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Oct 1987

Volume 30, Issue 10, pp. 2911-3311

Page 1 of 3 Pages Next Page | Jump to Page

Bridging in vortex reconnection

S. Kida and M. Takaoka

Phys. Fluids 30, 2911 (1987); http://dx.doi.org/10.1063/1.866066 (4 pages) | Cited 13 times

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The mechanism of vortex reconnection is investigated by solving the Navier–Stokes equation numerically starting with a closed knotted vortex tube, which gives a nonzero helicity. A new type of vortex reconnection mechanism—bridging—is observed. Small regions of high vorticity bursting out of the vortex tube become larger and bridge different portions of the tube. A relation between the change of the helicity and the mechanism of the vortex reconnection is discussed.
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47.52.+j Chaos in fluid dynamics

Numerical simulations of turbulent spots in plane Poiseuille and boundary‐layer flow

Dan Henningson, Philippe Spalart, and John Kim

Phys. Fluids 30, 2914 (1987); http://dx.doi.org/10.1063/1.866067 (4 pages) | Cited 30 times

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Direct numerical simulations of turbulent spots in plane Poiseuille and boundary‐layer flows are performed. Mature, self‐similar spots are obtained. The propagation velocities and spreading angles are found to compare well with corresponding experiments. The difference in shape of the two spots is also clearly discernible: the turbulent parts are contained within arrowhead regions that point in opposite directions for the two cases. The wing‐tip region of the Poiseuille spot is also found to consist of a large‐amplitude semiturbulent wave packet.
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47.27.Cn Transition to turbulence
47.10.-g General theory in fluid dynamics

Lower bounds on permeability

Jacob Rubinstein and Joseph B. Keller

Phys. Fluids 30, 2919 (1987); http://dx.doi.org/10.1063/1.866068 (3 pages) | Cited 5 times

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A method is presented for obtaining lower bounds on the permeability of a porous medium. It is applied to media composed of periodic and random configurations of spheres and cylinders.
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47.56.+r Flows through porous media
62.10.+s Mechanical properties of liquids
68.08.Bc Wetting

Attenuation of a compressional sound wave in the presence of a fractal boundary

Donald L. Koch

Phys. Fluids 30, 2922 (1987); http://dx.doi.org/10.1063/1.866069 (6 pages) | Cited 6 times

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The attenuation of a compressional sound wave propagating through a fluid bounded by a solid surface of fractal dimension 2≤df<3 is studied. At high sound wave frequency ω, the attenuation is caused primarily by the viscous dissipation within a boundary layer near the solid surface of thickness δ=(μ/ρω)1/2, where μ is the viscosity and ρ the density of the fluid. Because the surface area ‘‘seen’’ by the boundary layer increases with decreasing δ, one might expect the attenuation γ to scale in a self‐similar manner with δ, i.e., γ∼δ2‐da, where 2≤da<3. A multiple scales analysis based on a wide separation in the length scales of successively smaller levels of surface structure is used to determine the dependence of the attenuation on the boundary layer thickness. While the possibility of a self‐similar scaling of the attenuation is confirmed, the attenuation exponent da is generally quite different from the fractal dimension df. In fact the presence of a fractal surface area df≠2 is neither a necessary nor sufficient criterion for a self‐similar scaling of the attenuation da≠2.
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62.60.+v Acoustical properties of liquids
47.56.+r Flows through porous media

Stability of displacement processes in porous media in radial flow geometries

Y. C. Yortsos

Phys. Fluids 30, 2928 (1987); http://dx.doi.org/10.1063/1.866070 (8 pages) | Cited 13 times

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The linear stability of certain displacement processes in porous media for two‐dimensional radial flows induced by a point source is examined. Both two‐phase, immiscible displacement and single‐phase miscible displacement in the presence of equilibrium adsorption are discussed. In agreement with Tan and Homsy [Phys. Fluids 30, 1239 (1987)], it is found that disturbances grow or decay algebraically in time. Via appropriate transformations the eigenvalue problems are shown to be identical to those in rectilinear flow geometries with suitably modified base states and parameters. Thus several stability features are inferred directly from the analysis in rectilinear geometries. The results indicate the existence of critical values for the capillary (NCa) or Peclet (Pe) number, above which the displacement is unstable for wavenumbers in a band of finite width. For large NCa or Pe the most dangerous and the highest cutoff modes scale linearly with NCa or Pe. The different scaling found by Tan and Homsy [Phys. Fluids 30, 1239 (1987)] follows directly as a singular limit of the miscible displacement problem in the absence of adsorption.
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47.56.+r Flows through porous media
47.20.-k Flow instabilities
68.08.-p Liquid-solid interfaces
68.43.-h Chemisorption/physisorption: adsorbates on surfaces

