A phenomenological,kinematical model of the coronal magnetic fields in terms of thin flux tubes rising from the photosphere

A kinematical model is necessary for understanding the gross structure of the coronal magnetic field and its slow evolution in consistency with the small scale structure of the photospheric fields. Here we have developed a preliminary phenomenological model in terms of flux tubes of flux amounts ≈ 10¹⁷ − 10^18.5 Mx rising across the inner corona in the form of arches and opening out in the outer corona. In contrast to Parker’s estimate, this model is consistent with the observed spans of the chromospheric fibrils and x-ray arches. It is also consistent with the number of flux tubes present above the photosphere as estimated from the observed abundance of spicules.     

Role of equilibrium plasma flow on damping of slow MHD waves

In the solar corona waves and oscillatory activities are observed with modern imaging and spectral instruments. These oscillations are interpreted as slow magneto-acoustic waves excited impulsively in coronal loops. This study explores the effect of steady plasma flow on the dissipation of slow magneto-acoustic waves in the solar coronal loops permeated by uniform magnetic field. We have investigated the damping of slow waves in the coronal plasma taking into account viscosity and thermal conductivity as dissipative processes. On solving the dispersion relation it is found that the presence of plasma flow influences the characteristics of wave propagation and dissipation. We have shown that the time damping of slow waves exhibits varying behavior depending upon the physical parameters of the loop. The wave energy flux associated with slow magnetoacoustic waves turns out to be of the order of 10⁶ erg cm⁻² s⁻¹ which is high enough to replace the energy lost through optically thin coronal emission and the thermal conduction below to the transition region.     

Optimising dislocation-engineered silicon light-emitting diodes

This article presents a study of the possibilities of optimising the electroluminescence (EL) efficiency of dislocation-engineered silicon light-emitting diodes (DELEDs). The diodes were produced by implantation of boron in n-type (100)Si wafers, at a constant ion energy and fluence, of 30 keV and 1×10¹⁵ ions/cm², respectively. The density and the areal coverage by dislocation loops were varied by applying different annealing times in a rapid thermal processing, from 30 s to 60 min. It is shown that the EL efficiency is directly correlated to the number and areal coverage by the loops. The highest population of loops, ∼5×10⁹ /cm², and an areal coverage of around 50% were achieved for 1–5 min annealing. This loop distribution results in optimal DELEDs, having the highest EL response and the largest increase of EL intensity with operating temperature (80–300 K). The results of this work confirm a previously introduced model of charge-carrier spatial confinement by a local stress induced by the edge of the dislocation loops, preventing carrier diffusion to non-radiative recombination centres and enhancing radiative transitions at the silicon band edge. PACS 85.60.Jb; 78.60.Fi; 61.72.Tt     

Effect of the electromagnetic field of an eruptive prominence on coronal and chromospheric plasmas (CME and Hα emission formation)

The frozen- in chromospheric and coronal plasma motions during an eruption of a filament with a magnetic field configuration described by the inverse polarity model are considered. At the initial stage of the filament motion the magnetic field compresses the chromospheric gas within two strips located symmetrically about the inversion line. The compression is accompanied by plasma heating and emission enhancement in the lineH _α. The distance between the strips increases with filament altitude above the photosphere. This mechanism is sufficient to describe the dynamics ofH _α emission kernels in two- ribbon flares. In the corona region in which the magnetic pressure of the filament field is greater than the gas pressure, plasma rarefaction and cavity formation occur. Near the boundary β=1the plasma is decelerated and its density increases, which corresponds to the formation of an outer shell of the CME.     

Gamma-ray bursts from evaporating primordial black holes

It is believed that the detection of gamma-ray bursts from evaporating primordial black holes is highly improbable in the near future since the expected photon flux, consisting mainly of photons with energies ≳ GeV, is too low. Contrary to this point of view, we show that a large fraction of the black hole power at the final stage of evaporation (the last 10³ s) can be liberated as a burst of soft γ-ray emission of duration 10⁻¹–10³ s and luminosity 10²⁸–10³¹ erg/s in the energy range 0.1–1 MeV. According to our calculations of the black hole evaporation rate (within the Standard Model of elementary particles), when the black hole temperature exceeds approximately 10 GeV, the charged particle outflow from a black hole forms a well-defined plasma and can be described in the hydrodynamic approximation. In this case more than half of the rest energy of a black hole can be converted into soft gamma-rays due to the presence of the magnetic field with energy density comparable to that of charged particles. We consider various mechanisms leading to such transformation and estimate their efficiency. It is shown that, at least, some of the gamma-ray bursts detected by BATSE can be associated with evaporating black holes. Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 1, pp. 36–45, January, 1998.     

