Parametric Instabilities of Waves in Magnetized Plasmas

Results from kinetic theory are reformulated in order to generalize previous equations for wave-wave interactions in magnetized plasmas.     

Soliton Chains of Interchange Modes in Plasmas

The equation governing nonlinear two-dimensional interchange modes is derived and an exact solution consisting of an infinite chain of solitons is found. It is suggested that soliton chains of interchange modes in plasmas could be observed experimentally.     

Positron-Impact Excitation of Hydrogen Atoms in Debye Plasmas

The positron-impact excitation of hydrogen atoms embedded in plasma environments is investigated using the close-coupling approximation from the low to intermediate energy region without including any positronium formation channel, and the excitation cross sections for 1s→2s, 1s→2p and 2s→2p processes are calculated in a wide Debye parameter range. The screening interactions, described by the Debye-Hückel model, decrease the coupling matrix elements, resulting in the reduction of the excitation cross sections from a few percent to one magnitude of ten. This will alter remarkably the spectroscopy of hydrogen in intensity and position, which should be considered in the simulation and diagnostics under some specific plasma conditions.     

Analysis of Atomic Electronic Excitation in Nonequilibrium Air Plasmas

Electronic excitation of atoms is studied in nonequilibrium air plasmas with the electronic temperature be- tween 8000 K and 2000OK. By using the modified Saha-Boltzmann equation, our simplified method takes into account significant radiative processes and strong self-absorption of the vacuum ultraviolet lines. Calculations are carried out at three trajectory points of the Fire 1I flight experiment. Good agreement with the detailed collisional-radiative model is obtained, and the performance of this method in applications to highly nonequi- librium conditions is better than Park＇s quasi-steady-state model and Spradian-9.0. A short discussion on the influence of optical thickness of the vacuum ultraviolet radiation is also given. It costs about 2.9 ms on the average to solve one cell of the shock layer on a low cost computer, which shows that the present method is fast and efficient.     

Modes of Excitation in Two-Dimensional Quantum Dots

The electronic structures of low-lying excited states of a polarized quantum dot with 6 electrons has been studied. The Hamiltonian has been diagonalized to obtain the eigenstates. All results are extracted from a detailed analysis of wave functions. Six modes were found that lead to distinct excited core-ring structures. As a result, the core or the ring, or both may be excited, different core-ring structures may coexist. Both crystal-like and liquid-like pictures were found. The role of symmetry constraint was found to be important, the angular momenta of the core and the ring are adjusted to meet the requirement of symmetry constraint.     

Low Frequency Electromagnetic Modes in Strongly Magnetized Coupled Plasmas

We consider the effect of Coulomb correlation on the low frequency part of the spectrum of electromagnetic waves propagating in a non‐ideal electron‐ion plasma. The dielectric tensor constructed by means of the theory of moments is employed.     

Geometric Optics of Lower Hybrid Waves in Nonuniform Plasmas

The propagation of lower hybrid waves in the presence of strong density and field gradient-produced refractive effects is studied in the geometric optics limit. Attention is focused on the electrostatic wave and the modification of the parallel wavenumber k? due to gradients. It is found that in cases where the gradients occur along the direction of the magnetic field the resulting decrease of k? gives rise to a cusp or reflection of the ray at the resonance layer. An asymptotic series for the field amplitudes is developed which is valid in the short wavelength limit everywhere except near the cusp point. It is found that the cusp represents a singularity where the geometric optics assumption is invalid; however, the inclusion of thermal effects removes the singularity by linear mode conversion (LMC). The analysis is applied to toroidal geometry and is extended to include distributed sources.     

Nonlinear Structures of Lower Hybrid Wave in Collision Plasmas

Nonlinear structures of lower hybrid wave in collision plasmas are studied using the two-fluid theory.The oscillatory shock wave is observed due to the effects of the electron-neutral collision and the density inhomogeneity.In the cold electron limit,the oscillatory shock wave becomes the ordinary shock wave.In the collisionless limit,the dominated equation becomes Kd V equation and the lower hybrid solitons arise.The amplitude of the nonlinear structure is depressed by the plasma inhomogeneity,but is hardly affected by the electron-neutral collision.     

REE Spectral Lines for the Determination of Excitation Temperature in Analytical Plasmas

The spectra of rare earth elements (REE) have been investigated to select thermometric species for spectroscopic diagnostic of analytical plasmas. Groups of lines of Y II, La II, Eu II and Yb II were found appropriate for the determination of ionic excitation temperature in argon wall-stabilized plasma arc (WSA) and inductively coupled plasma (ICP). Boltzman plots with excellent Fitting to straight lines were obtained. Temperature values deduced with the different groups of spectral lines agree with each other as well as with that obtained with the most familiarly used Ti II lines.

