arXiv subjects

Yurii V. Dumin

Publications and source records attributed to Yurii V. Dumin.

At least 19 recordsLinked to original sources

arXiv2026

Exact Solution of the Direct and Inverse Dynamo Problem in the Expanding Plasma Ball

It was found that the differential equation of dynamo effect (i.e., generation of the electric fields and currents) in a uniformly-expanding plasma ball with strongly anisotropic conductivity possesses the unique mathematical property: namely, the spectrum of its eigenvalues is universal and independent of physical parameters of the medium. As a result, it becomes possible to introduce a special set of eigenfunctions - which we called the generalized spherical functions - that can be used to solve the dynamo problem in exactly the same way as ordinary spherical functions are used to solve the Laplace equation. The corresponding exact solutions should be especially valuable for treating the inverse dynamo-problem, i.e., determination of the plasma parameters from the experimentally measured electric fields and currents.

physics.plasm-ph↗

arXiv2026

Conductor-Insulator Crossover in the Steady-State Ultracold Plasmas

We present a theoretical model of the ionization-recombination balance in the ultracold Rydberg gas-plasma mixture, which is caused by the collective processes rather than by individual interparticle interactions. We consider the electron-ion system where each electron moves for the most part of its time in the effective centrifugal potential formed by the nearest ion and sometimes jumps to the neighboring potential wells due to the perturbations from remote particles. These perturbations are described by a thermal bath with the effective "virial" temperature. Then, the electron with a sufficiently high energy, which can escape from the local potential well, should be considered as free (conducting) one; while the electron with low energy, confined within the well, as forming the Rydberg atom. As follows from our calculations, there is a sharp crossover from the insulating phase (Rydberg gas) to the conducting one (plasma) with increase in the particle density, which somewhat resembles the Mott transition in condensed-matter physics. This model should be well relevant to the steady-state ultracold plasmas obtained in the most recent experiments and represents a promising direction for further research.

physics.plasm-ph↗

arXiv2025

Non-equilibrium classical recombination in the expanding ultracold plasmas

The efficiency of recombination is of crucial importance for the existence of ultracold plasmas (UCP), particularly, the ones formed in the magneto-optical traps. Unfortunately, the equilibrium thermodynamic treatment of the ionization-recombination processes is inappropriate for the evolving UCP clouds, while the straightforward kinetic simulation encounters the problem of huge difference in the spatial and temporal scales for free and bound motion of the electrons. As a result, only the "virtual" electron-ion pairs are usually reproduced in such modeling, and it is necessary to employ some heuristic criteria to identify them with the recombined atoms. It is the aim of this paper to present the first successful ab initio simulation of the non-equilibrium recombination in the evolving UCP plasmas. We employed a special algorithm, which is based on using the "scalable" reference frame, co-moving with the expanding substance. Then, the recombination events are identified by a series of sharp equidistant peaks in the kinetic and/or potential energies, which are caused by the captured electrons passing near the pericenters of their orbits; and this is confirmed by a detailed inspection of their trajectories. Thereby, we were able to trace the real - rather than "virtual" - electron-ion pairs, and the total efficiency of their formation was found to be about 20%, which is in agreement with the laboratory measurements.

physics.plasm-ph↗

arXiv2025

Estimating the Local Hubble Parameter from the Thermal Evolution of Earth and Mars

The problem of local (e.g., interplanetary) Hubble expansion is studied for a long time but remains a controversial subject till now; and of particular interest is a plausible value of the local Hubble parameter at the scale of the Solar system. Here, we tried to estimate the corresponding quantity by the analysis of surface temperatures on the Earth and Mars, which are formed by a competition between a variable luminosity of the Sun and increasing radii of the planetary orbits. Our work employs paleochemical and paleobiological data on the temperature of the ancient Earth, on the one hand, and geological data on the existence of an ocean of liquid water on the ancient Mars, on the other hand. As follows from our analysis, the martian data impose only a weak constraint on the admissible values of the Hubble parameter because of the unknown salinity - and, therefore, the freezing point - of the martian water. On the other hand, the terrestrial data turn out to be much more valuable, especially, for the Precambrian period, when temperature variation was sufficiently smooth and monotonic. For example, in the framework of standard LambdaCDM model with 70% of dark energy, contemporary value of the local Hubble parameter was found to be 70-90 km/s/Mpc under assumption that the Earth's surface temperature in the end of Precambrian equaled 45 C. This is in reasonable agreement both with the intergalactic data and with an independent estimate of the local Hubble parameter from tidal evolution of the Earth-Moon system.

