In 2023, the Thomson scattering diagnostics with tangential probing geometry was installed and put into operation at the T-15MD tokamak. The new system is based on a 100-Hz Nd:YAG laser with a pulse energy of up to 3 J at the first harmonic, λ = 1064 nm. The system allows measurements to be carried out throughout the plasma discharge with its duration of up to 10 s with a time interval of 10 ms. Laser radiation is introduced into the tokamak vessel in the equatorial plane, passing through the entire plasma volume from the inner to the outer periphery of the plasma. The scattered radiation acquisition system is located inside the equatorial port of the facility. The range of scattering angles is from 11° to 56°. The recording system is based on 10 polychromators on interference filters. Using this diagnostics, the electron temperature and density have been measured in the experimental campaign at the end of 2023. The system operation was demonstrated throughout the entire tokamak discharge in a wide temperature range and with a discharge duration of up to 2 s.

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.

The high-confinement mode in tokamaks (H-mode) is characterized by high pressure gradients at plasma edge, which results in the appearance of edge localized modes (ELMs). They are studied at the Globus-M2 spherical tokamak too, where edge localized modes are observed mainly in regimes with neutral beam injection. One of the ways for studying ELMs is the use of the Doppler backscattering (DBS) diagnostics installed at Globus-M2. It makes possible to estimate the amplitude of plasma density fluctuations and measure the radial electric field Er. In this work, the effect of edge localized modes on the Er field is studied in the radial range 0.4 < ρ < 1.1. It is shown that during ELMs the electric field increases in the entire measurement range. This indicates that ELMs affect the inner plasma regions as well. This is not consistent with the general ideas concerning the peripheral localization of ELMs, but is confirmed experimentally not only at Globus-M2. In addition, the results for the regime with ELMs are compared with those for the regime with limit cycle oscillations (LCOs) and it is shown that during LCOs such effect is not observed.

Data on plasma disruption processes in the modernized Globus-M2 spherical tokamak are presented. Electron temperature and density profiles before the disruption, immediately after thermal quench and in the stage of plasma current quench are measured using the diagnostics of Thomson scattering of laser radiation. The dependence of the plasma current decay time during disruption on the pre-disruption current value is determined. The distribution of the toroidal current, which is induced during disruption, in the shell of the vessel is determined on the basis of magnetic measurements. Electromagnetic loads on the vessel are calculated.

Technical solution were presented for a foil spectrometer installed on the Globus-M2 and TUMAN-3M tokamaks for measuring the electron plasma temperature. Measurements have been carried out of the time dependence of the plasma temperature in the central region of tokamaks. Using of integrated photodetectors and unique beryllium foils with a thickness of 14-80 μm made it possible to increase the sensitivity of the spectrometer. An important quality of the foils used were the increased values of strength, plasticity, homogeneity, and the absence of surface and internal defects. The combined use of the spectrometer with Thomson scattering diagnostics made it possible to carry out regular temperature measurements in the Globus-M2 tokamak with a high spatial and temporal resolution. The influence of impurities is estimated on the measurement of the electron temperature of the plasma. Keywords: foil spectrometry, tokamak, plasma, continuum, bremsstrahlung, electron temperature, soft-X-Ray, Si-photodiode.

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.

The intermediate mode between the ohmic, or low confinement (L-mode), and the increased confinement (H-mode) regimes, or the so called I-phase, which is characterized by the existence of zonal flows in the form of limit cycle oscillations (LCOs), was observed on the Globus-M tokamak. Depending on the LCO frequency, the I-phase resulted in either a transition to H-mode or back to L-mode. The possibility of L-I-H transition initiation induced by LCOs and the effect of LCO frequency were studied by means of numerical modeling of the density profile evolution, taking into account turbulence suppression by the inhomogeneous radial electric field. The modeling results show that lower LCO frequency could be a factor facilitating the L-H transition, whereas higher frequency LCOs are more likely to cause the backward transition to L-mode. The results are in qualitative agreement with the results of the studies of geodesic acoustic mode (GAM)-initiated L-H transition in the TUMAN-3M tokamak, where a lower GAM frequency was found to be beneficial for L-H transition initiation.

A set of magnetic coils used to correct the error fields at the Globus-M2 spherical tokamak, which appear due to the imperfections of the production and assembly of the tokamak magnetic system, is described. The magnetic sensors that are used to monitor the locked helical MHD modes are also described. The results of experiments on detecting the locked modes in the discharges with plasma heating by neutral beam injection are presented. A correlation is found between the appearance of the locked modes accompanied by the loss of fast ions and the confinement of the main plasma.

It is shown that the radial profile of the electron temperature in the Globus-M2 spherical tokamak is related to the radial profile of the electron density by a power law T_e(ρ ) = const 1ptn_e(ρ )^1.65 . An analytical model of the density attractor, assuming the dependence of n_e on the specific poloidal volume v, previously tested on the TCV and JET tokamaks with a large aspect ratio, holds on the spherical tokamak, and the approximation of 162 experimental profiles has resulted in n_e(ρ )v(ρ )^1.06 = const . The proposed model makes it possible to calculate the spatial distribution T_e(ρ ) and n_e(ρ ) according to a known magnetic configuration.

The dispersion interferometry diagnostic (DI) based on the CO2-laser was commissioned at the Globus-M2 tokamak for absolute measurements of the line-integrated electron density (IED) along the chord in the equatorial plane. IED measurement error corresponding to the intrinsic noise of the acquisition device was below 1017 m−2 with time and spatial resolution 20µs and 2 cm, respectively. Inference of the IED using the second harmonic interference was done by means of spectral algorithm. Execution of the algorithm is performed at the FPGA in real-time mode. During the year long operation, DI was proven to be reliable and robust IED diagnostic at Globus-M2.