bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonlinear evolution of drift cyclotron modes
Authors: Aamodt R. E. , Cohen Bruce I. , Lee Y. C. , Liu C. S. , Nicholson Dwight R. , Rosenbluth M. N.
Published: March 2003

The space-time evolution of the drift-cyclotron instability as influenced by the nonlinear shift in the ion-cyclotron frequency is studied analytically, numerically, and by computer simulation. The analysis is specialized to the case of a single coherent wave with frequency near both a cyclotron harmonic and the ion diamagnetic frequency. Such an analysis is motivated by observations of large-amplitude ion-cyclotron waves in the 2XIIB mirror experiment, which were highly monochromatic and often exhibited these frequency characteristics. A nonlinear dispersion relation describing saturation of the instability is derived by means of a self-consistent analytical solution of the Vlasov–Poisson equations to third order in the wave amplitude. Solitary wave and self-similar solutions are obtained that describe nonlinear wave propagation. Numerical solution of a nonlinear evolution equation and particle simulation confirm the analysis.
Effects of toroidal coupling on the stability of tearing modes
Authors: Carreras B. , Hicks H. R. , Lee D. K.
Published: March 2003

The time evolution of tearing modes in toroidal geometry is studied in the low-β and large aspect ratio limit. An initial value three-dimensional computer code which numerically advances the reduced set of resistive magnetohydrodynamic equations is employed. Toroidicity has, in general, a destabilizing effect on tearing modes in this limit. A generalization of Δ′ formalism can be used to study the linear regime. The results obtained in this way are in very good agreement with the results from the initial value code. The nonlinear phase of the evolution is also followed numerically. In the case of strong interaction of different helicities, a larger region of stochastic magnetic field lines results than in the cylindrical geometry case.
Generalization of the Kelvin–Kirchhoff equations for the motion of a body through a fluid
Authors: Miloh T. , Landweber L.
Published: March 2003

The classical Kelvin–Kirchhoff equations of motion of a rigid body in an inviscid, unbounded fluid are generalized for the case where other fixed boundaries are present. An interesting by-product of the derivation is a relation, new to the authors, between the direction cosines of the body axes relative to fixed axes and kinematic parameters of the angular motion of the body.
Electrohydrodynamic stability in the presence of a thermal gradient
Authors: Castellanos A. , Velarde M. G.
Published: March 2003

The effect of a temperature-dependent dielectric constants is considered in the stability analysis of a liquid layer subjected to an electric field, weak unipolar injection, and temperature gradient.
Resonant shadowgraph and schlieren studies of magnetized laser-produced plasmas
Authors: Jellison G. , Parsons C. R.
Published: March 2003

Resonant shadowgraph and schlieren techniques provide instantaneous photographs of a laser-produced barium plasma flowing across a transverse magnetic field. The field is seen to impose considerable structure upon the expanding plasma. The flow separates into several well-defined regions, according to velocity. The slow plasma component displays internal striations. These are interpreted as shock waves excited by plasma flow across the field.
Nonlinear evolution equations, recurrence and stochasticity
Authors: Hafizi B.
Published: March 2003

Perturbative, spatially–periodic solutions of the Korteweg–deVries, the modified Korteweg–deVries, and the nonlinear Schrödinger equations are shown to be recurrent and nonstochastic, densely covering parts of the phase space bounded by level surfaces of the constants of motion. The connection of this result with the numerical phenomena of recurrences and the slow randomization of nonlinear systems is discussed.
Excitation of convection cells by ion-cyclotron waves
Authors: Rahman H. U. , Shukla P. K. , Das A. C.
Published: March 2003

It is shown that convective cells can be excited by large-amplitude propagating ion-cyclotron waves in a plasma. Using the two-fluid model, a coupled set of differential equations is obtained. A nonlinear dispersion relation for the modulational instability is then derived. This relation is investigated for different parameter regimes and expressions for the growth rates are obtained analytically. Relevance of the work to space physics as well as magnetically confined plasmas is discussed.
Nonlinear evolution of the ion beam mode
Authors: Honzawa T. , Hollenstein Ch.
Published: March 2003

The nonlinear evolution of the wave envelope of the fast ion beam mode has been studied experimentally. At large amplitudes above threshold, the beam mode is observed to be self-amplitude-modulated. When the self- modulation has fully evolved, the wave splits into a train of wave packets. Finally, it is shown that the self-modulation observed can be explained by a theory for the modulational instability.
Transport studies in reversed field theta pinches
Authors: Manheimer Wallace M. , Finn John M.
Published: March 2003

Anomalous transport in a reversed field theta pinch is examined. The principal effects are anomalous resistivity and rotation generation. Similarity solutions for the resistive decay are found which agree qualitatively with experiment. Also, it is shown that the spin up and anomalous resistivity may be the effect of a single underlying cause, a current-driven microinstability.
Collisional end losses from conventional and tandem mirrors
Authors: Catto P. J. , Bernstein Ira B.
Published: March 2003

A simple variational procedure is employed to obtain an analytic expression for the collisional particle end-loss rate in a mirror for the electrostatically confined species. The technique circumvents the need for an accurate solution for the distribution function, and is valid when both mirror ratio and barrier height are large, in which case it reproduces the previous results for the loss rate. The analytic result is also in reasonably good agreement with a numerical solution of the full linearized Fokker–Planck equation.
Kinetic theory of Bumpy Torus transport
Authors: Pao Young-Ping , Mond Michael
Published: March 2003

