The results of heat and particle transport simulations for ohmic plasma in the T-10 tokamak with a circular limiter and for D-shaped plasma in the COMPASS tokamak with a divertor are presented. In addition, the H-mode with ohmic heating and with additional heating by the neutral beam injection (NBI) in the COMPASS was simulated. The simulations were carried out with the Canonical profile transport model (CPTM) using the ASTRA code. The obtained electron temperature and density profiles agree with the measured ones with standard deviations within the experimental accuracy of 10–15

The dependence of the focal length of the thallium Tl+ ion beam on the parameters of the ion-optical system of the injector for diagnostics of plasma by heavy ion beam probe has been studied. The possibility of obtaining quasi-parallel beams and converging beams with a focal length of more than 4 m has been shown. Experimental results are compared with the results of computer modeling of the beam trajectory in the injector.

The potential of utilizing a multiple cell array detector (MCAD) [8] has been demonstrated as an additional tool for correlation studies of density and poloidal field fluctuations in a plasma as a part of the heavy ion beam probe on the T-15MD tokamak. The optimum position and size of the MCAD have been found, and its cell size has been determined. Trajectories of probing particles have been calculated and the plasma region for measurements has been estimated for the toroidal magnetic fields BT = 1.2, 1.5, 1.7, and 2.0 T. It has been shown that simultaneous measurements with the MCAD and the energy analyzer as the main measurement tool are possible, which allows the study of radial and poloidal spatial correlations of medium scale comparable to the small plasma radius. The spatial resolution of measurements and attenuation of the beam current signal during its passage through the plasma have been estimated.

Heavy ion beam probing (HIBP) is a unique diagnostic technique that enables independent and simultaneous measurement of the plasma electric potential φ and its fluctuations φ̃ , as well as the electron density fluctuations ñ_e and poloidal magnetic field B̃_pol in the hot plasma region. A method for calculating the spatial resolution of the designed HIBP diagnostics for the T-15MD tokamak has been presented. The dependence of the size of the measurement area point on the width of the input slits in the energy analyzer has been studied.

The development of reduced models provide efficient methods that can be used to perform short term experimental data analysis or narrow down the parametric range of more sophisticated numerical approaches. Reduced models are derived by simplifying the physics description with the goal of retaining only the essential ingredients required to reproduce the phenomena under study. This is the role of the gyro-fluid code FAR3d, dedicated to analyze the linear and nonlinear stability of Alfvén Eigenmodes (AE), Energetic Particle Modes (EPM) and magnetic-hydrodynamic modes as pressure gradient driven mode (PGDM) and current driven modes (CDM) in nuclear fusion devices. Such analysis is valuable for improving the plasma heating efficiency and confinement; this can enhance the overall device performance. The present review is dedicated to a description of the most important contributions of the FAR3d code in the field of energetic particles (EP) and AE/EPM stability. FAR3d is used to model and characterize the AE/EPM activity measured in fusion devices as LHD, JET, DIII-D, EAST, TJ-II and Heliotron J. In addition, the computational efficiency of FAR3d facilitates performing massive parametric studies leading to the identification of optimization trends with respect to the AE/EPM stability. This can aid in identifying operational regimes where AE/EPM activity is avoided or minimized. This technique is applied to the analysis of optimized configurations with respect to the thermal plasma parameters, magnetic field configuration, external actuators and the effect of multiple EP populations. In addition, the AE/EPM saturation phase is analyzed, taking into account both steady-state phases and bursting activity observed in LHD and DIII-D devices. The nonlinear calculations provide: the induced EP transport, the generation of zonal structures as well as the energy transfer towards the thermal plasma and between different toroidal/helical families. Finally, FAR3d is used to forecast the AE/EPM stability in operational scenarios of future devices as ITER, CFETR, JT60SA and CFQS as well as possible approaches to optimization with respect to variations in the most important plasma parameters.

Plasma was heated at the second harmonic of electron cyclotron resonance (ECR) in the L-2M stellarator and the T-10 tokamak. The concept of equivalent tokamak and stellarator discharges was extended to the case of both full and partial absorption of EC power. Comparison of experimental electron temperature profiles with profiles calculated using the canonical profiles transport model allows us to estimate the efficiency of ECR heating in the L-2M discharges without suprathermal electrons, which distort the distribution function, preventing reliable measurements of temperature. The dependence of the ECR heating efficiency on the plasma density was obtained, describing experiments on the L-2M and TJ-II stellarators, and on the T-10 tokamak. The energy characteristics (the stored energy and the confinement time) for L-2M discharges were calculated. Predictions for ECR heating in the T-15MD tokamak are considered. The features of solving the ill-posed transport problem for the L-2M are discussed.

Alfvénic activity has been observed in the TJ-II stellarator which resembles the frequency sweeping demonstrated by Alfvén cascade modes in tokamaks. A numerical validation study was conducted using a reduced magnetohydrodynamic (MHD) model to show that such modes could only have been observed in discharges where the rotational transform profile was non-monotonic. During experiments, coil current was varied which resulted in shifting of the minimum value of the rotational transform profile. To mimic this effect, we study the Alfvénic activity predicted by the reduced MHD model for a set of input rotational transform profiles with varying minima. A mode is found whose toroidal and poloidal mode numbers match those predicted in experiments which sweeps downward/upward in frequency as the minimum value of the rotational transform profile is increased/decreased. The results serve as a demonstration of the validity and utility of MHD spectroscopy.