Self-regulation of solar coronal heating process via the collisionless reconnection condition

I propose a new paradigm for solar coronal heating viewed as a self-regulating process keeping the plasma marginally collisionless. The mechanism is based on the coupling between two effects. First, coronal density controls the plasma collisionality and hence the transition between the slow collisional Sweet-Parker and the fast collisionless reconnection regimes. In turn, coronal energy release leads to chromospheric evaporation, increasing the density and thus inhibiting subsequent reconnection of the newly reconnected loops. As a result, statistically, the density fluctuates around some critical level, comparable to that observed in the corona. In the long run, coronal heating can be represented by repeating cycles of fast reconnection events (nanoflares), evaporation episodes, and long periods of slow magnetic stress buildup and radiative cooling of the coronal plasma.     

Nonlinear diffusion of water molecules in glycerol

The dependence of the concentration of water molecules in water vapor brought into contact with glycerol surface was measured in a time window of 10⁻¹–10³ s. An obvious nonlinearity of water molecule diffusion was found in a short time approximation (within a minute). A proposal is made with regard to the convective character of diffusion due to heat release during absorption.     

Induced γ-ray fluorescence of isomeric nuclei in a magnetic trap

Gamma-ray fluorescence induced in isomeric nuclei in a magnetic trap by x radiation from a laser plasma is studied. It is shown that under these conditions it is possible to obtain a γ-ray pulse with a duration of 100 ps and energy 10⁻⁵ J. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 9, 674–680 (10 November 1998)     

Experiments on two-step heating of a dense plasma in the GOL-3 facility

This paper presents the results of experiments on two-stage heating of a dense plasma by a relativistic electron beam in the GOL-3 facility. A dense plasma with a length of about a meter and a hydrogen density up to 10¹⁷ cm⁻³ was created in the main plasma, whose density was 10¹⁵ cm⁻³. In the process of interacting with the plasma, the electron beam (1 MeV, 40 kA, 4 μs) imparts its energy to the electrons of the main plasma through collective effects. The heated electrons, as they disperse along the magnetic field lines, in turn reach the region of dense plasma and impart their energy to it by pairwise collisions. Estimates based on experimental data are given for the parameters of the flux of hot plasma electrons, the energy released in the dense plasma, and the energy balance of the beam-plasma system. The paper discusses the dynamics of the plasma, which is inhomogeneous in density and temperature, including the appearance of pressure waves. Zh. éksp. Teor. Fiz. 113, 897–917 (March 1998)     

Studies of solar flares and CMEs related to the space solar missions in the future

Solar eruptions and the related processes involve magnetic fields and plasma flows of various scales in both time and space. These processes include the convective motions of the mass and magnetic field in the photosphere, evolutions of magnetic fields in both the chromosphere and the corona prior to and during the disruption of magnetic fields in response to the photospheric motions. These evolutions constitute a whole process of transporting the magnetic energy and the helicity from the photosphere to the corona, and then to interplanetary space. The present work, on the basis of a solar eruption model, discusses these processes, and the related questions, unanswerable at present, but could be the scientific objectives of the space solar missions in the future.     

Optical properties of BiFeO<Subscript>3</Subscript> ceramics in the frequency range 0.3–30.0 THz

Reflection and transmission infrared spectra of BiFeO₃ ceramic samples have been measured using submillimeter spectroscopy (on a backward-wave tube spectrometer) and Fourier-transform infrared spectroscopy in the frequency range from 5 to 1000 cm⁻¹ at temperatures in the range from 10 to 500 K. New resonant modes (probably, magnetic in nature) with the eigenfrequencies decreasing with an increase in the temperature have been recorded in the range 10–30 cm⁻¹ by IR spectroscopy for the first time. An additional absorption with a fairly large dielectric contribution has been revealed in the range 30–60 cm⁻¹. It has been demonstrated that the corresponding oscillators couple with both the lowest frequency phonon mode and the magnetic subsystem.     