The poloidal electric field is included in the Elmo Bumpy Torus (EBT) transport theory. The contribution of the poloidal electric field to the particle and energy fluxes is seen to be comparable to that of the curvature and gradient drifts.
Decay of scalar variance in isotropic turbulence
Authors: Sreenivasan K. R.
Published: March 2003

Two consequences of a recent theory for the decay of scalar variance in isotropic turbulence are shown to be in essential agreement with measurements.
Stability of toroidal equilibria to uniform vertical displacements
Authors: Perrone M. R.
Published: March 2003

The energy principle is used to study the stability of an axisymmetric toroidal plasma to uniform vertical displacements ξz. It is shown that large-aspect-ratio configurations of circular cross section, can be stable to rigid vertical shifts even if the decay index N is not positive everywhere over the plasma surface.
Comments on ‘‘Effect of anisotropy and rotation on turbulence production’’
Authors: Tritton D. J.
Published: March 2003

The effect of rotation on the production terms in the turbulence energy equations is discussed. The resolution of a discrepancy among previous proposals for the condition of maximum production is indicated.
Reply to the comments by D. J.Tritton
Authors: Ferziger Joel H. , Shaanan Shlomo
Published: March 2003

There is no contradiction as Tritton has suggested, but there is an ambiguity that ought to be cleared up.
Excluded flux analysis of a field-reversed plasma
Authors: Tuszewski M.
Published: March 2003

The separatrix profile of a purely poloidal field-reversed configuration is determined from excluded flux data, allowing an improved determination of the plasma dimensions. Only gross features of the external separatrix, with scale lengths comparable to the coil radius, can be resolved.
Resistive ballooning modes
Authors: Strauss H. R.
Published: March 2003

Resistive ballooning modes are analyzed in the neighborhood of the magnetic axis. There are two mode branches, one connecting to the usual tearing mode and the other to the magnetohydrodynamic ballooning mode. Unstable modes satisfy the generalized tearing dispersion relation. Resistive ballooning modes can be unstable for a wide range of beta, but may be stabilized by interchange effects and finite sound speed. The analytic results are in qualitative agreement with low mode number numerical solutions.
Kinetic ballooning-interchange modes in tandem mirrors
Authors: Lee X. S. , Catto P. J.
Published: March 2003

A hybrid fluid-gyrokinetic derivation of the kinetic modifications to the ballooning-interchange eigenmode equation is presented which removes the large and small wave frequency restrictions of Tang and Catto. The derivation employs a long-thin ordering and an eikonal ansatz, but otherwise allows arbitrary asymmetry, beta, pressure anisotropy, and unperturbed parallel and perpendicular electrostatic field.
Finite Larmor radius stabilization of ballooning modes in tokamaks
Authors: Tsang K. T.
Published: March 2003

A ballooning mode equation that includes full finite Larmor radius effects has been derived from the Vlasov equation for circular tokamak equilibrium. A numerical solution of this equation shows that finite Larmor radius effects are stabilizing.
Invariants for the one-point vorticity and strain rate correlation functions
Authors: Siggia Eric D.
Published: March 2003

An algorithm to enumerate the number of independent scalars that determine the general tensor formed from n velocity gradients at a point in homogeneous-isotropic turbulence is elaborated for n = 4. The physical content of the invariants that result as well as their determination from experiment is discussed.
Structure of shock waves in gas-particulate fluidized beds
Authors: Fanucci Jerome B. , Ness Nathan , Yen Ruey-Hor
Published: March 2003

The structure of a two-phase shock wave in a gas-particulate fluidized bed is investigated. The present study gives (i) the jump relation across the two-phase shock, (ii) the critical condition beyond which the stable two-phase shock breaks up, and (iii) the distribution of the dependent variables through the two-phase shock and the two-phase shock thickness.
Heat flux induced wave fronts
Authors: Ahlborn Boye , Liese Wolfgang
Published: March 2003

The thermalization of a large energy flux W in a medium of density ρ leads to heat waves consisting of compression and expansion fronts, associated with substantial bulk motion. Particles can enter or leave the thermalization front at subsonic, sonic, or supersonic speed, allowing for a wide variety of wave modes. The wave mode depends on power input, thermodynamic response of the medium, and the boundary conditions. The intake Mach number mainly determines the degree of compression achieved across the front. Using macroscopic conservation equations the thermodynamic properties of the wave fronts are discussed in a pressure–density diagram and compared to other thermodynamic processes. The fluid dynamic properties are shown as a function of the absorbed power input W/ρ. Finally, the hydrodynamic properties of the entire two front heat wave are presented for specified boundary conditions in the response plane h–W/ρ, showing the enthalpy h of the heated target material as a function of an external energy flux W/ρ. Examples of the boundary conditions of free and retarded flow and heat transport due to inverse bremsstrahlung are discussed.
Quasi-steady expansion of plasma ablated from laser-irradiated pellets
Authors: Sanz J. , Liñán A. , Rodríguez M. , Sanmartín J. R.
Published: March 2003

