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Abstract

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%.

Abstract

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 Te of the emission at the second electron cyclotron harmonic are shifted relative to the plasma column, which allows one to study the Te 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 χe 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 Te profile details with rapid movement of the plasma column.

Abstract

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.

Abstract

Using an approximate approach that is valid for a large ratio of the ion mass to the mass of the neutral particle, the mobility of O \(_{2}^{ + }\) , N \(_{2}^{ + }\) , O \(_{2}^{ - }\) , and O \(_{4}^{ - }\) ions was calculated in helium and good agreement was obtained with the available results of Monte Carlo calculations and experimental data at high values of the reduced electric field. This simplified approach was used to determine the average energy of O \(_{4}^{ - }\) ions and the rate constants of dissociation of these ions in helium. The obtained ion characteristics were compared with the results of more accurate calculations using the Monte Carlo method. Good agreement has been obtained between these two approaches for the average ion energy, but for the dissociation rate constant the difference is quite significant, reaching an order of magnitude or more. It was shown that this difference is associated with the peculiarities of the energy distribution of ions for a large ratio of the ion mass to the mass of the neutral particle.

Abstract

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.

Abstract

The interaction of a circularly polarized electromagnetic wave with a layer of photoionized inert gas plasma in the magnetic field has been studied. A detailed analysis of the reflection and transmission coefficients of the wave under conditions where the wave frequency is the same as the photoelectron cyclotron frequency is given. The possibility of a strong increase in the reflection and transmission coefficients, when negative small absolute values of the imaginary part of the photoionized plasma dielectric permittivity are released, has been revealed. It is shown that in the photoionized plasma layer obtained in the process of fast multiphoton ionization of xenon atoms at atmospheric pressure, there is a possibility of increasing the field strength of terahertz radiation by more than two orders of magnitude.

Abstract

In the paper, we examine the α inclination of the magnetic field of sunspots relative to the vertical. To determine the deviation angle α, a method to search for differences in the maximum of the longitudinal component of the magnetic field at various distances of spots from the central meridian in the eastern and western hemispheres of the Sun was used. Particular attention has been paid to the difference in the angles α for spots of leading and tail polarity of the magnetic field. Deviation angles α were shown to depend on the logarithm of the area while the dependences have opposite signs: αL = 0.45°(±0.5) + 2.085°(±0.5) log S, (r = 0.95) for nuclei of leading polarity spots (L) and αT = 5.43°(±1.0) – 3.95°(±0.7) log S, (r = 0.93) for nuclei of tail polarity (T). Here, the deviation of magnetic fields to the western limb is taken as a positive value. The found dependencies indicate the ascent of U-shaped force tubes.

Abstract

Recently, Samara et al. (2022) showed that proportionality between the solar fast wind velocity V from the low latitude coronal holes (CH) and their area Sch is satisfied only for small-sized CH, while the saturation effect for larger CH is revealed; i.e., a plateau is formed in a V(Sch) plot. This is explained by the geometric complexity of CH, described by the fractal dimension. Previously, Akhtemov and Tsap (2018, 2019) established that the correlation coefficient between V and Sch reaches a maximum for a CH located within a fractional area ±10° in longitude and ±40° in latitude. They suggested that this inference is related to the radial propagation of the solar wind and, hence, the increasing of Sch should not be accompanied by an increase of V for large CH. The presented work provides a detailed comparative analysis of the results obtained by Samara et al. (2022) and Akhtemov and Tsap (2018, 2019). Arguments are given in favor of the model related to the saturation effect with the radial propagation of the fast solar wind.

Abstract

The maximum energy of a solar flare is found using a model of particle acceleration in a magnetic X-singularity. Based on a comparison of this model with observed extreme events, it was determined that flares with the highest possible energy have already been observed. These include events of 1859, 1940, 2003, which had an X-ray class of X40 ± 5 (according to the GOES classification). In this case, the maximum flare energy in the modern era does not exceed 5 × 1032 erg, and such powerful flares occur at intervals of about 70 years.

