Steven Zalesak

• (interested citizen)

The Nernst effect plays the dominant role in the subsonic transport of magnetic flux in magnetized high-energy-density (HED) plasmas, where the plasma beta is high and the temperature diffusivity is much greater than the magnetic diffusivity. This parameter range is characteristic of the Magnetized Liner Inertial Fusion and other magnetoinertial fu...

A family of exact self-similar solutions of the compressible Euler equations developed for hydrocode verification is described. This family generalizes the classic Noh problem, which has served as a standard verification test of numerical methods for modeling inviscid compressible flows for three decades. This generalization allows finite pressure...

The ablative Rayleigh-Taylor (RT) instability is a central issue in the performance of laser-accelerated inertial-confinement-fusion targets. Historically, the accurate numerical simulation of this instability has been a challenging task for many radiation hydrodynamics codes, particularly when it comes to capturing the ablatively stabilized region...

The magnetized liner inertial fusion (MagLIF) approach to inertial confinement fusion [1] involves subsonic/isobaric compression and heating of a deuterium-tritium plasma with frozen-in magnetic flux by a heavy cylindrical liner. In order to understand the transport of magnetic flux, a recent paper [2] developed self-similar solutions in one dimens...

Stagnation of a cold plasma streaming to the center or axis of symmetry via an expanding accretion shock wave is ubiquitous in inertial confinement fusion (ICF) and high-energy-density plasma physics, the examples ranging from plasma flows in x-ray-generating Z pinches [Y. Maron et al., Phys. Rev. Lett. 111, 035001 (2013)] to the experiments in sup...

Stagnation of a cold plasma streaming to the center or axis of symmetry via an expanding accretion shock wave is ubiquitous in inertial confinement fusion (ICF) and high-energy-density plasma physics, the examples ranging from plasma flows in x-ray-generating Z pinches [Y. Maron et al., Phys. Rev. Lett. 111, 035001 (2013)] to the experiments in sup...

The magnetized liner inertial fusion (MagLIF) approach to inertial confinement fusion [Slutz et al., Phys. Plasmas 17, 056303 (2010); Cuneo et al., IEEE Trans. Plasma Sci. 40, 3222 (2012)] involves subsonic/isobaric compression and heating of a deuterium-tritium plasma with frozen-in magnetic flux by a heavy cylindrical liner. The losses of heat an...

The MagLIF approach to inertial confinement fusion involves subsonic/isobaric compression and heating of a DT plasma with frozen-in magnetic flux by a heavy cylindrical liner. The losses of heat and magnetic flux from the plasma to the liner are thereby determined by plasma advection and gradient-driven transport processes, such as thermal conducti...

The classic Noh problem [1] describes in simple analytic formulae the divergent hydrodynamic shock resulting from the stagnation of a supersonic flow against a wall, axis, or point. It has been used for years as a verification test for simulation codes. In a recently published work the cylindrical version of the Noh problem was generalized to the m...

One component of the MagLIF approach to inertial fusion ignition involves compression and heating of a DT plasma with frozen-in magnetic flux by a heavy cylindrical liner. The liner implosion velocity most of the time is lower than the speed of sound in the compressed DT plasma, which makes the plasma motion subsonic and isobaric. The losses of hea...

Recent designs for laser driven, direct drive inertial confinement fusion (ICF) indicate that substantial gains (G>100) might be achieved with lower total laser energy (E∼500 kJ) than previously considered possible. A leading contender is the shock ignition approach which compresses low aspect ratio pellets with high intensity laser pulses (1015 W/...

Krypton-fluoride laser is an attractive inertial fusion energy driver from the standpoint of target physics. Target designs taking advantage of zooming, shock ignition, and favorable physics with KrF reach energy gains of 200 with sub-MJ laser energy. The designs are robust under 2D simulations. Experiments on the Nike KrF laser support the physics...