The ablative, quasi-steady expansion of the spherical coronal plasma produced by irradiating an overdense pellet by a high-intensity laser pulse, is studied for large ion charge number Zi. The entire structure of the flow and its changes as the laser power is increased, are determined. The instantaneous power W required to generate a given ablation pressure Pa and pellet radius ra at any time is determined in terms of Zi, ion mass mi, and critical density; the mass ablation rate is also found. If the time law Pa(t) and (consequently) ra(t) for a desired optimal compression of the pellet are determined independently, the results allow one to obtain the laser power history W(t) = W[Pa(t), ra(t), Zi, mi,  nc]. For a critical radius much larger than ra, most of the energy flows outward; this seems to invalidate known simple estimates of the relation W(Pa).
Electron drift velocity deduced from lower oblique (whistler) resonance-cone measurements
Authors: Boswell R. W. , Thiel J.
Published: March 2003

Numerical solutions of the electrostatic wave equations in a field-angled, drifting Maxwellian magnetoplasma are fitted with measurements of lower oblique (Whistler) resonance-cone angles. The drift velocities so deduced are consistent with the Child–Langmuir law.
Dependence of stimulated Brillouin scattering on target material and f number
Authors: Clayton C. E. , Joshi C. , Yasuda A. , Chen F. F.
Published: March 2003

Stimulated Brillouin scattering of CO2 laser radiation from a pre-ionized gas target is observed and studied with the following parameter changes: (1) f/7.5 focusing versus f/2 focusing, (2) nitrogen plasma versus hydrogen plasma, (3) pure nitrogen versus nitrogen with a hydrogen impurity, and (4) single line operation of the laser versus multiline operation. The f-number dependence is found to be weak because the increased intensity with the smaller f number is offset by the shorter interaction length for the Brillouin instability. The instability growth in nitrogen is found to be more severe than in hydrogen because the nitrogen plasma has a higher ZTe/Ti resulting in a lower damping rate for the ion-acoustic wave. In all the above cases the Brillouin reflectivity reaches saturation and the inferred saturation amplitudes of the ion-acoustic waves are consistent with ion trapping being the saturation mechanism. Addition of a small amount (≃6%) of a light ion impurity (hydrogen) to a heavy ion plasma (nitrogen) virtually extinguishes the Brillouin instability. Finally, multiline operation of the CO2 laser pump, with the line separation Δω and the instability growth rate γ such that Δω/γ≫1, is seen to reduce the Brillouin reflectivity as if each line were acting independently, as expected.
Interaction of long-pulse CO2 laser radiation with solid targets
Authors: Lachambre J.-L. , Neufeld C. R.
Published: March 2003

The interaction of CO2 laser pulses of 25 nsec duration with solid targets for laser power densities up to 2×1012 Wcm−2 on target is described. Measurements were made of the plasma electron density, electron temperature, infrared plasma emission, and plasma blow-off ion velocity. The results are discussed in terms of their implications for future compression experiments involving long-pulse lasers.
Dielectric tensor of a weakly relativistic, nonequilibrium, and magnetized plasma
Authors: Tsai S. T. , Wu C. S. , Wang Y. D. , Kang S. W.
Published: March 2003

The dielectric tensor of a weakly relativistic magnetized plasma is discussed for wave frequencies very close to the fundamental or higher harmonics of the electron or ion cyclotron frequency. Since in real situations the plasmas of interest are often in nonequilibrium states, the present paper generalizes Shkarofsky’s result to include three nonequilibrium features; namely, a loss-cone distribution, anisotropic temperatures, and a field-aligned drift. The discussion is motivated by current interest in the study of absorption and emission of radiation near the electron cyclotron harmonics.
Absorption and emission of extraordinary-mode electromagnetic waves near cyclotron frequency in nonequilibrium plasmas
Authors: Wu C. S. , Lin C. S. , Wong H. K. , Tsai S. T. , Zhou R. L.
Published: March 2003

Two cases are investigated. In the first case the electron distribution is assumed to have a loss-cone feature. It is found that the plasma can amplify electromagnetic waves near the electron cyclotron frequency, as expected. However, the growth rate is significantly larger than that used in an approximate calculation in which a slightly different physical model was considered. The present discussion is restricted to the fast extraordinary- mode radiation. One of the important conclusions is that, due to the combined relativistic and loss-cone effects, the cutoff frequency can be lower than the electron cyclotron frequency, a result in contrast with that obtained with the usual ’’cold plasma’’ approximation. In the second case a drift motion along the ambient magnetic field is studied. It is found that the cyclotron damping can occur under certain conditions.
Electromagnetic radiation from an inhomogeneous plasma: Theory and experiment
Authors: Means R. W. , Muschietti L. , Tran M. Q. , Vaclavik J.
Published: March 2003

The problem of the linear conversion of a Langmuir wave to a transverse electromagnetic wave in the presence of a density gradient has been solved numerically with appropriate boundary conditions. A reciprocity principle was found, allowing the deduction of solutions of this problem from those obtained from the transverse-Langmuir conversion. This model has been applied to study the spectrum emitted from an inhomogeneous plasma, including the effect of the antenna radiation pattern. Experiments have been performed in a large unmagnetized dc discharge plasma (ne∼5×1010 cm−3, Te = 1.3 eV, gradient scale length L = 100−1000 cm). The shape of the spectrum observed with a horn antenna agrees with the theoretical one, but the deduced level of Langmuir fluctuations is much higher than the thermal level. This enhancement is due to the presence of primary energetic (E = 60 eV) electrons.
Kinetic theory of the plasma sheath transition in a weakly ionized plasma
Authors: Riemann K.-U.
Published: March 2003

