Volume 49, Nº 6 (2023)

The divertor operation in the detached plasma regime is necessary to reduce the loads on the divertor plates in the ITER and DEMO tokamaks to acceptable values. The results of the analysis for a number of effects that directly affect the operating window of the detachment and its stability are discussed: transverse heat transport in the divertor, radiation trapping, development of plasma instabilities, stability features of the double-null divertor, obtained using numerical simulations, including modeling in the transport code SOLPS4.3 and turbulent code BOUT++. The operation of a divertor with liquid metal plates is considered using lithium as an example. The verification issues for the computational model used for detachment modeling are discussed.

Diagnostics based on laser-induced quenching (LIQ) and laser-induced fluorescence (LIF) is planned to be used at the T-15MD tokamak for local measurements of the atomic hydrogen density na(HI) in divertor plasma. Both physical and technical aspects of the diagnostic system development are considered. For plasma diagnostic, it is proposed to use the time-modulated thulium fiber laser with the wavelength of 1875 nm and peak power of 5 W. Two light collection systems will be used for observing the signals. The intravacuum and “atmospheric” systems will be used for performing measurements in the region of the separatrix strike-point and in the rest of the divertor region, respectively. Using the modified collisional-radiative model, the applicability of the diagnostics was physically justified by the calculations of the expected quenching and fluorescence signals, as well as the background radiation at the wavelengths of hydrogen lines. In the calculations, the 2D-distributions of plasma parameters are used obtained by the SOLPS 4.3 code for tokamak operation scenarios with and without additional plasma heating. When using the LIQ method, the expected errors in measuring the na(HI) density are within 10% for most points and do not exceed 25% for all scenarios of tokamak operation considered, provided that the signals are averaged over 10 ms. The LIF method makes it possible to carry out measurements with relative errors up to 50%.

A digital model of a grazing-incidence X-ray spectrograph and methods for reconstruction of soft X-ray spectra of a Z-pinch plasma at the Angara-5-1 facility in the 2–40 nm range have been developed. The main problems hindering reliable qualitative and quantitative reconstruction of the initial Z-pinch X-ray spectra are the superposition of signals from different diffraction orders and the complex form of the device instrumental function. Two techniques for reconstructing the spectrum are presented. In the first one, a digital model of the spectrograph was developed in the Geant4 Monte Carlo simulation toolkit, taking into account the geometry of the experiment and the processes of interaction of X-ray radiation with a diffraction grating. In this model, taking into account the specific shape of the groove profile of the diffraction grating and the differential method for solving the diffraction problem, the X-ray intensity distribution in different diffraction orders depending on the wavelength is calculated. Using the developed model of the spectrograph, its instrumental function was calculated. The second technique does not use a specific grating groove shape, but, based on the analysis of calibration spectrograms, it constructs a dispersion relation and allows one to reconstruct the spectrum. At the end of the work, the results of reconstruction by the first and second techniques are compared and fairly good agreement between the spectra obtained by different techniques is shown.

The results are presented from the probe measurements of plasma parameters in the tubular plasma source used in research on plasma relativistic microwave electronics. Tubular plasma is produced as a result of background gas ionization by the electron beam emitted by the annular heated tungsten cathode in the axial magnetic field. The current–voltage characteristics of the probe were obtained for three discharge currents of 5, 9, and 20 A at three plasma column lengths of 10, 20, and 30 cm. It was shown that for all discharge currents and for all plasma column lengths, the electron temperature is equal to 20 eV at the time of performing measurements. It is also shown that in this source, the plasma density does not depend on the plasma column length in the lengths range from 10 to 30 cm. It was demonstrated that the discharge current is a linear function of the probe current, which makes it possible to control the relative changes in the plasma density during the experiment. For different discharge currents, the absolute value of plasma density was estimated to be in the range of 1012–1013 cm–3.

Two-dimensional description of nonlinear dust-acoustic waves in the dusty Saturn’s magnetiosphere that contains electrons of two types (the hot and the cold ones) obeying the kappa distribution, along with magnetospheric ions and charged dust particles, is presented. The Kadomtsev–Petviashvili equation that describes the nonlinear dynamics of the nearly one-dimensional wave structures is derived for the conditions of the dusty Saturn’s magnetosphere. The possibility of propagation of localized wave structures of the dust-acoustic soliton type is analyzed. It is demonstrated that the Kadomtsev–Petviashvili equation has solutions in the form of one-dimensional solitons and two-dimensional N-solitons under the conditions of the Saturn’s magnetosphere. The possibility of observation of the discussed solitons during future space missions is discussed.

The paper presents a study of diffuse plasma jets (DPJs), which have a red color and consist of streamers (ionization waves). It has been found that plasma generated in air at pressures of 0.2–4 Torr by a repetitively pulsed capacitive discharge in a dielectric tube initiates two DPJs in one pulse, each with up to three streamers. It has been found that two streamers propagating from the circular electrodes in opposite directions are formed by one voltage pulse of positive polarity. Using an ICCD camera and a silicon PMT, it is shown that the arrival of the front edge of a positive streamer in the region finally reached by the front edge of a negative streamer that was generated first at the front edge of the negative voltage pulse leads to the formation of a third thin streamer in the form of a cone with a small apex angle. It has been found that the direction of motion of the third streamer coincides with the direction of the streamers initiating it, but its speed is two orders of magnitude lower. It is shown that, at low air pressures, the speed of the first positive streamers is higher than that of the negative streamers and the distance to which they propagate at a generator voltage of 7 kV and an air pressure of 0.2 Torr exceeds 1 m.