We will present results from follow-on experiments to the record-high velocities achieved using the ultra-uniform deep-uv drive of the Nike KrF laser [Karasik et al, Phys. Plasmas 17, 056317 (2010)], in which highly accelerated planar foils of deuterated polystyrene were made to collide with a witness foil to produce ˜1 Gbar shock pressures and res...

form only given. It had been noticed long ago that the requirements for inertial confinement fusion (ICF) ignition in a cylindrical target can be significantly relaxed if the plasma were compressed simultaneously with the flux of the entrained magnetic field from its seeded value 4100 kG to the peak value of 4100 MG. The ultrahigh axial magnetic fi...

A self-similar solution is derived for a radially imploding cylindrical plasma with an embedded, azimuthal magnetic field. The plasma stagnates through a strong, outward propagating shock wave of constant velocity. This analysis is an extension of the classic Noh gasdynamics problem to its ideal magnetohydrodynamics (MHD) counterpart. The present e...

We will present results from follow-on experiments to the record-high velocities of 1000 km/s achieved on Nike [Karasik et al, Phys. Plasmas 17, 056317(2010)], in which highly accelerated planar foils of deuterated polystyrene were made to collide with a witness foil to produce ˜1 Gbar shock pressures and result in heating of matter to thermonuclea...

Advanced simulations of high energy density Z-pinch plasmas involve 2D and 3D computer codes. The classic Noh problem of a strong, self-similar expanding shock accreting inflowing gas of constant velocity is often used for verification of hydrodynamic codes. The more relevant test of the M in MHD appropriate for a stagnating pinch are the new, exac...

We report on the status of directly driven shock ignition targets designed for mega-joule scale laser drivers. We have examined the impacts of laser-plasma-instability (LPI) induced intensity limitations and hydrodynamic instability on the gain and robustness of these targets. Increasing the target's initial aspect ratio will limit the drive intens...

Recent progress of impact ignition is reported: First, a maximum velocity ∼ 1000 km/s has been achieved under the operation of NIKE KrF laser at Naval Research Laboratory (laser wavelength = 0.25µm) in the use of a planar target made of plastic. Two-dimensional simulation have been performed for burn and ignition to show the feasibility of the impa...

form only given. Advanced simulations of high energy density plasma involve 2D and 3D computer codes. To ensure reliable results such codes should be subjected to verification tests, i.e., compared against exact analytic solutions. The present work examines the appropriateness of the 3D Cartesian code Athena for modeling stagnating Z-pinch implosio...

Recent 3D RMHD simulations at Sandia and experiments at Weizmann Institute of Science have demonstrated that axially and azimuthally averaged dynamics of a strongly radiating stagnated Z-pinch column resembles a self-similar, cylindrically symmetric motion. The cold, rapidly imploding plasma transforms into the hot stagnated plasma heated and compr...

We report 1D and 2D numerical and theoretical investigation of the thermal neutron production in deuterium and DT 100-300 ns Z-pinch implosions driven by the currents now accessible on refurbished Z and higher. On-axis plasma compression and thermal fusion neutron yield have been found to increase if D in the outer shell is replaced with a high-Z g...

The stagnation phase of a Z pinch is examined for two alternative scenarios: (i) the reflection of a dense shell off of a hot but low density core, and (ii) the expansion of a shock wave from the axis as it accretes inflowing material. The former case is characteristic of 1D Lagrangian simulations and the latter is an extension of Noh's classic pro...

ICF direct-drive targets perform best when the pressure of the driving pulse is maximized: the targets can then be designed with small aspect ratios that are more hydrodynamically stable. However the drive pressure in direct drive targets is limited by laser plasma instabilities, which must be avoided to limit unwanted preheat of the fusion fuel. I...

We will present results from follow-on experiments to the record-high velocities of 1000 km/s achieved on Nike [Karasik et al., Phys. Plasmas 17, 056317 (2010) ], in which highly accelerated planar foils of deuterated polystyrene were made to collide with a witness foil to produce extreme shock pressures and result in heating of matter to thermonuc...