The boundary layer of a weakly ionized rare gas discharge is treated using kinetic theory. A self-consistent two-scale analysis is performed and the exact presheath and sheath solutions are constructed for the following model: A plasma consisting of Boltzmann distributed electrons and singly charged atomic ions is in contact with a negative absorbing wall. The ion kinetics is dominated by charge exchange with cold neutrals (T0≪T−). The mean-free-path λ is constant and large compared with the electron Debye length λD. This model represents a collision-dominated counterpart to the well known Tonks–Langmuir model of the collision-free plasma.
Electron motion in a wave of slowly varying amplitude
Authors: Pocobelli G.
Published: March 2003

A theory of electron motion in a spatially sinusoidal wave of slowly varying amplitude is presented. On the basis of a reformulation of classical conservative motion, a set of approximate analytical, adiabatic solutions for the case of a temporally varying amplitude is derived. The set can describe electron transitions from trapped to untrapped conditions, or vice versa, and provides a formally unified description of both kinds of motion through Jacobi’s real transformation.
Damping of an electron plasma wave with detrapping of the electrons
Authors: Pocobelli G.
Published: March 2003

A self-consistent calculation of the damping of an electron plasma wave is presented including, for the first time, the contribution of all electrons (untrapped, detrapped, and trapped). The effect of the detrapped electrons, which is strong at the higher damping rates, is to lower the first minimum of the amplitude after the initial stage of Landau damping and the general level of its oscillation afterward. At γLτ0≊−0.75, a qualitative change is observed from amplitude oscillation to near-plateau behavior. The existence of an important secularity in the Vlasov–Poisson system is pointed out.
Anomalous impurity ion transport due to magnetic fluctuations
Authors: Hsu J. Y. , Harvey R. W. , Wong S. K.
Published: March 2003

A positive ambipolar potential arising from large transport rates of electrons relative to ions in stochastic magnetic fields gives an outward force on the ions. It can reverse the neoclassical inward convection of the impurity ions in tokamaks. This process may by responsible for the observed decays of line emissions from high charge states of silicon in an impurity study experiment in Alcator.
Magnetic field generation in the underdense plasma
Authors: Mora Patrick , Pellat René
Published: March 2003

Magnetic field generation in the underdense plasma due to the nonlinear interaction of an electromagnetic wave and a plasma is investigated. It is shown that the collisional absorption of the electromagnetic wave induces a nonlinear anistropy in the electron pressure tensor, which is responsible for a large source of the dc magnetic field. Six different regimes of interest appear, depending on four characteristic parameters related to the collision rate, the thermal effects, hydrodynamic convection, and the duration of the experiment. The theory is supported by a detailed comparison with recent microwave plasma experiments.
Necessary stability conditions for field-reversed theta pinches
Authors: Cary J. R.
Published: March 2003

Toroidal systems of arbitrary cross section without toroidal magnetic field are analyzed via the double adiabatic fluid equations. Such systems are shown to be unstable if there exists one closed field line on which the average of κrB2 is positive, where κ is the curvature. A similar criterion is derived for linear system and is applied to a noncircular z pinch.
Finite Larmor radius effect on thermosolutal instability of a plasma
Authors: Sharma R. C. , Sharma K. N.
Published: March 2003

The thermosolutal instability of a plasma in the presence of a transverse magnetic field is studied to include the effects of the finiteness of the ion Larmor radius. The finite Larmor radius and stable solute gradient are found to have stabilizing effects on stationary convection. The case of overstable modes is also considered wherein necessary conditions for the existence of overstability are derived.
Most probable magnetohydrodynamic tokamak and reversed field pinch equilibria
Authors: Ambrosiano John , Vahala George
Published: March 2003

The statistical theory of Montgomery, Turner, and Vahala, which determines the most probable ideal magnetohydrodynamic equilibrium compatible with given information on only a few global parameters (e.g., energy E, magnetic helicity H, flux Φ, current I, ⋅⋅⋅) is extended and investigated for both the tokamak regime (in which experimentally Φ≫μ0aI, with a being the plasma radius) and the reversed field pinch regime (Φ≪μ0aI). One obtains typical experimentally relevant profiles in the appropriate regimes. Most probable equilibria sequences are investigated as the energy/magnetic helicity ratio is decreased at fixed flux and current: In the tokamak regime (flux≫current) the diamagnetic toroidal field Bz becomes less diamagnetic and tends to a uniform field, while in the reversed field pinch regime (flux≪current), field reversal sets in Bz with the radial reversal position moving farther into the plasma and the eventual appearance of hollow pressure profiles. It appears that, in both regimes, the most probable equilibria are becoming more stable as μ0aE/H decreases. Linearized analytic force-free states can also be constructed for certain regimes of the global parameters together with their nonlinear quasi-force-free numerical counterparts.
Strongly-localized ballooning modes in an axisymmetric tandem mirror
Authors: D’Ippolito D. A. , Myra J. R.
Published: March 2003