astro-ph.EP↗

arXiv2025

Krizek-Somer Anthropic Principle and the Problem of Local Hubble Expansion

According to the Krizek-Somer hypothesis [New Astron. 17, 1 (2012); Grav. Cosmol. 21, 59 (2015)], a biological evolution of the Earth is possible only at certain values of the Hubble parameter, because the increasing luminosity of the Sun should be compensated by the increasing orbital radius of the Earth due to the local Hubble expansion, thereby keeping the Earth's surface temperature sufficiently stable. Here, we examine this hypothesis in light of the recent data on the surface temperature on the early Earth, thereby imposing a few constraints on the admissible values of the local Hubble parameter. As follows from our analysis, the Krizek-Somer mechanism might be a valuable tool to resolve the important geophysical and paleontological puzzles, but the particular value of the local Hubble parameter is substantially affected by the current uncertainties in our knowledge about the temperature and other properties of the early Earth.

physics.gen-ph↗

arXiv2025

Topological ignition of the stealth coronal mass ejections

One of hot topics in the solar physics are the so-called 'stealth' coronal mass ejections (CME), which are not associated with any appreciable energy release events in the lower corona, such as the solar flares. It is often assumed recently that these phenomena might be produced by some specific physical mechanism, but no particular suggestions were put forward. It is the aim of the present paper to show that a promising explanation of the stealth CMEs can be based on the so-called 'topological' ignition of the magnetic reconnection, when the magnetic null point is produced by a specific superposition of the remote sources (sunspots) rather than by the local current systems. As follows from our numerical simulations, the topological model explains very well all basic features of the stealth CMEs: (i) the plasma eruption develops without an appreciable heat release from the spot of reconnection, i.e., without the solar flare; (ii) the spot of reconnection (magnetic null point) can be formed far away from the location of the magnetic field sources; (iii) the trajectories of eruption are usually strongly curved, which can explain observability of CMEs generated behind the solar limb.

astro-ph.SR↗

arXiv2024

On the Nature of Subharmonics of the Electron Emission from Ultracold Plasmas

One of the most interesting phenomena in the ultracold plasmas are multiple subharmonics of the electron emission observed after its irradiation by the monochromatic radiowaves. Unfortunately, the early interpretation of this phenomenon as the so-called Tonks-Dattner resonances (i.e., actually the standing Langmuir waves) encountered a number of serious obstacles, such as a lack of the adequate boundary conditions, an incorrect dependence on the electron temperature, and an insensitivity to the shape of the cloud. Here, we suggest an alternative interpretation based on the quasi-classical multiphoton ionization of the 'secondary' Rydberg atoms formed in the expanding and cooling plasma clouds. As follows from our numerical simulations, the efficiency of such ionization exhibits a series of well-expressed peaks. Moreover, this process is evidently irrelevant to the boundary conditions and global shape of the cloud. Therefore, this should be a viable alternative to the earlier idea of Tonks--Dattner resonances.

physics.plasm-ph↗

arXiv2023

Effects of Disorder on Electron Heating in Ultracold Plasmas

Starting from the beginning of their research in the early 2000's, the ultracold plasmas were considered as a promising tool to achieve considerable values of the Coulomb coupling parameter for electrons. Unfortunately, this was found to be precluded by a sharp spontaneous increase of temperature, which was often attributed to the so-called disorder-induced heating (DIH). It is the aim of the present paper to quantify the effect of spontaneous heating as function of the initial ionic disorder and, thereby, to estimate the efficiency of its mitigation, e.g., by the Rydberg blockade. As a result of the performed simulations, we found that the dynamics of electrons exhibited a well-expressed transition from the case of the quasi-regular arrangement of ions to the disordered one; the magnitude of the effect being about 30%. Thereby, we can conclude that the two-step formation of ultracold plasmas - involving the intermediate stage of the blockaded Rydberg gas - can really serve as a tool to increase the degree of Coulomb coupling, but the efficiency of this method is moderate.

physics.plasm-ph↗

arXiv2023

The unipolar solar flares as a manifestation of the 'topological' magnetic reconnection

Solar flares - which are the most prominent manifestation of the solar activity - typically manifest themselves as a single or a set of luminous arcs (magnetic flux tubes) rooted in regions of opposite polarity in the photosphere. However, a careful analysis of the archival data by Hinode satellite sometimes reveals surprising cases of flaring arcs whose footpoints belong to regions of the same polarity or to areas without any appreciable magnetic field. Despite the counterintuitive nature of this phenomenon, it can be reasonably interpreted in the framework of the so-called 'topological model' of magnetic reconnection, where a magnetic null point is formed due to specific superposition of influences from remote sources rather than by local current systems. As a result, the energy release propagates along a separator of the flipping two-dome structure rather than along a fixed magnetic field line. Therefore, the luminous arc needs not to be associated anymore immediately with the magnetic sources. Here, we report both observational cases of the above-mentioned type as well as provide their theoretical model and numerical simulations.