Abstract

In this paper, the dynamics of loop-like structures and related phenomena during the solar flare on February 24, 2023 are investigated. A new character of the dynamics of the coronal loop system during the flare has been studied, consisting in compression (lowering) of the loops both during the growth and decay phases of the flare. It was found that a sharp decrease in height began with the appearance of intense nonstationary plasma fluxes (ejections) observed mainly in the vicinity of the eastern footpoints of the coronal loop system. It was concluded that the rapid (at a speed of up to 25 km/s) compression of the coronal loop system can be explained by a decrease in free magnetic energy (a decrease in the vortex phi-component of the magnetic field) caused by the observed non-stationary plasma eruptions from the vicinity of the loops, as well as possible Joule dissipation of electric currents in the loops.

Abstract

A reconstruction of the average monthly values of sunspot areas—the physical index of solar activity—is proposed. The uncertainty of the obtained values for a significance level \(\alpha = 0.05\) is estimated. The duration of the number of monthly means has become 275 years. It is shown that the AR index, when used in reconstructions of solar activity of historical observations with small telescopes, is more advantageous than the indices of the number of spots or groups thereof. This index is not sensitive to the possible loss of small groups, which on average make up about a third of the overall number.

Abstract

The cause of the asymmetry in the sunspot distribution in the northern and southern hemispheres of the Sun at the end of the Maunder Minimum is studied. It is demonstrated that the expected asymmetry of generation sources is insufficient for such an explanation. To study the influence of asymmetry of generation sources, numerical simulation is used, based on modifications to the Parker model.

Abstract

The presence of groups of cycles with larger/smaller amplitudes and alternation of these groups suggests the existence of a long-period solar activity (SA) cycle with epochs of increased/decreased activity. Since SA and its changes significantly influence climate and humans across the near-Earth space, it is reasonable to have a portrait (template) that reflects the main characteristics of these groups, making it possible to qualitatively and semiquantitatively assesses of SA epochs in the past and future. In the study, the properties of epochs SA of maximum/minimum are determined by the characteristics of reliable cycles 10–23 (14 cycles, a total period of 153 years, and the relationship between the amplitude of the cycles and their duration is taken into account). The formation of the pattern is based on the “envelope” of the maxima of these cycles. The possibility of correcting the Dalton minimum is discussed and a long-term forecast of SA is constructed.

Abstract

The results of analyzing the relationship between large-scale epidemics (pandemics) caused by the Ebola, influenza AH1N1, and AH7N9 viruses and the MERS-CoV coronavirus with global solar factors for the period from 2008 to 2019 (24th cycle of solar activity) are presented. A variable change in the annual values of pandemic cases has been established, corresponding to the regular course of F10.7 cm (r ~ 0.65), MF (r ~ 0.85) and λ315 nm (r ~ 0.83) in the 24th SA cycle. It was concluded that the dynamics of the spread of pandemics depend on temporary changes in UVB radiation power, in particular, at the boundary of the spectral bactericidal efficiency curve (λ315 nm).

Abstract

Samples with a short-term (less than a year) increase in the content of the radioactive isotope 14C were recently discovered in tree rings, in four cases accompanied by concentration growth of 10Be and 36Cl in other natural archives. Most publications suggest that this increase is due to a sharp increase in the flux of solar cosmic rays (SCR) at the boundary of the Earth’s atmosphere caused by solar superflares. Other reasons may be connected with the flux rise of the galactic cosmic rays (GCR) as the Solar System passes through a dense interstellar cloud, or a galactic gamma-ray burst. To reconcile the amount of 14C with cosmogenic isotopes 10Be and 36Cl formed in the atmosphere, it is necessary to assume that the proton spectra in such superflares should be harder than most modern experimentally recorded ones. Measurements of the 14C content in lunar regolith cores returned by the Apollo 15 expedition showed a significant drop in radiocarbon concentration to a depth of 5 g/cm2, followed by an increase to maximum values at about 50 g/cm2 then a decrease. At shallow depths, the contribution from low-energy SCRs predominates, and at large depths, the contribution from high-energy GCRs prevails. Analysis of the depth profile of the 14Cconcentration makes it possible to establish SCR fluxes and spectra over several radiocarbon half-lives (10 000–20 000 years) and highlight the possible contribution of hypothetical superflares. Our analysis shows that the hypothesis of solar superflares worsens the agreement with the observed depth variations of 14C in the lunar regolith.