Detailed spatially resolved spectroscopic analysis of a neon gas puff z pinch on the Weizmann 1 MA generator indicates that the radius of the K-shell emitting region grows to a maximum and then decreases during the radiation pulse1,2. ID Lagrangian simulations show the opposite trend because the emission arises from the inside surface of a dense sh...

In this paper, we report on recent numerical simulations of inertial-confinement-fusion (ICF) implosions using the FAST radiation hydrocode at the U.S. Naval Research Laboratory. Our study focuses on three classes of shock-ignited target designs utilizing less than 1 MJ of direct, krypton-fluoride (KrF) laser energy, which was ``zoomed'' to maximiz...

The Nike krypton fluoride laser [ S. P. Obenschain, S. E. Bodner, D. Colombant, et al., Phys. Plasmas 3, 2098 (1996) ] is used to accelerate planar plastic foils to velocities that for the first time reach 1000 km/s. Collision of the highly accelerated deuterated polystyrene foil with a stationary target produces ∼ Gbar shock pressures and results...

In inertial confinement fusion (ICF), the possibility of ignition or high energy gain is largely determined by our ability to control the Rayleigh-Taylor (RT) instability growth in the target. The exponentially amplified RT perturbation eigenmodes are formed from all sources of the target and radiation non-uniformity in a process called seeding. Th...

Continuing work in the design of shock ignition targets is described. Because of reduced implosion velocity require-ments, low target adiabats, and efficient drive by short wavelength lasers, these targets produce high gain (> 100) at laser energies well below 1 megajoule. Effects of hydrodynamic instabilities like Rayleigh-Taylor or Richtmyer-Mesh...

The kinetic theory is developed for the mass mixing of two incompressible immiscible fluids due to Rayleigh-Taylor instability (as an example for turbulence in variable-density statistically inhomogeneous incompressible fluids). An expression is derived for the fine grain force in terms of the mass-density and velocity fields. This expression enabl...

Shock ignition target designs can produce high gains at modest driver energies.footnotetextR. Betti, C.D. Zhou, K.S. Anderson, et al., Phys. Rev. Lett. 98, 155001 High resolution 2D simulations that include nominal pellet perturbations have shown that gains well over 100 can be generated with targets driven by short-wavelength sub-megajoule KrF las...

Accurate shock timing is a key issue of both indirect- and direct-drive laser fusions. The experiments on the Nike laser at NRL presented here were made possible by improvements in the imaging capability of our monochromatic x-ray diagnostics based on Bragg reflection from spherically curved crystals. Side-on imaging implemented on Nike makes it po...

Experimental study of a shock-decelerated ablation front is reported. A planar solid plastic target is accelerated by a laser across a vacuum gap and collides with a lower-density plastic foam layer. While the target is accelerated, a fast Rayleigh-Taylor (RT) growth of the seeded single-mode perturbation at the ablation front is observed. After th...

New approaches in target design have increased the pos-sibility that useful fusion power can be generated with sub-MJ lasers. We have performed many 1D and 2D simulations that examine the characteristics of target designs for sub-MJ lasers. These designs use the recently-proposed shock-ignition target scheme, which utilizes a separate high-intensit...

The NRL SAMI3 three-dimensional simulation code is used to examine the effect of meridional winds on the growth and suppression of equatorial spread F (ESF). The simulation geometry conforms to a dipole field geometry with field-line apex heights from 200 to 1600 km at the equator, but extends over only 4 degrees in longitude. The full SAMI3 ionosp...

In inertial confinement fusion (ICF) and high-energy density physics (HEDP), the most important manifestations of the hydrodynamic instabilities and other mixing processes involve lateral motion of the accelerated plasmas. In order to understand the experimental observations and to advance the numerical simulation codes to the point of predictive c...

In our experiments done on the Nike KrF laser, we study instability growth at shock-decelerated interfaces in planar colliding-foil experiments. We use streaked monochromatic (1.86 keV) x-ray face-on imaging diagnostics to measure the areal mass modulation growth caused by the instability. Higher x-ray energies up to 5.25 keV are used to follow the...

