bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of strong inhomogeneities on high-frequency mirror-drift-cone and convective-loss-cone instabilities
Authors: Davidson R. C. , Gladd N. T.
Published: March 2003

The basic linear local theory of the mirror-drift-cone and convective-loss-cone instabilities is extended to include modifications due to strong spatial inhomogeneities (‖∂lnN/∂x‖−1=LN≲rLi), assuming high-frequency perturbations characterized by ωci≪‖ωr+ iγ‖≈ (ωceωci)1/2 and k2yr2Li≫1. The continuous deformation of the convective-loss-cone instability from a regime where maximum growth occurs for k⋅B0≠0 (weak inhomogeneities) to a regime where maximum growth occurs for k⋅B0=0 (strong inhomogeneities) is investigated. Moreover, it is found that the reference dispersion relation for the mirror-drift-cone instability (derived in the weak inhomogeneity limit with r2Li≪L2n) gives a remarkably good (albeit fortuitous) estimate of the linear growth rate even when rLi≳Ln. Finally, we compare several properties of the mirror-drift-cone and convective-loss-cone instabilities (loss-cone ions) with properties of the lower-hybrid-drift and modified-two-stream instabilities (Maxwellian ions).
Unified formalism of lower hybrid parametric instabilities in plasmas
Authors: Tripathi V. K. , Grebogi C. , Liu C. S.
Published: March 2003

A unified theory of parametric instabilities in the lower hybrid frequency region is formulated using the drift kinetic equation for electrons and the Vlasov equation for unmagnetized ions. The three wave decay process into various decay channels (viz., two lower hybrid waves, lower hybrid and ion acoustic waves) are examined and compared for various pump frequencies and powers. Nonlinear scattering rates by electrons and ions (i.e., nonlinear Landau damping) are evaluated and compared with previous calculations. It is seen that the dominant channel of decay is through ion acoustic and lower hybrid waves when Te/2Ti≳4 and through lower hybrid waves and lower hybrid quasi-modes when Te/2Ti<4.
Evolution and thermonuclear yield of a high β plasma column
Authors: McMullin J. N. , Capjack C. E.
Published: March 2003

The evolution of a high β linear ϑ pinch plasma is investigated by assuming a square density profile. A new analytic solution for the self-similar area wave is found for the case β=1, γ=2 and an exact integral of the motion of the reflected area wave is derived in the general case. The evolution of the plasma variables in the region between the reflected area waves is calculated numerically. Except for cases in which (1−β)1/2 is approximately equal to a/b (plasma radius/solenoid radius), the density in this region is a slowing varying function of position. The relative fusion power production and total energy field is estimated, assuming constant temperature, for combinations of β and b/a relevant to two conceptual designs. It is found that in most cases significant power is produced after the area waves have reflected from the midplane of the solenoid. The model predicts that programming the applied magnetic field to simulate infinite b/a enhances the yield by approximately 85% for a 3-m neutron source but only by approximately 18% a 1-km fusion reactor.
Energy loss rates of energetic ions injected into the FM-1 spherator
Authors: Davis S. L. , Arunasalam V. , Hawryluk R. J. , Okabayashi M. , Schmidt G. L. , Schmidt J. A. , Suckewer S.
Published: March 2003

Energy loss rates of energetic ions were studied during neutral beam injection experiments on the FM-1 spherator. Under typical experimental conditions, the injected beam ions slowed-down on the plasma electrons resulting in electron heating. The measured slowing-down rate was found to be in agreement with classical predictions.
Adiabatic modifications to plasma turbulence theories
Authors: Catto P. J.
Published: March 2003

Improved particle trajectories are employed to treat the adiabatic or Maxwell–Boltzmann response of a plasma in order to choose between contradictory prescriptions for obtaining the nonlinear dispersion relation from the linear one.
Model of the Rayleigh-Taylor stability of an ablating fluid
Authors: Catto Peter J.
Published: March 2003

An incompressible and inviscid model for the Rayleigh–Taylor stability of an ablating fluid in the absence of convection is presented and solved analytically for boundary conditions appropriate to laser produced plasmas. The wavenumbers k perpendicular to the density gradient of scale length L are found to be relatively insensitive to ablative stabilization for the most unstable radial eigenmodes, k2L2≳1.
Interaction of electromagnetic waves with a moving ionization front
Authors: Lampe Martin , Ott Edward , Walker Jerome H.
Published: March 2003

