An important part of high-temperature plasma study is the determination of the electron temperature dynamics in the tokamak plasma. At spherical tokamaks, one can use Thomson scattering diagnostics ...as well as soft X-ray emission diagnostics (SXR). The capabilities of electron temperature measurement by the first diagnostics are limited by the repetition rate of laser pulses and their number in one tokamak discharge. Data of the second diagnostics are continuous in time and are determined by the time resolution of the detectors; however, obtaining the electron temperature using these data encounters a number of difficulties considered in this study. A method of combined processing of results of these diagnostics using machine learning algorithms was developed for overcoming these difficulties and applying the adVoprosy Atomnoi Nauki i Tekhniki, Seriya: Termoyadernyi Sintezages of both diagnostics. Training data include soft X-ray diagnostic data, hard X-ray diagnostic data, and CIII line emissivity diagnostic data. Thomson local scattering measurements were used as labels for supervised machine learning. The developed technique provides significant extension of the possibilities of determining the electron temperature at the Globus-M2 tokamak.
•The laser-induced fluorescence diagnostic system for measuring the ITER divertor plasma parameters is described.•The LIF spectroscopic schemes and lasers are chosen for measurements of HeII density ...and temperature.•The LIF and background signals and the relative accuracies are calculated for both He and DT discharges of ITER.
Laser-induced fluorescence (LIF) on ITER will be used for local measurement of helium density nHe and ion temperature Ti in divertor. The LIF diagnostic is combined with the divertor Thomson scattering (DTS) via common laser injection and signal collection optics. Collisional-radiative model developed for helium ions is used to estimate laser parameters required for robust measurement of laser-induced signals against plasma background radiation. The estimations demonstrate feasibility of measuring nHeII with laser parameters provided by available optical parametric oscillator pumped by Nd:YAG. New approach for measuring Ti is proposed and the expected errors are estimated using numerical simulations.
It is shown that the radial profile of the electron temperature in the Globus-M2 spherical tokamak is related to the radial profile of the electron density by a power law
. An analytical model of the ...density attractor, assuming the dependence of
on the specific poloidal volume
v
, previously tested on the TCV and JET tokamaks with a large aspect ratio, holds on the spherical tokamak, and the approximation of 162 experimental profiles has resulted in
. The proposed model makes it possible to calculate the spatial distribution
and
according to a known magnetic configuration.
The high-confinement mode in tokamaks (H-mode) is characterized by high pressure gradients at plasma edge, which results in the appearance of edge localized modes (ELMs). They are studied at the ...Globus-M2 spherical tokamak too, where edge localized modes are observed mainly in regimes with neutral beam injection. One of the ways for studying ELMs is the use of the Doppler backscattering (DBS) diagnostics installed at Globus-M2. It makes possible to estimate the amplitude of plasma density fluctuations and measure the radial electric field
E
r
. In this work, the effect of edge localized modes on the
E
r
field is studied in the radial range 0.4 < ρ < 1.1. It is shown that during ELMs the electric field increases in the entire measurement range. This indicates that ELMs affect the inner plasma regions as well. This is not consistent with the general ideas concerning the peripheral localization of ELMs, but is confirmed experimentally not only at Globus-M2. In addition, the results for the regime with ELMs are compared with those for the regime with limit cycle oscillations (LCOs) and it is shown that during LCOs such effect is not observed.
A project is proposed of the complex of diagnostics of the plasma-facing elements of the first wall and divertor of tokamak with reactor technologies (TRT). The main objectives of the complex are ...control of the integrity of plasma-facing elements, monitoring of the state of the first wall and the thermal flows onto the first wall and divertor targets as well as studies of the physical processes in the material of the first wall during its interaction with plasma. A review of expected effects of interaction of plasma with the plasma-facing elements is given; in the first place, with the tungsten facing of the divertor. Based on the analysis of the methods that were tested at existing tokamaks and methods that are being developed within the framework of the international ITER project, a complex of complementary diagnostics is proposed, which satisfies the TRT tasks. In the paper, a variant of implementation at TRT is discussed of frequency/amplitude modulated laser radar, two-wavelength digital holography, active (laser) and passive IR thermography, diagnostics of fuel build-up based on laser desorption and ablation, and the placement of witness samples. A variant is proposed of the placement of these diagnostics at TRT and their physical integration.
Technical solution were presented for a foil spectrometer installed on the Globus-M2 and TUMAN-3M tokamaks for measuring the electron plasma temperature. Measurements have been carried out of the ...time dependence of the plasma temperature in the central region of tokamaks. Using of integrated photodetectors and unique beryllium foils with a thickness of 14–80 μm made it possible to increase the sensitivity of the spectrometer. An important quality of the foils used were the increased values of strength, plasticity, homogeneity, and the absence of surface and internal defects. The combined use of the spectrometer with Thomson scattering diagnostics made it possible to carry out regular temperature measurements in the Globus-M2 tokamak with a high spatial and temporal resolution. The influence of impurities is estimated on the measurement of the electron temperature of the plasma.
The injection complex that heats plasma of Globus-M2 spherical tokamak consists of two injectors which supply high-energy beams of hydrogen (deuterium) atoms into the device’s plasma. Injectors are ...autonomous and allow for preparing and setting up the device and measuring the parameters of the atomic beam independently of the other injector and of the tokamak. The authors provide detailed analysis of each injector’s configuration, substantiate their selection of the experiment layout for introducing beams into the tokamak plasma, set forth characteristics of both injectors’ atomic beams injected into the tokamak plasma, and discuss the results of experiments on additional heating of Globus-M2 tokamak plasma obtained by injecting two atomic beams.
In high confinement mode (H-mode) in the tokamak Globus-M2, the development of edge-localized modes (ELMs) is accompanied by the appearance of filament structures. Using the Doppler backscattering ...method allowed to determine the parameters of the filaments during ELMs triggered by and independent from saw-tooth crashes. It was shown that the number of filaments observed during ELMs synchronized with saw-tooth crashes is greater and the area of their observation is wider. The filament velocity during all observed ELM types on Globus-M2 is higher than was the case on the Globus-M tokamak. Filaments that developed immediately before an ELM burst are characterized by smaller amplitudes and velocities. Two diagnostics, Doppler backscattering and poloidal correlation Doppler reflectometry, were used to determine the poloidal velocity of such filaments and the results demonstrated that the velocity values obtained had similar values, which may indicate linear backscattering taking place off these filaments.
The thermal energy stored in plasma
, normalized internal plasma inductance
and current beta
are calculated via the free-boundary equilibrium PET code. The equilibrium reconstruction algorithm is ...iterative method of minimizing two parameters, the distance between the reconstructed plasma boundary and that simulated by the PET code, as well as the difference between the plasma diamagnetic flux from PET and the experimental one. The discharges from the Globus-M2 tokamak with a toroidal magnetic field up to 0.9 T and a plasma current of 0.3–0.4 MA in a mode with auxiliary heating by two atomic injectors are analyzed. The possibility of using approximate formulas for estimating
and
is considered. The measured diamagnetic flux is used to determine
and then to calculate
. The normalized internal plasma inductance
is additionally determined from the measured vertical magnetic field under the assumption that
.
