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Sep 1988

Volume 31, Issue 9, pp. 2383-2729

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Gallery of fluid motion

Helen L. Reed

Phys. Fluids 31, 2383 (1988); http://dx.doi.org/10.1063/1.866590 (12 pages) | Cited 2 times

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This article displays winning photographs from the fifth Annual Fluid Mechanics Photo Contest held at the November 1987 meeting of the American Physical Society, Division of Fluid Dynamics, Eugene, Oregon.
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82.33.Vx Reactions in flames, combustion, and explosions
47.27.W- Boundary-free shear flow turbulence
07.68.+m Photography, photographic instruments; xerography

Depression of nonlinearity in decaying isotropic turbulence

Robert H. Kraichnan and Raj Panda

Phys. Fluids 31, 2395 (1988); http://dx.doi.org/10.1063/1.866591 (3 pages) | Cited 47 times

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Simulations of decaying isotropic Navier–Stokes turbulence exhibit depression of the normalized mean‐square nonlinear term to 57% of the value for a Gaussianly distributed velocity field with the same instantaneous velocity spectrum. Similar depression is found for dynamical models with random coupling coefficients (modified Betchov models). This suggests that the depression is dynamically generic rather than specifically driven by alignment of velocity and vorticity.
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47.27.Gs Isotropic turbulence; homogeneous turbulence
05.45.-a Nonlinear dynamics and chaos
05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion

Truncation effect in a Fourier series expansion on the nonlinear evolution of disturbances in free convection between vertical parallel plates

Kaoru Fujimura and Jiro Mizushima

Phys. Fluids 31, 2398 (1988); http://dx.doi.org/10.1063/1.866592 (3 pages) | Cited 1 time

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The effect of truncation in a Fourier series expansion on the nonlinear evolution of a disturbance has been investigated numerically in free convection between vertical parallel plates with different temperatures. Qualitatively different solutions were obtained, depending on the number of terms involved in the expansion. Transition from a stationary wave to an oscillatory traveling wave associated with the breakdown of the spatial symmetry was also obtained
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47.20.Ft Instability of shear flows (e.g., Kelvin-Helmholtz)
47.20.Ky Nonlinearity, bifurcation, and symmetry breaking

Cross‐linking of two vortex rings

Yuko Oshima and Naoki Izutsu

Phys. Fluids 31, 2401 (1988); http://dx.doi.org/10.1063/1.866593 (3 pages) | Cited 18 times

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The mechanism for cross‐linking two vortex rings has been investigated experimentally. Phase‐locked velocity measurements using x‐type hot wires were carried out point by point over the entire flow field, and time‐dependent vorticity fields were educed. It is found that a new pair of vortex tubes is created, which connects the interacting vortex rings and grows gradually, while the vorticity intensity of the main rings decreases. This is considered to be a type of bridging phenomenon of the vortex tubes, as proposed by Kida and Takaoka [Phys. Fluids 30, 2911 (1987)] in their numerical simulation.
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47.32.Ef Rotating and swirling flows

A nonlocal theory for the heat transport in composites containing highly conducting fibrous inclusions

Eric S. G. Shaqfeh

Phys. Fluids 31, 2405 (1988); http://dx.doi.org/10.1063/1.866594 (21 pages) | Cited 15 times

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A theory is developed to describe the heat transfer in composites containing highly conducting fibrous inclusions under conditions in which the average temperature field scales on lengths comparable to the length of the included fibers. Thus, in contrast to previous developments, the fiber samples the details of a rapidly varying temperature field rather than simply a local linear field. Using the method of averaged equations and slender body theory, the average ‘‘extra flux’’ created by the presence of the fibers is demonstrated to be an integral of the temperature gradient about any point weighted by a function which is the appropriate nonlocal conductivity. This representation of the thermal transport in the material is derived explicitly for (a) dilute composites in which nf l3≪1, where nf is the number density of the fiber and l is their length; and (b) semidilute composites in which nfl3≫1 but nflb2≪1, where b is the fiber thickness. In both instances the expressions derived are rigorously valid for fibers that are very long and thin. Associated with the derivation of the semidilute nonlocal theory is the first complete derivation of the semidilute local result, which justifies the arguments made by Batchelor [J. Fluid Mech. 46, 813 (1971)] and demonstrates the mechanisms of ‘‘screening’’ in these multiparticle systems.
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82.70.-y Disperse systems; complex fluids
44.30.+v Heat flow in porous media