Shear‐layer‐driven transition in a rectangular cavity

M. D. Neary and K. D. Stephanoff

Phys. Fluids 30, 2936 (1987); http://dx.doi.org/10.1063/1.866071 (11 pages) | Cited 13 times

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An experimental study of the flow over a shallow rectangular cavity indicates that, between the states of periodic and fully developed turbulent flow, three different regimes of fluid motion occur as the Reynolds number increases. In the first regime, regime I, the time trace from a pressure transducer, located at the downstream corner of the cavity, varies weakly in amplitude. The frequency spectrum of the trace shows that a single frequency, its’ first harmonic, and a second frequency are selectively amplified. In the second regime, regime II, there is intermittency in the pressure time trace and the two incommensurate frequencies are further apart from each other than in regime I. The primary frequency is the result of a shear‐layer instability but the secondary frequency is believed to depend on a transverse wave on the primary cavity vortex. The exchange of fluid between this vortex and the free stream is enhanced when the two waves are constructively interfering and the exchange is attenuated when the two waves are destructively interfering. If the amplitude of the transverse wave is sufficiently large and the two waves are in phase, fluid from the primary vortex is observed to burst through the shear layer giving rise to a period of apparently random motion. In the third regime, regime III, the pressure oscillations vary strongly with time, and include frequent periods of intense irregular behavior. At times, the pressure cycles have double peaks when the vortices that form in the shear layer are partially clipped by the downstream edge of the cavity. This clipping does not, however, coincide with a decay in the shear‐layer oscillations, as it does in regime II.
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47.20.-k Flow instabilities
47.27.Sd Turbulence generated noise
47.27.N- Wall-bounded shear flow turbulence

Higher eigenmodes in the Blasius boundary‐layer stability problem

Lennart S. Hultgren

Phys. Fluids 30, 2947 (1987); http://dx.doi.org/10.1063/1.866072 (5 pages) | Cited 2 times

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The higher spatial‐stability eigenmodes for the Blasius boundary layer are examined by using asymptotic theory and an infinite number of modes are found. The asymptotic results are shown to be in close agreement with results from a direct numerical solution of the Orr–Sommerfeld problem. The asymptotic theory would therefore provide an efficient tool in exploratory searches for the eigenvalues.
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47.20.-k Flow instabilities
47.15.Cb Laminar boundary layers
47.10.-g General theory in fluid dynamics

Phase space density representation of inviscid fluid dynamics

Henry D. I. Abarbanel and A. Rouhi

Phys. Fluids 30, 2952 (1987); http://dx.doi.org/10.1063/1.866073 (13 pages) | Cited 2 times

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A formulation of inviscid fluid dynamics based on the density F(x,v,t) in a single‐particle phase space [x=(x1,x2,x3), v=(v1,v2,v3)] is presented. This density evolves in time according to a Poisson bracket of F with H(x,v,t)—a Hamiltonian in the same single‐particle phase space. Compressible flows of barotropic fluid and homogeneous, incompressible flows are disscussed. The main advantage of the phase space density formulation over either Euler or Lagrange formulations is the algebraic and conceptual ease in making fully Hamiltonian approximations to the flow by altering H(x,v,t) and the Poisson brackets appropriately. The example of a shallow layer of rapidly rotating fluid where a Rossby number expansion is desired will be discussed in some detail. Changes of phase space coordinates that give an approximate H (expanded in Rossby number) and exact Poisson brackets will be exhibited. The resulting quasigeostrophic equations for F are two‐dimensional partial differential equations to every order in Rossby number. The extension to multiple layers will be presented.
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47.10.-g General theory in fluid dynamics
02.60.Lj Ordinary and partial differential equations; boundary value problems
92.10.-c Physical oceanography

Instability of compound vortex layers and wakes

C. Pozrikidis and J. J. L. Higdon

Phys. Fluids 30, 2965 (1987); http://dx.doi.org/10.1063/1.866074 (11 pages) | Cited 3 times