astro-ph.SR↗

arXiv2022

Electron Temperature Relaxation in the Clusterized Ultracold Plasmas

Ultracold plasmas are a promising candidate for the creation of strongly-coupled Coulomb systems. Unfortunately, the values of the coupling parameter Gamma_e actually achieved after photoionization of the neutral atoms remain relatively small because of the considerable intrinsic heating of the electrons. A conceivable way to get around this obstacle might be to utilize a spontaneous ionization of the ultracold Rydberg gas, where the initial kinetic energies could be much less. However, the spontaneous avalanche ionization will result in a very inhomogeneous distribution (clusterization) of the ions, which can change the efficiency of the electron relaxation in the vicinity of such clusters substantially. In the present work, this hypothesis is tested by an extensive set of numerical simulations. As a result, it is found that despite a less initial kinetic energy, the subsequent relaxation of the electron velocities in the clusterized plasmas proceeds much more violently than in the case of the statistically-uniform ionic distribution. The electron temperature, firstly, experiences a sharp initial jump (presumably, caused by the "virialization" of energies of the charged particles) and, secondly, exhibits a gradual subsequent increase (presumably, associated with a multi-particle recombination of the electrons at the ionic clusters). As a possible tool to reduce the anomalous temperature increase, we considered also a two-step plasma formation, involving the blockaded Rydberg states. This leads to a suppression of the clusterization due to a quasi-regular distribution of ions. In such a case, according to the numerical simulations, the subsequent evolution of the electron temperature proceeds more gently, approximately with the same rate as in the statistically-uniform ionic distribution.

physics.plasm-ph↗

arXiv2022

Topological Quantification of the "Anemone" (Branching) Solar Flares

The so-called "anemone" solar flares are an interesting type of the space plasma phenomena, where multiple null points of the magnetic field are connected with each other and with the magnetic sources by the separators, thereby producing the complex branching configurations. Here, using the methods of dynamical systems and Morse-Smale theory, we derive a few universal topological relations between the numbers of the null points and sources of various kinds with arbitrary arrangement in the above-mentioned structures. Such relations can be a valuable tool both for a quantification of the already-observed anemone flares and for a prediction of the new ones in complex magnetic configurations.

astro-ph.SR↗

arXiv2020

New Types of the Chromospheric Anemone Microflares: Case Study

The chromospheric anemone microflares (AMF) are the transient solar phenomena whose emission regions have a multi-ribbon configuration. As distinct from the so-called "atypical" solar flares, also possessing a few ribbons, the temporal and spatial scales of AMFs are a few times less, and the configuration of their ribbons is more specific (star-like). The previously reported AMFs had typically three or, less frequently, four ribbons; and it was shown in our recent paper (Dumin and Somov: 2019, Astron. Astrophys. 623, L4) that they can be reasonably described by the so-called GKSS model of magnetic field, involving as few as four point-like magnetic sources with various polarity and arrangement. To seek for the new types of AMFs, we performed inspection of the large set of the emission patterns in the chromospheric line Ca II H recorded by Hinode/SOT and confronted them with the respective magnetograms obtained by SDO/HMI. As follows from this analysis, it is really possible to identify the new unusual AMFs. Firstly, these are the flares occurring in the regions with unbalanced magnetic flux. Secondly, and most interesting, it is possible to identify the AMFs with much more complex spatial configurations, e.g., involving five luminous ribbons with a nontrivial arrangement. As follows from the corresponding magnetograms, they are produced by the effective magnetic sources (sunspots) of different polarity with intermittent arrangement, but their number is greater than in the standard GKSS model.

astro-ph.SR↗

arXiv2020

Anticorrelated temperature-density profiles in the quiet solar corona and coronal mass ejections: Approach based on the spin-type Hamiltonians

The problem of solar corona heating remains one of key puzzles in astrophysics for a few decades; but none of the proposed mechanisms can give a definitive answer to this question. As a result, the novel scenarios are still suggested. Here, we perform a critical consideration of the recently-proposed mechanism for the formation of anticorrelated temperature and density profiles due to specific features of relaxation in the strongly non-equilibrium plasmas described by the so-called spin-type Hamiltonians (L.Casetti & S.Gupta. Eur. Phys. J. B 87, 91, 2014; T.N.Teles et al. Phys. Rev. E 92, 020101(R), 2015). We employ the universal property of these systems to produce the long-lived anticorrelated temperature-density distributions and analyze their most important qualitative features in the context of coronal plasmas. As follows from our consideration, such anticorrelated profiles can be hardly relevant to explanation of the temperature distribution in the quiet solar corona. However, they might be interesting for the interpretation of the large-scale inhomogeneity in the coronal mass ejections and the resulting solar wind.

astro-ph.SR↗

arXiv2018

A Unified Model of Dark Energy Based on the Mandelstam-Tamm Uncertainty Relation

It is commonly recognized now that Dark Energy (Lambda-term) is of crucial importance both at the early (inflationary) stage of cosmological evolution and at the present time. However, little is known about its nature and origin till now. In particular, it is still unclear if Lambda-term is a new fundamental constant or represents just an effective contribution from the underlying field theory. Here, we show that a quite promising and universal approach to this problem might be based on the Mandelstam-Tamm uncertainty relation of quantum mechanics. As a result, we get the effective Lambda-term that is important throughout the entire history of the Universe. Besides, such an approach requires a substantial reconsideration of some other cosmological parameters, e.g., the age of the Universe.

physics.gen-ph↗

arXiv2018

Can the Dark-Matter Deficit in the High-Redshift Galaxies Explain the Persistent Discrepancy in Hubble Constants?