The problem of an electromagnetic wave packet, incident on a relativistically moving plane ionization or recombination front in a stationary gas, is considered. The frequency of the reflected wave packet is found to obey the usual double Doppler shift relation. However, the reflection coefficients and the physics can differ significantly from the case of reflection from moving material objects. In the unmagnetized case, the ratio of the energy in the reflected wave packet to that in the incident wave packet is found to be εr*/εi*=ωi*/ωr* for an oncoming overdense ionization front, for which ωi*<ωr* (where ωi* and ωr* are the incident and reflected wave frequencies in the laboratory frame). For an oncoming ionization front in the presence of an applied magnetic field normal to the front, εr*/εi* can considerably exceed ωi*/ωr*. For a retreating recombination front (ωi*≳ωr*), in the overdense unmagnetized case, εr*/εi*=ωr*/ωi*. These results have important implications for the production of sub-millimeter wavelength pulses by upshifted reflection from a relativistically moving ionization front.
Ponderomotive force and dc magnetic field generation induced by laser absorption
Authors: Woo Wee , DeGroot J. S.
Published: March 2003

A new expression for the ponderomotive force induced by high frequency electromagnetic and electrostatic waves propagating in plasma including the effects of dissipation is derived. Besides the usual irrotational leading term, a new simpler expression for the leading rotational term, which can contribute to the generation of mega-Gauss dc magnetic fields is found. The leading irrotational term is proportional to the dissipation rate and vanishes for a standing wave. This expression is applied to the absorption of a planar electromagnetic wave, with polarization in (p) or out of (s) the plane of incidence, obliquely incident onto a half-space of plasma with a linear density profile. The result for the dc magnetic field source term compares very well with the result from a two and one-half dimensional particle simulation calculation for p polarization. Direct acceleration by the resonantly excited electrostatic waves is the dominant dissipation process in this case. At high power, the dominant dissipation process for s polarization is parametric decay into plasma waves which are Landau damped by the electrons. The magnetic field source term is found to be comparable to that of p polarization.
Experiments on current-driven three-dimensional ion sound turbulence. Part I: Return-current limited electron beam injection
Authors: Stenzel R. L.
Published: March 2003

The injection of an electron beam into a weakly collisional magnetized background plasma is investigated experimentally. The beam-plasma system is so large that boundary effects are unimportant for establishing the current flow. It is shown that the injected beam current is balanced by a field-aligned return current provided by background electrons drifting toward the beam source. The conditions for an ion sound instability driven by the return current are met. The maximum injected beam current is found to be limited to the background electron saturation current to the beam source.
Irreversible thermodynamics of thermoviscous solids with microstructures
Authors: Lam L. , Lax M.
Published: March 2003

The irreversible thermodynamics of viscous solids with microstructures is developed in a new approach. In this general theory, the ’’particle’’ in the continuous medium is a composite ’’molecule.’’ The field equations describing the motions of the mass points making up the molecule are written down in terms of an internal energy potential U and a dissipation function D. The irreversible mechanical force acting on the mass point is related to D. The conservation laws of momentum, energy, and angular momentum are derived from the spatial invariance properties of U and D, and are thus automatically satisfied. The balance of entropy is a built-in process. The cases of anisotropic liquids and liquid crystals can be developed in a similar fashion.
Parametric excitation of coupled plasma waves
Authors: Kuo S. P. , Cheo B. R.
Published: March 2003

A general approach to analyze the parametric decay processes of plasma waves is presented. The approach is based on the modal Hamiltonians of the decay waves and is valid for all wave types. In the limiting cases of B0=0 and of longitudinal waves, results of previous investigations are recovered. Comparisons with experiments are favorable.
Guiding center helically symmetric plasmas
Authors: Schmidt Michael J. , Vahala George
Published: March 2003

The stability analysis of nearly cylindrical magnetically confined plasma is generalized to include the effects of pressure anisotropy. Specifically, the equilibrium and normal mode equations for helically symmetric plasmas are derived and it is shown that these equations reduced to all previous diffuse profile bumpy theta pinch and helical calculations. The equations presented are valid for arbitrary helical wavenumber k, arbitrary degree of helicity L, and O (δ0) pressure anisotropy, where δ measures the percent deviation of the plasma surface from that of a cylinder. Numerical calculations of the effect of pressure anisotropy on locally unstable modes are presented.
Cascade and collapse of Langmuir waves in two dimensions
Authors: Nicholson Dwight R. , Goldman Martin V.
Published: March 2003

