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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.

This paper is devoted to the studies of the T-10 plasma impurity composition during experimental campaigns of 2014–2016, when a carbon limiter was replaced by a tungsten one and a movable lithium limiter was installed. In these experiments, the effective charge of the plasma was determined from the bremsstrahlung intensity and from CXRS measurements. The total concentration of tungsten ions in the column was estimated from the intensity of the radiation detected by AXUV. The source of light impurities (C, N, O, Li), as well as of tungsten atoms, was estimated from absolute measurements of line emission profiles. The experiment showed that the use of lithium as a limiter material can significantly reduce the flow of light impurities into the discharge and also reduce the dispersion of the W diaphragm. At the same time, the concentration of lithium nuclei in the column does not reach values measurable by CXRS diagnostics of the T-10 (0.3–0.5% of the plasma density).

The results of numerical modeling of impurity concentration profiles of tungsten ions for discharges with ohmic heating (OH) on the T-10 tokamak with W limiter (for Zeff ≈ 1) are described. It is shown that in OH discharges the maximum values of relative concentrations for each tungsten ion state are located on their radii of coronal equilibrium. Fulfillment of coronal equilibrium on the T-10 tokamak makes it possible to determine the full radiation intensity from the total concentration of tungsten ions. The results show that modeling of the Prad(r) profile for tungsten using currently accepted scaling of anomalous transport coefficients of light and moderate impurities for T-10 plasma does not make it possible to obtain complete alignment with the experimental data. The dependences of tungsten radiation intensity profiles on different published data on excitation, ionization, recombination rates, and anomalous transport coefficients are shown in the paper. A conclusion about the value of the anomalous diffusion coefficient and its radial distribution for heavy impurity (tungsten) in OH discharges at the T-10 tokamak is made.

The applicability of the CXSFIT code to process experimental data from Charge-eXchange Recombination Spectroscopy (CXRS) diagnostics at the T-10 tokamak is studied with a view to its further use for processing experimental data at the ITER facility. The design and operating principle of the CXRS diagnostics are described. The main methods for processing the CXRS spectra of the 5291-A line of C5+ ions at the T-10 tokamak (with and without subtraction of parasitic emission from the edge plasma) are analyzed. The method of averaging the CXRS spectra over several shots, which is used at the T-10 tokamak to increase the signal-to-noise ratio, is described. The approximation of the spectrum by a set of Gaussian components is used to identify the active CXRS line in the measured spectrum. Using the CXSFIT code, the ion temperature in ohmic discharges and discharges with auxiliary electron cyclotron resonance heating (ECRH) at the T-10 tokamak is calculated from the CXRS spectra of the 5291-A line. The time behavior of the ion temperature profile in different ohmic heating modes is studied. The temperature profile dependence on the ECRH power is measured, and the dynamics of ECR removal of carbon nuclei from the T-10 plasma is described. Experimental data from the CXRS diagnostics at T-10 substantially contribute to the implementation of physical programs of studies on heat and particle transport in tokamak plasmas and investigation of geodesic acoustic mode properties.

The investigations of tungsten transport in T-10 plasma are presented in the current paper. The process of tungsten accumulation in OH discharges and its dependence on parameters ne, Ip, and Zeff are discussed. Peaked tungsten density profiles nW(r) are observed in plasmas with Zeff ≈ 1–1.5. In plasmas with Zeff ≈ 3–4, W accumulation is mainly integral with no profile peaking with regard to electron density ne(r). Lower densities of W are observed in discharges with a lithized T-10 vacuum vessel in comparison with plasma contaminated with light impurities. The disposal of W accumulation is produced by auxiliary ECRH input. During the central ECRH, the tungsten density profile flattens with the central density drop off by ~10 times together with W source increase up to 4 times.

The experiments on recording molecular emission in the edge plasma of the T-10 tokamak are described. To obtain reliable spectra with sufficient spectral, temporal, and spatial resolution, the optical circuit is optimized for various experimental conditions. Typical spectra measured in two sections of the tokamak are shown. It is shown that, upon varying the parameters of the discharge, the molecular spectrum not only changes significantly in intensity but also undergoes a qualitative change in the rotational and vibrational structure. For a detailed analysis, we use the Fulcher-α system (d3Πu–a3Σ g + ) of deuterium in the wavelength range from 590 to 640 nm. The rotational temperatures of ground state X1Σ g + and upper excited state d3Πu are estimated by the measured spectra.