Transport processes in random arrays of cylinders. I. Thermal conduction

A. S. Sangani and C. Yao

Phys. Fluids 31, 2426 (1988); http://dx.doi.org/10.1063/1.866595 (9 pages) | Cited 33 times

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A numerical method is developed that takes into account the many‐particle interactions in a rigorous manner to determine the effective thermal conductivity Km of a composite medium consisting of parallel circular cylinders of thermal conductivity αk suspended in a matrix of conductivity k. Numerical results for Km are presented for a wide range of α and ϕ, the area fraction of the cylinders, after averaging over several computer‐generated random arrays of cylinders. The results obtained via this exact method are compared with those of various approximate analytical methods to assess their utility in predicting Km.
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82.70.Kj Emulsions and suspensions
44.30.+v Heat flow in porous media

Transport processes in random arrays of cylinders. II. Viscous flow

A. S. Sangani and C. Yao

Phys. Fluids 31, 2435 (1988); http://dx.doi.org/10.1063/1.866596 (10 pages) | Cited 56 times

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The method described in Part I [Phys. Fluids 31, XXXX (1988)] is extended to treat the problem of determining the permeability of random arrays of infinitely long cylinders. The results for the transverse and longitudinal permeabilities averaged over several configurations of random arrays of cylinders are presented as a function of the area fraction of the cylinders. A detailed comparison is made with the estimates of the permeability obtained by various approximate and asymptotic theories to determine their range of validity.
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44.30.+v Heat flow in porous media
82.70.Kj Emulsions and suspensions

Mobility functions for two unequal viscous drops in Stokes flow. I. Axisymmetric motions

Yuris O. Fuentes, Sangtae Kim, and David J. Jeffrey

Phys. Fluids 31, 2445 (1988); http://dx.doi.org/10.1063/1.866597 (11 pages) | Cited 24 times

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Analytical results are obtained for mobility functions which describe the hydrodynamic interactions between two unequal viscous drops. It is assumed that the surface tension is sufficiently high so that the drops retain a spherical shape. Exact solutions are introduced for the velocity images for Stokeslets and higher‐order Stokes singularities near a viscous drop and then these image solutions are used to generate expressions valid for all two‐sphere geometries except those for which the gap is much smaller than the diameter of the smaller drop. For rigid spheres, these results are used to obtain a closed‐form expression for the Stokes–Einstein Brownian diffusion coefficient.
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47.55.Kf Particle-laden flows
66.10.C- Diffusion and thermal diffusion

Convection in rotating binary mixtures. I. Thresholds

Jayanta K. Bhattacharjee

Phys. Fluids 31, 2456 (1988); http://dx.doi.org/10.1063/1.866598 (6 pages) | Cited 6 times

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Onset of convection in rotating binary mixtures is considered with both idealized and realistic boundary conditions. Stationary and oscillatory convection are possible. The threshold Rayleigh numbers, critical wavenumbers, and frequency are determined analytically.
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47.20.Bp Buoyancy-driven instabilities (e.g., Rayleigh-Benard)
47.32.Ef Rotating and swirling flows
47.27.T- Turbulent transport processes

Convection in rotating binary mixtures. II. Küppers–Lortz instability

Jayanta K. Bhattacharjee

Phys. Fluids 31, 2462 (1988); http://dx.doi.org/10.1063/1.866599 (5 pages) | Cited 6 times

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Nonlinear effects on the stationary convection in rotating binary mixtures are studied. It is found that the nonequilibrium tricritical point is unaffected by the rotation. The threshold for the Küppers–Lortz instability is studied as a function of the separation parameter (ψ). It is seen that the threshold has a minimum when ψ∼L2, where L is the Lewis number. These results have been obtained for idealized boundary conditions.
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47.20.Bp Buoyancy-driven instabilities (e.g., Rayleigh-Benard)
47.32.Ef Rotating and swirling flows
47.27.T- Turbulent transport processes

Low Rayleigh number convection in horizontal, eccentric annuli

YuZhou Wang and Haim H. Bau

Phys. Fluids 31, 2467 (1988); http://dx.doi.org/10.1063/1.866600 (7 pages) | Cited 9 times