We discuss the development of high-gain directly-driven targets for energy applications. We have simulated, in 1D and 2D, implosions of both conventional and shock-ignition targets in the low energy regime (

We report on recent numerical simulations with the FAST radiation hydro-code of direct-drive target implosions. Our discussion focuses on both conventional and ``shock-ignited'' target designs that utilize about 1 MJ of KrF laser light. Each class of designs has its own advantages, but it appears that shock-ignited targets may be superior in that g...

The problem we wish to address is that of accurately modeling the evolution of small-amplitude perturbations to a time- dependent flow, where the unperturbed flow itself exhibits large-amplitude temporal and spatial variations. In particular, we wish to accurately model the evolution of small-amplitude perturbations to an imploding ICF pellet, whic...

Interest in experiments on colliding planar CD foils has recently been stimulated by (a) the Impact Fast Ignition approach to laser fusion [1], which involves the collision of a shell accelerated to ˜1000 km/s with high-density DT fuel, and (b) the approach to a high-repetition rate ignition facility based on direct drive with the KrF laser and a v...

Interest in experiments on colliding planar foils has recently been stimulated by (a) the Impact Fast Ignition approach to laser fusion [1], and (b) the approach to a high-repetition rate ignition facility based on direct drive with the KrF laser [2]. Simulating the evolution of perturbations to such foils can be a numerical challenge, especially i...

A major challenge for direct-drive inertial fusion energy (IFE) is to create targets that produce significant gain and yet are resistant to the hydrodynamic instabilities that degrade yield. The seeds for these instabilities are the imperfections in both target manufacture and laser illumination. We consider fabrication flaws that occur primarily a...

The response of a shock front to small preshock nonuniformities of density, pressure, and velocity is studied theoretically and numerically. These preshock nonuniformities emulate imperfections of a laser target, due either to its manufacturing, like joints or feeding tubes, or to preshock perturbation seeding/growth, as well as density fluctuation...

New direct-drive laser target designs with KrF laser light take advantage of the shorter wavelength to lower the laser energy required for substantial gain (>30x) to sub-MJ level. These low laser-energy pellets are useful in systems that could form an intermediate step towards fusion energy, such as the proposed Fusion Test Facility [S. P. Obenscha...

We report an experimental study of hydrodynamic Rayleigh-Taylor and Richtmyer-Meshkov-type instabilities developing at the material interface produced in double-foil collisions. Our double-foil targets consist of a plastic foil irradiated by the 4 ns Nike KrF laser pulse at ˜50 TW/cm^2 and accelerated toward a stationary plastic or foam foil. Eithe...

Recent proposed designs (Obenschain et al., Phys. Plasmas 13 056320 (2006)) for direct-drive ICF targets for energy applications involve high implosion velocities combined with higher laser irradiances. The use of high irradiances increases the likelihood of deleterious laser plasma instabilities (LPI) that may lead, for example, to the generation...

Theoretical work has shown that a short sub-ns laser pulse (spike) and a rarefaction wave behind it shape a density/adiabat gradient in the target that suppresses laser imprint, reduces the RT seeding due to the surface roughness, delays the onset [1] and reduces the rate [2] of the RT perturbation growth in the target. At the same time, the decayi...

Recent work by various authors has suggested that there are hydrodynamic advantages to using ``spikes'' or ``pickets'' prior to the driving laser pulse in ICF target interactions. These spikes can suppress laser imprint [1] and reduce the growth rate of the Rayleigh-Taylor instability of targets by tailoring the target's adiabat (increasing the abl...

A study--based on simulations and experiments as well as analytical derivations--of the internal structure of the fragmented ("mixed") state induced by the Rayleigh-Taylor instability at the interface between two fluids is presented. The distribution of sizes and the energy spectrum in the fragmented state are derived from the symmetries exhibited...

A study, based on simulations and experiments as well as analytical derivations, of the fragmented (``mixed'') state induced by the Rayleigh-Taylor instability at the interface between two fluids is presented. The distribution of sizes and the energy spectrum in the fragmented state are derived from the symmetries exhibited by the data. The exact (...