     

Inductively Coupled Plasmas as Excitation Sources for Atomic Fluorescence Spectrometry

The inductively coupled Ar plasma (ICP) is introduced as a multielement excitation source for flame atomic fluorescence spectrometry. The ICP-excited and the EDL-excited atomic fluorescence detection limits are compared for 20 elements.     

Hybrid Parametric Solitons in Nonlinear Photonic Crystals

We analyze the characteristics of a three-frequency spatial parametric soliton formed by virtue of the cascade frequency tripling in quadratic, periodically poled crystals. A variational approach and a method of averaging are developed, which make it possible to describe analytically, with good accuracy, the characteristics of the spatial solitons studied numerically.     

Wave Trajectories and Damping of Lower Hybrid Wave in Tokamak Plasmas

Incident lower hybrid waves (LHW) propagate toward the center of the plasma in a spiral form in the poloidal and the toroidal sections, and finally are absorbed by the ion Landau damping (ILD) and/or the electron Landau damping (ELD) in accordance with the refractive index parallel to the magnetic field N?, which is varied considerably along the trajectory because of the toroidicity and the rotational transform. We propose the scaling law of the wave trajectories on plasma parameters, which shows that the control of N? or the applied frequency is necessary during the lower hybrid heating (LHH).     

Parametric Excitation of Electromagnetic Fields by two Pump Waves

A collisionless plasma in the presence of two monochromatic electric fields is considered. By means of a kinetic analysis, a dispersion relation that governs the excitation of transverse electromagnetic fluctuations is derived and analysed.     

Suppression of Edge Localized Modes in High-Confinement KSTAR Plasmas by Nonaxisymmetric Magnetic Perturbations

Edge localized modes (ELMs) in high-confinement mode plasmas were completely suppressed in KSTAR by applying n=1 nonaxisymmetric magnetic perturbations. Initially, the ELMs were intensified with a reduction of frequency, but completely suppressed later. The electron density had an initial 10% decrease followed by a gradual increase as ELMs were suppressed. Interesting phenomena such as a saturated evolution of edge T_{e} and broadband changes of magnetic fluctuations were observed, suggesting the change of edge transport by the applied magnetic perturbations.     

Parametric Excitation of Electron-Acoustic Mode in a Plasma of Two-Temperature Electrons

Using hydrodynamical model of the two-electron-temperatere plasma, the analytical investigation of parametric instability of electron-acoustic wave has been made. It is found that the growth rate decreases with increasing concentration ratio of the hot to the total electrons n_h0/n₀. The growth rate is found to be more for      

Parametric Excitation of the Electron-Acoustic Wave in a Multiply Ionized Plasma

Parametric excitation of the electron-acoustic wave (EAW) has been analysed using a hydrodynamical model. The plasma has been assumed to consist of multiply charged ions. The ratio (α) of the hotter ion concentration to that of the electrons is a sensitive parameter. The condition for the occurrence of the EAW is well satisfied for the smaller values of α. The growth rate of the instability gets enhanced by increasing α and the charge state of the hotter ions. The values of α can be varied within short range only.     

Hybrid Modes in a Square Corrugated Waveguide

By using two scalar eigenfunctions, electric and magnetic fields in the rectangular (or square) corrugated waveguide are analyzed. In a rectangular corrugated waveguide, the boundary conditions on two corrugated and two smooth walls can be satisfied to excite the hybrid mode. In a highly oversized waveguide where the wavelength of dominant mode is close to that in vacuum, two smooth walls can be exchanged with the corrugated walls because the boundary condition at those walls is satisfied approximately. The replacement is possible due to almost no penetration of the electromagnetic fields into the gap of the replaced walls when the direction of main electric field is parallel to the gap of replaced walls. This characteristic enables us to rotate the polarization of the hybrid mode in the oversized square waveguide with all four corrugated walls and is applicable to the remote steering antenna for electron cyclotron heating in the ITER.     

Parametric Study of Nonplanar Dust Acoustic Solitons in Two‐Dimensional Superthermal Dusty Plasmas

The nonlinear properties of two dimensional low‐frequency electrostatic excitations of charged dust particles (or defects) are studied in a collisionless, unmagnetized dusty plasma. A fully ionized three‐component model plasma consisting of kappa distributed electrons, Maxwellian ions, and negatively charged massive dust grains is considered. In this regard, the well known reductive perturbation technique is used to the hydrodynamical equations and the Poisson equation, obtaining the cylindrical Kadomtsev–Petviashvili (CKP) equation. A parametric investigation indicates that the structural characteristics of these nonlinear excitations (width, amplitude) are significantly affected by the plasma nonthermality as well as by the relevant plasma parameters, such as dust concentration and dust temperature. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)