The temporal evolution of intense Langmuir waves in an unmagnetized plasma of two spatial dimensions is studied numerically. When the inequality W≳ (kλe)2 is satisfied, the evolution quickly leads to a state of collapsing solitons. Here, W is the ratio of electric field energy density to the particle kinetic energy density, k is a typical Langmuir wavenumber, and λe is the electron Debye length.
Light absorption by ion acoustic turbulence in laser-produced plasmas
Authors: Manheimer Wallace M. , Colombant Denis G.
Published: March 2003

A review of experiments on light absorption by laser-produced plasmas is presented and the need for another efficient absorption mechanism besides resonant absorption is clearly demonstrated. Laser light absorption by ion acoustic fluctuations is proposed as the missing absorption mechanism. Calculations of this absorption mechanism in a magnetized plasma are then presented.
Experiments on the injection, confinement, and ejection of electron clouds in a magnetic mirror
Authors: Eckhouse S. , Fisher A. , Rostoker N.
Published: March 2003

A cloud of (5 to 10 keV) electrons is injected into a magnetic mirror field. The magnetic field rises in 40–120 μsec to a maximum of 10 kG. Two methods of injection were tried: In the first, the injector is located at the mirror midplane and electrons are injected perpendicular to the magnetic field lines. In the second scheme, the injector is located near the mirror maximum. Up to about 1011 electrons were trapped in both schemes with a mean kinetic energy of 0.3 MeV. Measured confinement time is limited only by the magnetic field decay time. The compressed electron cloud executes electrostatic oscillations. The frequency of the oscillation is proportional to the number of electrons trapped, and it is independent of the value of the magnetic field and the initial electron energy. The electron cloud was ejected along the mirror axis and properties of the ejected electron cloud were measured by x-ray pulses from bremstrahlung of electrons on the vacuum system wall and by collecting electrons on a Faraday cup.
Stabilization of the axisymmetric instability in the poloidal divertor experiment tokamak
Authors: Jardin S. C.
Published: March 2003

Passive stabilization, associated with the mutual inductances of the field shaping coils with the plasma and with each other, can stabilize the axisymmetric magnetohydrodynamic instability in the Princeton poloidal divertor experiment device that was observed in earlier numerical studies.
Self-consistent theory of cyclotron maser instability for intense hollow electron beams
Authors: Uhm Hwan-sup , Davidson R. C. , Chu K. R.
Published: March 2003

A self-consistent theory of the cyclotron maser instability, assuming azimuthally symmetric perturbations about a slowly rotating hollow electron beam propagating parallel to a uniform axial magnetic field B0êz is developed. The stability analysis is carried out within the framework of the linearize Vlasov–Maxwell equations. It is assumed that the beam is thin with radial thickness (2a) much smaller than the beam radius (R0), and that ωp2/ω2c≪1, where ωp and ωc are the electron plasma frequency and electron cyclotron frequency, respectively, in a frame of reference moving with the beam axial velocity cβb. The analysis is carried out for the specific choice of equilibrium electron distribution function in which all electrons have the same value of canonical angular momentum and the same value of energy in a frame of reference moving with axial velocity cβb. Stability properties are investigated including the important influence of finite radial geometry, finite beam temperature, and transverse magnetic perturbations (δB≠0). It is shown that instability exists for a very narrow range of axial wavenumbers satisfying ‖k−βbω/c‖≪1/R0. Detailed stability properties are calculated for a variety of system parameters.
Stability of laminar flows of micropolar fluids between parallel walls
Authors: Kuemmerer Harro
Published: March 2003

Numerical results on the stability of laminar flow of micropolar fluids between two parallel walls are presented. A sixth-order stability eigenvalue problem is obtained by the usual perturbation techniques and solved by means of Noumerov difference approximations and the Newton iteration method. As far as the model considered in the present investigation is concerned, the microstructure has a destabilizing effect on two-dimensional flows of micropolar fluids.
Laboratory study of the growth of a turbulent layer of fluid
Authors: Dickinson Stuart C. , Long Robert R.
Published: March 2003

An experiment was designed to measure the position of a front separating turbulent and nonturbulent fluid as the front moves away from an oscillating grid located near the plane z=0. The theory predicts D∝ (Kt)1/2, where D is the distance of the front from z=0, t=0 is time at which the oscillation begins, and K is a quantity of the dimensions and character of eddy viscosity, called the ’’action’’ of the idealized plane energy source that replaces the grid in the theoretical model. The experimental results support the theory.
Unstable behavior of hot, magnetized plasma in contact with a cold wall
Authors: Lindemuth I. R. , Pettibone J. S. , Stevens J. C. , Harding R. C. , Kraybill D. M. , Suter L. J.
Published: March 2003

