Instability Of Surface Waves Research Articles

Surface wave instability in bounded magnetized plasma with inhomogeneous particle stream

The instability of surface wave modes in a semi infinite magnetoactive plasma with a non-homogeneous particle stream is studied. The existence of two possible mechanisms for the development of the instability: induced anomalous Doppler effect and induced Cherenkov effect is demonstrated. Related growth-rates and stability criteria are calculated.

On Nonlinear Resonant Absorption of Surface Waves

AbstractWe consider the resonant absorption of surface waves in a cold electron plasma by taking into account the nonlinear change in the electron density profile which is caused by the wave pressure in the transition layer. Equations, which describe the time evolution of the amplitudes of the electric fields of the surface waves, are obtained and solved. It is shown that the time‐behaviour of the surface waves can be significantly different from that obtained from linear theory, and nonlinear effects can thus change the rate of absorption of the surface wave energy and can also stabilize linear surface wave instabilities.

The dissipative instability of a relativistic electron beam

The theory of the wall instabilities of surface waves excited by an electron beam is developed. Their classification, linear, quasilinear and nonlinear theory is given. It is shown that dissipative instabilities convert practically all the energy lost by the beam into the heating of the lossy walls confining the beam.

Correction to "Absolute instability of magnetostatic surface waves interacting with drifting carriers in closed ferrite-semiconductor structure"

Correction to "Absolute instability of magnetostatic surface waves interacting with drifting carriers in closed ferrite-semiconductor structure"

Absolute instability of magnetostatic surface waves interacting with drifting carriers in closed ferrite-semiconductor structure

The dispersion relation of magnetostatic surface waves (MSSW) in a semiconductor-ferrite-semiconductor system between two metal plates is analyzed. The coupling between a propagating mode and an evanescent mode occurs and splits both spectra of these modes that degenerated in the absence of the semiconductors in the vicinity of the point at which the group velocity changes its sign due to the effect of metal. When the drift velocity of carriers exeeds the phase velocity of the waves in the splitting portion of the dispersion relation, the function \omega(k) has a saddle point for complex frequency. On this condition, the two waves propagating direction of which are opposite to each other near the saddle point frequency are amplifying in each propagating direction, while at the saddle point these two waves degenerate and are amplifying without propagating since the group velocity d\omega/dk=0 at this point, that is, an absolute instability occurs.

Observations of long-period pulsations in electron precipitation at 75° magnetic latitude

X ray pulsations with a period of ∼150 s were observed in the predawn hours during a balloon flight from Sondre Stromfjord, Greenland (L = 14.5). Simultaneous riometer observations of auroral absorption at the south pole showed absorption pulsations with a period of ∼300 s. These results suggest surface wave instabilities with different temporal features on portions of the magnetopause above and below the magnetic equator.

Instability of electromagnetic surface waves supported by a bounded plasma stream

The characteristics of electromagnetic surface waves supported by a plane interface separating a semi-infinite region of free space from another semi-infinite region consisting of a plasma streaming parallel to the interface are investigated for the case in which the wave is progressing either in or opposite to the direction of the stream. The behavior of the surface wave is drastically different from the case in which the plasma is stationary. The surface wave has backward-wave regions. For a certain range of frequencies below the plasma frequency, the surface wave undergoes traveling wave amplification in the direction of the stream. When its wave number is in a certain range, the surface wave progressing in a direction opposite to that of the stream is convectively unstable. The characteristics of this surface wave instability are analyzed.

Stabilization of beam instability by the high-frequency pressure

The effect of the pressure of an h.f. field (strictional nonlinearity) induced by a beam of charged particles on the character of beam-plasma interaction is investigated. It is demonstrated that allowance for h.f. pressure results in two phenomena, which are missing from a linear approximation. Firstly, the instability that arises under conditions of Čerenkov resonance resembling the instability of surface waves degenerates into that of volumetric waves under the effect of the h.f. pressure. Secondly, which is more important, to a nonlinear approximation the frequency of the excited wave turns out to be dependent on its amplitude (loss of isochronism). The resonance between the beam and the excited waves disappears, thereby reducing the growth rate and with certain parameters the instability might be totally disrupted. Another conclusion, worthy of attention, is that concerning the possibility of a parametric build-up of oscillations in the plasma. The expressions for the wave-amplification coefficients and conditions of the parametric instability are obtained; the instability mechanism is clarified.

Interaction between radiation and a superfluid liquid surface

The surface motion of a superfluid liquid due to ponderomotive effect of radiation on matter is discussed. In particular, the possibility of optical excitation of surface (capillary) waves in a superfluid liquid (He II) is considered. Under certain conditions this effect is shown to cause instability of surface waves, i.e., stimulated surface scattering of light in a superfluid liquid.

