Hot Magnetized Plasma Research Articles

On application of the reciprocity theorem to calculation of a microwave radiation signal in inhomogeneous hot magnetized plasmas

A general expression for a radiation signal received by a wave-guide antenna from an arbitrary inhomogeneous medium with the spatial dispersion is obtained using the electrodynamics reciprocity theorem. The radiation may be either a spontaneous noise emission or it may result from the scattering of the incident wave off fluctuations. The signal calculation is reduced to finding the electromagnetic field radiated by the receiving antenna into a physically realizable substance whose wave properties differ, to some extent from these of the real medium. This problem is usually much simpler than direct signal calculation with the use of the Green function. The reciprocity approach is especially useful in the presence of cut-offs and resonances or/and when the radiation source is located in the antenna near-field zone.

Some Aspects of Anomalous Transport Due to Stochastic Magnetic Fields

A variety of diagnostics indicate the presence, in a hot magnetized plasma, of a wide spectrum of fluctuations, δñ, δĒ, δB̄, δT̄, which are probably due to microinstabilities. The theories of anomalous transport try to explain the observed transport in terms of the measured fluctuations. We consider some recent applications of stochastic methods to the study of plasmas in a turbulent state.

Diagnostics for Radial Electric Field Measurements in Hot Magnetized Plasmas

Measurements of the radial electric field profile in magnetically confined plasmas have yielded important new insights in the physics of L-H transitions, edge biasing and/or the active control of Internal and Edge Transport Barriers. The radial electric field is not an easy plasma parameter to diagnose. Techniques to measure the radial electric field in the plasma core are the Heavy Ion Beam Probe and the Motional Stark Effect. An indirect method that is quite often applied is to derive the electric field from measurements of the poloidal and toroidal rotation velocities via the radial ion force balance. This paper will first briefly explain the need for detailed measurements of the radial electric field profile. Subsequently, the various diagnostics to measure this parameter will be reviewed. The emphasis will be especially put on recent trends, rather than on an exhaustive overview.

Determination of electron distribution functions from thick-target Bremsstrahlung

The energy distribution functions of electrons are obtained by analysing thick-target Bremsstrahlung spectra. The method consists of expanding the unknown function on an appropriate functions basis and of solving the resulting system of linear equations. The various atomic processes involved can be treated with the desired accuracy. Applications are given for a variety of cases such as hollow cathode discharge plasmas, hot magnetized plasmas, and electron beams of travelling wave tubes. The analysis includes cases when the thick target is covered by an impurity coat.

Interest of thick-target bremsstrahlung for an innovative compact X-ray source

A compact X-ray source (1 dm 3) has been built, the basis of X-ray production being that of bremsstrahlung (Br) of the hot electrons generated in situ in the core of a hot magnetized plasma. Among the advantages of this device are that it can be pulsed or operated in a stable continuous mode and that there is no requirement for any filament nor high-voltage power supply. Thick-target Br (from a solid material) is involved, first in view of investigating runaway electrons leaking to the lateral walls. Second and more importantly, the features of thick-target Br are exploited in order to make the X-ray source point-like and more intense, a small target being inserted in the way of the hot electrons. The brightness obtained at 20 keV is 3.5×10 11 photons s −1 mm −2 sr −1 keV −1, which for example allows the obtaining of mammographic images in exposure times of a few seconds.

On the fluctuation of line radiation emitted during aluminum micro-pellet ablation in magnetized plasmas

The phenomenon of striation observed during pellet ablation in hot magnetized plasma is investigated experimentally injecting aluminum micro-pellets into MT-1M and TEXTOR-94 tokamak and W7-AS stellarator plasmas. Changes in pellet cloud shape and temporal fluctuations of total emitted line radiations are studied. Special attention is paid to the investigation of the dependence of fluctuation frequency on pellet velocity. The results show that the light fluctuation frequency is characterized by a characteristic time rather than by a characteristic length, and that the striation is caused by a phenomenon that occurs during the evolution of the ionized-pellet cloud. The compatibility of these experimental observations with different theories of striation is discussed.

On the electromagnetic fields generated by a slowly moving conducting body in a magnetized plasma. Possible applications for the Io-Jovian system, spacecraft, and plasma probes

To explain self-consistently some energetic processes, radiation features, and the electromagnetic environment near the Io satellite moving in the Jovian magnetospheric plasma, as well as a spacecraft body or a plasma probe, we consider, by means of plasma kinetic theory, the process of electromagnetic interaction between a moving conducting body and the surrounding hot magnetized plasma described by the tensoreij(ω, k). We study the field structure in terms of the low-frequency, non-propagating, inductive electromagnetic mode, which is usually ignored. We investigate the plasma dielectric properties for the frequency ranges\(k_{||} v_i \ll \omega \ll k_{||} v_e ,\omega \ll \Omega _{i,e} \) and\(\omega \ll k_{||} v_i \ll k_{||} v_e \omega \ll \Omega _{i,e} \), showing the importance of the spatial dispersion connected with particle thermal motion for the behavior of inductive electromagnetic fields. These fields are localized in the vicinity of the moving conducting body and decay in space due to collisionless energy dissipation, forming some kind of local magnetosphere. Along with the influence of energy losses of the moving conducting body, inductive fields could be responsible for the appearance near the body of electromagnetic structures where charged particles will be effectively accelerated. The general analysis developed here is also applicable for the cases of any artificial spacecraft body or tethered satellite system slowly (V0≪VA, Ve) moving in the magnetized plasma of the ionosphere and in a low earth orbit.