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Low Rayleigh number thermal convection in a Newtonian fluid confined between two horizontal, circular cylinders is studied analytically using a regular perturbation expansion. Both cylinders are impermeable and maintained at different, uniform temperatures. The line connecting the cylinders’ centers (referred to as the intracenter line) may be inclined at an arbitrary angle with respect to the gravity vector. When the intracenter line is parallel to the gravity vector, bicellular convection is observed in the annulus and the flow is symmetrical with respect to the intracenter line. When the intracenter line is inclined with respect to the gravity vector, the flow domain is doubly connected. The flow is asymmetrical vis‐math‐vis the intracenter line; and, in addition to the cellular convection, there is net circulation around the inner cylinder. This circulation consists of fluid ascending on one side of the inner cylinder and descending on the other.
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47.27.T- Turbulent transport processes
47.15.G- Low-Reynolds-number (creeping) flows
47.10.-g General theory in fluid dynamics

Numerical simulation of Rayleigh–Bénard convection in shallow tanks

Wayne Arter and Alan C. Newell

Phys. Fluids 31, 2474 (1988); http://dx.doi.org/10.1063/1.866601 (12 pages) | Cited 5 times

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The FLOW3D [Numerical Methods for Fluid Mechanics II, edited by K. W. Morton and M. J. Baines (Clarendon, Oxford, 1986), p. 499] code, originally designed to simulate industrial heat flow problems, is found to be suitable for studying Rayleigh–Bénard convection in carefully controlled laboratory experiments. The structures of both rolls and defects in fully developed, laminar convection in shallow tanks are described in detail. Simulations at parameters near the threshold for the onset of turbulence in water show a transition between two time‐dependent patterns, one roll‐like and the other cellular, in which short wavelength instabilities of known type (skew varicose) are implicated. Evidence for spatiotemporal intermittency is seen, although the turbulence is clearly not fully developed.
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02.60.Cb Numerical simulation; solution of equations
47.20.Bp Buoyancy-driven instabilities (e.g., Rayleigh-Benard)
47.27.Cn Transition to turbulence
47.27.T- Turbulent transport processes

Broadening of interfacial solitary waves

R. E. L. Turner and J.‐M. Vanden‐Broeck

Phys. Fluids 31, 2486 (1988); http://dx.doi.org/10.1063/1.866602 (5 pages) | Cited 31 times

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Progressing interfacial gravity waves are considered for two fluids of differing densities confined in a channel of finite vertical extent and infinite horizontal extent. An integrodifferential equation for the unknown shape of the interface is derived. This equation is discretized and the resulting algebraic equations are solved using Newton’s method. It is found that, for a range of heights and densities of the two fluids, the system supports a branch of solitary waves. Progression along the branch produces a broadening of the wave. With increased broadening both the amplitude and the wave speed approach limiting values. The results are in good agreement with analytical studies and indicate the existence of internal surges.
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47.35.-i Hydrodynamic waves
47.60.-i Flow phenomena in quasi-one-dimensional systems

Turbulence structure in free‐surface channel flows

M. Rashidi and S. Banerjee

Phys. Fluids 31, 2491 (1988); http://dx.doi.org/10.1063/1.866603 (13 pages) | Cited 42 times

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A turbulence structure in horizontal liquid streams bounded by a free surface and a wall has been investigated using 10–25 μm oxygen bubbles as tracers. High speed video movies indicate that the dominant flow structure is caused by the periodic ejection of intensely turbulent fluid with low streamwise momentum from the wall region into the relatively quiescent bulk fluid which it displaces and mixes with slowly. The motion of these bursts is constrained by the free interface. Between bursts and the interface a high speed region with a steep velocity gradient develops as a consequence. This in turn causes progress of the burst fluid toward the interface to slow down and eventually to turn back toward the wall, giving rise to characteristic rolling structures, which rotate clockwise if the flow is viewed as going from left to right. To complement the video studies, quantitative data were obtained by analyzing bubble streak lines generated by photography of optically chopped flashes. These data show that in the vicinity of the interface the velocity fluctuations normal to it are damped whereas those parallel to it are enhanced. Analysis of conditional samples of the data indicate that fluid with relatively low streamwise momentum tends to move toward the interface while fluid with high momentum moves away giving rise to rotating structures that roll along with the flow in agreement with the video studies. A high degree of correlation between ejection events near the wall and the fluid motion near the interface also confirm that the bursts extend across the flow stream. This has important implications for surface renewal theories of turbulent transport at fluid–fluid interfaces.
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47.27.T- Turbulent transport processes
47.55.Hd Stratified flows
47.60.-i Flow phenomena in quasi-one-dimensional systems
06.60.Jn High-speed techniques (microsecond to femtosecond)