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The stability of two adjoining vortex layers with constant vorticity of opposite sign is analyzed. Linear stability analysis shows that two families of instability may exist, depending on the relative strength of the vortex layers. The first type for moderate and long waves produces simultaneous growth of disturbances on both layers, while the second for short waves is associated primarily with the weaker layer. Numerical calculations show that the nonlinear growth of the various types of instability leads to asymptotic states of different character. For wake‐like flows with equal but opposite vorticity distributions, the fastest growing eigenmodes lead to the formation of a classic vortex street with an aspect ratio of 0.345. Longer waves lead to the break up of the layer into a number of small vortex regions producing disorganized motion and a general dispersal of the wake vorticity. For compound shear layers with unequal strength, the fastest growing modes show a progression from wake‐like behavior to pure shear‐layer behavior as the strength of the second layer diminishes. In addition, there is a new type of instability associated with short‐wavelength disturbances on the weaker layer. In this case, the shear layer ejects the opposite signed vorticity along with an equal quantity of its own circulation. The ejected vorticity propagates away from the layer at a 45° angle in the form of neutral vortex pairs. The remaining vorticity forms a simpler shear layer of reduced strength.
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47.32.Ef Rotating and swirling flows
47.20.Ky Nonlinearity, bifurcation, and symmetry breaking
47.15.Cb Laminar boundary layers
68.03.Kn Dynamics (capillary waves)
68.05.-n Liquid-liquid interfaces

Surface waves in closed basins under parametric and internal resonances

Ali H. Nayfeh

Phys. Fluids 30, 2976 (1987); http://dx.doi.org/10.1063/1.866075 (8 pages) | Cited 9 times

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The method of multiple scales is used to analyze the nonlinear response of the free surface of a liquid in a cylindrical container to a harmonic vertical oscillation in the presence of a two‐to‐one internal (autoparametric) resonance. Four first‐order ordinary‐differential equations are derived for the modulation of the amplitudes and phases of the two modes involved in the internal resonance with the lower mode is excited by a principal parametric resonance. In the presence of small damping, the long‐time response may be any of (a) a trivial motion, (b) a limit cycle involving both modes, (c) an amplitude‐ and phase‐modulated sinusoid (motion on a two torus), and (d) a chaotically modulated sinusoid.
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47.35.-i Hydrodynamic waves
47.20.Ky Nonlinearity, bifurcation, and symmetry breaking
47.52.+j Chaos in fluid dynamics

Long‐wave instability of periodic flows at large Reynolds numbers

A. Libin, G. Sivashinsky, and E. Levich

Phys. Fluids 30, 2984 (1987); http://dx.doi.org/10.1063/1.866076 (3 pages) | Cited 7 times

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It is shown that simple unidirectional and helical periodic flows are unstable to long‐wave perturbations at large Reynolds numbers. Consideration is given to the cases of periodic flow sustained by an applied force and periodic flow freely decaying owing to viscosity.
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47.35.-i Hydrodynamic waves
47.20.-k Flow instabilities

Infrared properties of an anisotropically stirred fluid

Robert Rubinstein and J. Michael Barton

Phys. Fluids 30, 2987 (1987); http://dx.doi.org/10.1063/1.866077 (6 pages) | Cited 13 times

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A renormalization group is developed for the Navier–Stokes equations driven by an anisotropically correlated random stirring force. The stirring force generates homogeneous turbulence with a preferred direction. The force correlation is the sum of a small anisotropic perturbation and an isotropic correlation chosen so that the fixed point of the renormalization group has a k−5/3 energy spectrum. Fixed points for the anisotropic correlation are found near this isotropic fixed point. Two types of anisotropy are analyzed. When the additional stirring is in the plane perpendicular to the preferred direction, the renormalized viscosity is increased. When it is aligned with the preferred direction, the viscosity is decreased. A possible connection with the inverse energy cascade of 2‐D turbulence is discussed.
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47.27.Gs Isotropic turbulence; homogeneous turbulence

The structure of the turbulent boundary layer on a cylinder in axial flow

Richard M. Lueptow and Joseph H. Haritonidis

Phys. Fluids 30, 2993 (1987); http://dx.doi.org/10.1063/1.866078 (13 pages) | Cited 15 times