Obliquely propagating electrostatic solitary structures in a magnetized hot dusty plasma with trapped ions

A theoretical investigation has been made of obliquely propagating electrostatic solitary structures in a hot magnetized three-component dusty plasma, which consists of a negatively charged hot dust fluid, Blotzmann distributed electrons, and free and trapped ions. It has been found that owing to the departure from the Boltzmann ion distribution to a trapped ion one, the dynamics of small but finite-amplitude electrostatic waves in a magnetized hot dusty plasma is governed by the modified Korteweg–de Vries (KdV) equation. The latter admits a stationary solitary wave solution that has a larger amplitude, a smaller width, and higher propagation velocity, than that involving Boltzmann distributed ions. It has been shown that the effects of obliqueness, external magnetic field, trapped ions, and free electrons change the behavior of these electrostatic solitary structures that have been found to exist with only negative potential in this dusty plasma model.

Dust-acoustic waves in a magnetized dusty plasma

The modification and damping of the dust-acoustic wave in a uniformly magnetized dusty plasma have been investigated using the Vlasov-kinetic model for the plasma with dust particles as a third component having average constant charge and mass. It is noticed that for the strong finite Larmor radius (FLR) effect, the frequency and damping of the mode depend significantly on the magnetic field and they are independent of the magnetic field for the case of weak FLR effect. For exact transverse propagation (k‖=0), the dust-acoustic mode ceases to exist, however, a new mode known as the “dust-lower-hybrid” mode comes into play in the hot magnetized dusty plasma.

Nonlinear propagation of ion-acoustic waves in a hot magnetized plasma with vortexlike electron distribution

Effects of external magnetic field, ion temperature, and vortexlike electron distribution are incorporated in the study of nonlinear ion-acoustic waves in a hot magnetized plasma that consists of a positively charged, hot ion fluid and trapped, as well as, free electrons. It is found that, owing to the departure from the Boltzmann electron distribution to a vortexlike one, the dynamics of small but finite amplitude ion-acoustic waves is governed by a nonlinear equation of K-dV (Korteweg-de Vries) type. The latter admits a stationary ion-acoustic solitary wave solution, which has larger amplitude, smaller width, and higher propagation velocity, than that involving isothermal electrons. The effects of external magnetic field and ion temperature on the properties of these ion-acoustic solitary structures are also discussed.

Near-forward scattering in magnetized plasma: Are laser spots whistling?

Near-forward scatter of laser light off lower hybrid and whistler waves in hot magnetized plasmas is investigated. Important gains might be obtained at relatively high intensity, as well for low (≪ωpi) as for high (≫ωpi) frequency waves, leading to unexpected features in the scattered light spectrum.

Two-fluid magnetohydrodynamic simulation of confinement of pellet-produced hydrogen clouds in hot magnetized plasmas

The structure of dense particle clouds surrounding ablating hydrogen isotope pellets is investigated, with particular emphasis on the B-perpendicular expansion, ionization, and deceleration dynamics. A time-dependent single-temperature two-fluid one and one-half-dimensional Lagrangian model is used in which the neutral and ionized fluid components are allowed to move with different velocities. The expansion of the Lagrangian cells along the magnetic field lines is also taken into account. For given ablation rates, the confinement radii and the radial distributions of the velocities, particle densities, magnetic field strength, temperature, and other flow and field properties are calculated as functions of the background plasma parameters. The results show that collisional coupling between the neutral and ionized components is strong enough to change the initially spherically symmetric expansion of the neutral particles to a field-aligned, funneled flow pattern, in full agreement with experimental observations. The calculated cloud parameters are compared with measured data and results stemming from earlier single-velocity models.

Oscillating two-stream instability of beat waves in a hot magnetized plasma

It is shown that an electrostatic electron plasma beat wave is efficiently unstable for a low-frequency and short-wave-length purely growing perturbation (ω, k), i.e. an oscillating two-stream instability in a transversely magnetized hot plasma. The nonlinear response of electrons and ions with strong finite Larmor radius effects has been obtained by solving the Vlasov equation expressed in the guiding-center coordinates. The effect of ion dynamics has been found to play a vital role around ω ∼ ω ci, where ω ci is the ion-cyclotron frequency. For typical plasma parameters, it is found that the maximum growth rate of the instability is about two orders higher when ion motion is taken into account in addition to the electron dynamics.

