We investigate the Kelvin–Helmholtz instability occurring at the interface of a shear-flow configuration in 2D compressible magnetohydrodynamics (MHD). The linear growth and the subsequent nonlinear saturation of the instability are studied numerically. We consider an initial magnetic field aligned with the shear flow, and analyse the differences between cases where the initial field is unidirectional everywhere (uniform case) and those where the field changes sign at the interface (reversed case). We recover and extend known results for pure hydrodynamic and MHD cases, with a discussion of the dependence of the nonlinear saturation on the wavenumber, the sound Mach number and the Alfvénic Mach number for the MHD case. A reversed field acts to destabilize the linear phase of the Kelvin–Helmholtz instability compared with the pure hydrodynamic case, while a uniform field suppresses its growth. In resistive MHD, reconnection events almost instantly accelerate the build up of a global plasma circulation. They play an important role throughout the further nonlinear evolution as well, since the initial current sheet is amplified by the vortex flow and can become unstable to tearing instabilities, forming magnetic islands. As a result, the saturation behaviour and the overall evolution of the density and the magnetic field are markedly different for the uniform versus the reversed-field case.

The generation of axial and lateral magnetic fields due to the interaction of intense laser fields with a plasma is investigated analytically. For a CO2 laser of 10.6 μm wavelength and 5×1014 W cm−2 power flux with a plasma of temperature 3 keV, the numerical results show that the magnitude of the lateral magnetic field dominates over the axial field, and the peak value of the lateral field is at less than the critical density, whereas the axial magnetic field peaks at the critical density level. This axial field combined with the lateral field may allow the construction of a new type of tokamak, and may also be important for studying energy transport in laser-fusion schemes.

Electron-beam propagation from a gas-filled diode is investigated. The beginning portion of the electron beam pulse creates an ion channel not only inside the diode but also in the region beyond the anode. A theoretical model is developed for the space-charge-limited current of a relativistic electron beam propagating through an ion channel. A simple analytical expression for the space-charge-limited current is obtained within the context of a thin-beam approximation, where the conducting-tube radius is much larger than the beam radius. The beam current propagating through an ion channel is measured experimentally for a mildly relativistic electron beam. Whenever the ion density inside the diode is the same as the beam electron density, the diode is short-circuited. The ion-channel density at the short-circuiting time is calculated numerically and is used to estimate the space-charge-limited current. It is shown that the experimental data agree well with the analytical results predicted by the theoretical model.

The hydrodynamic start-up problem is one of the most crucial issues in laser-driven symmetrical implosion. The target-surface roughness and initial imprint by nonuniform laser irradiation result in Rayleigh–Taylor instability in the acceleration and deceleration phase. To estimate the tolerance of the target-surface roughness, the temporal behaviour of corrugated ablation surface and rippled shock-wave propagation are investigated using a perturbation analysis of the fluid equation, which is solved under the boundary model of a fire-polished ablation surface. The results show good agreement with two- dimensional hydrodynamic simulation and experimental results [T. Endo et al., Phys. Rev. Lett.74, 3608 (1995)].

A kinetic analysis of the electrostatic dust cyclotron instability in a weakly ionized collisional dusty plasma is presented. In a plasma with negatively charged dust and a current along the magnetic field B, it is found that the instability can be excited by ions drifting along B. The effect of dust–neutral collisions is stabilizing, while the effect of ion–neutral collisions can be destabilizing. Possible applications to laboratory environments are discussed.

This work shows creation of phase-space holes when an initially perturbed plasma evolves in time, in the absence of external magnetic fields. When such a field is applied to the plasma ab initio, these structures are not created. If such hole structures are created with the magnetic field turned off, the holes are destroyed under the influence of a magnetic field when one is applied to the plasma.

The dynamics and thermonuclear fusion parameters of a spinning gas-puff staged pinch are investigated by considering a DT-fibre plasma seeded with a Kr impurity. The effects of anomalous heating, line radiations from Kr, α-heating and radiative collapse are studied for different spin velocities Ω0, keeping the spin coupling parameter f0 (=0.1) fixed. Numerical results indicate that the choice of Ω0 is highly critical. Large values of the spin velocities although provide stabilization against the R–T instability in the final stage of compression, but causes an adverse reduction in the values of the plasma parameters that are essential to achieve controlled fusion. Our analysis suggests that a judicious choice of spin velocity can provide the desired temperature and density when we seed a DT-fibre plasma with a small fraction of Kr impurity to initiate radiative collapse.

The Langevin approach to the kinetics of a collisional plasma is developed. Some collision models are considered, and the corresponding stochastic differential equations are derived. These equations can be regarded as an alternative to the description of a plasma in terms of a distribution function. The method developed here allows one to simulate plasma processes, taking account of both collective kinetics effects and Coulomb collisions. Results of the numerical simulation of the intervention of laser pulses with an overdense plasma are presented. The dependence of the absorption coefficient on the plasma parameters is calculated. The features of the plasma dynamics under the action of intense laser radiation are observed and discussed. The results of numerical tests of the validity of this method are also presented.

