N. F. Cramer

THE ALFVEN RESONANCE IN A MAGNETIZED DUSTY PLASMA

Wave propagation in a dusty magnetized plasma at frequencies below and of the order of the ion-cyclotron frequency, and with a non-zero electron temperature is considered. The general dispersion relation for waves propagating at an arbitrary angle with respect to the external magnetic field and for finite ion-cyclotron frequency is derived and discussed. Modification of the Alfven resonance absorption mechanism due to the presence of a finite proportion of the negative charge of the plasma on stationary dust grains is investigated.

Surface waves in a magnetized plasma with mobile dust grains

Wave propagation in a dusty, magnetized, strongly inhomogeneous plasma at frequencies below the ion–cyclotron frequency, and near the dust cyclotron frequency, is considered. The dust grains are assumed to carry a proportion of the negative charge of the plasma. Wave resonances and cutoffs in a homogeneous plasma are discussed. The dispersion relation for surface waves propagating on an interface between a dusty plasma and a vacuum is derived and studied, and their connection to surface waves in general two-ion-species plasmas is analyzed. The damping of the waves due to Alfven resonance absorption in a narrow but nonzero width interface is derived, and it is shown that for a range of frequencies above the dust cyclotron frequency the surface wave can propagate undamped by resonance absorption.

Parametric instabilities of Alfvén waves in a dusty plasma

The excitation of low frequency modes of oscillations in a magnetized dusty plasma with parametric pumping of the magnetic field is analyzed. The dust is taken to be stationary, but acts as a sink for negative charge: The absence of a proportion of the electrons in the overall neutral plasma modifies the dispersion properties of the pump and excited waves. The pump is a magnetoacoustic wave modified by the dust, and the excited waves are modifications of Alfven waves due to the dust and due to ion cyclotron effects. The equation of motion governing the perturbed plasma is derived and pump wave fields are found. The stability of the pump to modes propagating parallel to the magnetic field is investigated as a function of the plasma parameters. It is found that pairs of slow and fast parallel propagating modes are parametrically excited. The growth rates of the various interactions are calculated, and it is shown that the growth rates of slow–fast and fast–fast mode interactions can be maximized by varying ...

Low-frequency modes in the dust–plasma crystal

It is shown that there are two low-frequency modes associated with vertical oscillations in the Coulomb crystal of dust grains arranged in two horizontal chains in a sheath region of a low-temperature gas discharge plasma. The dispersion relations and characteristic frequencies of the modes are found.

The Alfvén resonance in a dusty plasma with a distribution of grain sizes

The resonance absorption of low-frequency electromagnetic waves in a dusty magnetized plasma is considered. The dust grains are assumed to carry a proportion of the negative charge of the plasma, and there is assumed to be a distribution of dust sizes, typical of that deduced to be present in interstellar molecular clouds. The resonances and cutoffs of the waves in a homogeneous plasma are discussed. The waves are shown to be damped due to Alfven resonance, and it is shown that the effects of the distributed dust sizes are to produce a broad spatial region of resonance absorption due to dust cyclotron damping.

Parametric instabilities in magnetized multicomponent plasmas.

This paper investigates the excitation of various natural modes in a magnetized bi-ion or dusty plasma. The excitation is provided by parametrically pumping the magnetic field. Here two ionlike species are allowed to be fully mobile. This generalizes our previous work where the second heavy species was taken to be stationary. Their collection of charge from the background neutral plasma modifies the dispersion properties of the pump and excited waves. The introduction of an extra mobile species adds extra modes to both these types of waves. We first investigate the pump wave in detail, in the case where the background magnetic field is perpendicular to the direction of propagation of the pump wave. Then we derive the dispersion equation relating the pump to the excited wave for modes propagating parallel to the background magnetic field. It is found that there are a total of twelve resonant interactions allowed, whose various growth rates are calculated and discussed.

Transverse electric field and density gradient induced instabilities in a cylindrical magnetron discharge

Recent one-dimensional particle-in-cell simulations of a cylindrical postcathode direct current magnetron discharge have shown a transition from the usual positive space charge mode, dominated by a strong cathode fall, to a higher impedance negative space charge mode, characterized by a broad anode fall, as either the pressure is decreased or the magnetic field is increased. Such behavior is consistent with a steady decrease in the cross-field electron transport coefficients as calculated from classical fluid theory. However, experimental measurements of the distribution of electric potential between the electrodes do not exhibit any systematic variation with changes in magnetic field or pressure. This suggests that anomalous transport mechanisms increase the electron transport above the level predicted by classical transport theory, so maintaining the positive space charge mode at low pressures. It is shown using a fluid model that electrostatic oscillations with ω≳νi, where νi is the ion-neutral collisi...

Rotational modes of oscillation of rodlike dust grains in a plasma.

Three dimensional rotatory modes of oscillations in a one-dimensional chain of rodlike charged particles or dust grains in a plasma are investigated. The dispersion characteristics of the modes are analyzed. The stability of different equilibrium orientations of the rods, phase transitions between the different equilibria, and a critical dependence on the relative strength of the confining potential are analyzed. The relations of these processes with liquid crystals, nanotubing, and plasma coating are discussed.

Calculation of the Grain Charge Fluctuations in a Dusty Plasma

The time characteristics of grain charging, namely, the relaxation time of the steady grain charge and the charge fluctuations of grains of different sizes, are computed from particle simulations. The results obtained are compared with some theoretical predictions (primarily those derived from the drift-diffusion model). The simulations are carried out for nonmoving and moving two-temperature argon plasmas.

Instabilities of Alfvén and magnetosonic waves in dusty cometary plasmas with an ion ring beam

The effects of charged dust grains on the instabilities of electromagnetic waves in the solar wind plasma due to ring-beam cometary ion velocity distributions are considered. The waves are assumed to propagate parallel to the solar wind magnetic field. Collisionless cold plasma theory is used to derive the dispersion relations of linear waves in the solar wind, for a delta-function ring-beam velocity distribution of cometary water-group ions. The resonant and nonresonant instabilities are considered, and it is shown that the dust has its greatest effect on the nonresonant firehose instability at very long wavelength. The dust can cause an unstable dust-free firehose mode to be stable, and vice versa. It is also shown that as the frequency approaches the cometary ion cyclotron frequency, there is an upper limit to the wave number for the unstable firehose mode. For the left-hand polarized wave, the presence of dust increases this upper wave number limit, until the firehose mode merges with the resonant mode. The right-hand polarized firehose mode also has an upper wave number limit, which is almost independent of the presence of dust. It is shown that, although there is a high frequency resonant instability of the normal whistler mode induced by the ring beam, there is no corresponding instability of the dust-induced whistler-like mode at low frequencies.