Freak waves in laboratory and space plasmas

Generation of large-amplitude short-lived wave groups from small-amplitude initial perturbations in plasmas is discussed. Two particular wave modes existing in plasmas are considered. The first one is the ion-sound wave. In a plasmas with negative ions it is described by the Gardner equation when the negative ion concentration is close to critical. The results of numerical solution of the Gardner equation with the modulationally unstable initial condition are presented. These results clearly show the possibility of generation of freak ion-acoustic waves due to the modulational instability. The second wave mode is the Alfvén wave. When this wave propagates at a small angle with respect to the equilibrium magnetic field, and its wave length is comparable with the ion inertia length, it is described by the DNLS equation. Studying the evolution of an initial perturbation using the linearized DNLS equation shows that the generation of freak Alfvén waves is possible due to linear dispersive focusing. The numerical solution of the DNLS equation reveals that the nonlinear dispersive focusing can also produce freak Alfvén waves.     

Transition regions in solar system and astrophysical plasmas

A brief review is presented of basic particle and field characteristics of plasmas observed within the solar system, especially near transition regions, and their parameter ranges are compared with those inferred for stellar winds and the interstellar medium. Parameter ranges for solar system and astrophysical plasmas are found to have considerable overlap. In addition, astrophysics provides unique, global perspectives of large-scale systems, whereas solar-system space physics provides for direct quantitative testing of physical processes. Astrophysics and solar-system space physics studies thus have complementary and synergistic roles     

Computational study of impulsively generated standing slow acoustic waves in a solar coronal loop

We numerically investigated standing slow acoustic waves impulsively excited in a solar coronal loop by gas pressure and mass density perturbations in one-dimensional space. The corresponding computer model is described by the hydrodynamic equations that are solved numerically by means of the so-called flux limiters methods on uniformly structured mesh. We discuss the fundamental mode and the first harmonic mode which are generated in dependence on position of the initial perturbation in the numerical box. We show how the standing slow acoustic waves are generated in the corona, where they are trapped in space between two dense layers as in the resonator, and how their energy leaks from the corona to the dense layers. We found that this leakage increases with the decrease of the density jump at the transition region. We also studied the case when the perturbation is initiated at the transition region. We found that even in this case the standing wave is formed, but their energetics is influenced by the evaporation of the plasma from the transition region into the corona.     

Electron impact excitation coefficients for laboratory and astrophysical plasmas

Electron impact excitation rate coefficients have been obtained for a number of transitions in highly ionized ions of interest to astrophysical and laboratory plasmas. The calculations were done using the method of distorted waves. Results are presented for various transitions in highly ionized Ne, Na, Al, Si, A, Ca, Ni and Fe.     

Variability of coronal structures and ion components in the solar wind

The variations of solar wind ion fluxes of protons and-particles are studied in a wide timescale: from parts of a second to several months. A persistence time of about 60 hours was obtained for the large-scale variations of-particles. Power density spectra of velocity, density and magnetic field were studied in the frequency range from 10^–5 to 10^–3 Hz. Middle-scale fluctuations of both protons and-particles are close to each other and the spectrum for-particles has a somewhat greater slope than that for protons. Estimates of the variations of the flux power density are given in the frequency range from 10^–3 to 3 Hz.Presented at the VII STP-Symposium in the Hague (Netherlands), 1990.     

Non-equilibrium ionization and electron density in the coronal plasma during solar flares

Summary The Li-like to He-like ion population ratio for calcium at the onset of solar flares is observed to be about 60% higher than in steady-state ionization balance. The measurement of the duration of this initial period of transient ionization and of the population ratios of adjacent ionization states allows an estimate of the electron density of the coronal plasma at flare onset. The density found in this study, within 1·10⁹ and 7·10⁹ cm⁻³ is comparable with the density typical of pre-flare active regions.     

Diagnostics of interplanetary and flaring plasmas in impulsive solar energetic particle events

Using instruments onboard the ACE and Wind spacecrafts, we study temporal evolution, spectra, and ionization states of Fe in the impulsive solar energetic particle (SEP) events of September 6, 1998 and May 1, 2000. Proton and electron intensities and anisotropies were used to constrain the particle mean free path in interplanetary space. The derived values were used to explain the observed energy and charge spectra of heavy ions. It is concluded that the sharp increase in the average charge of Fe ions in the range from 200 to 600 keV per nucleon observed in both events cannot be explained within the framework of the model of single-temperature source even if the effects of interplanetary propagation are taken into account. At least two acceleration regions with temperatures ～10⁶ and 10⁷ K should exist in the source.     

Cluster of solar active regions and onset of coronal mass ejections

round-the-clock solar observations with full-disk coverage of vector magnetograms and multi-wavelength images demonstrate that solar active regions(ARs) are ultimately connected with magnetic field. Often two or more ARs are clustered, creating a favorable magnetic environment for the onset of coronal mass ejections(CMEs). In this work, we describe a new type of magnetic complex: cluster of solar ARs. An AR cluster is referred to as the close connection of two or more ARs which are located in nearly the same latitude and a narrow span of longitude. We illustrate three examples of AR clusters, each of which has two ARs connected and formed a common dome of magnetic flux system. They are clusters of NOAA(i.e., National Oceanic and Atmospheric Administration) ARs 11226 11227, 11429 11430, and 11525 11524. In these AR clusters, CME initiations were often tied to the instability of the magnetic structures connecting two partner ARs, in the form of inter-connecting loops and/or channeling filaments between the two ARs. We show the evidence that, at least, some of the flare/CMEs in an AR cluster are not a phenomenon of a single AR, but the result of magnetic interaction in the whole AR cluster. The observations shed new light on understanding the mechanism(s) of solar activity. Instead of the simple bipolar topology as suggested by the so-called standard flare model, a multi-bipolar magnetic topology is more common to host the violent solar activity in solar atmosphere.     