The problem we wish to address is that of accurately modeling the evolution of small-amplitude perturbations to a time- dependent flow, where the unperturbed flow itself exhibits large-amplitude temporal and spatial variations. In particular, we wish to accurately model the evolution of small- amplitude perturbations to an imploding ICF pellet, whi...

Recent advances in inertial confinement fusion (ICF) technology serve to ensure that imploding laser-driven ICF pellets will spend a significantly larger portion of their time in what is regarded as the ``linear'' portion of their perturbation evolution, i.e., in the presence of small-amplitude but nonetheless evolving perturbations. Since the evol...

An expansion wave is produced when an incident shock wave interacts with a surface separating a fluid from a vacuum. Such an interaction starts the feedout process that transfers perturbations from the rippled inner (rear) to the outer (front) surface of a target in inertial confinement fusion. Being essentially a standing sonic wave superimposed o...

The numerical tools typically used to model the evolution of fluid instabilities in inertial confinement fusion hydrodynamics codes are examined, and some are found to have properties which would seem to be incompatible with the accurate modeling of small-amplitude perturbations, i.e., perturbations in the linear stage of evolution. In particular a...

When attempting to numerically model a physical phenomenon of any kind, we typically formulate the numerical requirements in terms of the range of spatial and temporal scales of interest. We then construct numerical software that adequately resolves those scales in each of the spatial and temporal dimensions. This software may use adaptive mesh ref...

Targets have been designed that produce moderate to high gain when directly driven by lasers. The intrinsic sensitivity of these targets to hydro instabilities is found using the FAST(2D) multidimensional radiation hy-drocode [J.H. Gardner, A.J. Schmitt, J.P. Dahlburg, et al., Phys. Plasmas 5, 1935 (1998)], which simulates the simultaneous behavior...

Targets have been designed that produce moderate to high gain when directly driven by lasers. The intrinsic sensitivity of these targets to hydro instabilities can be vetted using ablative Richtmyer-Meshkov (RM) and Rayleigh-Taylor (RT) growth formulæ combined with the Haan saturation model and Bell-Plesset convergence effects. However, this stabil...

Modern front-capturing methods, such as flux-corrected transport (FCT) methods, total variation diminishing (TVD) methods, and high order Godunov methods (e.g., MUSCL, PPM, ENO, WENO, and discontinuous Galerkin methods), were developed to address the numerical difficulties that one encounters when attempting to solve problems where discontinuities...

The numerical modeling of inertial confinement fusion is but one among many fields that rely heavily on the use of shock-capturing methods, i.e., numerical methods robust enough to deal with the formation of shocks and other discontinuities in the numerical solution of partial differential equations. The more modern of such methods divide naturally...

Numerical simulations are presented of the evolution of overexpanding coronal mass ejections (OCMEs), which are also magnetic clouds. The OCME is assumed to arise from the evolution of a magnetic flux rope with high plasma and magnetic pressure and high plasma density near the Sun in a high-speed solar wind. It is shown that the flux rope maintains...

Dynamics are investigated for buoyant flux ropes in a gravitationallystratified solar atmosphere using realistic chromosphere and corona parameters. Two-dimensional magnetohydrodynamic simulations of horizontally-oriented flux ropes are performed under the approximation that the flux rope remains parallel to the solar surface as it rises. As expect...

We describe the basic physics of the gradient-drift instability and the collisional Rayleigh-Taylor instability, the two plasma instabilities which dominate the production of small-scale structure in the earth's ionosphere. We then focus our attention on the nonlinear evolution of these instabilities for two particular cases: 1) the recursive bifur...

[The following work was planned but was not completed. - MLR] Solar coronal activity is intimately connected with emerging magnetic flux. In this work we explore this connection through numerical simulation; we model the emergence of magnetic flux into the solar corona. We have previously seen emerging magnetic flux drive surge-like waves in our m...