A simple model of an axisymmetric tandem mirror without thermal barriers is employed to study the stability of ballooning modes which are confined to the central mirror cell. The central cell is treated as long-thin with isotropic pressure, while the end plug is modeled by a line-tying boundary condition. The scaling of βc with the mirror ratio R* and the connection length Lc is computed, and the sensitivity of these results to the magnetic field profile chosen is discussed.
Motion of a charged particle in a nearly axisymmetric magnetic field
Authors: Weitzner Harold
Published: March 2003

The motion of a charged particle in a static magnetic field is studied by means of repeated canonical transformations of a Hamiltonian system. Adiabatic invariants are generated based on the assumption that the particle Larmor radius is small compared with the characteristic distance over which the magnetic field varies. Unlike many earlier treatments the transformations presented here preserve the axisymmetry of the dynamics when the magnetic field is axisymmetric. It is assumed that the magnetic field consists of a small nonaxisymmetric part plus the axisymmetric toroidal and poloidal parts. After the introduction of the magnetic moment adiabatic invariant, the motion of the guiding center is studied. The results depend sensitively on the ratio of the poloidal magnetic field to the total magnetic field. In some cases a second adiabatic invariant exists and direct inferences concerning long time particle drifts are possible. In one case where a second adiabatic invariant fails to exist, long term drifts are studied by conventional perturbation expansions. At some points, resonance or lack of resonance phenomena appear and determine the drift effects.
Trapped electron modifications to tearing modes in the low collision frequency limit
Authors: Catto Peter J. , Rosenbluth M. N.
Published: March 2003

In the limit of weak collisions, a narrow boundary layer forms at the trapped/untrapped boundary in velocity space. When the electron collision frequency νe is small compared with the wave frequency ω times the inverse aspect ratio ε, a realistic collision operator must be employed to evaluate the response of the boundary layer electrons. The parallel current carried by the barely circulating boundary layer electrons results in tearing mode modifications which are evaluated from a slab model in the banana regime (νe<εω) by using a Lorentz model collision operator.
Lower-hybrid propagation cones and tail heating of electrons and ions
Authors: Matsuda Kyoko
Published: March 2003

Plasma heating by lower-hybrid waves has been studied using a two-and-one-half-dimensional electrostatic code with more realistic plasma and source models than previously used. Mode couplings between wavenumber modes of opposite sign occur when two propagation cones meet. The resulting smaller k∥ and/or higher ω modes propagate in the interior. These modes appear to be plausible mechanisms for tail heating of electrons and ions.
Laser induced density profiles in an isothermal plasma
Authors: Jones Roger D. , Aldrich C. H. , Lee K.
Published: March 2003

The absorption and scattering of laser light in laser fusion targets is very dependent on the exact form of the laser induced density profiles. The possible profiles that can exist are examined using a simple isothermal model. It is shown that four different structures are possible. The flow speed profiles and the speed of the critical surface are determined for each of these structures. It is shown that two of these structures are locally overdense and can exist in an underdense plasma, and thus may have a large effect on the amount of light reaching the critical surface.
Radial losses in high-β multiple mirror plasmas
Authors: Tuszewski M. , Lieberman M. A.
Published: March 2003

The importance of radial losses in collisional multiple mirror confinement is investigated for arbitrary values of β. Classical radial diffusion and complete fluid stability are assumed. Analytical and numerical solutions of the coupled axial and radial diffusion problem are found. The results can be characterized in terms of a single parameter α∼(τz/τx)1/2 where τz and τx are average values of the axial and radial confinement times. Radial losses are unimportant for α≲0.5 and improvement in overall confinement can be achieved by increasing β for these small values of α. When applied to existing reactor designs, the theory shows that radial losses are significant for one-component reactors but can be made negligible for two-component (wetwood burner) reactors.
Stimulated and spontaneous emission of acoustic waves from shock fronts
Authors: Fowles G. R.
Published: March 2003

In certain materials, shock waves of sufficient intensity spontaneously emit transverse rarefaction waves and are therefore unstable. A criterion is derived by calculating the relative amplitudes of reflected acoustic waves incident on the shock from behind. This criterion is found to delimit the conditions under which both acoustic amplification and acoustic emission can occur; it agrees with earlier results by Kontorovich.
Numerical modeling of an end-plugged theta pinch
Authors: Milroy Richard D. , Steinhauer Loren C.
Published: March 2003

Analytical and numerical studies of an end-plugged theta pinch are described. The analytical model treats the ablated plug plasma in the quasi-static limit where radiation losses balance energy flowing from the main plasma. This model is used to calculate the enhancement in energy confinement due to an ablating end plug for various plug species. The numerical model employs a one-dimensional, time-dependent magnetohydro-dynamic code. Results of calculations simulating the Scylla IV-P end-plugged theta pinch experiment are presented. The calculations achieve good agreement with the observed decay time of the energy line density. Moreover, the observed tendency toward longer decay times at lower atomic number is also predicted. However, certain notable discrepancies are found. For Si plugs, the calculations indicate a somewhat longer decay time than observed with SiO2 plugs. In addition, an axial compression wave driven by plug ablation causes the calculated energy line density to rise after 15 to 20 μsec which was not observed in the experiments. This is believed to be a feature of the one radial cell model which forbids axial wave dispersion; such dispersion would tend to mute the appearance of such waves. For fusion reactor scale plasma, the calculations predict that higher atomic number leads to negligible enhancements in confinement time.
Influence of equilibrium flows on the resistive internal kink and reconnecting modes
Authors: Galvão R. M. O. , Machado W. V. , Sakanaka P. H.
Published: March 2003

