Plasma Physics Reports最新文献

The analysis of possible divertor working regimes and edge plasma parameters for TRT tokamak project is performed basing on modeling. It is shown that for the separatrix power of 18 MW corresponding to approximately twice higher full input power the low divertor integral heat flux 5 MW/m² can be provided for the separatrix plasma density lower than 7 × 10¹⁹ m^–3 and the effective charge Z_eff lower than 2. These parameters are realistic for this device. In case of bigger separatrix power the working regime is possible with higher divertor heat load still within the technological limits of the machine. Modeling also shows positive effect of the increase of the distance between the separatrix and the vacuum vessel structures and better performance of the corner divertor configuration comparing to the “ITER-like” one.

The characteristics of water spray have been measured in the presence of dielectric barrier discharge in the region where the film of liquid flowing out of the nozzle hole disintegrates into droplets. The discharge has been initiated in the region between the water film and the high-voltage electrode surrounded by a dielectric material. The measurements were performed using the direct shadow method based on obtaining multiple shadow instantaneous microphotographs of droplets. Current and voltage oscillograms in the barrier discharge initiation circuit have been recorded. The average parameters, such as the average diameter and Sauter mean diameter, of droplets have been compared in two cases: without discharge initiation and when it has been created in the region where the spray is formed, at a voltage frequency of 5 kHz and its amplitude of 10 kV. It is shown that in the case of discharge initiation, the average parameters of droplets significantly decrease and their number increases.

The results of a study of plasma pyrolysis of methane using a DC plasma torch with hollow electrodes are presented. Data on the effect of the ratio of methane consumption in the plasma torch and the reactor connected to it on the composition of pyrolysis products have been obtained. The arc power of the plasma torch is 40–50 kW, the methane consumption is ~0.7–1.6 g/s. The ratio of methane flows supplied to the reactor and the plasma torch varied within the range of 0–1.63. Results demonstrate that increasing this flow ratio decreases the hydrogen concentration while increasing the proportion of unconverted methane. The acetylene yield exhibits a maximum within the ratio range of 0.6–1.3, reaching a volumetric concentration of 10.52%. The methane conversion rate in the plasma torch reaches 98–99%, and the volumetric hydrogen concentration ranges from 92 to 97%.

The question of the existence of internal transport barriers (ITBs) around low-rational number values of the stability factor q = 1, 2, … in the usual L-mode of tokamaks with central additional heating and positive magnetic shear remains open. To clarify the existence of such ITBs, experiments were carried out with a programmed linear time shift of the plasma column, in which the positions of the electron temperature measurements T_e of the emission at the second electron cyclotron harmonic are shifted relative to the plasma column, which allows one to study the T_e profile details. A series of experiments with perpendicular input of EC radiation with a power of 0.4 and 0.85 MW at a central ECRH and a fast (60 ms) shift of the column by 0.13a (minor plasma radius a) were carried out on the T-10 tokamak in plasma with a carbon limiter. In both cases, outside the q = 1 surface narrow (about 0.03a wide) and weak (a decrease in the coefficient of electron thermal conductivity χ_e by approximately two times) ITBs detected, which disappeared when the discharge parameters changed. These ITBs are 2–3 times narrower and an order of magnitude weaker than the ITBs near the surface q = 1, which was previously proposed to explain the RTP tokamak results. ITBs were not detected in the L-mode in experiments with simultaneous generation of a co-current and counter-current in the plasma center by two gyrotrons with a total power of 1.5 MW in a plasma with a tungsten limiter (column shift by 0.1a in 30 ms). This article appears to be the first journal publication on the study of T_e profile details with rapid movement of the plasma column.

