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.

The heavy ion beam probe (HIBP) diagnostics at the TUMAN-3M tokamak was updated to provide measurements in the regime with neutral beam injection co-directed with plasma current (co-NBI). By means of HIBP, plasma potential measurements in the center of plasma were carried out. Plasma potential evolution in the discharge with the LH transition (transition to the improved confinement mode) is in good agreement with the concept of negative radial electric field generation during formation of the transport barrier.

A multi-diagnostic study of the fast ion losses and redistribution during toroidal Alfvén eigenmodes at the Globus-M and Globus-M2 spherical tokamaks was performed. Mode amplitude and frequency evolution are discussed. Local energy-resolved spatial transport was examined using an active neutral particle analyzer. Losses and transport dependences on the mode amplitude were obtained. The change in the ion transport with the increase in plasma current and toroidal magnetic field is reported. The experimental data are compared with the modeling results.

A neutron diagnostic system was developed at the Ioffe Institute as part of the Globus-M2 tokamak to optimize NBI heating conditions and evaluate heating efficiency. The system contains two compact neutron spectrometers based on the liquid organic scintillator BC-501A and two gas-discharge counters based on a 10B isotope. The BC-501A spectrometers were calibrated by measuring neutron emission produced in a 9Be(α,n)12C nuclear reaction on the cyclotron facility at the Ioffe Institute. In addition, in situ calibrations of the system, including the neutron spectrometers and the gas-discharge counters, was carried out using an Am–Be neutron source to provide accurate measurements of the total neutron yield from the plasma of the Globus-M2 tokamak. During the plasma experiments at the Globus-M2 tokamak, a deuterium beam was injected into the deuterium plasma that causes a yield of the DD-neutrons with ∼2.45 MeV energy. The neutron spectrometry diagnostic system was used to provide neutron measurements and detect the DD-neutrons in these experiments. The neutron yield and the DD-reaction rate during plasma discharges were evaluated. The energy distributions of neutrons emitted from plasma during discharges with neutron beam injection were reconstructed from the measured neutron spectra.

Heavy ion beam probe (HIBP) diagnostics on TUMAN-3M tokamak was updated to provide measurements in the regime with neutral beam injection co-directed with plasma current (co-NBI). By means of HIBP plasma potential measurements in the center of plasma were carried out. Plasma potential evolution in the discharge with L-H transition (transition to improved confinement mode) is in good agreement with the concept of negative radial electric field generation during the formation of transport barrier.

The study of the spectral properties of the electromagnetic radiation in the ion cyclotron frequency range from the TUMAN-3M tokamak plasma in the neutral beam injection (NBI) heating mode has been performed. The spectrum of this emission consists of several (up to four) narrow lines corresponding to different harmonics of the ion cyclotron resonance of the injected fast ions in the center of the plasma. Wave vectors corresponding to individual spectral lines are determined from the delays of signals from spatially separated probes. It is shown that under the assumption that the measured frequencies and wave vectors are described by a common dispersion relation, the observed emission can be explained by the appearance in the plasma an unstable fast magnetosonic wave propagating almost normally to the magnetic field.

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.

Paper reports a physical model of the beam transportation through the duct with realistic geometry. The beam losses are explained by interaction of the energetic particles of the beam with the duct walls resulting in strong influx of neutral gas, which interact with beam particles and cause their reionizaton. Using the model new design of the beam duct was developed. Ratio of the neutron fluxes values obtained under similar experimental conditions with the new transition duct and the old one fitted well with the model predictions.

The results of experiments on determining the polarization of two types of Alfvеn oscillations observed with magnetic probes in the TUMAN-3M tokamak are presented. The difference in the polarization of short and long bursts of Alfvеn oscillations, arising both in ohmic regime and during neutral beam injection, is found. The role of high-energy electrons in the excitation of Alfvеn oscillations is discussed.

A compact neutron spectrometer based on the BC-501A liquid organic scintillator was applied to neutron measurements at the TUMAN-3M tokamak. The spectrometer was calibrated using measurements from the ion beam of the cyclotron accelerator. Neutron spectra were measured during discharges using a neutral deuterium beam injection into the TUMAN-3M D-plasma. An energy distribution of the neutrons from the plasma that hit the spectrometer was obtained from the measured BC-501A instrumental spectra by the DeGaSum code using detector response functions obtained in the course of the calibration. This allowed for the estimation of the 2.45 MeV neutron yield and the evaluation of both the time evolution of the DD fusion rate and the characteristic time of the injected deuterium slowing down in discharges with neutral beam injection heating.

The results of experiments on determining the polarization of two types of Alfvén oscillations observed with magnetic probes in the TUMAN-3M tokamak are presented. The difference in the polarization of short and long bursts of Alfvén oscillations, arising both in ohmic regime and during neutral beam injection, is found. The role of high-energy electrons in the excitation of Alfvén oscillations is discussed.