Vortex deformation in elliptic‐core jets from the perspective of linear instability analysis

Shozo Koshigoe, Arnold Tubis, and Chih‐Ming Ho

Phys. Fluids 31, 2504 (1988); http://dx.doi.org/10.1063/1.866604 (14 pages) | Cited 4 times

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An attempt is made to identify the underlying mechanisms for the deformation of coherent structures that occurs in the initial state of axis switching of elliptic‐core jets. The generalized shooting method is applied to jets with elliptic‐core regions of constant flow. The analysis shows that there are three conditions on groups of eigenmodes of elliptic‐core jets which are necessary for the deformation. They are (1) proper localizations without excessive overlapping; (2) sufficiently large phase‐speed differences; and (3) comparable spatial amplification rates. The qualitative behaviors of elliptic‐core jets in relation to these three conditions are studied with respect to independent and joint variations of core eccentricity, azimuthal distribution of momentum thickness, and compressibility.
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47.27.W- Boundary-free shear flow turbulence
47.20.-k Flow instabilities

Drag reduction caused by the injection of polymer thread into a turbulent pipe flow

Hiromoto Usui, Katsuhiro Maeguchi, and Yuji Sano

Phys. Fluids 31, 2518 (1988); http://dx.doi.org/10.1063/1.866605 (6 pages) | Cited 11 times

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Drag reduction caused by the injection of concentrated polymer solutions into a turbulent pipe flow was studied. Measurements were made of the radial distribution of fluctuating velocities by means of video image analysis. The results showed that a higher velocity was observed for injected polymer threads and both the radial fluctuation and the Reynolds stress were significantly suppressed. It was suggested that the wall turbulence structure might be controlled by suppressing the large scale turbulent motion in the turbulent core region.
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47.50.-d Non-Newtonian fluid flows
47.27.T- Turbulent transport processes
47.60.-i Flow phenomena in quasi-one-dimensional systems

Near‐field pressure radiation and flow characteristics in low supersonic circular and elliptic jets

E. Gutmark, K. C. Schadow, K. J. Wilson, and C. J. Bicker

Phys. Fluids 31, 2524 (1988); http://dx.doi.org/10.1063/1.867011 (9 pages) | Cited 8 times

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The near‐field pressure fluctuations of circular and elliptic underexpanded supersonic jets were studied experimentally. Unlike the case of low subsonic jets, the pressure fluctuation characteristics at the minor axis plane of the elliptic jet were very different from those of the major axis plane. The amplitude of the pressure fluctuations at the minor axis was more than an order of magnitude higher than at the other plane. This section of the jet was also characterized by a larger spreading rate and higher amplification rate of the velocity fluctuations. The circular jet was similar to the major axis plane of the elliptic jet. The spectra of the near‐field pressure fluctuations of both jets exhibited the highest peak at a frequency corresponding to the jets’ preferred mode frequency. The spectral peak related to the screech tone was much stronger at the minor axis plane and had the same frequency as at the other plane. The amplitude of the dominant pressure fluctuation frequencies was mapped in the entire near field, and each one was found to be dominant in a different region.
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47.40.Ki Supersonic and hypersonic flows
47.27.Sd Turbulence generated noise
47.60.Kz Flows and jets through nozzles
47.20.Ft Instability of shear flows (e.g., Kelvin-Helmholtz)

The statistics of the organized vortical structure in turbulent mixing layers

L. P. Bernal

Phys. Fluids 31, 2533 (1988); http://dx.doi.org/10.1063/1.866606 (11 pages) | Cited 13 times

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The statistics of the large scale vortex structure in turbulent mixing layers have been investigated theoretically. It is shown that similarity in the fully developed flow results in a common description of the Eulerian and Lagrangian statistics. In the Eulerian frame of reference, a conservation equation is derived and solved to show that the distribution of vortex circulation is lognormal. It is also shown that the standard deviation normalized by the mean value of the distribution depends only on the amalgamation mechanism. The value for pairing is in good agreement with experimental measurements. These results are used to calculate the life span and survival probabilities of the vortices in the Lagrangian frame of reference. These distributions are in good agreement with direct measurements of the life span probability and with space‐time correlation measurements, respectively. Some implications of these results on the dynamics of the large scale vortices in the fully developed turbulent flow are discussed.
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47.27.W- Boundary-free shear flow turbulence
47.32.Ef Rotating and swirling flows
47.10.-g General theory in fluid dynamics