This work presents the results of modernization of the CXRS (charge exchange recombination spectroscopy) diagnostics [1] at the T-10 tokamak. The relevance of this work is due to the importance of measurements of the ion temperature and nuclei density of the working gas and impurities for analysis of transport processes in the plasma ion component. Measurements of radial profiles of the ion temperature are extremely important for investigating the geodesic acoustic mode behavior which is conducted at the T-10 [2]. The modernized scheme of CXRS measurements, as well as the design and operational features of the spectrometer created for the new diagnostics, is described. Principles of data recording and further processing are considered in detail; attention is given to the problem of calibration of the whole complex of equipment. The performed changes in diagnostics allow the measurements to be taken simultaneously in three spectral intervals: in the region of the beam line Hα, the CXRS line of carbon ion C5+, and the CXRS line of one of the hydrogen-like ions: He1+, Li2+, N6+, O7+ or Ne9+. This makes it possible to measure the density profiles of two plasma impurities simultaneously, as well as the ion temperature from CXRS lines of different elements. The modernized diagnostics significantly broadens the possibilities of studying the physics of transport processes and quasi-coherent modes of plasma oscillations at the T-10.

The report addresses a remote molecular diagnostics system for studies of the edge plasma inT-10 tokamak at National Research Centre Kurchatov Institute. Web control of a monochromator and a CCD camera based on Internet technologies was used to monitor radiation. The structure and communications chart of the software components implemented in the system are described. A special web application has been developed to visualize, identify and analyze protium and deuterium molecular spectra. It is accessible to remote users through their private accounts during and after a remote control session. The system allows researchers located far away from the unique high-temperature plasma test facility to take an active part in experiments.

In 2020 a modernized tokamak T-15MD (R=1.5 m, a=0.67 m, κ=1.8, Ipl≤2 MA, Bt≤2 T, discharge duration ≤10 s, Paux≤24 MW) will be launched in the National Research Center "Kurchatov Institute". For this installation, a modern Charge eXchange Recombination Spectroscopy (CXRS-diagnostics) has been developed. It can function both on a diagnostic injector (EDNB=60 keV) and heating injector (ENBI=80 keV) . CXRS-diagnostics of T-15MD can be used to measure local values of the following plasma parameters with high spatial (≈1 cm) and temporal (≈1 ms) resolutions: ion temperature (Ti), density of main gas and light impurities nuclei (nz), toroidal and poloidal rotation velocity (Vpol, Vtor) and the fast-ion spectrum. The composition of the CXRS-diagnostic complex and its schematic is presented. Its main components are the DNB (H, 60 keV, 150 kW), four spectrometers (two of them based on Echelle gratings, one based on holographic grating and another utilizes both types of gratings), and EMCCD-cameras. The attenuation of the diagnostic beam in the plasma is calculated considering its ionization and charge exchange by the main gas and impurities (C, O), as well as electron impact ionization. The intensities of active and passive components of λ=5291 Aline of C5+ ion are calculated considering the line fine structure, Doppler, and Zeeman effects. The active and passive signals emitted by C5+ ion are estimated for toroidal and poloidal registration systems. It is established that the acquisition time of 1 – 3 ms is enough to achieve the valid signal level to measure Ti with a statistical error ≈ 3 %. The calculated ratio between the active and passive CXRS-signal in the plasma center is 2.2 – 3.7. Measurement error is estimated for λ=5291 ACX-line and calculations show low measurement errors for Ti and nz (around 2 – 5 %), Vpol and Vtor (around 2 km/s). This indicates that CXRS-diagnostics have potential to provide reliable and accurate measurements of the named plasma parameters on T-15MD.

An investigation of lithium influx to plasma, radiation, transport, and its influence on plasma parameters is carried out using spectroscopy and transport modeling methods. Lithium source in discharge of the T-10 tokamak is a moving Li-limiter based on tungsten capillary-pore system (CPS). A strong dependence of Li influx to plasma on a distance between the Li-limiter and plasma current boundary in Scrape-Off Layer (SOL) region is found. It is shown that if the Li-limiter is located on the radius of the chamber wall (≈40 cm), lithium influx to plasma is at a low level with value ~21018 s-1 and Li nuclei concentration in plasma does not exceed ~0.5 % of electron density ne with effective charge value Zeff ≈ 1.2. If the Li-limiter is moved to the current radius (aL =30 cm), lithium influx to plasma reaches ~31020 s-1, that leads to a formation of lithium plasma with the density limit of ≈ 0.5ne Gw (Greenwald density limit) with Zeff value of ≈2.9 and ≈10 % of remaining deuteron density. In this case, lithium radiation losses power estimated in Li-plasma is extremely low and does not exceed ≈15 % of ohmic power. All obtained results are interpreted using transport models. Changing the lithization level of the chamber walls can significantly reduce the level of impurities C, O, and W and greatly affect the Zeff values. Dependencies of energy confinement times in the electron and ion components on the value of averaged electron density are investigated in regimes with significantly varying Zeff values. The paper presents the computational analysis of the lithium radiation power at the plasma periphery and in SOL as a function of boundary conditions, transport characteristics, and confinement times of lithium ions.

