摘要:

Experimental observation of transitions between discrete longitudinal wave modes in a dc neon glow discharge is reported. Experimental findings concerning the pattern selecting instability agree with observations of the Eckhaus instability in fluid systems. This is supported by theoretical considerations of a model equation (Complex Ginzburg–Landau equation) based on a fluid model. ©1998 American Institute of Physics.

ISSN:1070-664X    

DOI:10.1063/1.873089

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Considering the effect of the finite ion gyroradius, the kinetic Alfve´n wave in an anisotropic medium driven by a parallel velocity flow was investigated and the full dispersion relation was given. In deducing the dispersion relation, the coupling between electrostatic and electromagnetic oscillations, effects of the resonant electrons and the longitudinal motion of ions are considered. Based on the analytical and numerical calculations, two instability boundaries are found. They are1<(k⊥dV0/dx)/kz&ohgr;ci<&ngr;A2/(Ti⊥/mi)and(k⊥dV0/dx)/kz&ohgr;ci>&ngr;A2/(Ti/mi).Resonant electrons serve as the main energy source in these two regimes, while the ion longitudinal motion only suppresses the mode in the second regime. In the boundary layer of the magnetopause, the temperature anisotropy also modifies the instability by lowering the frequency and reducing the growth rate. The above results show that the low-frequency Alfve´n waves with the scale of perpendicular wavelengths greater than the ion gyroradius in the magnetopause can be efficiently driven by a velocity-sheared flow. ©1998 American Institute of Physics.

ISSN:1070-664X    

DOI:10.1063/1.872650

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The one-dimensional (1-D) spatially periodic system ofNclassical particles, interacting via a Coulomb-like repulsive long-range force, is studied using classical mechanics. The usual Bohm–Gross dispersion relation for the collective modes is obtained in the absence of quasiresonant particles. In the presence ofRquasiresonant particles, the evolution equations forMlong-wavelength modes are coupled to the particles’ motion through a self-consistent wave–particle Hamiltonian. The wave–particle Lagrangian is derived from the fullN-body Lagrangian. The derivation relies on an explicit scale separation argument and avoids the use of kinetic theory and continuous medium formalism. ©1998 American Institute of Physics.

ISSN:1070-664X    

DOI:10.1063/1.872651

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Electron surface waves in a metal bound plasma slab have been detected and analyzed. In this work it is shown that the presence of a matrix sheath between the central quasineutral region and the metal walls allows for the propagation of surface waves analogous to those found in dielectric bound plasmas. Measurements of the dispersion relations and eigenfunctions of asymmetric and symmetric, electrostatic, surface, and body waves are made via particle-in-cell simulation of a plasma slab with sheaths. The plasma slab has finite temperature electrons and fixed ions of uniform density. The sheaths consist of electron free, fixed, uniform ion regions (“matrix sheath”) of thickness∼&lgr;De.A linearized Vlasov theory is developed for comparison with the simulation. It is shown that the long wavelength approximation(k&lgr;De≪1)is not valid even for long wavelengths in the propagation direction. Collisionless damping of both surface and body waves is measured which compares well with theoretical estimates. ©1998 American Institute of Physics.

ISSN:1070-664X    

DOI:10.1063/1.872652

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Electron surface waves in a nonuniform, metal bound, thermal plasma slab have been analyzed and detected. Measurements of the dispersion relations of these waves, as well as the eigenstructure of the perturbed electron density, reveal a spectrum of waves with frequencies above and below the peak electron plasma frequency in the slab. These waves are analogous to the Gould–Trivelpiece and Tonks–Dattner waves found in dielectric bound plasma columns. Measurements have been made using particle-in-cell simulation of an argon plasma and are compared with linear fluid theory in which the adiabatic approximation is made for the perturbed pressure. The presence of the metal boundary leads to regions near the plasma sheaths in which the fluid theory breaks down; we explore the differences between theory and measurement in this region. ©1998 American Institute of Physics.