Two-Rotating-Stream Instability in a Non-Neutral Plasma

A new surface wave instability is derived for a magnetically confined pure electron gas column with density 34<2ωp02/Ω02<1. The equilibrium configuration consists of two superimposed electron beams aligned parallel to the confining magnetic field B0, and rotating with different azimuthal velocities about the axis of symmetry. The instability, which is of the two-stream form, results from the interaction of surface waves on each of the two superimposed beams.

Surface Wave Instability in Helicon Wave Propagation. III. Theory of Multilayered Structures

The surface wave instability, investigated by Baraff and Buchsbaum for helicon propagation along a sandwich structure, is investigated here for a multilayered structure in which alternating layers of material carry a drift current which can transfer energy to the wave. The resulting growth rates agree with what would be predicted by using the analysis of the sandwich structure to calculate power transferred at each interface as though the others were not there and then summing the result over all interfaces.

Surface-Wave Instability in Helicon Propagation. II: Effect of Collisional Losses

The surface-wave instability analyzed by Baraff and Buchsbaum in the limit of infinite ωcτ is investigated here for ωcτ large but finite. In the previous analysis, the carrier drift velocity required to establish the instability was found to be proportional to (K1−K2), the effective dielectric mismatch across the interface at which the surface wave was excited. Here we find that with ωcτ large but finite, this threshold velocity is increased by an amount proportional to (ωcτ)−1 and inversely proportional to (K1−K2). For a given value of ωcτ there thus exists an optimum choice of (K1−K2) which minimizes the required threshold velocity. These new results can be obtained from heuristic arguments which do not require the calculation of field components beyond lowest nonvanishing order in (ωcτ)−1. The heuristic arguments are here justified rigorously for the physically interesting case of small (K1−K2).

High-Frequency Behavior of the Surface-Wave Helicon Instability

The surface-wave instability in helicon wave propagation analyzed by Baraff and Buchsbaum is reinvestigated here for the purpose of extending the analysis to values of ωτ greater than unity. We find that although collisions are essential for the mechanism of instability, the formulas and analysis of Baraff and Buchsbaum, derived for ωτ«1, are unchanged until ωτ exceeds some large value ω0τ. This value ω0τ is typically much greater than unity. At higher frequencies the surface wave penetrates from one boundary to the next and some of the Baraff-Buchsbaum approximations start to lose validity.

Surface wave instability in Helicon wave propagation: Gain in multilayered structures

Surface wave instability in Helicon wave propagation: Gain in multilayered structures

Surface wave instability in Helicon wave propagation

Surface wave instability in Helicon wave propagation

An Analysis of Surface Wave Instability in Grinding

A graphical method of analysis of surface wave instability in grinding is presented. This form of instability is characterized by uneven wear of the wheel, causing surface waves to form about its circumference. A progressive deterioration in the finish of the work results, together with an increase in the level of vibration. This is a type of self-excited vibration, and is not due to inhomogeneities in the wheel. The factors affecting the number of waves which can build up are discussed. The method of analysis is applied to a cylindrical grinding machine, and the results obtained are compared with those obtained from an experimental investigation.

Taylor instability of finite surface waves

The instability of the accelerated interface between a liquid (methanol or carbon tetrachloride) and air has been investigated experimentally for approximate sinusoidal disturbances of wave-number range from well below to well above the cut-off. The growth rates are measured and compared with theoretical results. A third-order theory shows the phenomena of overstability which is found in the experimental results. Some measurements of later stages of growth agree moderately well with the available theory and disclose some additional phenomena of bubble competition, Helmholtz instability with transition to turbulence, and jet instability with production of drops.

LXIX. Correspondence. Wave motions on a free oil surface

Abstract In 1954 I published an account of some experiments where air was blown over lubricating oil in a wind tunnel (Francis 1954). At a certain critical windspeed tiny ripples were seen on the surface, and some of them rapidly grew and accelerated down-wind. The appearance of the phenomenon and the windspeed at which it occurred corresponded closely with the instability of surface waves forecasted by Kelvin and Helmholtz (quoted by Lamb 1932) but which does not appear on a water surface such as the sea. The experiments were done on one oil only, Shell S2883, and its viscosity μ (2·2 poise) was such that the other type of instability (Jeffreys 1925) should have occurred at a windspeed only just higher than the critical windspeed actually found. There may therefore be a possibility that the phenomenon was fortuitous and was not really due to the Kelvin–Helmholtz instability. However, some additional experiments with still more viscous fluids seem to confirm the earlier results.