Charge-exchange recombination spectroscopy (CXRS) based on a diagnostic neutral beam has been developed at the T-10 tokamak. The diagnostics allows one to measure the ion temperature profile in the cross section of the plasma column. In T-10 experiments, the measurement technique was adjusted and the elements of the CXRS diagnostics for ITER were tested. The used spectroscopic equipment makes it possible to reliably determine the ion temperature from the Doppler broadening of impurity lines (helium, carbon), as well as of the spectral lines of the working gas. The profiles of the plasma ion temperature in deuterium and helium discharges were measured at different plasma currents and densities, including with the use of active Doppler measurements of lines of different elements. The validity and reliability of ion temperature measurements performed by means of the developed CXRS diagnostics are analyzed.

The charge exchange recombination spectroscopy (CXRS) diagnostics on the T-10 tokamak is described. The system is based on a diagnostic neutral beam and includes three high etendue spectrometers designed for the ITER edge CXRS system. A combined two-channel spectrometer is developed for simultaneous measurements of two beam-induced spectral lines using the same lines of sight. A basic element of the combined spectrometer is a transmitting holographic grating designed for the narrow spectral region 5291 ± 100 Å. The whole CXRS system provides simultaneous measurements of two CXRS impurity spectra and Hα beam line. Ion temperature measurements are routinely provided using the C(6+) CXRS spectral line 5291 Å. Simultaneous measurements of carbon densities and one more impurity (oxygen, helium, lithium etc.) are carried out. Two light collecting systems with 9 lines of sight in each system are used in the diagnostics. Spatial resolution is up to 2.5 cm and temporal resolution of 1 ms is defined by the diagnostic neutral beam diameter and pulse duration, respectively. Experimental results are shown to demonstrate a wide range of the CXRS diagnostic capabilities on T-10 for investigation of impurity transport processes in tokamak plasma. Developed diagnostics provides necessary experimental data for studying of plasma electric fields, heat and particle transport processes, and for investigation of geodesic acoustic modes.

A diagnostic neutral beam injector DINA-KI60 has been developed and produced for upgraded T-15 tokamak (Kurchatov Institute, Moscow). The system will be primarily used for measurement of the ion temperature by charge-exchange recombination spectroscopy (CXRS), for magnetic field measurements via motional Stark effect (MSE) and investigation of plasma turbulence by Beam emission spectroscopy (BES). The ion source provides 60 keV, 6 A hydrogen beam with low angular divergence less than 10 mrad. Ions are extracted from a plasma created by an arc-discharge source with cold cathode and, after accelerating and focusing, are neutralized in a gas target. The extracted beam has about 86% of full energy specie. The grids of ion optical system are spherically curved providing geometric focusing of the beam at a distance 4 m. Diagnostic neutral beam has been successfully tested at Budker Institute of Nuclear Physics at 2 seconds pulse duration with modulation of the beam (duty ratio from 1:1 to 1:3).

Tungsten limiters were tested in the T-10 tokamak. The limiters were made from the ITER-grade WMP "POLEMA" tungsten. The influence of the edge tokamak plasma on tungsten limiters leads to significant cracking of tungsten. The heat load of up to 2 MW m−2 leads to the micro-crack development at the grain boundaries accompanied by the loss of grains. The heat loads that exceed 5 MW m−2 lead to the macro crack development. Under the present T-10 tokamak conditions, the heat and particle fluxes in the edge plasma lead to the significant destruction of tungsten limiters during the experimental campaign. During the disruption and runaway electron formation, extreme heat loads of more than 1 GW/m2 cause strong melting of tungsten on the inner and outer part of the ring limiter.