Magnetically stabilized electron-hole liquid in indium antimonide

Luminescence spectra of sufficiently pure n-type indium antimonide crystals (N _D−N _A=(1–22)·10¹⁴ cm⁻³) in a magnetic field of up to 56 kOe, at temperatures of 1.8–2 K, and high optical pumping densities (more than 100 W/cm²) have been studied. More evidence of the existence of electron-hole liquid stabilized by magnetic field has been obtained, and its basic thermodynamic parameters as functions of magnetic field have been measured. When the magnetic field increases from 23 to 55.2 kOe, the liquid density increases from 3.2·10¹⁵ to 6.7·10¹⁵ cm⁻³, the binding energy per electron-hole pair rises from 3.0 to 5.2 meV, and the binding energy with respect to the ground exciton level (work function of an exciton in the liquid) rises from 0.43 to 1.2 meV. Zh. éksp. Teor. Fiz. 111, 737–758 (February 1997)     

Assembly of γ-Fe2O3/polyaniline nanofilms with tuned dipolar interaction

The internal morphology and magnetic properties of layer-by-layer assembled nanofilms of polyaniline (PANI) and maghemite (γ-Fe₂O₃—7.5-nm diameter) were probed with cross-sectional transmission electron microscopy (TEM) and magnetization measurements (magnetic hysteresis loops, magnetization using zero-field cooled/field-cooled protocols, and ac magnetic susceptibility). Additionally, simulations of the as-produced samples were performed to assess both the nanofilm’s morphology and the corresponding magnetic signatures using the cell dynamic system (CDS) approach and Monte Carlo (MC) through the standard Metropolis algorithm, respectively. Fine control of the film thickness and average maghemite particle–particle within this magnetic structure was accomplished by varying the number of bilayers (PANI/γ-Fe₂O₃) deposited onto silicon substrates or through changing the concentration of the maghemite particles suspended within the colloidal dispersion sample used for film fabrication. PANI/γ-Fe₂O₃ nanofilms comprising 5, 10, 25 and 50 deposited bilayers displayed, respectively, blocking temperatures (T _B) of 30, 35, 39 and 40 K and effective energy barriers (ΔE/k _B) of 1.0 × 10³, 2.3 × 10³, 2.8 × 10³ and 2.9 × 10³ K. Simulation of magnetic nanofilms using the CDS model provided the internal morphology to carry on MC simulation of the magnetic properties of the system taking into account the particle–particle dipolar interaction. The simulated (using CDS) surface–surface particle distance of 0.5, 2.5 and 4.5 nm was obtained for nanofilms with thicknesses of 36.0, 33.9 and 27.1 nm, respectively. The simulated (using MC) T _B values were 33.0, 30.2 and 29.5 K for nanofilms with thicknesses of 36.0, 33.9 and 27.1 nm, respectively. We found the experimental (TEM and magnetic measurements) and the simulated data (CDS and MC) in very good agreement, falling within the same range and displaying the same systematic trend. Our findings open up new perspectives for fabrication of magnetic nanofilms with pre-established (simulated) morphology and magnetic properties.     

Target plasma formation by UHF power

The properties of plasma injected into an open magnetic trap of uniform field from an independent UHF source have been investigated. Plasma is created in the UHF source at the frequency of 2400 MHz (power input 150 W) in the electron cyclotron resonance (ECR) regime at the pressure of neutral argon (10⁻⁵−10⁻²) torr. It is established that a rather quiescent target plasma with controlled density within the range of (2 × 10⁸−2 × 10¹²) cm⁻³ and temperature 2–3eV is accumulated in the trap. It turned out that plasma lifetime in the trap is determined by a classical mechanism of particle escape at the expense of collisions, at fixed value of magnetic field in the trap it practically is not changed with the variation of neutral gas pressure and reaches the value ≈ 4×10⁻³ s at the magnetic field strength in the trap equal 1600 Oe.     