Particle size effects on Lagrangian turbulence

John B. McLaughlin

Phys. Fluids 31, 2544 (1988); http://dx.doi.org/10.1063/1.866607 (10 pages) | Cited 24 times

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Perturbation methods are used to show that the equations of motion for a small rigid sphere in a steady laminar flow take the form of a dynamical system in which phase volume is not conserved. In the absence of stagnation points, particle inertia and virtual mass effects destroy Lagrangian turbulence and the particles are captured by periodic or quasiperiodic orbits that are associated with the vortices of the flow. When gravitational effects are included, it is found that point particles can sediment chaotically, but that particle inertia and virtual mass effects tend to eliminate the chaotic behavior. An interesting consequence of the latter phenomenon is that finite particles which are denser than the fluid can be permanently suspended in three‐dimensional cellular flows. Numerical results are presented for the Arnold–Beltrami–Childress [C. R. Acad. Sci. Paris 261, 17 (1965)] flows.
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47.15.-x Laminar flows

Dynamics of explosive boiling of a droplet

D. L. Frost

Phys. Fluids 31, 2554 (1988); http://dx.doi.org/10.1063/1.866608 (8 pages) | Cited 19 times

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The dynamical behavior of the unstable explosive boiling of single droplets (1–2 mm diam) of diethyl ether, pentane, and isopentane at the superheat limit has been exhibited in detail. A+high ambient pressures, boiling consists of normal stable growth of a smooth bubble. At intermediate pressures a transitional regime of stability occurs in which a drop initially vaporizes stably for several milliseconds while incipient instability waves develop on the evaporating interface, then increased heat flux from the host liquid initiates violent boiling near the edge of the remnant volatile liquid. Direct evidence has been obtained that during violently unstable boiling, fine liquid particles are torn from the liquid–vapor interface, generating a mass flux orders of magnitude greater than that characteristic of ordinary boiling. In this regime of transitional stability, one of a number of different possible kinds of disturbances could externally trigger a breakdown to violent instability. After the evaporative instability becomes nonlinear and saturates, the boiling appears quasisteady, with the evaporative front moving into the volatile liquid at a roughly constant velocity. Results obtained by modeling the evaporation wave as a Chapman–Jouguet deflagration show that the temperature at the unstably boiling interface is substantially above the saturated value.
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44.25.+f Natural convection
64.70.F- Liquid-vapor transitions
64.60.Q- Nucleation
68.03.Fg Evaporation and condensation of liquids

Numerical experiments on modon stability to topographic perturbations

G. F. Carnevale, M. Briscolini, R. Purini, and G. K. Vallis

Phys. Fluids 31, 2562 (1988); http://dx.doi.org/10.1063/1.866533 (5 pages) | Cited 6 times

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A summary of a numerical study of the stability of modons to topographic perturbation is presented. Previous studies have suggested a monotonic relationship between the horizontal scale of the perturbation and the amplitude needed to destroy a modon—as the scale of the perturbation increases the strength needed for destruction decreases. The results presented here show that this relationship does not hold for scales larger than the modon radius. For large‐scale perturbations, the strength needed for destruction again increases. The modon is most stable to perturbations of horizontal scale either much larger or much smaller than the modon radius. Stability graphs are presented for three types of perturbations; ridges, hills, and irregular terrain.
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92.60.-e Properties and dynamics of the atmosphere; meteorology
92.10.-c Physical oceanography
52.30.-q Plasma dynamics and flow

The role of initial conditions in flow stability with an application to modons

G. F. Carnevale, G. K. Vallis, R. Purini, and M. Briscolini

Phys. Fluids 31, 2567 (1988); http://dx.doi.org/10.1063/1.866534 (6 pages) | Cited 10 times

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Lyapunov stability arguments may be used to show that an otherwise unstable flow can be stabilized by restriction of the class of possible perturbations. It is shown that, in general, such a restriction applied only to the initial perturbation does not imply stability for dynamics on the entire phase space nor does it necessarily imply a delay of the onset of instability. As a result, proofs of linear stability based on a restriction of the initial perturbation actually are not valid. In particular, certain criteria for the stability of modons given by Pierini [Dyn. Atmos. Oceans 9, 273 (1985)] and Swaters [Phys. Fluids 29, 1419 (1986)] and synthesized by Flierl [Annu. Rev. Fluid Mech. 19, 493 (1987)] do not, in fact, ensure stability. A model is used to demonstrate that these stability criteria do not preclude instantaneous onset of linear instability. The model also demonstrates that, although conservation of energy and enstrophy implies that the transfer of energy in an instability must be to scales both larger and smaller than the modon scale, the principal direction of transfer remains undetermined.
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47.20.-k Flow instabilities
47.10.-g General theory in fluid dynamics