We investigated the correlation between density perturbations (bursts), having stochastic or intermittent character and magnetic fluctuations detected by Mirnov coils. To achieve this, we designed and constructed a novel Mixed-Probe system in the IR-T1 tokamak. Our experimental approach involved two steps: first with Resonant Helical magnetic Fields (RHF) and then without RHF. The conditional averaged analysis of the probe ion saturation current (({{tilde {I}}_{{{text{sat}}}}})) revealed that stochastic density bursts or intermittencies were more likely to exist during the time interval between t = 10 and 12 ms. Before applying RHF, the intermittencies exhibited a strong cross-correlation with magnetic fluctuations. The predominant frequencies observed are below 7 kHz. Interestingly, after applying RHF, the peaks in the frequency of the ({{tilde {I}}_{{{text{sat}}}}}) signal disappeared, and there was no predominant peak in the FFT of ({{tilde {I}}_{{{text{sat}}}}}). We further analyzed the radial and poloidal velocities of bursts and magnetic fluctuations using diagnostic data. The results suggested that magnetic fluctuations induced oscillations in the background plasma, affecting the radial motion of the density perturbations. Notably, the poloidal velocity of the magnetic field perturbations exceeded that of the bursts, allowing it to shear the poloidal plasma flux and generate the density bursts. The differing velocities confirmed their coupling for a specific time, followed by decoupling. Overall, in the IR-T1 tokamak, applying RHF reduced the cross-correlation between magnetic fluctuations and stochastic density bursts.

The influence of the toroidal magnetic field ripples on the spatial structure and frequency of the geodesic acoustic mode (GAM) in tokamak plasma has been investigated. It is shown that the toroidal asymmetry of the magnetic configuration leads to coupling of oscillations of the GAM electric potential with toroidal and poloidal inhomogeneous perturbations of the plasma pressure. For tokamaks with a large aspect ratio, the GAM dispersion law is derived, taking the non-uniformity of the ripple in the tokamak cross-section into account. Increasing the number of coils (n) of the toroidal field reduces the effect of ripple as ( {sim} {text{1/}}{{n}^{2}}). The applicability of the standard theory to finding the frequency and spatial structure of GAM in large tokamaks is shown.

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 calculations demonstrated very similar density profiles in the H-mode both with the ohmic and with additional NBI heating. The electron temperature profiles in the H-mode with additional heating have higher pedestals than in the ohmic H-mode, that agree with the measurements. The comparison showed that the ohmic regimes in COMPASS and T-10 can be described by the same stiffness coefficients in the heat and particle transport equations.

The frequency dependence of the energy and ion current at the output of an RF plasma source with SPT geometry has been investigated. It has been shown that the ion energy is maximum when operating at a frequency of 6.8 MHz. An increase in the operating frequency is accompanied by a decrease in ion energy. The ion current depends nonmonotonically on frequency. At frequencies less than 27.12 MHz, an increase in the ion energy is accompanied by a decrease in the current, and a decrease in the energy by an increase in the current. Increasing the frequency to 27.12 MHz does not lead to an increase in the ion current.

The paper presents the results of numerical simulation of the initial stage of expansion of plasma formations resulting from the injection of high-speed aluminum plasma jets into the Earth’s ionosphere at different altitudes corresponding to two “North Star” experiments. The influence of an artificial atmosphere represented by an air cloud on the plasma formation parameters in the North Star-I experiment is studied. Gas-dynamic parameters of plasma formations and their optical characteristics are determined. We present a comparison of the calculation results with the results of measurements of the luminosity curves in two wavelength ranges of photometers, which shows good agreement between the calculated and experimental data.

A method for prompt estimation of a number of key parameters that determine the features of the evolution and dynamics of current sheets produced in laboratory experiments has been proposed and realized experimentally. The method is based on the analysis of time dependences of the integral plasma current during its first half-period. The transverse dimensions of the current sheets and the strength of the initial electric field that initiates the sheet formation can be estimated on the base of defining the inductances of both the entire oscillatory contour and the region where the plasma current flows. Data on the plasma conductivity can be obtained by measuring the active resistance of the plasma gap and the dimensions of the current sheet. It is shown that the conductivity increased under conditions that corresponded to an increase in plasma density, indicating a turbulent nature of the conductivity.