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The thick, turbulent boundary layer, which develops as a fluid flows parallel to a cylinder, has been experimentally characterized for the case where the boundary layer is thick compared to the radius of transverse curvature. Measurements of the turbulence intensity, velocity spectra, and intermittency are qualitatively similar to those for the planar boundary layer. Although measurements of wall shear stress using several different techniques have substantial scatter, the wall shear stress appears to be larger than that for the turbulent boundary layer on a flat plate at the same Reynolds number based on streamwise distance. The variable interval time averaging (VITA) and uv‐quadrant techniques were used to detect the burst cycle near the wall. Conditionally averaged velocities were similar to those for a flat plate boundary layer indicating a similar burst cycle near the wall. However, the VITA frequency scaling indicates an interaction between the flow in the wall region and the outer flow. Flow visualization was used to observe the crossflow of structures in the boundary layer of a cylinder moving through a tank of quiescent water. Large‐scale structures were observed moving from the outer region on one side of the cylinder to the outer region on the opposite side of the cylinder suggesting that the wall may be less important in controlling the size and motion of coherent structures in the cylindrical boundary layer than in the planar boundary layer.
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47.27.Gs Isotropic turbulence; homogeneous turbulence

Structural similarity and lifetimes of turbulence structures in fully developed pipe flow

K. J. Bullock, R. E. Cooper, R. E. Kronauer, and J. C. S. Lai

Phys. Fluids 30, 3006 (1987); http://dx.doi.org/10.1063/1.866079 (13 pages) | Cited 1 time

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Cross correlation measurements of the longitudinal velocity fluctuations in fully developed pipe flow have been performed with a reference hot‐wire probe at a distance y+1 =100 from the wall for five different y+2 locations (namely, 50, 100, 200, 400, and 600) of a second probe with zero longitudinal separation but nonzero transverse separations. The pipe flow Reynolds number is 69 000 based on the pipe radius and the centerline velocity. The covariant (Co) and quadrature (Quad) correlations, which have been determined for each of the seven frequencies ω+ used to constrain the longitudinal wavenumber k+x, have been Fourier transformed with the transverse wavenumber k+z, y+1, y+2, and ω+ as the independent variables. The data presented in this form enable similarity to be examined in terms of waves of different sizes and inclinations. By using a similarity variable k+y+, where k+=[k+2x k+2z]1/2, the relative phases determined from the Co and Quad correlations and the wave intensity function for various wave angles have been shown to collapse. These results support the similarity hypothesis that the phase and intensity of the turbulance components is scaled by wave size k+ and distance from the wall y+. The dimension over which a turbulence structure retains its coherence has been deduced from the correlation data for various wave angles. Two estimates for the lifetime of turbulence structures have been derived, one from the phase‐shifting effects of shear contained in the relative phase data, and the other from spectral sheet thickness data. Their significance and implications have been discussed.
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47.27.N- Wall-bounded shear flow turbulence
05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion
47.60.-i Flow phenomena in quasi-one-dimensional systems

Wall‐pressure fluctuations in turbulent pipe flow

Gerald C. Lauchle and Mark A. Daniels

Phys. Fluids 30, 3019 (1987); http://dx.doi.org/10.1063/1.866080 (6 pages) | Cited 10 times

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Wall‐pressure fluctuation measurements are reported for the fully developed turbulent flow of glycerine in a long pipe. Because of the relatively large viscous scales associated with glycerine, it has been possible to perform pressure fluctuation spectral measurements for 0.7≤d+≤1.5, where d+ is the transducer diameter expressed in wall units. The data presented are for d+ values smaller than ever before reported.
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47.60.-i Flow phenomena in quasi-one-dimensional systems
47.27.Gs Isotropic turbulence; homogeneous turbulence
05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion

The structure of a turbulent shear layer embedded in turbulence

S. Tavoularis and S. Corrsin

Phys. Fluids 30, 3025 (1987); http://dx.doi.org/10.1063/1.866081 (9 pages) | Cited 2 times

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Measurements are reported on the growth rate and the turbulent characteristics of a two‐dimensional, free shear layer generated by a nonuniform array of parallel turbulent jets and wakes. Although bounded by roughly isotropic turbulence and not having any detectable initial periodicity, this layer develops weak, plane, periodic vortices that grow in relative strength and scale downstream. Their scale and frequency match those reported for shear layers that begin with strong vortices.
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47.20.Ft Instability of shear flows (e.g., Kelvin-Helmholtz)
47.27.W- Boundary-free shear flow turbulence
47.27.Gs Isotropic turbulence; homogeneous turbulence
47.32.Ef Rotating and swirling flows

Structure of weak shocks in fluids having embedded regions of negative nonlinearity