Karhunen–Loéve expansion of Burgers’ model of turbulence

D. H. Chambers, R. J. Adrian, P. Moin, D. S. Stewart, and H. J. Sung

Phys. Fluids 31, 2573 (1988); http://dx.doi.org/10.1063/1.866535 (10 pages) | Cited 43 times

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Characteristics of the Karhunen–Loéve expansion of a strongly inhomogeneous random process possessing small viscous length scales and a large outer scale have been investigated in relation to the application of the expansion to turbulent flow fields. Monte Carlo simulations of a randomly forced Burgers’ equation with zero velocity boundary conditions generate the random process numerically and the Karhunen–Loéve (KL) eigenfunctions and the eigenvalue spectra are computed for different Reynolds numbers. The eigenfunctions possess thin viscous boundary layers at the walls and are independent of Reynolds number in the core, where the random process is quasihomogeneous. The eigenfunctions and eigenvalues of the outer, large scale motions obey a principle of Reynolds number similarity. Eigenvalue spectra contain much of the energy in the first few modes, but they are as broad as ordinary trigonometric power spectra. The rate at which the expansion converges to within 90% of the total energy decreases with increasing Reynolds numbers and the expansion of the mean plus the fluctuation converges more rapidly than the expansion of the fluctuation alone.
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47.27.T- Turbulent transport processes

Nonlinear flows along magnetic flux tubes: Mathematical structure and exact simple wave solutions

A. Ferriz‐Mas

Phys. Fluids 31, 2583 (1988); http://dx.doi.org/10.1063/1.866536 (11 pages) | Cited 5 times

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The mathematical structure of nonlinear, isentropic longitudinal flows of an ideal magnetohydrodynamic plasma confined to a magnetic flux tube embedded in a quiescent nonmagnetic fluid is investigated. Exact analytical solutions are derived for a special type of nonlinear flow in the absence of gravity: the simple waves, for which all the unknowns depend on single functions of space and time. These exhibit analytically the formation of shock waves. Emphasis is placed on new features introduced by the magnetic distensibility, which acts as an additional restoring force, as compared with the hydrodynamic flow of gas along a rigid tube. Introducing a series expansion in a suitable parameter, it is shown that the hydrodynamic problem can be considered as the zeroth‐order approach to the magnetic flux tube problem. Finally, the motion in a magnetic flux tube under the action of a piston advancing in a prescribed manner has been briefly considered. This problem is of current interest in relation to the generation of tube‐guided waves in the solar atmosphere.
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52.30.-q Plasma dynamics and flow
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Tc Shock waves and discontinuities
96.60.Ly Helioseismology, pulsations, and shock waves

Diamagnetic drift effects on ion Bernstein mode propagation in a plasma slab

R. D. Ferraro and B. D. Fried

Phys. Fluids 31, 2594 (1988); http://dx.doi.org/10.1063/1.866537 (8 pages) | Cited 1 time

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A one‐dimensional infinite‐order differential equation that describes the propagation of small amplitude electrostatic waves through a uniformly magnetized inhomogeneous plasma slab is derived. The spatially varying coefficients of the equation may be written in terms of an arbitrary density profile function provided that the velocity space distribution of the equilibrium is Maxwellian and the plasma is charge neutral. Ion Bernstein waves with frequencies between the first and second ion cyclotron harmonics and wavelengths along the density inhomogeneity larger than the ion Larmor radius are adequately modeled by truncating the differential equation at second order. Using a single mode electrostatic antenna to investigate the role of the diamagnetic drift on Bernstein wave propagation, a wavenumber dependence in the position of the low density cutoff for propagation is found, resulting in a preferential coupling of the antenna to waves with moderate kz∥ B propagating antiparallel to the ion diamagnetic drift. Moderate levels of Bernstein wave activity inside the plasma are demonstrated for an antenna located in the evanescent region.
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52.40.Fd Plasma interactions with antennas; plasma-filled waveguides
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
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