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In 2023, the Thomson scattering diagnostics with tangential probing geometry was installed and put into operation at the T-15MD tokamak. The new system is based on a 100-Hz Nd:YAG laser with a pulse energy of up to 3 J at the first harmonic, λ = 1064 nm. The system allows measurements to be carried out throughout the plasma discharge with its duration of up to 10 s with a time interval of 10 ms. Laser radiation is introduced into the tokamak vessel in the equatorial plane, passing through the entire plasma volume from the inner to the outer periphery of the plasma. The scattered radiation acquisition system is located inside the equatorial port of the facility. The range of scattering angles is from 11° to 56°. The recording system is based on 10 polychromators on interference filters. Using this diagnostics, the electron temperature and density have been measured in the experimental campaign at the end of 2023. The system operation was demonstrated throughout the entire tokamak discharge in a wide temperature range and with a discharge duration of up to 2 s. [ABSTRACT FROM AUTHOR]

At the T-10 tokamak, the Thomson scattering diagnostics was upgraded in 2016. The new system is based on the Nd:YAG laser with the pulse repetition frequency of 100 Hz; the measurements can be performed every 10 ms during the entire plasma discharge at the spatial resolution of up to 5 mm. Using the upgraded diagnostics, the electron temperature measurements were performed during experimental campaigns of the T-10 tokamak in 2016−2018. In the regimes with the electron cyclotron resonance heating, it was demonstrated that the regions with increased temperature gradients form in the plasma, which was interpreted as the formation of internal transport barrier. The ASTRA-code-based simulations of the current profile time evolution made it possible to correlate the positions of the barrier and the rational surface q = 1. [ABSTRACT FROM AUTHOR]

This article presents estimates of the operating region of the KTM tokamak in terms of plasma density and current for ohmic regimes on the basis of machine design parameters. The discharge parameters obtained in the experiments in 2021 are plotted on the diagram (ne, Ip). The increase in operating values of plasma current and achievement of boundary values of stability factor q ~ 4 are mentioned. It has been demonstrated that progressing into the region of higher plasma currents in the implemented density range leads to achievement of the limit in development of beams of accelerated electrons. Accordingly, the increase in operating plasma density is one of the aims of the next experimental campaign at the KTM tokamak. [ABSTRACT FROM AUTHOR]

This article presents the first results of calculations of power contribution of electron cyclotron heating power and driven current in the DEMO-S and DEMO-FNS facilities for their design parameters and model distributions of temperature, density, and effective plasma charge. The calculations were based on OGRAY code for in-axis and off-axis power contribution. It has been demonstrated that, for electron cyclotron heating and current drive in the central part of plasma thread in the DEMO-FNS, the wave sources are required to operate in the frequency range available in modern experiments: ~140–160 GHz. The off-axis power contribution in the DEMO-FNS in calculations is provided by displacement of resonance region toward the high field side. It has been shown that, in order to generate EC current at ρ ~ 0.65 in the equatorial plane at the high field side, the wave frequency should be increased to ~185 GHz. In order to heat plasma and to generate current using EC waves in the DEMO-S the EC radiation sources are required to operate in the range of 200–230 GHz. In the regimes with low plasma temperature (Te(0) < 10 keV) in both facilities, the fraction of single-pass absorption upon off-axis power contribution has been lower than 50%, which requires further optimization of the power contribution and, probably, discharge scenario. [ABSTRACT FROM AUTHOR]

Electron cyclotron resonance heating is one of the methods of additional plasma heating in the T-15MD tokamak. The article considers the possibility of plasma heating using an extraordinary wave at the third harmonic of electron cyclotron resonance at a frequency of 140 GHz. It has been shown that, in accordance with the calculations by the quasi-linear OGRAY code, a high fraction of single-pass absorption (up to 96%) can be expected even when the ECR is turned on with an ohmic background. Increase in this fraction with the increase in plasma temperature agrees with the theoretical predictions. Vertical power launch seems to be the most attractive. Possible engineering solutions for implementation of such a scheme are proposed. [ABSTRACT FROM AUTHOR]

Electron cyclotron heating is one of the methods of additional plasma heating and noninductive current drive in the T-15MD tokamak. One to eight gyrotrons with a total power up to 7 MW will be used. The frequency of the microwave used depends on the parameters of the experimental scenarios in which the heating will be used and on the physical tasks for which it is intended. This article provides justification for the choice of the gyrotron frequency f1 ≅ 82.6 GHz for the start-up phase and for the first plasma experiments and considers the possibility of using this frequency at the stage of full-scale experiments. In order to provide flexibility of the Т-15MD ECH system, it is proposed to consider the possibility of the development of a gyrotron complex based on two-frequency gyrotrons with f1 ~ 82.6 GHz and f2 in the range of ~102–110 GHz. [ABSTRACT FROM AUTHOR]

