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.

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.

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.

This paper highlights the most important results achieved at the spherical tokamak Globus-M2 with a high magnetic field. This paper also covers the most important topics of fusion research: thermal energy confinement in regimes with neutral beam injection, toroidal Alfvén eigenmode and correspondent fast ions confinement issues, L-H transition, turbulence suppression and edge-localized modes' behavior, experimental and theoretical study of regimes with nitrogen seeding that allow to significantly reduce thermal loads on the divertor plates, and experiments and simulations of lower hybrid current drive. The research results provide the basis for the next step toward a fusion neutron source—the development of the Globus-3 spherical tokamak.

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.

The paper presents the improved FCDI plasma equilibrium reconstruction algorithm implemented at the Globus-M2 tokamak. The algorithm has been improved to be able to operate in real time. The FCDI-FF (Fixed Filaments) operation mode was added, in which the plasma is modeled by current filaments at fixed positions. New user interface for the algorithm displays reconstructed plasma separatrix and contours of the internal magnetic surfaces, the poloidal flux distribution, and graphs of the reconstructed plasma parameters, including profiles of plasma pressure, poloidal current and safety factor q, plasma energy, poloidal beta and internal inductance, which can be exported in *.mat, *.json and G-eqdsk formats.

The thermal energy stored in plasma Wp, normalized internal plasma inductance li and currentbeta bi are calculated via the free-boundary equilibrium PET code. The equilibrium reconstruction algorithmis iterative method of minimizing two parameters, the distance between the reconstructed plasmaboundary and that simulated by the PET code, as well as the difference between the plasma diamagnetic fluxfrom PET and the experimental one. The discharges from the Globus-M2 tokamak with a toroidal magneticfield up to 0.9 T and a plasma current of 0.3–0.4 MA in a mode with auxiliary heating by two atomic injectorsare analyzed. The possibility of using approximate formulas for estimating and is considered. The measureddiamagnetic flux is used to determine bdia and then to calculate Wdia . The normalized internal plasmainductance is additionally determined from the measured vertical magnetic field under the assumption that bp=bdia.

The pyGSS code constructed for computation of free-boundary plasma equilibrium in spherical Globus-M2 tokamak is described. Currents in the coils of the electromagnetic system, their coordinates, plasma current, positions of the limiter and current-conducting wall, etc., are used as the input parameters. Free parameters determining spatial distribution of equilibrium pressure and current density are selected in the course of code execution in such a way that the results of reconstruction would agree with the experimental measurements of the poloidal magnetic flux by means of toroidally closed loops. The results of computation of equilibrium are compared with those obtained by means of other codes and experimentally measured thermal plasma energy, position of the separatrix outer leg, the diamagnetic-loop signal, etc.

Among the peripheral instabilities observed at the Globus-M2 tokamak, two types of edge localized modes (ELMs) are brought into focus: ELMs synchronized and desynchronized with the sawtooth oscillations. The desynchronized ELMs appear in regimes that are characterized by high values of pressure in the pedestal, p ped ≥ 3 kPa, and they are observed in discharges with the toroidal magnetic field B T > 0.6 T and plasma current I P > 0.3 MA. The desynchronized ELMs belong to the type-III/V with the dominating effect of the peeling mode. The synchronized ELMs were observed in a wider range of discharge parameters, including at B T < 0.6 T and I P < 0.3 MA. Calculations of the stability of the peeling-ballooning (PB) mode showed that at pedestal width ψ norm = 0.09 and p ped > 3.5 kPa, destabilization of PB modes is possible without additional influence. Experimental data shows that the microtearing mode plays a dominant role in the pedestal. The microtearing mode does not allow the pedestal at Globus-M2 tokamak to reach the state of the unstable kinetic ballooning mode (KBM), which explains the low predictive power of the EPED model at this tokamak.

The description of the zero-dimensional engineering-physical code GLOBSYS (Globus spherical tokamak system code), designed for parametric analysis of the next step of the program Globus-M, Globus-M2, is given. Within the framework of the zero-dimensional approximation, the definitions of the main scaling parameters of the plasma (poloidal beta, the fraction of bootstrap current, the energy lifetime of the plasma), as well as the specifics of calculating the inductance and resistance of the plasma in spherical tokamaks, are refined. The results of calculations of the plasma parameters by the code were compared with the experimental data of one of the Globus-M2 discharges (no. 38800) with neutral beam heating and showed good agreement. It is proposed to perform a comparison of calculations based on the code with the achieved and predicted parameters of the spherical tokamaks NSTX, NSTX-U, MAST, MAST-U, and ST40 in a separate paper. The goals of the next step (Globus-3) are formulated, the main ones of which are long pulse, high toroidal field, and powerful heating, which allow us to consider Globus-3 as a hydrogen prototype of a neutron source. The infrastructural restrictions on the Globus-3 parameters are given, which require further analysis of various versions of the electromagnetic system. Using the example of Globus-M2 discharge no. 38800, the effect of restrictions on the flow balance and heating of the elements of the electromagnetic system is shown.