The effect of a finite diffusion velocity on the stability of the resistive internal kink and reconnecting modes is investigated. It is shown that the diffusion velocity modifies the growth rate of only the second mode.
Nonlinear diverging ion-acoustic waves
Authors: Okutsu E. , Schott L.
Published: March 2003

A unified analytical model is presented for sinusoidal diverging nonlinear ion-acoustic waves of plane, cylindrical, and spherical geometry. In contrast to plane waves, cylindrical and spherical waves do not show complete recurrence of the initial waveform.
Influence of ion motion in the inverse Faraday effect
Authors: Chian Abraham C.-L.
Published: March 2003

It is shown that ion motion can significantly affect the magnetic field generated by an intense circularly polarized electromagnetic wave in a plasma. For extremely strong waves, the magnetic field induced by the electron current in an electron-ion plasma can be nearly canceled by the ion current.
Initial damping of large amplitude waves
Authors: Sugihara R. , Yamanaka K. , Ohsawa Y. , Kamimura T.
Published: March 2003

Nonlinear damping rates of finite amplitude electrostatic waves are obtained by using an invariant perturbation method. The result is valid in an initial phase defined by 0<t≲tb≡r/wb (wb is the bounce frequency). As e‖f‖/T (f is the wave potential, and T is the temperature) increases, the nonlinear initial damping becomes significant and it dominates the linear damping rate gl when, for example, e‖f‖/T≳0.3 for k = 0. 2kD (kD the Debye shielding constant) and e‖f‖/T≳0.7 for k = 0.3kD. The theory does not assume a constant slope of the velocity distribution function f0 at the phase velocity vp since higher order derivatives of f0 at vp, ∂nf0/∂vpn (n = 3,5) play an essential role in enhanced damping. First, a dispersion relation is obtained, is solved for the Langmuir wave, and the theory is applied to an ion-acoustic wave. A simulation study is carried out on the latter wave. The result confirms the validity of the theory.
Onset of convection in a permeable medium between vertical coaxial cylinders
Authors: Bau Haim H. , Torrance K. E.
Published: March 2003

The onset of natural convection is examined for a fluid-saturated permeable medium contained between vertical coaxial cylinders of inner and outer radii r*i and r*0. The annular space is of height h*. The horizontal boundaries are isothermal, with heating from below and cooling from above. Both permeable and impermeable upper boundaries are considered. Critical Rayleigh numbers Rac and the preferred convective modes are determined as functons of the geometric ratios h*/r*i and r*0/r*i. The confining vertical walls of the annular space tend to increase Rac above the value for an infinite horizontal layer. The preferred modes are predominantly asymmetric.
A steady-state fluid model of a rotating plasma
Authors: Simpson S. W.
Published: March 2003

A steady-state, three-fluid model of the boundary layer in a rotating plasma is presented. Predictions of the model are compared with discharge voltage measurements from rotating plasma experiments. These measurements have previously been interpreted in terms of Alfvén’s critical velocity interaction. The model here, which takes centrifuging in the rotating plasma into account, offers an alternative description.
Modulational instability in a plasma with suprathermal electrons
Authors: Freund H. P. , Smith Robert A. , Papadopoulos K. , Palmadesso P.
Published: March 2003

The consequences of the presence of suprathermal electrons on the linear stage of modulational instabilities are investigated for a range of parameters appropriate to both laboratory and astrophysical plasmas. Substantial modifications to the growth rate and secondary spectrum are found to occur for instabilities driven by large amplitude Langmuir waves in the dipole limit due to the kinetic effects of the suprathermal electrons. In particular, for reasonable choices of pump amplitude and suprathermal energy density, additional modes become unstable.
Saturation of stimulated Brillouin scattering by ion wave decay in a dissipative plasma
Authors: Karttunen S. J. , McMullin J. N. , Offenberger A. A.
Published: March 2003

Secondary decay of an ion-acoustic wave is shown to provide an efficient saturation mechanism for stimulated Brillouin scattering in underdense plasma (n<0.5ncr). Phase effects and linear damping of ion waves are included in the analysis. In the weak damping regime, secondary decay dominates linear damping providing efficient saturation of Brillouin scattering. Heavy linear damping of ion waves increases the threshold for secondary decay considerably and very small densities are required to obtain saturation.
Nonlinear evolution of Buneman instability
Authors: Ishihara O. , Hirose A. , Langdon A. B.
Published: March 2003

The nonlinear evolution of one-dimensional electron-ion two-stream instability in a field-free plasma is studied both analytically and numerically (computer simulation). The instability is dominated by the fastest growing mode and its harmonics, provided that the initial fluctuation level is sufficiently small. A nonlinear dispersion relation is derived and solved numerically, taking into account; (a) the frequency and growth rate modulation, (b) the electric field up to ‖Ek‖4, and (c) the ’’renormalized’’ particle distribution functions. The model can successfully explain the results of a computer simulation, particularly the presence of an algebraic growth stage following the breakdown of the exponential linear growth, the appearance of harmonics, and the final saturation level. The minimum conductivity found scales as (M/m)0.61wpe, where M/m is the ion/electron mass ratio.
Nonlinear effects of ion cyclotron heating of bounded plasmas
Authors: Kindel J. M. , Lin A. T. , Dawson J. M. , Martinez R. M.
Published: March 2003