Abstract

In the recent work by Usoskin et al. (2021) a series of annual sunspot indices for the years 971 to 1899 was reconstructed. Using this series, we study behavior of the “length-amplidude rule” (LAR), according to which the mininum-to-minimum length of a given 11-year solar cycle anticorrelates with the amplitude of the next one. We show that approximately since the 14th century two regimes exist in the series: I) epochs of normal activity, when the LAR is observed; II) epochs of the Maunder, Spörer and Wolf grand minima, when there were no significant links between the amplitudes and lengths of the 11-year cycles. Before the 14th century the LAR and its relation to the level of global activity of the Sun is less pronounced, which, probably, is a consequence of inaccuracies of the 11-year cycle parameters determination in this epoch.

Abstract

For the first time, several flare events are analyzed based on multifrequency observations using the Radio Solar Telescope Network. The purpose of the analysis is to identify signs of flare preparation. In all considered cases, preflare quasi-periodic fluctuations (QPFs) of radio emission were detected. The duration of preflare wavetrains is 6–20 min. Wavetrains consist of 3–5 pulses. QPFs at lower frequencies (200–600 MHz) begin later than those at high frequencies by 2–6 min. QPFs at frequencies of 2695–8800 MHz occur almost synchronously. The highest amplitude of QPFs is observed at a frequency of 4995 MHz. The observed QPFs can be explained by the force-free magnetic rope model (Solov’ev and Kirichek, 2023).

Abstract

The results of observations of coronal jets on the Sun are briefly reviewed. Data on jets of different types (jets, jetlets) were collected. Their properties are considered, such as lifetime, length, width, velocities, coupling to the magnetic field, and their putative role in hot plasma and energy transfer into the corona. Observational data obtained with ground-based and space telescopes were used. There is growing evidence that jets play a key role in imparting mass to the corona and solar wind and can provide sufficient energy to power the solar wind (see, e.g., (Tian et al., 2014)). Modern observations by the Parker Solar Probe and Solar Orbiter spacecraft will contribute to the understanding of solar jets and related phenomena.

Abstract

The paper studies the dynamics of high-temperature structures (with a temperature of T ≥ 10 MK) in the corona above active regions (ARs) in quiet temporal intervals, before solar flares of high X-ray classes and during and after individual flare events, and determines the role of electric currents in heating the coronal plasma. In the study, we used data from the Solar Dynamics Observatory (SDO) spacecraft: magnetograms obtained by the Helioseismic and Magnetic Imager (HMI) instrument (used to detect and calculate the magnitude of large-scale electric current) and photoheliograms of the solar corona in ultraviolet radiation 94, 131, 171, 193, 211, and 335 Å channels of the Atmospheric Imaging Assembly (AIA/SDO) instrument (used to construct maps of temperature distribution in the corona above the AR, detect high-temperature structures, and study their evolution). The objects of the study were ARs NOAA 12 192 (October 2014) and 12 371 (June 2015) of the 24th solar activity cycle, which have high absolute values of large-scale electric current. The following results were obtained: (1) The discovered high-temperature structures represent a channel of large-scale electric current at coronal heights. (2) High-temperature structures in the corona above the studied ARs exist over a long (several days) time interval, which indicates the presence of a constant source of plasma heating; the temperature of the structures, the area they occupy, and their spatial orientation change over time. (3) High-temperature structures in the corona consist of individual elements with a cross section of ~108 cm. (4) Several hours before the X-ray flares of classes M and X datected in the studied ARs during their monitoring time, a significant decrease in the area occupied by high-temperature structures was observed, and in some cases, a decrease in temperature to 3–5 MK, which indicates a change in the physical conditions in the corona before powerful flares.

Abstract—

In solar activity, in addition to the 11-year Schwabe cycle, there are also shorter-period oscillations in the range from 27 days to 11 years, which are called mid-term oscillations. In our study, we identify quasi-6-year oscillations in solar activity expressed by the sunspot number SN using wavelet analysis and investigate the characteristics of these variations during 1750–2020. The analysis shows that the ~6-year cycle in SN is a real independent oscillation. A similar quasi-6-year periodicity has been found in the monthly mean records of geomagnetic field components at the Sitka and Honolulu observatories during 1910–2020. It was found that the variations of the geomagnetic field in the range of 5–6-year periods can be caused by the effect of variations in solar activity in the same frequency range. In addition, in the SN series and geomagnetic field variations, a quasi-biennial cycle is well observed, the amplitude of which in some time intervals exceeds the amplitude of the cycle with a period of 5–6 years.