The relativistic expressions for the dielectric-tensor elements can be expressed as a double integral over both parallel and perpendicular momenta. The anti-Hermitian (damping) parts can be integrated over a delta function for either one of these two momenta, leaving a single integral over the other momentum variable. We review these expressions for either integration option, and compare them with statements in the literature. We give the limits on the remaining integral explicitly, for all positive or negative values of the parallel refractive index, whose magnitude can be less or greater than one. This single-integral form can be applied to electron cyclotron harmonic damping for any distorted electron momentum distribution function. As an example, we recover the results for a Maxwellian distribution. We also provide approximate results when the distribution function can be taken as a Maxwellian only in the perpendicular-momentum direction. A computer program will be written for a distribution function subjected to distortion by both electron cyclotron and lower-hybrid waves.

To trace rays very close to the nth electron cyclotron harmonic, we need the mildly relativistic plasma dispersion function and its higher-order derivatives. Expressions for these functions have been obtained as an expansion for nearly perpendicular propagation in a region where computer programs have previously experienced difficulty in accuracy, namely when the magnitude of (c/vt)2 (ω−nωc)/ω is between 1 and 10. In this region, the large-argument expansions are not yet valid, but partial cancellations of terms occur. The expansion is expressed as a sum over derivatives of the ordinary dispersion function Z. New expressions are derived to relate higher-order derivatives of Z to Z itself in this region of concern in terms of a finite series.

A nonlinear dispersion relation that governs the interaction between a high-frequency pump wave and the low-frequency modes in a plasma is derived. Previous results are generalized and discussed.

Waves in a magnetized electron–positron plasma, supporting a large-amplitude electric field E0 of superluminal phase speed, are considered. The case of perturbations with the same phase speed as the large-amplitude wave can be treated exactly, and we restrict our attention to this case, obtaining analytical results. The exact analytical results provide insight into the effect of the magnetic field and the large-amplitude wave on the harmonic structure of the perturbations. Three solutions are found for waves polarized perpendicular to E0. Waves are amplitude-modulated for weak magnetic fields (relative to the strength of the large-amplitude wave) and frequency-modulated for strong magnetic fields. This suggests that frequency modulation may be relevant to pulsars.

The resonant interaction of compressive and rarefactive ion acoustic solitons is studied experimentally in a multicomponent plasma containing additional negative-ion species. With increasing concentration of negative ions, the resonance amplitude increases for compressive ion acoustic solitons when the angle of collision is fixed. When the negative-ion concentration is larger than a critical value, the rarefactive ion acoustic solitons undergo resonant interaction for a lower resonance amplitude. Theoretical predictions of the Korteweg–de Vries equation agree with experimental findings.

Using a particle-in-cell code, we are able to simulate the excitation of ion acoustic solitons from a grid whose potential is suddenly increased. The numerical results are in substantial agreement with previous laboratory experiments.

The dispersion relation and boundary conditions for surface waves propagating on the plane interface between a vacuum and a drifting plasma have recently been derived by Lee and Cho [J. Plasma Phys.58, 409 (1997)]. It is the purpose of the present comment to show that the boundary conditions and dispersion relation are incorrect.

Shoucri (1999) has commented on our paper (Lee and Cho 1997) in view of his relativistic calculation, and has stated that the boundary condition and the dispersion relation obtained there are incorrect. In this response, we reaffirm that all the results contained in Lee and Cho (1997) are correct in so far as one uses the nonrelativistic equation of motion. In particular, the boundary condition that we used (equation (57) in Lee and Cho 1997) is valid in both the nonrelativistic and the relativistic theory, and is equivalent to equation (11) of Shoucri (1999). Shoucri's hasty conclusion that our boundary condition (57) is incorrect appears to be due to his neglect of the fact that a boundary condition can be put into different forms depending upon problems under consideration.

One way to derive a boundary condition for the surface-wave problem with a sharp boundary is to assume an inhomogeneous plasma having a varying density N(x) (in the notation of Lee and Cho 1997), integrate the inhomogeneous wave equation or the Maxwell equations across the infinitesimal transition layer, and specialize N(x) as a step function, as was done in Lee (1995). Starting from the Maxwell equations on p. 418 of Lee and Cho (1997) and calculating the currents relativistically, we find that the following three boundary conditions are equivalent, and any one of them is acceptable:

(i) equation (57) in Lee and Cho (1997);

(ii) equation (11) in Shoucri (1999);

(iii) formula here

(in the notation of Lee and Cho (1997), with γ as the relativistic factor).