The formation of a non-equilibrium steady-state distribution function of particles with the power law interaction potentials $U\,{=}\,\alpha/r^{\rm s}$, where $1 \,{\le}\, \beta \,{<}\, 4$, is studied numerically. Consideration is based on the one-dimensional nonlinear kinetic equation of a Landau–Fokker–Planck type in the presence of particle (energy) sources. Non-equilibrium quasi steady-state local distributions exist inside the momentum interval between the energy (particle) source and the bulk (or sink) of the particle distribution and have the form of gradually decreasing functions. Numerical calculations based on the completely conservative difference schemes are accompanied by the analytical consideration and comparison with the experimental results is given. Obtained results can be useful in connection with the development of high-power particle and energy sources and for the prediction of the semiconductors behavior with an intrinsic or extrinsic conductivity under the action of particle fluxes or electromagnetic radiation.

A dispersion relation is derived detailing the effect of a population of charged dust grains on the growth of lower-hybrid waves excited by a ring distribution of ions in a plasma. Numerical solutions show that the instability can be enhanced or reduced depending on the parameter regime.

We investigate the gravitational stability of partially ionized astrophysical plasmas, embedded in a large-scale magnetic field. The collisions between the charged particles and neutrals are incorporated into our model, and we study the influence of the ion–neutral collisions on the gravitational stability of a large space plasma, e.g. a large molecular cloud, and on the relevant growth/damping rates. The effects of the ion–neutral friction on the growth rate of a gravitationally unstable space plasma are presented for a range of possible wavenumbers.

If an initially mainly rectilinear electron beam is subject to significant magnetic compression, the conservation of the magnetic moment results in the ultimate formation of a horseshoe distribution in phase space. A similar situation occurs where particles are accelerated into the auroral region of the Earth's magnetic dipole. Such a distribution has been shown to be unstable to a cyclotron resonance maser type of instability and it has been postulated that this may be the mechanism required to explain the production in these regions of auroral kilometric radiation (AKR) and also possibly radiation from other astrophysical objects such as stars with a suitable magnetic field configuration. In this paper we describe a laboratory experiment to investigate the evolution of an electron beam subject to a magnetic compression of up to a factor of 30.

It was demonstrated that low pressure ($\sim$0.2 torr) water vapor plasmas generated in a 10 mm inner diameter quartz tube with an Evenson microwave cavity show at least two features that are not explained by conventional plasma models. First, significant ($\gt$2.5Å) hydrogen Balmer $\alpha$ line broadening, of constant width, up to 5 cm from the microwave coupler was recorded. Only hydrogen, and not oxygen, showed significant line broadening. This feature, observed previously in hydrogen-containing mixed gas plasmas generated with high voltage dc and rf discharges, was explained by some researchers as resulting from acceleration of hydrogen ions near the cathode. This explanation cannot apply to the line broadening observed in the (electrodeless) microwave plasmas generated in this work, particularly at distances as great as 5 cm from the microwave coupler. Second, inversion of the line intensities of both the Lyman and Balmer series, again at distances up to 5 cm from the coupler, were observed. The line inversion suggests the existence of a hitherto unknown source of pumping of the optical power in plasmas. Finally, it is notable that other aspects of the plasma including the OH* rotational temperature and low electron concentrations are quite typical of plasmas of this type.

The growth and damping of the low-frequency electrostatic dust-lower-hybrid (DLH) wave have been examined in the presence of dust charge fluctuations in a uniform magnetized dusty plasma. To obtain the dust charge fluctuation effects, the charging currents of electrons and ions to a spherical dust grain in a uniform magnetized dusty plasma have been calculated under the orbit-limited motion approximation. It is found that the external magnetic field reduces the charging currents, thereby reducing the dust charge fluctuation damping of a low-frequency electrostatic wave in a dusty plasma. However, for sufficiently low-frequency DLH wave having a finite parallel wave number, the thermal electrons may give rise to an instability of the DLH wave.

The influence of non-thermal ions on linear dust-acoustic waves is studied in an unmagnetized plasma consisting of ions which have a non-thermal velocity distribution, Boltzmann-distributed electrons and streaming dust particles. A detailed examination is conducted of the dependence of the real frequency and growth rate of the excited instability on the dust drift speed, temperature, particle densities and the parameter $\alpha$ that determines the non-thermal nature of the energetic ions. Comparisons with approximate analytical solutions are also made.