Dynamics of an electron beam from a high-current picosecond accelerator

The dynamics of a high-current (10²–10⁴ A) electron beam with energies of 10⁵–10⁶ eV and picosecond duration (10⁻¹⁰ s) at the output of the accelerator tube is investigated. The slowing of electrons by the residual positive charge on the surface of the tube is found to have a significant influence in the case of short pulse durations. The distance of the electron beam from the surface of the tube in vacuum is estimated on the basis of a one-dimensional model. It is shown that the electron radiation can travel to a distance of several centimeters from the surface at current densities below 20 A/mm², whereas at high current densities the beam is trapped near the surface. Zh. Tekh. Fiz. 69, 111–115 (May 1999)     

Experimental and computational study of the passage of an electron beam through the curvilinear element of the Drakon stellarator system in a tenuous plasma

Results are presented from the first stage of studies on the passage of an electron beam with energy 100–500 eV in a magnetic field of 300–700 Oe through the curvilinear solenoid of the KRéL unit, the latter being a prototype of the closing segment of the Drakon stellarator system, in the plasma-beam discharge regime. The ion density at the end of the curvilinear part of the chamber, n _i ≈8×10⁸–10¹⁰ cm⁻³, the electron temperature T _e ≈4–15 eV, and the positions at which the beam hits the target for different distances from it to the electron source are determined experimentally. The motion of the electron beam is computationally modeled with allowance for the space charge created by the beam and the secondary plasma. From a comparison of the experimentally measured trajectories and trajectories calculated for different values of the space charge, we have obtained an estimate for the unneutralized ion density of the order of 5×10⁷ cm⁻³. Zh. Tekh. Fiz. 69, 22–26 (February 1999)     

On the origin of soft x-ray and microwave sources of emission in solar magnetic loops

One possible mechanism is proposed for the appearance of high-temperature sources of emission in solar magnetic loops visible sometimes in the microwave and soft x-ray bands in active regions, even out of flares. The main concept of this mechanism is as follows. Due to the existence of current in the magnetic loop, there is a component of the electric field E which is longitudinal to the magnetic field. In this case, at some heights the parameters of solar atmospheric plasma (density and temperature) appear to cause a certain number of electrons to be in a runaway regime. These electrons can be accelerated to energies of about 1–2 keV. This corresponds to the temperature of the observed microwave and x-ray source. Accelerated electrons satisfying the trapping condition will gradually fill the magnetic tube, and after a while a hot x-ray loop can occur. Similar mechanisms of the appearance of hightemperature sources of emissions in active regions probably take place in the simple loop flare for the class of thermal flares visible in the microwave and soft x-ray bands.Department of Astrophysics and Cosmic Plasma Physics, Applied Physics Institute, Russian Academy of Sciences, Nizhnii Norgorod. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 37, No. 7, pp. 836–850, July, 1994.     

Modelling of Lévy walk kinetics of charged particles in edge electrostatic turbulence in tokamaks

We model and discuss the possible types of motion that charged particles may undergo in a stationary and spatially periodic electrostatic potential and a homogeneous magnetic field. The model is considered to be the simplest approximation of more complex phenomena of plasma edge turbulence in tokamaks. Therein, low frequency turbulence appears in the plasma edge, resulting in a fluctuation of the electron density, and also in the generation of a turbulent electrostatic field. Typical parameters of this turbulent electrostatic field are an electrical potential amplitude of 10–100 V and wave numbers k≈10³ m^-1. In our model, we consider these regimes, together with a homogeneous magnetic field with a magnitude of 1 T. We investigate the dynamics of singly-ionized carbon ions – a typical plasma impurity – with kinetic energies on the order of 10 eV. Besides the obvious Larmor and drift motions, a motion of random-walk and of Lévy walk character appear therein. All of these types of motion can play an important role in the modelling of the anomalous diffusion of particles from the plasma edge turbulence region. The dynamics mentioned will cause an inevitable escape of energetic particles and thus of power loss from the thermonuclear reactor. Moreover, Lévy walk kinetics represents a very interesting kind of kinetics, currently of great interest, which was previously not so often discussed.