The phenomenon of improved energy confinement during radiative cooling at the plasma edge was studied experimentally in the T-10 tokamak. It was shown that the effect is independent on the kind of radiating gas. No substantial differences were observed using Ne, which radiates at two-thirds of the plasma radius, or He, which radiates at the very edge. This phenomenon is explained in frames of nonequilibrium thermodynamics. In a self-organized plasma, the energy balance is described by a Smoluchowski-type equation, where the plasma thermal conductivity and its functional dependence on the intensity of the heat flux, perturbing the pressure profile, is determined from experiment. [ABSTRACT FROM AUTHOR]

The influence of the scrape-off layer (SOL) on the energy confinement time of the core plasma is analyzed by using computer simulation of the self-consistent evolution of turbulence and anomalous transport. The simulation is performed for the conditions of a series of discharges with auxiliary heating in the T‑10 tokamak. It is demonstrated that the role of the SOL region in core-plasma confinement increases considerably relative to the conventional diffusion model of transport processes in the presence of turbulent convection that maintains self-consistency of pressure profiles in plasma. In this case, the influence of the SOL region on the energy confinement time of the core plasma is modeled by nonlinear boundary conditions of the third type at the boundary between the core plasma and the SOL region in which the heat fluxes at the SOL boundary are expressed in the form of power-law dependences on local values of the electron and ion temperatures. The specific form of this power-law dependence is related to power-law scaling for effective plasma confinement time in the SOL. The results of numerical simulation of turbulent-plasma evolution revealed that such an approach allows to provide self-consistent evolution of the energy confinement time τE in transient regimes with auxiliary heating, resulting in τE attaining stationary values close to those observed in real experiments. [ABSTRACT FROM AUTHOR]

Improvement of plasma energy confinement in the T-10 tokamak by injection of impurity gases was studied experimentally. Injection of Ne and He in the ohmic and ECR heating regimes allows one to separate the dependences of energy confinement on the plasma density and on the edge plasma cooling rate. It is shown that the well-known dependence of the energy confinement time on the plasma density is, in fact, the dependence on the radiative loss power. This phenomenon can be explained by plasma self-organization. The experiments are described by a thermodynamic model for self-organized plasma in which the transport coefficient depends on the difference between the actual and self-consistent pressure profiles. The reduction in the heat flux at the plasma edge due to radiative cooling leads to a decrease in the transport coefficient in this region and, accordingly, improves energy confinement. Results of approximate model calculations for experiments with Ne injection are presented. [ABSTRACT FROM AUTHOR]

In T-10 experiments, attempts were made to significantly exceed the Greenwald limit n[sub Gr] during high-power (P[sub ab] = 750 kW) electron-cyclotron resonance heating (ECRH) and gas puffing. Formally, the density limit (n[sub e])[sub lim] exceeding the Greenwald limit ((n[sub e])[sub lim]/n[sub Gr] = 1.8) was achieved for q[sub L] = 8.2. However, as q[sub L] decreased, the ratio (n[sub e])[sub lim]/n[sub Gr] also decreased, approaching unity at q[sub L]approx. 3. It was suggested that the “current radius” (i.e., the radius of the magnetic surface enclosing the bulk of the plasma current I[sub p]), rather than the limiter radius, was the parameter governing the value of (n[sub e])[sub lim]. In the ECRH experiments, no substantial degradation of plasma confinement was observed up to n[sub e]∼0.9(n[sub e])[sub lim] regardless of the ratio (n[sub e])[sub lim]/n[sub Gr]. In different scenarios of the density growth up to (n[sub e])[sub lim], two types of disruptions related to the density limit were observed. © 2000 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

An improved confinement regime with an external transport barrier (H-mode) is obtained during electron-cyclotron resonance heating of a plasma in the T-10 tokamak. A characteristic feature of this regime is a spontaneous density growth accompanied by a drop in the intensity of D[sub α] line and an increase in β[sub p] by a factor of ∼1.6. The threshold power for the L–H transition is close to that predicted by the ITER scaling. The best characteristics of the H-mode are achieved with decreasing q[sub L] to 2.2. It is shown that the external transport barrier arises for electrons, whereas the heat transport barrier insignificantly contributes to improved confinement. © 2000 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

Results from T-10 experiments in regimes with nonmonotonic plasma current profiles are presented. The possibility of controlling the current profile j(r) by electron-cyclotron current drive is demonstrated experimentally. Nonmonotonic q profiles with the reversed shear are obtained in which the q[sub min] value varies in a wide range, q[sub min] = 1–2.3. It is shown that the current profiles with q[sub min]∼2 (in this case, there are two resonant magnetic surfaces q = 2 in the plasma) can cause the onset of MHD instabilities. The possibility of the formation of an internal transport barrier in reversed-shear discharges in the T-10 tokamak is analyzed. In T-10, electron transport is governed by short-wavelength electron turbulence. As a result, there is no clear evidence of the formation of an inner transport barrier in these experiments. © 2000 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]