We discuss here some of the physical problems related to the recently proposed scheme for solar sailing, using an artificial magnetosphere. We will concentrate on the forces acting on the plasma bubble, and their transfer to the spacecraft. Upper and lower limits of the force acting on the bubble are established. The results of test particle dynamics are presented, concerning the interaction of the solar wind with the modified magnetic dipole resulting from the spacecraft coils and the plasma expansion. Propagation of the forces along the magnetic flux tubes, from the bubble magnetopause down to the spacecraft vicinity, is discussed by using a simple MHD theoretical model. Emphasis is made on the distribution of currents flowing in the immediate vicinity of the spacecraft. Finally, results of PIC code simulations of the magnetized plasma expansion are presented and an overall qualitative picture of the physical processes is given, with a discussion of the strategy for obtaining more quantitative estimates of the magnetospheric propulsion efficiency.

The high-β operating regime of spherical tori (ST), such as in the National Spherical Torus Experiment (NSTX) and the Mega Amp Spherical Tokamak (MAST), makes them attractive fusion devices. For access to such high-β regimes it is necessary to heat and to drive currents in ST plasmas. In the electron cyclotron range of frequencies, such plasmas are overdense to conventional electron cyclotron waves. However, in this frequency range, electron Bernstein waves (EBWs) offer an attractive alternative as they have no density cutoffs. EBWs can be excited in a ST plasma by mode conversion of the extraordinary or the ordinary mode at the upper hybrid resonance. The applications of EBWs in STs range from plasma start-up and heating of the plasma to modifying and controlling its current profile. The controlling of the current profile could provide better confinement as well as help suppress neoclassical tearing modes. The mode conversion to EBWs has been detailed in a variety of papers. This paper deals with two particular topics that further quantify the role of EBWs in spherical tori. The first topic is on the relevance of relativistic effects in describing the propagation and damping of EBWs. The second topic is on plasma current generation by EBWs.

In this paper an analysis is given for the conditions under which compressive and rarefactive ion-acoustic solitons may exist in a plasma containing two electron populations, one hot and the other cool. Compressive solitons exist in the collective Mach number range $1\,{<}\,M\,{<}\,M_{\rm c}$, which, for a given abundance ratio of the cool population, translates into an annular region in the ion-acoustic Mach numbers space. The upper limit $M_{\rm c}$ corresponds to a degenerate sonic point for the protons in which they tend to an infinite compression and are brought to rest at the wave centre. To form a charge neutral point in the rarefactive regime (a prerequisite to the existence of rarefactive solitons) it is necessary that the ‘scale height’ of the hot electrons be sufficiently large that their number density, which is nearly constant, approximately balances that of the protons, before the cool electrons experience their ‘atmospheric lid’. Furthermore, a sufficient condition for the existence of rarefactive solitons is found by requiring a solution to the wave structure equation at the ‘lid’. The case of very hot electrons (highly sub-ion-acoustic) is considered, and various parameter regimes in which compressive and rarefactive solitons exist are evaluated in this super-hot electron approximation, both for the polytropic case, $\gamma \neq 1$, and the isothermal case, $\gamma = 1$. This approximation is formally equivalent to the problem of a bi-ion plasma, including a super-massive negative species.

An intense laser beam guided through a low-density plasma channel produces second harmonic emission that leaks out in the high-density outer region, propagating in a low-angle hollow cone with respect to channel axis. For a channel with interior density 0.25$n_{\rm cr}$, outer region density 0.64$n_{\rm cr}$ ($n_{\rm cr}$ being the critical density), laser wavelength 1 $\mu$ and channel radius ${\sim}5~\mu$m, the angle $\theta$ of the cone ${\sim}19^{\circ}$. The second harmonic power shows an oscillatory behavior with the density of the channel. It peaks at certain densities of the plasma channel. The heights of the peaks of second harmonic power are higher at greater densities.

In the present paper, the xenon plasmas containing argon and caesium as additives and pertaining to the above-mentioned type (high-pressure, low-temperature) are studied, and a theoretical evaluation of their basic transport parameters are presented. The numerical calculations were based on the assumption that the system is kept under constant pressure and temperature and has attained local thermodynamical equilibrium (LTE). Particular attention is given to the evaluation of electron collision frequencies within the temperature interval from 2000 to 20000K, and for initial pressures ranging from 0.1 to 1.5 MPa in plasmas in the mixtures of xenon, argon and caesium. The equilibrium plasma composition was evaluated with the use of the modified Debye radius.

It is found that the addition of as little as 1% of caesium profoundly alters the properties of the plasma. The presence of the added caesium in the thermal xenon and argon plasma is indeed quite significant for its transport properties, especially at temperatures below and around 10000K. Thus, electron number density, monotonically increasing with temperature (with pressure kept constant) much as in the pure noble-gas plasma, becomes considerably higher. The characteristics of the electrical and thermal conductivities are basically caused by the specificities of the processes of thermal ionization taking place in the system considered, as these processes determine the multiplier electron number density.