The results of an analysis of the mechanisms of losses of a high-energy atomic beam in the connecting duct of the TUMAN-3M tokamak are presented. A numerical model is developed describing the effect of reduction of the duct transmission coefficient and allows reducing the power losses of the beam injection. Based on the model, a new duct with an increased cross section was constructed and installed on the tokamak. It was found that the replacement of the duct with the new one led to a 1.5- to 2-fold increase in the integral rate of the neutrons originated from dd-reactions of energetic deuterons with the target plasma.

A study of the spectral properties of electromagnetic radiation in the ion-cyclotron range from the plasma of the TUMAN-3M tokamak in the NBI heating mode has been carried out. The spectrum of this radiation consists of several (up to four) narrow lines corresponding to different harmonics of the ion-cyclotron resonance frequency of injected fast ions in the center of the plasma. Wave vectors corresponding to individual spectral lines are determined from the signal delays between spatially separated probes. It is shown that under the assumption that all the measured frequencies and wave vectors follow the same dispersion relation, the observed radiation can be explained by the appearance in the plasma of an unstable fast magneto-acoustic wave propagating almost normally to the direction of the magnetic field.

Numerous theoretical and experimental studies have proved the important role of radial electric field inhomogeneity, or shear, in LH-transition initiation, and established heating power threshold for transition, although some experiments provide the observation of LH-transition dependency on particle source. It is necessary to apply a concerted approach to describe LH-transition initiation possibility and dynamics, considering E-r shear, particle source and turbulence properties as the main factors responsible for LH-transition initiation.

In TUMAN-3M tokamak ohmic hydrogen and deuterium discharges oscillations with ion cyclotron (IC) frequency were detected. Fast magnetic probes poloidal array in TUMAN-3M is capable of detecting several harmonics of IC frequency of main plasma isotope. Fuel pellet injection significantly reduces IC oscillations intensity, though after complete pellet evaporation returns to initial level. IC oscillations localization and excitation conditions are of certain interest. Based on drift-cyclotron instability excitation theory and numerical modeling of scenarios with ohmic LH-transition and pellet-injection plasma parameters (density gradient primarily) effect on IC oscillations excitation was studied.

A compact neutral particle analyzer that has been modified for studying thermal and suprathermal ions in neutral-beam heated plasma is described. Results of the analyzer calibration performed using an atomic beam are presented. The possibility of adjusting the analyzer channel energies by varying the voltage applied to the acceleration module of the analyzer is tested. The measured ion temperatures and suprathermal-ion spectra are presented for discharges with the neutral beam injection at the TUMAN-3M tokamak.

Some factors limiting an increase in the plasma pressure at the periphery of the tokamak plasmas can arise when the improved confinement is achieved in the H-mode. It happens when the edge localized modes (ELMs) develop in tokamak plasmas, and the factors mentioned above manifested themselves in the form of quasi-periodic filamentary structures, or filaments. The formation of such structures results in the occurrence of the anomalous energy and particle flows onto the first wall and divertor plates of tokamaks. Studies of the filaments were previously performed at tokamaks with divertor configuration using various plasma diagnostic methods, including the Doppler backscattering method. The paper presents the first observations of the filaments at the TUMAN-3M, which is the tokamak with limiter configuration. The filaments were studied using the Doppler backscattering method. Plasma was probed by the double-frequency microwave radiation of the O-wave in the frequency range of 27–37 GHz. The data were obtained in the H-mode regime initiated by the pulsed gas injection, in which the ELM-like events are observed. The poloidal velocity of the filaments and their radial localization were determined, and the radial and poloidal sizes of the filaments were also estimated.

Geodesic acoustic mode (GAM) observations in TUMAN-3M tokamak show that in ohmic discharges with low plasma density GAM have intermittent character; transition to high confinement regime (LH-transition) is usually preceded by a short (up to 5 ms) GAM burst series with distinctive frequency drop, or there exists long (up to 30 ms) GAM burst series evolution with several characteristic timescales and varying amplitude. To determinate the effect of GAM temporal parameters on the possibility of LH-transition initiation numerical modeling of plasma density profile evolution under the effect of GAM burst sequence with varying frequency and amplitude was carried out.

Recent research at three small tokamaks with different parameters located at the Ioffe Institute—the spherical tokamak Globus-M, the large aspect ratio tokamak FT-2 and the compact tokamak TUMAN-3M—are reviewed. This overview covers energy confinement (Globus-M and FT-2), L–H transition (TUMAN-3M and FT-2), Alfvén waves (Globus-M and TUMAN-3M), ion cyclotron emission (TUMAN-3M), major plasma discharge disruption (Globus-M) and scrape-off layer (Globus-M) studies. A full-f global gyrokinetic modeling benchmark using synthetic diagnostics in FT-2 is described. Anomalous absorption and emission in electron cyclotron resonance heating experiments due to the parametric excitation of localized upper hybrid waves are analyzed theoretically. Progress in the development of the neutral particle analysis, gamma-ray spectrometry and divertor Thomson scattering combined with laser-induced fluorescence diagnostics for ITER is discussed. The status of the new Globus-M2 spherical tokamak is reported.