ISSN:1070-664X    

DOI:10.1063/1.872653

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The kinetic analysis introduced by Prasad, Morales, and Fried [Prasad &etal;, Phys. Fluids30, 3093 (1987)] is used to derive damping conditions and a differential equation for azimuthally propagating waves in a non-neutral plasma column in the limitsrl/L≪1andkrl≪1(whererlis the Larmor radius,kis the wave number, andLis the density scale length). The predictions of the kinetic analysis are verified using a two-dimensional particle-in-cell simulation of Bernstein modes in a thermal rigid-rotor equilibrium. Differences between modes in a strongly magnetized limit and near the Brillouin limit are studied in the simulation. ©1998 American Institute of Physics.

ISSN:1070-664X    

DOI:10.1063/1.872654

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Detailed ray tracing, of wave propagation in a plasma near electron cyclotron resonances, suggests that refraction can lead to reduced absorption, in some cases. By studying the full wave equation for the ordinary wave near the fundamental, in a slab model, it is shown that such refraction does indeed reduce absorption, for this particular case, but that wave energy tunnelling can significantly modify the result. ©1998 American Institute of Physics.

ISSN:1070-664X    

DOI:10.1063/1.872655

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

In dense plasmas, dynamic plasma screening effects are investigated on antiscreening channels for excitation of a one-electron ion target by a one-electron ion projectile. The ion–ion interaction potential is considered by the introduction of the longitudinal plasma dielectric function. A semiclassical straight-line trajectory method is applied to the ion projectile path in order to visualize the dynamic plasma screening effects on the transition probabilities in dense plasmas as a function of the impact parameter and the collision energy. The transition probabilities including the dynamic plasma screening effects are found to always be greater than those including the static plasma screening effects. When the projectile velocity is greater than the electron thermal velocity, the interaction potential is almost unshielded. The difference between the dynamic and static plasma screening effects is more significant for low-energy projectiles. It is also found that the quadrupole transitions (dipole-quadrupole and quadrupole–quadrupole) show the double peaks due to the node of the2sradial wave function. ©1998 American Institute of Physics.

ISSN:1070-664X    

DOI:10.1063/1.872656

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

In a non-neutral plasma column of constant density it is shown that, for certain parameter values, an infinitely degenerate internal mode, which has no variation in the axial direction, can be stationary in the laboratory frame. However, this mode cannot be driven resonantly by stationary electric or magnetic field asymmetries. When the plasma density is nonuniform the possibility of resonance of stationary field asymmetries with the continuous spectrum is pointed out. ©1998 American Institute of Physics.

ISSN:1070-664X    

DOI:10.1063/1.872657

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Flow of a collision-dominated weakly ionized gas over a solid sphere is investigated in the limit&lgr;m≪&lgr;D≪rp,where&lgr;mis the mean free path,&lgr;Dis the Debye length, andrpis the sphere radius. Such flow is encountered in plasma heating of metallic/ceramic powders in rf plasma-aided manufacturing processes. The flow Reynolds number (Re) based on sphere diameter is in the intermediate range(Re∼5–100).The continuity, the momentum conservation, and the energy conservation equations for the neutrals and those for the charged particles are simultaneously solved with the Poisson’s equation for the self-consistent electric field. A model for production and recombination of the charged particles is incorporated in the formulation. The surface of the sphere is considered as a sink for the charged particles and is at the floating potential. A finite difference method is employed to solve the governing equations. The flow field, the temperature distributions, the charged particle number density variations are obtained and the heat transport to the sphere surface is determined for a range of flow Reynolds number. The effects of Reynolds number, the far field temperature, and the surface temperature on the electric sheath around the sphere surface and on the heat transport to the sphere, are delineated. ©1998 American Institute of Physics.

ISSN:1070-664X    

DOI:10.1063/1.872658

出版商:AIP    

年代:1998

数据来源: AIP