A theory of self-fields in a free-electron laser with a helical wiggler and ion-channel guiding is presented. The effects of self-electric and magnetic fields on electron trajectories are investigated. It is shown that, under the Budker condition, there is one group of orbits (group I) for which the wiggler-induced self-magnetic field is negative and acts as a diamagnetic correction to the wiggler magnetic field. The function $\Phi $ that determines the rate of change of axial velocity with energy in the presence of the self-fields is derived and studied numerically.

Photon kinetic theory provides a framework for the study of intense electromagnetic fields interacting with underdense plasmas. It is particularly useful when studying forward scattering four-wave modulational type instabilities. The most powerful features are its simplicity and its strong connection with particle beams, and the natural way in which broadband and angular spread effects can be included in the formalism. In this paper we derive the dispersion equations describing four-wave stimulated Raman and Brillouin scattering and Langmuir wave modulational instability for induced spatially incoherent pump waves.

Non-thermal ion distributions are a characteristic feature of space plasmas, and in the current work the influence of such non-thermal ion distributions on the Jeans instability is examined. Following previous general models, the electrons are taken to be Boltzmann on the timescales involved, whilst the negative dust component is modelled by the continuity and momentum equations. The ion dynamics are described via a non-thermal Cairns distribution. The linear dispersion relation is derived and analysed for varying degrees of deviation from ordinary thermal behaviour, determined by the characteristic parameter of the Cairns distribution.

This paper investigates the implications and consequences of choosing special gauges or gauge-invariant or non-gauge-invariant approximations in the action integral for the variational formulation of theories involving electromagnetic fields. After some interesting special gauges are considered, it is shown that non-gauge-invariant approximations always lead to inconsistent Euler–Lagrange equations. As a concrete example, Maxwell–Vlasov theory is investigated. The special non-gauge-invariant case considered, which is sometimes used in the literature, is obtained by replacing the contribution of the electric field to the Maxwell part of the Lagrangian density by the contribution of the gradient of the scalar potential alone. The detailed investigation concerns the local energy conservation law, and it is shown that the law thus derived is incorrect since it contains non-physical, spurious terms. An improvement of this situation can be obtained by the introduction of a Lagrange multiplier in the non-gauge-invariant theories in order to avoid inconsistencies in the local charge conservation law. The results are also valid for drift-kinetic and gyrokinetic theories, and for other theories, e.g. two-fluid theories.

In certain circumstances, small amplitude, weakly nonlinear ion-acoustic waves in a magnetized plasma are governed by a Zakharov–Kuznetsov equation or by a reduced form of the equation. Both equations have a plane solitary travelling-wave solution that propagates at an angle αto the magnetic field. The multiple-scale perturbation method developed by Allen and Rowlands is used to calculate the initial growth rate of a small, transverse, long-wavelength perturbation to these solitary-wave solutions. Previous results in the literature are corrected. A numerical determination of the growth rate is given. For k[mid ] secα[mid ][Lt ]1, where k is the wavenumber of the perturbation, there is excellent agreement between our analytical and numerical results.

The nonlinear wave propagation characteristics of ion acoustic (IA) solitary waves in a dusty plasma, i.e. dust ion acoustic (DIA) solitary waves in the presence of ionization, collisions of ions with dust grains and with the background neutral gas, have been investigated by employing a reductive perturbation technique. It has been found that the nonlinear DIA wave is governed by Korteweg–de Vries (KdV) equation with a positive or negative linear damping term. It has also been found that the ionization instability leads to the exponential growth of the DIA solitary wave amplitude with time, whereas ion–dust and ion–neutral collisions reduce the growth rate.

The Nonlinear self-modulation of dust acoustic waves is studied in the presence of non-thermal (non-Maxwellian) ion and electron populations. By employing a multiple scale technique, a nonlinear Schrödinger-type equation (NLSE) is derived for the wave amplitude. The influence of non-thermality, in addition to obliqueness (between the propagation and modulation directions), on the conditions for modulational instability to occur is discussed. Different types of localized solutions (envelope excitations) which may possibly occur are discussed, and the dependence of their characteristics on physical parameters is traced. The ion deviation from a Maxwellian distribution comes out to be more important than the electron analogous deviation alone. Both yield a de-stabilizing effect on (the amplitude of) DAWs propagating in a dusty plasma with negative dust grains, and thus favour the formation of bright- (rather than dark-) type envelope structures (solitons) in the plasma. A similar tendency towards amplitude de-stabilization is found for the case of the presence of positively charged dust in the plasma.