We present the first results from a new unstructured mesh three dimensional finite element MHD code which uses dynamic solution-adaptive mesh refinement in a manner similar to our two dimensional finite element MHD code /31/. The problem being considered here is the interaction of the solar wind with the earth's magnetosphere, using a three-dimensi...

The collisional Rayleigh-Taylor instability plays a crucial role in explaining the onset and development of equatorial spread F. A number of linear and nonlinear analyses of the instability have been developed for the F region that include recombinative damping. It has been argued that recombination damps the unstable density perturbations and prov...

Magnetohydrodynamic simulations of the evolution of a flux tube accelerated through a stationary magnetized plasma are presented. As the flux tube moves through the external plasma, its shape becomes distorted and reconnection can take place between the flux tube and external fields. The coupling between the moving flux tube and the external plasma...

We describe a particle in the cell scheme which incorporates finite elements in space and finite difference in time to follow the trajectories of particles in their self consistent fields. As such the model exploits the power of finite element techniques to better investigate the rich physics embedded in the particle or kinetic models. A brief desc...

A finite element MHD algorithm is used to simulate a two-dimensional, viscous and resistive turbulent model, namely the Orszag-Tang vortex. The results are compared to a pseudo-spectral simulation of the same system reported by Dahlburg and Picone (Phys. Fluids B 1 (1989) 2153). The agreement of results from both methods supports the contention tha...

Two dimensional magnetohydrodynamic simulations are presented of the distortion of a magnetic flux rope that is being accelerated through ambient solar wind plasma. The flux rope magnetic field has an axial component parallel to the solar wind field and an azimuthal component, which lies in the simulation plane. As the flux rope moves through the s...

Two dimensional magnetohydrodynamic simulations of the distortion of a magnetic flux tube, accelerated through ambient solar wind plasma, are presented. Vortices form on the trailing edge of the flux tube, and couple strongly to its interior. If the flux tube azimuthal field is weak, it deforms into an elongated banana-like shape after a few Alfven...

Three methods are described to obtain ionospheric electron densities from transionospheric, rocket-beacon TEC data. First, when the line-of-sight from a ground receiver to the rocket beacon is tangent to the flight trajectory, the electron concentration can be obtained by differentiating the TEC with respect to the distance to the rocket. A similar...

The results of fully three-dimensional numerical simulations of ionospheric plasma cloud evolution are presented. The evolution of the plasma cloud considered by Drake and Huba (1987) in the limit of vanishingly small ion compressibility is discussed. Simulations support the results of the analytical theory: finite plasma temperature, combined with...

The Naval Research Laboratory high latitude ionosphere-magnetosphere mesoscale coupling model has been generalized to include scale-size dependent magnetospheric coupling and E-region Hall and Pedersen conductivity effects. With this model, the nonlinear evolution of plasma interchange-like instabilities in the high latitude F-region ionosphere has...

Without Abstract

A simple model is postulated for the freezing scale in nuclear plumes, whose success depends strongly on the high M ratios of nuclear plumes, and on the existence of some mechanism which causes the slab growth rate gamma(k) to be sharply peaked when regarded as a function wavenumber k. Although the model derivation is quite different from another m...

The role of magnetic viscosity (i.e., Larmor radius effects) and collisional viscosity on the Ex B gradient drift instability is investigated in both the collisional and inertial regimes. The equations describing the time evolution of small perturbations to an equilibrium two dimensional (x,y) magnetized plasma are derived where the equilibrium ele...

In this paper we will present the first fully three-dimensional analytic study of plasma cloud dynamics, as well as computational results based upon a recently developed three-dimensional electrostatic code. We derive a stability criterion for the large-scale structuring of an ionospheric cloud based on a water bag model for the special case Lz = r...

The first numerical simulations of the nonlinear evolution of the electrostatic Kelvin-Helmholtz (K-H) instability with ionospheric Perderson conductivity coupling are presented. It is found that the K-H instability develops in a distinctly different manner in the nonlinear regime with Pedersen coupling than without it. Pedersen coupling effects, i...