In this work the phenomenon of the quasi-coherent mode of plasma fluctuations in purely ohmic plasmas of the T-10 tokamak is investigated. The plasma magnetic fluctuation spectra along with spectra of relative electron density oscillations and plasma potential fluctuation spectra were studied. The presence of both electrostatic and magnetic components of the quasi-coherent mode has been established in the core and as well at the edge regions of the plasma column. This fact allows one to consider the quasi-coherent mode as one of the types of electromagnetic turbulence of fusion plasma.

Heavy ion beam probe (HIBP) is a unique plasma diagnostics that makes it possible to measure the electric potential φ of high-temperature plasma and its fluctuations φ̃ , as well as the density ñ_e and poloidal magnetic field B̃_pol fluctuations. Position of the point of performing measurements in the plasma vertical cross-section depends on the beam energy and angle of its entrance into the plasma. The variation of these two parameters makes it possible to construct a two-dimensional (2D) detector grid, which covers the domain of possible measurements. The measurement results obtained in the detector grid points provide for constructing 2D distributions of plasma parameters. For the OH and ECRH stages of the T-10 tokamak shots, 2D distributions of the plasma electric potential are presented for the regime with the on-axis magnetic field of Bt = 2.2 T, plasma current of Ipl = 230 kA, line-average density of n̅_e ≈ 1.1 × 1019 m–3 and off-axis ECRH power of PECRH = 1.7 MW.

Radial distributions of the electric potential and plasma density oscillations have been measured in the T-10 tokamak ohmic plasma. Radial distributions of the amplitude and frequency of the geodesic acoustic mode are plotted according to the data on the fluctuations of the electric potential of the plasma, and radial distributions of the amplitude and frequency of the quasi-coherent mode are plotted according to the data on the fluctuations of the plasma density. The quasi-coherent mode corresponds to the major part of the turbulent particle flow, the geodesic acoustic mode as a high-frequency branch of zonal flows is involved in the turbulence regulation, which makes these objects very important for plasma physics. The paper presents the results obtained in different operating modes of the T-10 tokamak.

The concept of equivalent tokamak and stellarator discharges with the same electron and ion temperatures and with full absorption of the injected ECRH power was introduced in Dnestrovskij et al (2021 Plasma Phys. Control. Fusion 63 055012). In the present paper, the concept of the discharges equivalence is extended to the case of partial ECRH power absorption. The conditions of discharges equivalence for this case are formulated. It is shown that in equivalent discharges not only the electron temperatures, but also the absorbed powers are the same. Examples of equivalent experimental discharges of the TJ-II stellarator and simulated discharges of the T-10 tokamak with partial ECRH power absorption are studied. The absorbed ECRH power and energy confinement time are found for TJ-II low-density shots heated with ECRH only.

Heavy ion beam probe (HIBP) is a unique tool for studying the electric potential and various turbulence characteristics both in the core and at the edge of toroidal plasmas. The position of the HIBP measurement point in the plasma is determined by the probe beam energy and its entrance angle into the plasma. The probe beam energy is constant during the plasma discharge and determines the maximum penetration depth of the beam into the plasma. The beam entrance angle into the plasma can vary during the discharge, and the set of positions of HIBP measurement points for different beam entrance angles creates a so-called detector line. The set of detector lines for different probe beam energies represents a 2D region (detector array) in the vertical cross section of the plasma. The article presents a method for constructing 2D distributions of plasma parameters over the detector array on the T-10 tokamak by the example of the plasma electric potential.

2D plasma potential ϕ distribution was measured in the electron cyclotron resonance heating (ECRH) and neutral beam injection (NBI) plasmas of the TJ-II stellarator with the heavy ion beam probe for the whole radial range and wide area of the poloidal angle, and supported by Langmuir probe data at the edge. The whole operation domain for the on-axis ECRH was explored ( nˉe = 0.45–0.8 ×1019 m−3, P EC = 220–470 kW), in addition, NBI plasmas with nˉe = 0.9–1.3 × 1019 m−3 and P NBI = 510 kW were studied. In ECRH plasmas the density ramp-up is accompanied by the evolution of the potential from the bell-like to the Mexican hat profile, while the density profiles were flat or slightly hollow. The potential has the positive peak at the centre, and LFS-HFS (low field—high field sides) and up-down symmetry. Equipotential lines are consistent with vacuum magnetic flux surfaces. In the high-density NBI scenario, the ϕ profile was fully negative with a minimum up to −300 V at the centre, while at low-density ECRH plasma, ϕ has a maximum up to +0.9 kV at the centre. Fluctuations of potential and density are stronger in low-density scenarios and not poloidally symmetric. At the mid-radius (area of the maximum density), root mean square (RMS) of fluctuations were up to ϕ ∼ 15 V at LFS vs ∼20 V at HFS; RMS n e ∼ 2% at LFS vs ∼3% at HFS. In the NBI plasmas with the density rise, the asymmetry decreases and finally vanishing at nˉe = 1.2 × 1019 m−3. 2D distribution of the NBI-induced Alfvén eigenmodes (AEs) shows asymmetric ballooning structure: contrary to broadband turbulence, AE-associated potential perturbation dominates in the LFS with a factor up to 1.7 respect to the HFS. The electrostatic mode, excited in ECRH plasmas by suprathermal electrons also shows asymmetric structures: density perturbation dominates in the top-bottom direction compared to LFS-HFS direction.