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.

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 detailed study of the general transport properties of the FT-2 tokamak shows significant isotopic difference in ohmically heated quasi-stationary plasma in high density regimes 〈 n e 〉 ≈ (6–9) × 10 19 m −3 . For deuterium, the signatures of a transition to the H-mode are found at a plasma density exceeding a certain value, while hydrogen plasma remains in L-mode in all comparable discharge scenarios. The origin of this isotopic discrepancy is studied both with energy transport analysis and direct turbulence and plasma velocity measurements performed with Langmuir probes and microwave diagnostics. A special, more complicated dynamic experimental series with current ramp up, performed in these high density regimes, demonstrated the stability and robustness of an improved energy confinement in deuterium, whereas a comparable confinement improvement in hydrogen plasma was observed.

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.

Babinov N. Bader A. Badziak J. Baek S. Bagryansky P. Bakharev N. Ball J. Bandyopadhyay I. Banerjee S. Banerjee S. Banon Navarro A. Bao J. Barbisan M. Barbui T. Bastiani S. Batani D. Batistoni P. Battaglia D. Baylor L. Becoulet M. Belokurov A. Belonohy E. Belova E. Bergmann A. Berk H. Beurskens M. Bhattacharjee A. Bhattacharyay R. Biel W. Bierwage A. Biewer T. Bilato R. Bin W. Bisai N. Bisson R. Bizarro J. Blanchard J. Boeglin W. Bolzonella T. Bombarda F. Bonanomi N. Bonnin X. Bonoli P. Boozer A. Borodin D. Borodkina I. Borthakur S. Bortolon A. Bosch H.-S. Bourdelle C. Breizman B. Bremer P.-T. Brezinsek S. Briguglio S. Brizard A. Brochard G. Bromberg L. Brookman M. Browning P. Brunetti D. Brunsell P. Bruzzone P. Bühler L. Bufferand H. Buller S. Buratti P. Burhenn R. Buzi L. Byggmästar J. Bykov I. Bykov V.

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.

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.

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.