Simulation results, based on a field-line-integrated, two-dimensional, electrostatic model, are presented for the motion of a barium cloud injected transverse to the geomagnetic field in the ionosphere at high speeds. It is found that the gross evaluation of injected plasma clouds depends on the initial conditions, as well as the nature of the back...

A magnetic-field-line-integrated model of plasma interchange instabilities is developed for the high latitude ionosphere including magnetospheric coupling effects. We show that primary magnetosphere-ionosphere coupling effect is to incorporate the inertia of the magnetospheric plasma in the analysis. As a specific example, we present the first simu...

Computer simulation studies have described the vertical and horizontal characteristics of plasma depletions in the equatorial ionosphere. Those results have been used to generate the airglow signatures of two F-region emissions (6300 A and 7774 A) that can be used to relate observed morphologies to theoretical models. The airglow patterns that emer...

We present a relatively simple analysis of the gradient drift instability in barium clouds which includes the effects of both finite temperature and finite parallel length. It is found that short-wavelength modes are stabilized as the electrons redistribute parallel to the magnetic field and neutralize the charge imbalance set up by the instability...

We postulate that under realistic ionospheric conditions, barium ion clouds hundreds of meters in diameter can be long-lived, quasi-stable, nonbifurcating structures. These structures may resemble “tadpoles,” with a dense head, steep density gradients at the front, and a long, less dense tail. We assume that these structures are the final products...

A simple model is used to show that the finite parallel length of ionospheric plasma clouds can affect the growth rate of striation instabilities (e.g., gradient drift). The finite parallel length of plasma clouds tends to favor the growth of striations with short perpendicular wavelengths.

We show that under realistic ionospheric conditions, barium ion clouds hundreds of meters in diameter can be long-lived, quasi-stable, nonbifurcating structures. These structures may resemble tadpoles, with a dense head, steep density gradients at the front, and a long, less dense tail. We assume that these structures are the final products of the...

We examine the linear stability of the steepened backside of two-dimensional ionospheric barium clouds. We derive expressions for the growth rate of perturbations on these backsides which are functions of (1) the ratio M of the integrated Pedersen conductivity inside the barium cloud to that of the background ionosphere; (2) the overall shape of th...

Derived is a general, nonlocal dispersion equation which describes the long wavelength limit of several interchange instabilities (viz., Rayleigh-Taylor, E x B gradient drift, and current convective). Analytical expressions for the growth rate of these modes are presented in both the collisional and collisionless regimes. The scaling of these growt...

Several aspects concerning the phenomenology of barium cloud striations still lack a satisfactory explanation. The motivation for the present investigation was an unexplained phenomenon known as 'freezing'. For the purposes of the current study, the term 'freezing' is defined to mean the cessation of bifurcation on the part of a specific ionospheri...

We describe in qualitative terms the cause and nonlinear evolution of the gradient drift and collisional Rayleigh-Taylor instabilities in the earth's ionosphere, by using the examples of ionospheric barium clouds and equatorial spread F 'bubbles' respectively. We then derive the nonlinear differential equations governing these instabilities. Finall...

The E x B instability is basically an interchange mode and can be excited in a weakly collisional, inhomogeneous, magnetized plasma containing a neutral wind or an ambient electric field orthogonal to the magnetic field. This instability is regarded as important in the structuring of ionospheric plasmas. An analytical expression is presented for th...

The possibility of artificially inducing the onset of equatorial spread F by the collision dominated Rayleigh-Taylor or ExB gradient drift instability mechanism via a hypothetical chemical release in the equatorial ionosphere is considered. Each of the factors affecting the outcome of such an experiment is examined, and recommendations are made wit...

Theoretical and numerical simulation techniques have been employed to study ionospheric F region plasma cloud striation phenomena, equatorial spread F phenomena, and high latitude diffuse auroral F region irregularity phenomena. Each of these phenomena can cause scintillation effects. The results and ideas from these studies are state-of-the-art, a...