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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. [ABSTRACT FROM AUTHOR]

In experiments with neutral beam injection on the Globus-M2 spherical tokamak, sequences of long-lasting harmonics of toroidal Alfvén modes were discovered, equidistant from each other in frequency and shifted from zero by a constant value. Using microwave Doppler backscattering diagnostics, the central localization of toroidal modes was determined. In this work, the possibility of "splitting" of toroidal harmonics due to the Doppler shift caused by the toroidal rotation of the plasma is being discussed. It is found that the unshifted frequency of the toroidal Alfvén mode obtained from the spectrum of the magnetic probe signal is in good agreement with the frequency of the mode calculated at the mode location radius, and the toroidal rotation frequency, also determined from the spectrum of the magnetic probe signal, correlates well with the rotation frequency measured using charge exchange spectroscopy diagnostics, but differs by a constant amount. Possible reasons for the discrepancies are being discussed. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

At the compact spherical Globus-M2 tokamak, a series of experiments was conducted to study the effect of the injection of nitrogen on the discharge parameters. The experiments were carried out in discharges in deuterium in the divertor configuration, and the auxiliary heating was performed by deuterium neutral beam injection. During the nitrogen seeding, a substantial decrease in electron temperature near the divertor was recorded as well as a sharp decrease of the heat flux onto the divertor plate, while the density and temperature of the main plasma changed insignificantly. Simulations by the SOLPS-ITER showed a satisfactory agreement with the experiment. [ABSTRACT FROM AUTHOR]

The thermal energy stored in plasma , normalized internal plasma inductance and current beta are calculated via the free-boundary equilibrium PET code. The equilibrium reconstruction algorithm is iterative method of minimizing two parameters, the distance between the reconstructed plasma boundary and that simulated by the PET code, as well as the difference between the plasma diamagnetic flux from PET and the experimental one. The discharges from the Globus-M2 tokamak with a toroidal magnetic field up to 0.9 T and a plasma current of 0.3–0.4 MA in a mode with auxiliary heating by two atomic injectors are analyzed. The possibility of using approximate formulas for estimating and is considered. The measured diamagnetic flux is used to determine and then to calculate . The normalized internal plasma inductance is additionally determined from the measured vertical magnetic field under the assumption that . [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

With an increase of magnetic field up to 0.8 T and plasma current to 400 kA, fast ion losses rate in the discharges with toroidal Alfven eigenmodes decreased in tokamak Globus-M2 comparing with Globus-M tokamak discharges. Taking into account the data on the discharges with increased magnetic field and plasma current, the regression fit of neutral particle analyzer flux drop in energy channel close to neutral beam energy on relative eigenmode magnitude, the value of magnetic field and plasma current was analyzed. The power of flux drop dependence on TAE magnitude was found to be ~0.5 and inverse proportional on the value of product of magnetic field and plasma current, which is highly likely is determined only by plasma current due to weak dependence on magnetic field. The result obtained indicates that fast ion losses in Globus-M2, stimulated by toroidal Alfven eigenmodes are mostly determined by the shift of passing orbits to the plasma edge. With the increase of plasma current and magnetic field, neutron flux drops arising in the moments of toroidal mode bursts have also decreased. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The paper presents the first ion temperature profile measurements results in the new spherical tokamak Globus-M2, which were obtained in discharges with neutral beam injection using the Charge eXchange Recombination Spectroscopy (CXRS) and the Neutral Particle Analyzer (NPA). Ion heat transport modeling using ASTRA code was carried out based on the obtained experimental ion temperature. The results of the modelling indicate the predominantly neoclassical ion heat transport. [ABSTRACT FROM AUTHOR]

The article presents the results of studying the transfer of heat and particles in the Globus-M2 spherical tokamak in discharges with neutral injection at the current ramp up. An atomic beam was injected into the tokamak plasma at a fixed toroidal magnetic field of 0.7 T. The plasma current on the plateau was varied in the range 0.2–0.3 MA. Based on the electron temperature and concentration spatial distributions measured by the Thomson scattering method, the transport of heat and particles in plasma was simulated using the ASTRA code. The energy confinement time of the plasma was determined, as well as estimates of the coefficients of thermal diffusivity and diffusion was made. [ABSTRACT FROM AUTHOR]

On the spherical tokamak Globus-M2 in discharges with toroidal magnetic field of 0.7 T by means of magnetic probes and a number of other diagnostics during neutral beam injection at the current ramp up stage, magnetic field oscillations in the range of 100–300 kHz having their frequency increasing in time, had been observed. Eigenmodes with wavenumbers n = 1–3 and m = 2–4 were being registered. These oscillations were identified as Alfvén cascades. By means of multi-channel fluctuation reflectometer, observed eigenmodes were found to be localized near the magnetic shear reversal radius. Application of MHD-spectroscopy technique allowed us to determine safety factor temporal evolution and experimental values are in well agreement with modelling results, provided by ASTRA transport code. [ABSTRACT FROM AUTHOR]

Globus-M2—a new 1-Tesla spherical tokamak—was recently launched. The main features and research directions of this machine in scope of fusion–fission reactor development are described. Main results of the first experimental campaign with toroidal magnetic field up to 0.73 T and plasma current up to 0.33 MA are discussed. Significant improvement of the discharge parameters as compared to Globus-M was achieved. Plasma total stored energy higher than 7 kJ was obtained. Energy confinement time increase was consistent with predictions by spherical tokamak scalings. Toroidal Alfvén eigenmode-induced losses decrease with increase of plasma current and toroidal magnetic field. For the first time, LHCD with the toroidal wave slowing-down was successfully used at a spherical tokamak. [ABSTRACT FROM AUTHOR]

The paper presents the latest results and summarizes the study of ion heat transport in the Globus-M spherical tokamak in regimes with neutral beam injection. Ion heat transport was investigated in discharges with various toroidal magnetic fields and plasma currents. Measurements of the ion temperature were carried out using charge-exchange recombination spectroscopy and a neutral particle analyzer. Plasma simulations using transport code ASTRA have shown that ion heat transport in Globus-M is predominantly neoclassical even for low collisionality range. The local transport analysis indicates that plasma core is stable to ion scale instabilities. [ABSTRACT FROM AUTHOR]

The article presents research on neutral beam current drive in Globus-M compact spherical tokamak. The experiments were performed in the plasma current range of 0.17–0.20 MA with a 0.4- or 0.5‑T toroidal magnetic field. The injection impact parameter was 33 cm. The variable parameters included compositions of plasma and the heating beam (hydrogen, deuterium), plasma density, and vertical displacement of the plasma column. The simultaneous increase in the plasma current and drop in the loop voltage were used to determine the neutral beam current drive. The injection of a hydrogen/deuterium beam into deuterium or hydrogen plasma resulted in a significant and reproducible drop in the loop voltage (up to 0.5 V). In order to process the obtained data, the authors developed an ASTRA code-based model, which allows one to calculate the neutral beam-driven current and bootstrap current. The share of noninductive currents as a function of plasma density during the injection of a hydrogen beam (28 keV, 0.5 MW) into the deuterium plasma was calculated. The authors analyze the results of experiments on off-axis beam injection achieved by vertical displacement of the plasma column and the effect of increasing the toroidal magnetic field on the consumption of the poloidal magnetic flux in discharges with atomic beam injection. [ABSTRACT FROM AUTHOR]