M. S. Cramer

Phys. Fluids 30, 3034 (1987); http://dx.doi.org/10.1063/1.866082 (11 pages) | Cited 7 times

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The dissipative structure of weak shock waves in fluids in which the fundamental derivative is negative for a finite range of pressures and temperatures has been examined. Conditions under which the shock thickness increases with strength rather than decreases are delineated. Nonclassical features of the entropy distribution and variation of local Mach number are also described.
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47.40.Nm Shock wave interactions and shock effects
41.20.Jb Electromagnetic wave propagation; radiowave propagation

Magnetoacoustic shock waves in a relativistic gas

A. Majorana and A. M. Anile

Phys. Fluids 30, 3045 (1987); http://dx.doi.org/10.1063/1.866479 (5 pages) | Cited 11 times

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Fast and slow magnetoacoustic shocks are studied in the framework of relativistic magneto‐fluid dynamics with the Synge equation of state. An approximate analytical solution is presented in a particular case. The general case is treated by numerical methods.
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52.35.Tc Shock waves and discontinuities
52.30.-q Plasma dynamics and flow
47.75.+f Relativistic fluid dynamics

Congruent reduction in geometric optics and mode conversion

Lazar Friedland and Allan N. Kaufman

Phys. Fluids 30, 3050 (1987); http://dx.doi.org/10.1063/1.866480 (9 pages) | Cited 32 times

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Standard eikonal theory reduces, to N=1, the order of the system of equations underlying wave propagation in inhomogeneous plasmas. The condition for this remarkable reducibility is that only one eigenvalue of the unreduced N×N dispersion matrix D(k,x) vanishes at a time. If, in contrast, two or more eigenvalues of D become simultaneously small, the geometric optics reduction scheme becomes singular. These regions are associated with linear mode conversion and are described by higher‐order systems. A new reduction scheme is developed based on congruent transformations of D, and it is shown that, in degenerate regions, a partial reduction of order is still possible. The method comprises a constructive step‐by‐step procedure, which, in the most frequent (doubly degenerate) case, yields a second‐order system, describing the pairwise mode conversion problem in four‐dimensional plasmas. This N=2 case is considered in detail, and dimensionality arguments are used in studying the characteristic ordering of the elements of the reduced dispersion tensor in mode conversion regions. The congruent reduction procedure is illustrated by classifying pairwise degeneracies in cold multispecies magnetized plasmas.
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52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.35.-g Waves, oscillations, and instabilities in plasmas and intense beams
41.20.Jb Electromagnetic wave propagation; radiowave propagation

Relativistic electron motion in the presence of cyclotron resonant electromagnetic waves

B. Hafizi and R. E. Aamodt

Phys. Fluids 30, 3059 (1987); http://dx.doi.org/10.1063/1.866481 (6 pages) | Cited 10 times

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The relativistic collisionless motion of magnetically trapped electrons under the influence of rf wave with frequency near an integral multiple of their ambient synchrotron frequency is studied analytically. A Hamiltonian formalism is used to determine the phenomena of losing or maintaining local resonance and the accumulation or dispersion of the electrons in the magnetic well as they heat. Sustenance of resonance is shown to be markedly dependent on the index of refraction of the wave; it is also shown that the inherently relativistic detrapping effect can be important even for low energies and can be enhanced by low energy collisions.
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52.50.Gj Plasma heating by particle beams
52.20.Dq Particle orbits
41.60.-m Radiation by moving charges
41.75.Ht Relativistic electron and positron beams

Statistical closure approximations and the fluctuation‐dissipation theorem for drift‐wave interaction

A. E. Koniges and C. E. Leith

Phys. Fluids 30, 3065 (1987); http://dx.doi.org/10.1063/1.866482 (10 pages) | Cited 6 times

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The statistical dynamics of a truncated (three‐wave) model for drift‐wave interaction are studied using numerical simulation in order to determine appropriate turbulence modeling approaches. The nonlinear dynamical equation is integrated for a Gaussian ensemble of initial states, and time‐lag correlation functions and infinitesimal response functions are computed. The fluctuation‐dissipation relation, an assumption of many statistical closure approximations, is shown to be qualitatively valid for statistical steady states of the system. Guided by the ensemble results, a Markovian turbulence model is selected and investigated.
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52.35.Ra Plasma turbulence
52.35.Kt Drift waves