Revised Landau damping rates of magnetohydrodynamic waves in hot magnetized equilibrium plasmas and its consequences for cosmic ray transport in the interplanetary medium

A relativistic theory of transverse oscillations in hot, magnetized, isotropic equilibrium plasmas is presented. The special theory of relativity enters the description with the requirement that the particle masses depend on the particle velocities which themselves are limited by the speed of light. Using the relativistic Maxwell‐Boltzmann‐Jüttner (MBJ) distribution correctly describing the equilibrium state of a plasma, we formulate the dispersion relations for subluminal as well as superluminal waves, using the Trubnikov representation. For Landau damping of transverse wave modes, the so‐called cyclotron damping, an analytical expression generalizing earlier results to a relativistically correct form is derived. The theory is applied to an electron‐proton plasma, the main constituents of the interplanetary medium. Special consideration is given to the regime of weak damping of low‐and high‐frequency waves in the interplanetary plasma. The resulting dispersion relations and damping rates are used to determine cosmic ray transport parameters in the interplanetary medium, in particular the mean free path of solar energetic particles and the related modulation parameter of galactic cosmic rays in a simple diffusion‐convection modulation model. It is shown that at particle rigidities below about 109 V/c the mean free path and the modulation parameter are significantly different for cosmic ray protons, negations, and positrons because of the different handedness of the particles in the ordered interplanetary magnetic field and the different Landau damping rates of right‐handed and left‐handed circularly polarized plasma waves.

Low-frequency electrostatic waves in a hot magnetized dusty plasma.

A gyrokinetic study of low-frequency---lower than the dust cyclotron frequency---electrostatic modes in a magnetized dusty plasma has been presented. It is found that the inequalities of charge and number densities of electrons, ions, and dust particles, and the finite-Larmor-radius thermal kinetic effects of the mobile charged dust grains, introduce the existence of low-frequency electrostatic eigenmodes in a three-component hot magnetized dusty plasma. The relevance of our investigation to space and astrophysical as well as laboratory experiments for dust-particulate attraction is pointed out.

Flow-shear instability of a potential hump in hot plasma

Low-frequency instability arising in hot magnetized plasma with a hump-shaped transverse profile of the potential has been observed experimentally. As a result of the instability, the plasma in the region of the maximum of the potential decomposes into an array of dense plasmoids and deep rarefactions. The instability is due to nonuniform E×B drift and is apparently a Rayleigh instability which reaches a strongly nonlinear stage. In the process, strong transverse transport arises, resulting in plasma losses.

Attraction of charged dust-grains in the presence of dust-lower-hybrid modes

The existence of the strong attractive force between the charged dust particulates in the presence of possible low-frequency dust-lower-hybrid modes in a magnetized dusty plasma has been examined. These modes arise on account of the inequalities of charge and number densities of electrons, ions, and dust particles, and finite Larmor radius effect of the massive dust grains in a hot magnetized dusty plasma.

High frequency radiation from a moving charged particle in an anisotropic hot plasma / Hochfrequenzstrahlung eines bewegten geladenen Teilchens in einem heißen anisotropen Plasma

The electromagnetic field components and a general expression for the energy losses caused by polarization of the medium and Cherenkov radiation are determined for a charged particle moving in an anisotropic medium. The energy losses are given for a particle moving in a plasma along an external magnetic field, which is the optical axis. The spectral functions of the total energy loss are calculated numerically, especially for nearly perpendicular propagation, in dependence on the plasma temperature, its anisotropy, the velocity of the moving particle, and the plasma density. An asymptotic expression for the dielectric tensor of an anisotropic hot magnetized plasma is given in a form suitable for numerical calculations.

Kinetic model of collective scattering off fast ion generated electromagnetic fluctuations in magnetized Vlasov plasma

From the general three-wave coupling formalism in magnetized nonrelativistic Vlasov plasma, an expression is derived that gives the differential cross section for the scattering of incident radiation off of thermal fluctuations induced by ions in a hot magnetized plasma. The model is valid to any order in thermal parameters, and can thus generalize the previous theory models to regimes where either the electron Larmor radius or the electron cyclotron resonance are significant for the scattered wave.

Excitation of VLF quasi-electrostatic oscillations in the ionospheric plasma

Abstract. A numerical solution of the dispersion equation for electromagnetic waves in a hot magnetized collisionless plasma has shown that, in a current-free ionospheric plasma, the distortion of the electron distribution function reproducing the downward flow of a thermal electron component and the compensating upward flow of the suprathermal electrons, which are responsible for the resulting heat flux, can destabilize quasi-electrostatic ion sound waves. The numerical analysis, performed with ion densities and electron temperature taken from the data recorded by the Interkosmos-24 (IK-24, Aktivny) satellite, is compared with a VLF spectrum registered at the same time on board. This spectrum shows a wide frequency band emission below the local ion plasma frequency. The direction of the electron heat flux inherent to the assumed model of VLF emission generation is discussed