An investigation of space charge effects associated with moving ions across dc magnetic field lines due to ion cyclotron heating is investigated. Within an electrostatic approximation, an inductive electric field is imposed across a highly inhomogeneous plasma. Two and one-half dimensional particle simulations examine this problem when electron motion is allowed along but not across the magnetic field. Finite k∥ driving structures which allow electron flow, appear to greatly minimize both surface and volume ion space charge effects. Left-hand electric fields are observed in the plasma which are comparable to the vacuum left-hand field. Substantial ion heating occurs to the point where ion Larmor radii can be compared to a scale length.
Effect of resonance broadening on the evolution of the edge of a turbulent spectrum
Authors: Kritz Arnold H. , Fisch Nathaniel J. , Karney Charles F. F.
Published: March 2003

The extent to which nonlinear wave-particle resonance broadening results in a narrowing of an incident lower-hybrid wave spectrum is investigated. This narrowing is of concern because it could make control of lower-hybrid heating difficult. It is shown numerically, however, that relatively uniform spatial power deposition occurs if resonance broadening effects are treated consistently on both the wave spectrum and the particle distribution.
Doppler shift of laser light reflected from expanding plasmas
Authors: Dewandre Thierry , Albritton James R. , Williams E. A.
Published: March 2003

The Doppler shift of light reflected from a plane stratified expanding plasma is analyzed. Nonlinear effects are not considered and oblique incidence is restricted to the case of s polarization. The frequency shift is shown to consist of two components, one due to the motion of the reflecting surface, and another due to plasma flow through that surface. The shifts have a different dependence on the angle of incidence. Typically, the two contributions are comparable in laser fusion applications, being of order dw/w∼cs/c∼10−3, where cs = (Z Te/M)1/2 is the ion sound speed in the underdense plasma. In general, the Doppler shift has a time variation which induces a bandwidth in the reflected wave.
Global stability of the Burgers’ vortex
Authors: Leibovich S. , Holmes Philip
Published: March 2003

Global monotonic stability of the Burgers’ vortex is studied using the energy method, and it is shown that no finite critical viscosity exists for the problem. For bounded domains, a criterion is established which ensures that the energy of any perturbation of bounded support initially decreases.
Asymptotic form of the longitudinal correlation function for isotropic homogeneous turbulence
Authors: Rosen Gerald
Published: March 2003

The Fourier interference inequality on the Hopf characteristic functional, ‖F[y,t]‖<1 for ‖curl y‖≠0, is shown to imply that f(r,t)∝ (a positive function of t) r−3 as r→∞.
Neoclassical ion heat flux in the presence of a poloidally asymmetric heat source
Authors: Wong Seung Kai , Burrell Keith H.
Published: March 2003

The ion radial heat flux in a tokamak resulting from collisions and guiding center drifts is shown to be given by Q = −nx[(∂Ti/∂r)+jeBR(SQ/nTi)] in the presence of a poloidally asymmetric heat source whose sinq component is SQ.
Perpendicular electron cyclotron resonance heating by ordinary modes
Authors: Kuo S. P. , Cheo B. R.
Published: March 2003

Electron heating at resonance by the ordinary mode is analyzed. The equations of motion are integrated along the resonance trajectory showing no parallel heating. Evolution of the distribution functions shows that T⊥ grows exponentially in t2 for second harmonic heating and algebraically at the fundamental.
Lower-hybrid-drift instability with axis encircling ions
Authors: Myra J. R. , Catto Peter J. , Aamodt R. E.
Published: March 2003

The stability of a cylindrical plasma to electrostatic flute perturbations in the ion-cyclotron to lower-hybrid frequency range is considered. The analysis exploits the large growth rates of these modes to reduce the governing radial eigenvalue problem from an integral equation to a second-order differential equation, but allows treatment of arbitrary ion Larmor radius to plasma radius. The fastest growing modes of the ion guiding-centers-on-axis model are shown to connect onto the lower-hybrid-drift modes of local slab theory. Numerical and analytical results for growth rates and most unstable mode numbers are obtained.
Resistive instabilities in reversed-field confinement configurations without shear
Authors: Galvão R. M. O. , Santiago M. A. M.
Published: March 2003

A resistive mode with azimuthal mode number m = 1 is shown to exist in reversed-field confinement configurations without shear. The mode has an almost constant radial profile from the magnetic axis to the radius where the magnetic field vanishes; its growth rate scales with the 1/3 power of the plasma resistivity, and the corresponding perturbed displacement parallel to the field lines is much larger than the perpendicular one in the resistive region. This mode may lead to the splitting of the plasma column into many rings, and may also be a triggering mechanism for the rotational m = 1 instability that is observed in q-pinch discharges.
Langmuir collapse in a weak magnetic field
Authors: Goldman Martin V. , Weatherall J. C. , Nicholson Dwight R.
Published: March 2003

With magnetic fields that are not too weak, Langmuir collapse times can be prolonged and the packet geometry significantly distorted.
On Stokes flow of a Newtonian fluid through a pipe with stationary random surface roughness
Authors: Phan-Thien N.
Published: March 2003

