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.

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.

Heavy Ion Beam Probing (HIBP) diagnostic is a powerful tool for electric field studies in the hot dense plasma of modern-day toroidal magnetic confinement devices. On the TUMAN-3M tokamak, the HIBP have been used in regimes with improved plasma confinement to clear up the role of the radial electric field in the transition to good confinement regimes. Recently, a modernization of the TUMAN-3M HIBP diagnostics was performed, aiming to reconfigure it for a work with a reversed plasma current direction and improvement of the overall stability of the diagnostic. The results of the first measurements of the plasma potential in the co-NBI scenario are reported and discussed.

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.

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.

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.

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.

Radial electric field shear is crucial for turbulence suppression and transition to the H-mode, although the high shear value alone may not be sufficient for the LH-transition initiation. Temporal and spatial parameters of shear perturbation, particle source and turbulence parameters are the main factors responsible for LH-transition initiation. Different plasma discharge scenarios in two Ioffe Institute conventional tokamaks are analyzed using the model of plasma density and ion temperature evolution to clear up the role of aforementioned factors.

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.

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 method of plasma boundary location based on last closed magnetic surface position detection as a maximum of electrostatic potential measured using Langmuir probes is presented. It is demonstrated that the method can be used for an absolute calibration of magnetic diagnostics of plasma position (TUMAN-3M) and as an independent diagnostic tool (Globus-M).

The possibility of determination of evolution of the plasma isotope composition from Alfven oscillation frequency in discharges with pulsed deuterium puffing into hydrogen plasma and hydrogen into deuterium plasma in ohmically heated plasma in TUMAN-3M tokamak is discussed. Isotopic ratio found from the Alfven oscillation spectra by this method is relative concentrations of hydrogen nH/(nH+nD) or deuterium nD/(nH+nD) in the mixed hydrogen-deuterium plasma. These values were found to agree qualitatively with the results of optical spectroscopy measurements and with neutral particle analysis data.

We discuss the possibility of determining the evolution of the isotopic composition of plasma by the frequency of Alfvén oscillations in ohmic discharges in the compact TUMAN-3M tokamak with pulsed deuterium puffing into a hydrogen plasma and hydrogen puffing into a deuterium plasma. The isotopic ratios, i.e., relative concentrations of hydrogen nH/(nH + nD) and deuterium nD/(nH + nD) in the mixed hydrogen–deuterium plasma obtained by this method are in qualitative agreement with the results of spectroscopic measurements and neutral particle analysis data.