Spectroscopic diagnostics of the edge ion temperature were developed on the T-10 tokamak. Spatially resolved measurements of C5+ and other ionization states of carbon spectral line shapes are provided. Spectra were measured with high spectral resolution using 14 lines of sight in one poloidal section of the tokamak. Each measured line-integrated spectrum contains a combination of multiple local spectra with corresponding values of ion temperature. Modeling of spatial distribution of line emissivity and spectral line shapes along the lines of sight allows the reconstruction of the ion temperature profile on the basis of the closest match of measured and modeled spectra. The fine structure of spectral line, Zeeman effect, and apparatus function are taken into account during data processing. Obtained ion temperature profiles, Ti(r), at the plasma edge are in good agreement with ion temperature profiles measured by Charge eXchange Recombination Spectroscopy (CXRS) diagnostics of T-10. Use of the CXRS equipment for measurements of passive spectra can provide additional information on the temporal evolution of the edge ion temperature. Developed diagnostics provide necessary data for the research of geodesic acoustic modes, which are strongly dependent on plasma edge ion temperature.

Transition to an all-metal wall was realized on T-10 by replacement of graphite limiters with tungsten ones. Light impurity levels remained high and W accumulation in the plasma core was revealed. A movable lithium (Li) limiter was added to investigate the possibility of the limitation of tungsten and light impurity levels in plasma. For the first time, tokamak results on tungsten protection with Li were obtained in OH and ECRH regimes. After lithization the tungsten density in the core dropped more than an order of magnitude, while W influx into plasma decreased 2–4 times. Drastic drops of light impurities in plasma were observed together with improvement of energy confinement time and density limit values. Nevertheless, Li levels in plasma remained low in both OH and ECRH regimes. Li density in the core as low as 0.5% of n e was obtained. Tungsten transport in T-10 plasma was investigated and results on prevention of W accumulation with central ECRH were obtained. Effects of plasma exposure on ITER-grade tungsten plates from limiters were studied. Investigations of density fluctuation with correlation reflectometry confirmed a decrease of fluctuation amplitude on high field side. Modeling showed that this effect can be, to a great extent, explained by the non-locality of reflectometry. Toroidal correlations at a distance of 2.5 m along field lines were studied. Three-wave interaction between geodesic acoustic modes and broad-band turbulence was found by analysis of heavy ion beam probe diagnostics data. The possibility of plasma current control and the prevention of non-thermal electron beams formation at density limit disruption by means of ECR heating and the controlled operation of OH power supply system has been demonstrated. The study of plasma density decay after gas puff switch off during density ramp-up phase in OH regimes and the effect of 'density pump out' during ECRH showed that both effects can be explained by the assumption regarding electron transport growth upon reaching marginal pressure profile. A new type of internal transport barrier in the narrow zone near q = 1 surface has been found.

the formation of transport barriers under electron cyclotron resonance heating and current drive in the t-10 tokamak is studied. in regimes with off-axis co-eccd and qL

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 Dα line and an increase in βp 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 qL to 2.2. It is shown that the external transport barrier arises for electrons, whereas the heat transport barrier insignificantly contributes to improved confinement.

The parameters of molecular plasma in closed magnetic trap is studied in this paper. Using the system of molecular diagnostics, which was designed by the authors on the «Tokamak T-10» facility, the radiation of hydrogen isotopes at the plasma edge is investigated. The scheme of optical radiation registration within visible spectrum is described. For visualization, identification and processing of registered molecular spectra a new software is developed using MatLab environment. The software also includes electronic atlas of electronic-vibrational-rotational transitions for molecules of protium and deuterium. To register radiation from limiter cross-section a network control system is designed using the means of the Internet/Intranet. Remote control system diagram and methods are given. The examples of web-interfaces for working out equipment control scenarios and viewing of results are provided. After test run in Intranet, the remote diagnostic system will be accessible through Internet.

Results of the electron cyclotron current drive experiment at the second harmonic resonance on the T-10 tokamak are presented. High frequency (HF) power up to 1.2 MW was launched from the low field side. A maximum driven current of 35 kA and current drive efficiency ηCD = 0.05 A/W at an electron temperature Tc(O) = 4 keV and a density nc(0) = 1 × 1013 cm-3 were obtained. For low HF power, the current drive efficiency was less than predicted by the linear theory unless the effect of the elliptical polarization from non-perpendicular injection is considered, in which case the efficiency is close to the theoretical value. The experimental dependence of HF on the absorbed HF power indicated a strong increase of ηCD with power. Suppression of sawtooth oscillations and improvement of confinement during electron cyclotron heating has also been demonstrated

In order to obtain breakdown and suitable plasma parameters for low-voltage OH start-up, high level of EC-power was injected into T-10 tokamak. Input HF-power was varied in the range of 0.15-1.0 MW. Two HF-launcher systems with different output beams allowed to inject EC-waves with maximum power density 0.25 MW/cm 2 and 0.01 MW/cm 2 . Dependence of breakdown time delay on HF-power was obtained. It was shown, that optimal plasma parameters were achieved in presence of plasma equilibrium currents I=3 kA (input HF-power=1.0 MW). Electron temperature Te=100÷150 eV and electron density ne=5•10 12 cm -3 was measured in these discharges. These parameters remained constant during full HF-pulse-length.