One of hot topics in the last years is a systematic discrepancy in the determination of Hubble parameter by various methods. Namely, the values derived "directly" from the distance scale based on Cepheids and supernovae--and referring to the relatively "local" part of the Universe--are about 10% greater than the ones following from the analysis of the cosmic microwave background (CMB) radiation, which refers to the "global" scales. The most popular interpretation of this discord, widely discussed nowadays, is variation of the dark-energy equation-of-state parameter w. However, there might be a much simpler explanation, following from the recent observations of the rotation curves in the high-redshift galaxies. Namely, it was found that they have much smaller dark-matter halos than galaxies in the vicinity of us [Genzel, et al. Nature 543 (2017), 397]. Since both the dark and luminous matter possess the same dust-like equation of state and, therefore, their average cosmological densities evolve by the same way, our local neighborhood is not quite typical but rather overfilled with the dark matter. Then, the local value of the Hubble constant should be greater than the global one. Roughly speaking, a twofold excess of the dark matter in our local Universe would give just the above-mentioned 10% increase in the value of Hubble parameter.

astro-ph.CO↗

arXiv2017

Is the Hubble Constant Scale-dependent?

An exact determination of the Hubble constant remains one of key problems in cosmology for almost a century. However, its modern values derived by various methods still disagree from each other by almost 10%; the greater values being obtained by measurements at the relatively small distances (e.g., by Cepheid stars as the standard candles), while the smaller values being characteristic of the methods associated with huge spatial scales (e.g., the analysis of the cosmic microwave background fluctuations). A reasonable way to resolve this puzzle is to assume that the Hubble constant is inherently scale-dependent. This idea seems to be particularly attractive in light of the latest observational results on the early-type galaxies, where the dark-matter haloes are almost absent. Therefore, an average contribution of the irregularly-distributed dark matter to the rate of the cosmological expansion should be substantially different at various spatial scales. As follows from the rough estimates, the corresponding variation of the Hubble constant can be 10% and even more, which well explains the spread in its values obtained by the various methods.

astro-ph.CO↗

arXiv2017

Observation of "Topological" Microflares in the Solar Atmosphere

We report on observation of the unusual kind of solar microflares, presumably associated with the so-called "topological trigger" of magnetic reconnection, which was theoretically suggested long time ago by Gorbachev et al. (Sov. Ast. 1988, v.32, p.308) but has not been clearly identified so far by observations. As can be seen in pictures by Hinode SOT in CaII line, there may be a bright loop connecting two sunspots, which looks at the first sight just as a magnetic field line connecting the opposite poles. However, a closer inspection of SDO HMI magnetograms shows that the respective arc is anchored in the regions of the same polarity near the sunspot boundaries. Yet another peculiar feature is that the arc flashes almost instantly as a thin strip and then begins to expand and decay, while the typical chromospheric flares in CaII line are much wider and propagate progressively in space. A qualitative explanation of the unusual flare can be given by the above-mentioned model of topological trigger. Namely, there are such configurations of the magnetic sources on the surface of photosphere that their tiny displacements result in the formation and fast motion of a 3D null point along the arc located well above the plane of the sources. So, such a null point can quickly ignite a magnetic reconnection along the entire its trajectory. Pictorially, this can be presented as flipping the so-called two-dome magnetic-field structure (which is just the reason why such mechanism was called topological). The most important prerequisite for the development of topological instability in the two-dome structure is a cruciform arrangement of the magnetic sources in its base, and this condition is really satisfied in the case under consideration.

astro-ph.SR↗

arXiv2017

Multi-Manifold Stark Splittings Lift the Rydberg Blockade

The spatial evolution of the Rydberg blockade is studied taking into account Stark-split energy levels across several manifolds. We find that the unexpected restoration of a blockaded Rydberg excitation at small interatomic distances, e.g., experimentally observed by P.Schauss, et al. [Nature 491, 87 (2012)], can be explained by the perturbed energy levels from neighboring manifolds that enter the energy window of excitation defined by the bandwidth of the exciting laser. The same mechanism can also explain why the pair correlation function of Rydberg atoms remains nonzero in the entire region of Rydberg blockade.

physics.atom-ph↗