The cusp map in the complex‐frequency plane for absolute instabilities

K. Kupfer, A. Bers, and A. K. Ram

Phys. Fluids 30, 3075 (1987); http://dx.doi.org/10.1063/1.866483 (8 pages) | Cited 22 times

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It is well known that absolute instabilities can be located by prescribed mappings from the complex‐frequency plane to the wavenumber plane through the dispersion relation D(ω,k)=0. However, in many systems of physical interest the dispersion relation is polynomial in ω while transcendental in k, and the implementation of this mapping procedure is particularly difficult. If one maps consecutive deformations of the Fourier integral path (originally along the real k axis) into the ω plane, points having (∂D/∂k)=0 are readily detected by the distinctive feature of their local maps. It is shown that a simple topological relationship between these points and the image of the real k axis determines the stability characteristics of the system, without mapping from the ω plane back into the k‐plane.
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47.20.Ft Instability of shear flows (e.g., Kelvin-Helmholtz)
47.10.-g General theory in fluid dynamics

Linear and nonlinear description of drift instabilities in a high‐beta plasma

A. Y. Aydemir, H. L. Berk, V. Mirnov, O. P. Pogutse, and M. N. Rosenbluth

Phys. Fluids 30, 3083 (1987); http://dx.doi.org/10.1063/1.866484 (10 pages) | Cited 8 times

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A nonlinear system of equations is derived for drift waves in a high‐beta plasma (β≫1). The magnetic field pressure is taken small compared to the particle pressure. Pressure balance is established by having a uniform particle pressure with the density and temperature gradients in opposite directions. The primary purpose of the magnetic field is to inhibit radial heat flux. This is the principle of such plasma fusion systems as the wall sustained multiple mirror, compressed liner, and magnetic‐insulated inertial fusion, where the heat is contained over a relatively short radial scale length and a long axial scale length. The nonlinear equations for the mathematical model contain drift instabilities that give rise to radial heat and particle fluxes that can enhance the losses expected from classical collisional effects. The linear and nonlinear evolution of the model is studied here.
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52.35.Kt Drift waves
52.55.Pi Fusion products effects (e.g., alpha-particles, etc.), fast particle effects

Cyclotron resonance phenomena in a non‐neutral plasma

S. A. Prasad, G. J. Morales, and B. D. Fried

Phys. Fluids 30, 3093 (1987); http://dx.doi.org/10.1063/1.866485 (13 pages) | Cited 12 times

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A kinetic theory of electrostatic cyclotron waves in a single component plasma slab of density n0(x) immersed in a uniform magnetic field B0math is presented. The space charge electric field E0(x)math in such a plasma modifies the single particle gyrofrequency from Ω=qB0/mc to Ω1(x)=[Ω2−ω2p(x)]1/2 in the limit rc/L ≪1 (where rc is the orbit size and L−1=d ln E0/dx), causing the upper hybrid frequency to have the value (Ω21+ω2p)1/2 =Ω. Finite Larmor radius effects introduce a velocity dependence into the single particle gyrofrequency Ω1, leading to energy transfer to the particles located at the resonant layers where ω−kyvE(x) =Ω1(x) [vE(x)math being the E×B drift velocity]. This energy transfer mechanism is operative even when kz =0. Another nonzero Larmor radius effect is the appearance of thermal modes that are the analogs of Bernstein modes of neutral plasmas. When driven by an external capacitor plate antenna, these modes exhibit behavior similar to Tonks–Dattner resonances.
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52.27.Jt Nonneutral plasmas
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.25.Dg Plasma kinetic equations
52.20.Dq Particle orbits

A cyclotron‐maser instability associated with a nongyrotropic distribution

H. P. Freund, J. Q. Dong, C. S. Wu, and L. C. Lee

Phys. Fluids 30, 3106 (1987); http://dx.doi.org/10.1063/1.866486 (7 pages) | Cited 7 times

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A stability analysis for the cyclotron‐maser instability in the presence of a nongyrotropic electron distribution is presented. The model configuration describes a uniformly magnetized cold ambient plasma that contains a relatively diffuse suprathermal electron component coherently bunched in gyrophase. The stability of perturbations propagating parallel to the ambient magnetic field is considered, and substantial growth rates are found to occur. The results are contrasted with those found for a comparable gyrotropic loss‐cone distribution, and it is found that the nongyrotropic instability is characterized by substantially higher growth rates.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.27.Ny Relativistic plasmas
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