Problems of spectroscopic diagnostics of ITER plasma are under consideration. Three types of diagnostics are presented: 1) Balmer lines spectroscopy in the edge and divertor plasmas; 2) Thomson scattering, 3) charge exchange recombination spectroscopy. The Zeeman-Stark structure of line shapes is discussed. The overlapping of isotopes H-D-T spectral line shapes are presented for the SOL and divertor conditions. The polarization measurements of H-alpha spectral lines for H-D mixture on T-10 tokamak are shown in order to separate Zeeman splitting in more details. The problem of plasma background radiation emission for Thomson scattering in ITER is discussed in details. The line shape of P-7 hydrogen spectral line having a wave length close to laser one is presented together with continuum radiation. The charge exchange recombination spectroscopy (CXRS) is discussed in details. The data on Dα, HeII and CVI measurements in CXRS experiments on T-10 tokamak are presented.

Poloidal asymmetry and radial correlation lengths of turbulence were investigated in T-10 at low field side and high field side by correlation reflectometry. Correlation of plasma confinement with the turbulence type was observed. Improvements in heavy ion beam probe diagnostic enabled us to measure the plasma potential during electron cyclotron resonance heating (ECRH) in a wide range of radial positions and operational regimes. The turbulence appeared to rotate close to E × B velocity. The concept of electron internal transport barrier (e-ITB) formation at low-order rational surfaces under conditions of low density of the rational surfaces was proved by the observation of e-ITB formation near the q = 1.5 surface in discharges with non-central ECRH and current ramp-up. The kinetic phenomena were investigated by means of electron cyclotron emission (ECE) under the strong on-axis ECRH. Lithium gettering of the limiter and the wall allowed us to significantly reduce the impurity level and obtain a recycling coefficient as low as 0.3. The rates of carbon film deposition were measured in the working and cleaning discharges. Second harmonic EC assisted start-up was investigated. ECRH allowed us to control the generation of runaway electrons and the current decay rate after the energy quench at the density limit disruption.

A direct comparison of the electric potential and its fluctuations in the T-10 tokamak and the TJ-II stellarator is presented for similar plasma conditions in the two machines, using the heavy ion beam probe diagnostic. We observed the following similarities: (i) plasma potentials of several hundred volts, resulting in a radial electric field E r of several tens of V cm−1; (ii) a negative sign for the plasma potential at central line-averaged electron densities larger than , with comparable values in both machines, even when using different heating methods; (iii) with increasing electron density n e or energy confinement time τ E , the potential evolves in the negative direction; (iv) with electron cyclotron resonance heating and associated increase in the electron temperature T e, τ E degrades and the plasma potential evolves in the positive direction. We generally find that the more negative potential and E r values correspond to higher values of τ E . Modelling indicates that basic neoclassical mechanisms contribute significantly to the formation of the electric potential in the core. Broadband turbulence is suppressed at spontaneous and biased transitions to improved confinement regimes and is always accompanied by characteristic changes in plasma potential profiles. Various types of quasi-coherent potential oscillations are observed, among them geodesic acoustic modes in T-10 and Alfvén eigenmodes in TJ-II.

The velocity of plasma rotation and the potential distributions are measured in the TM-4 device i n the Ohmic-heating regime. The potential is negative at the centre of the column, and its magnitude is significantly larger than the ion temperature. At the edge, the potential is positive while the rotation velocities are considerably lower than their neoclassical values.

ВОЗМОЖНОСТИ СПЕКТРОСКОПИЧЕСКОЙ ДИАГНОСТИКИ CXRS В ТОКАМАКЕ Т-10 Л.А. Ключников, В.А. Крупин, К.В. Коробов, М.Р. Нургалиев, А.Р. Немец, А.Ю. Днестровский, Н.Н. Науменко, С.Н. Тугаринов, С.В. Серов, Д.С. Деньщиков Отделение токамаков, НИЦ «Курчатовский институт», Москва, Россия Институт физики Национальной академии наук Беларуси, Минск, Республика Беларусь Частное учреждение «ИТЭР-Центр», Москва, Россия