paper. Additionally results of the magnetic field null reconstruction from signals of inductive total flux loops are shown in the paper.

The code TOKSCEN (TOKamak SCENario) for the modelling of plasma evolution is described in this paper. The modelling is based on numerical solution of the Grad-Shafranov equation of plasma equilibrium and circuit equations for eddy currents at each time step. The circuit equations for eddy currents are solved in matrix form using the technique of matrix inversion. The plasma current distribution should be given. The code enables the calculation of an increment of vertical instability at each time step of the plasma evolution. The algorithms of the code were used for the modelling of processes in KTM and other tokamaks.