The problems of Stokes’ flow through corrugated pipes are considered. The corrugations are of small amplitude e and are modeled by stationary random noises. A perturbation solution [up to O(e2)] is developed showing that the pressure drop enhancement is an order O(e2) effect and is always positive. Furthermore, for slowly varying corrugations, the pressure drop enhancement depends on the statistics of the corrugations em(z) only through its mean square e2<m2≳ and can be predicted by the simpler lubrication approach.
Thermal mixing layer downstream of half-heated turbulence grid
Authors: LaRue John C. , Libby Paul A.
Published: March 2003

Additional experimental results relative to the temperature in the thermal mixing layer downstream of a partially heated turbulence grid are given. Comparison is made of the distributions of mean temperature and temperature intensity with previous data. New results correspond to the characteristics of the higher moments, to the probability density functions at various points within the mixing layer, and the thickness of the temperature interface on the cold side of the layer. The present inability to predict the peak value of the temperature intensity is discussed.
Similar solutions in modified cumulant expansion
Authors: Kida Shigeo
Published: March 2003

A method of matching is applied to the energy spectrum equations in the modified cumulant expansion theory for Burgers and two- and three-dimensional Navier–Stokes turbulence, in order to investigate the asymptotic behavior of the energy spectrum in the limit of large Reynolds number and time. It is shown analytically that the spectrum has a similar structure with respect to both Reynolds number and time, and that there is no single similarity law which is valid throughout the wavenumbers, but instead there are several subranges of the wavenumbers which have different similarity laws.
Cubic turbulence: A model problem
Authors: Hansen P. J. , Nicholson Dwight R.
Published: March 2003

Many of the equations encountered in fluid dynamics and plasma physics are cubically nonlinear. The properties of a relatively simple statistical theory of cubically nonlinear equations, analogous to Kraichnan’s direct interaction approximation for quadratically nonlinear equations, are explored. Its predictions are compared with the numerical solution of a set of equations called the random-coupling model; good agreement is found.
Two-dimensional simulation of the formation of the Princeton spheromak
Authors: Lui H. C. , Chu C. K. , Aydemir A.
Published: March 2003

Various schemes proposed for the creation of the spheromak in the Princeton S1 experiment are simulated by our two-dimensional, time-dependent, compressible, resistive hydromagnetic code. In these schemes, the toroidal fields and poloidal currents in the plasma are induced by a solenoidal discharge in a core, while a toroidal coil inside the core produces the major part of the initial poloidal fields, as well as the main plasma toroidal current. Poloidal fields are reversed by programming current reversal in the toroidal coil. Poloidal field reconnection, toroidal field compression, and plasma accumulation into a spheromak geometry are achieved in the various schemes with or without the aid of pinching coils. For several schemes, using proper programming of currents, realistic parameter values give effective spheromak formation.
Effect of finite electron drift velocity on the resonant excitation of a nonuniform plasma
Authors: Morales G. J. , Lamb B. M. , Adler E. A.
Published: March 2003

An exact analytic solution of the external resonant excitation of a nonuniform plasma in the presence of a zero order finite electron drift is presented. The process of linear mode conversion of the long wavelength external radiation, of frequency w, into a Langmuir wave limits the peak amplitude of the cold plasma resonance at w = wp, where wp is the local electron plasma frequency. The finite electron drift alters the effective group velocity of the Langmuir wave, and thus it modifies the peak amplitude of the resonance in a significant manner. For drifts toward the overdense side an amplitude enhancement is obtained, while for drifts toward the underdense side a severe quenching takes place. The effect is governed by a single scaled drift parameter u = (2vd/3v̄) (3wpL/v̄)1/3, and significant modifications arise when ‖u‖≳1. Here, vd is the small drift velocity, v̄ is the electron thermal velocity, and L is the density scale length.
Transport of runaway and thermal electrons due to magnetic microturbulence
Authors: Mynick H. E. , Strachan J. D.
Published: March 2003

The ratio of the runaway electron confinement to thermal electron energy confinement is derived for tokamaks where both processes are determined by free streaming along stochastic magnetic field lines. The runaway electron confinement is enhanced at high runaway electron energies due to phase averaging over the magnetic perturbations when the runaway electron drift surfaces are displaced from the magnetic surfaces. Comparison with experimental data from LT-3, Ormak, PLT, ST, and TM-3 indicates that magnetic stochasticity may explain the relative transport rates of runaways and thermal electron energy.
Optical ray retracing of Brillouin backscatter from a nonisothermal plasma
Authors: Lehmberg R. H. , Tripathi V. K. , Liu C. S.
Published: March 2003

The optical ray retracing of stimulated Brillouin backscatter from a laser fusion plasma has been studied, including the effects of density gradient and flow velocity and allowing the acoustic wave to be weakly damped. The pump is comprised of two plane uniform beams propagating at some angle with respect to each other, producing an interference pattern that behaves as an active grating for the scattered radiation. When the convective loss due to plasma inhomogeneity is small, Bragg diffraction of the scattered radiation results in the reproduction of the same transverse spatial structure as the pump, i.e., the two beams are retraced. However, when the convective loss dominates, the Bragg diffraction is severely affected and the scattered radiation no longer reproduces both beams of the pump with equal intensities or in the correct backward directions.