Dust in the planetary system: Dust interactions in space plasmas of the solar system

Cosmic dust particles are small solid objects observed in the solar planetary system and in many astronomical objects like the surrounding of stars, the interstellar and even the intergalactic medium. In the solar system the dust is best observed and most often found within the region of the orbits of terrestrial planets where the dust interactions and dynamics are observed directly from spacecraft. Dust is observed in space near Earth and also enters the atmosphere of the Earth where it takes part in physical and chemical processes. Hence space offers a laboratory to study dust–plasma interactions and dust dynamics. A recent example is the observation of nanodust of sizes smaller than 10 nm. We outline the theoretical considerations on which our knowledge of dust electric charges in space plasmas are founded. We discuss the dynamics of the dust particles and show how the small charged particles are accelerated by the solar wind that carries a magnetic field. Finally, as examples for the space observation of cosmic dust interactions, we describe the first detection of fast nanodust in the solar wind near Earth orbit and the first bi-static observations of PMSE, the radar echoes that are observed in the Earth ionosphere in the presence of charged dust.     

Equation of state of hydrogen,helium, and solar plasmas

The equation of state (EOS) for plasmas of the two lightest elements H and He, and mixtures as typical for the plasmas in the sun are calculated. The contributions of deep bound states are included by using inverted fugacity expansions. The inversion of fugacities to densities is reduced to solvable algebraic problems and expressed by rational polynomials. The calculation of relative pressures is carried out separately for low and high densities. Near the crossing point, in between, the separate solutions are connected to each other by smooth concatenation. Applications to hydrogen–helium plasmas in the sun including estimates for the isentropic EOS are discussed.     

A study of methods for moving particles in RF processing plasmas

Methods for moving charged particles in RF processing plasmas are investigated. These methods include varying RF power, varying chamber pressure, attraction and repulsion by an electrostatic probe, and movement with magnetic fields. Varying RF power changes the depth of the potential wells where particles are trapped. The RF power affects shape and location of the traps and the bulk plasma potential. Increasing the chamber pressure moves the sheath edge closer to the wafer being processed. Since particle traps are found at the plasma sheath edge increasing the chamber pressure will move the particle traps (and any trapped particles) closer to the wafer being processed. The Langmuir probe can repel particles when under negative bias and attract them when positively biased. This probe can also distort the sheath edge when the tip resides within the sheath. Applying a magnetic field can change the characteristics of the particle traps and produce a force on the charged dust particles     

Direct mapping of space structure of a rotational instability in laboratory plasmas

The investigation of the radial ion density profile in the magnetoplasma is described. The method uses the Langmuir probe which is movable along the tube radius. The radial position of this probe destines the vertical beam position on the CRT. The oscilloscope time base is synchronized with the frequency of the instability and is proportional to the azimuthal position.     

A comparative study on the performance of hybrid solar cells containing ZnSTe QDs in hole transporting layer and photoactive layer

In this paper, ZnSTe quantum dots-based hybrid solar cells (HSC) with two different device architectures have been investigated. The improved performance of the poly(3-hexylthiophene) (P3HT) and [6,6]phenyl C₇₁ butyric acid methyl ester (PC₇₁BM)-based bulk heterojunction (BHJ) solar cells by the incorporation of ZnSTe quantum dots (QDs) with an average size of 2.96 nm in PEDOT:PSS layer and active layer that have been demonstrated. Although the efficiency of both types of devices is almost the same, a close comparison reveals different reasons behind their improved performance. The device prepared with QDs in the HTL has shown reduced series resistance, increased shunt resistance, and improved mobility. On the other hand, QDs in the photoactive layer demonstrates increased photo-generation leading to improved efficiency.     

Vibrational chaotic dynamics in triatomic molecules: A comparative study

Within Lie algebraic model, the vibrational chaotic dynamics in triatomic molecules are studied. The molecules of H₂S, NO₂, and O₃ are sampled to explore the dynamical differences between the local and normal mode molecules. The comprehensive effects of the local and normal mode vibrations, resonances and chaos on the dynamical entanglement are studied. The results demonstrate that the resonances as well as chaos can promote the evolution of dynamical entanglement.     

Anharmonic spectra of methanol and silanol: A comparative study

Anharmonic vibrational spectra of methanol and silanol as well as of some of their deuterated isotopomers are analysed using the vibrational self-consistent field approximation corrected by second order perturbation theory (cc-VSCF). Experimental frequencies in the case of methanol and its isotopomers are in general reproduced and anharmonic effects in their vibrational spectra are suitably explained. The similar species containing Si, i.e., silanol, is very unstable. Experimental data about its vibrational spectra are rare in the literature and the only theoretical data available come from the harmonic approach. Thus, to predict further anharmonic effects in its vibrational spectra, we extend our results on methanol to the silanol molecule.     

Random and aperiodic quantum spin chains: A comparative study

According to the Harris-Luck criterion the relevance of a fluctuating interaction at the critical point is connected to the value of the fluctuation exponent . Here we consider different types of relevant fluctuations in the quantum Ising chain and investigate the universality class of random as well as deterministic-aperiodic models. At the critical point the random and aperiodic systems behave similarly, due to the same type of extreme broad distribution of the energy scales at low energies. The critical exponents of some averaged quantities are found to be a universal function of , but some others do depend on other parameters of the distribution of the couplings. In the off-critical region there is an important difference between the two systems: there are no Griffiths singularities in aperiodic models. Received: 18 November 1997 / Received in final form: 24 November 1997 / Accepted: 8 January 1997