The behavior of a hot, magnetized plasma brought into contact with a cold wall is studied numerically in one and two dimensions. A fully nonlinear, time-dependent magnetohydrodynamic plasma model which includes thermal conduction, resistive diffusion, radiation, and ionization is used. The model is solved numerically with an Eulerian computer code which employs implicit finite difference methods. One-dimensional calculations for cylindrical geometry examine the effect of the electrical properties of the wall on the plasma. Two-dimensional calculations for cylindrical geometry show the formation of a wall-induced instability which enhances thermal conduction losses from the plasma; the re-emergence of short wavelengths, a new feature of unstable behavior, is evident in the calculations. Two-dimensional calculations for toroidal geometry show that heat losses to a cold wall lead to double-vortex convection flow of the plasma with no evidence of the formation of smaller scale convective cells.
Density dependence of electron cyclotron heating rate in a toroidal octupole
Authors: Wong K. L.
Published: March 2003

Electron cyclotron heating rates have been measured for low density plasmas (ωpe≪ω) in a toroidal octupole by the sweep method with resonance zones situated near the minor axis of the torus. The energy absorbed by the plasma from the 100 mW frequency sweep oscillator is determined from the broadening of the cavity modes. The scaling of heating rate with plasma density differs from previous results of high frequency (9.6 GHz) cavity mode measurements. The difference is explained by the accessibility of the waves to the resonance zones.
Characterization of turbulent temperature ramps by two length scales
Authors: Freymuth P.
Published: March 2003

The average length and amplitude of sawtooth temperature ramps observed in heated turbulent shear flows are large scales. The length of the steeper slope of the sawtooth has to be a temperature small scale to obtain Reynolds number independence of the temperature derivative skewness.
Augmentation of mixing across a diaphragm in a normal electric field
Authors: Hoburg James F. , Malihi Farrokh
Published: March 2003

Electrohydrodynamic mixing of liquids with differing conductivities through a diaphragm is induced by normal electric field. Mass transfer rates are described by diffusion coefficient proportional to electric pressure/viscosity and are compared with the corresponding rates in a tangential electric field.
Three-dimensional effects on nonlinear mode-converted lower-hybrid waves
Authors: Kuehl H. H.
Published: March 2003

The effect of the third dimension of nonlinear mode-converted lower-hydrid waves is considered. The nonlinear differential equation governing these waves is derived.
Self-similar motion of laser half-space plasmas. II. Thermal wave and intermediate regimes
Authors: Sanmartín Juan R. , Barrero A.
Published: March 2003

The one-dimensional self-similar motion of an initially cold, half-space plasma of electron density n0, produced by the (anomalous) absorption of a laser pulse of irradiation φ=φ0t/τ (0<t⩽τ) at the critical density nc, is considered; the analysis, which allows for electron heat conduction and ion-electron energy exchange, involves three dimensionless numbers: ε≡ nc/n0 assumed small, Zi (ion charge number), and a parameter α∝ (n02τ/φ0)2/3. For α≪1, a weak discontinuity develops, separating a thermal wave (where convection is negligible) moving into the undisturbed plasma, from a much thinner isothermal flow expanding into the vacuum. For 1≪α≪ε−4/3, there is an isentropic compression flow between a shock, bounding the undisturbed plasma, and a very thin transition layer bounding an expansion flow, much larger in extent than the compression region. In both regimes, the critical plane lies far in the expansion tail. The results break down when the density is so small that the plasma becomes collisionless. The analysis is also invalid for α too small. Using results previously found for α≫ε−4/3, a qualitative discussion of how plasma behavior changes with α, is given.
Inflows, density currents, and fronts
Authors: Kao Timothy W. , Park Cheol , Pao Hsien-Ping
Published: March 2003

The inflow of a fluid of different density into an ambient fluid of uniform density and finite depth is studied numerically using the full Navier–Stokes and diffusion equations. The problem is posed as an initial-boundary-value problem. In both the overflow (lighter buoyant inflow) and underflow (heavier inflow) cases, a gravity current is established with a pronounced headwave. A significant feature of the flows is the presence of strong downwelling (overflow case) and upwelling (underflow case) activity near the front. The overflow case has been applied by Kao, Park, and Pao to the study of small-scale oceanic fronts formed by the river discharge into the coastal region. The present paper deals with the fluid mechanical and numerical aspects of the overall problem in addition to presenting the results of the underflow case. It is found that the characteristics of the flow in the near field of the inflow are mainly governed by an inflow densimetric Froude number, Fe. In particular, the flow regime in the near field gradually changes from a plume-like to a jet-like behavior as Fe changes from less than to greater than unity. For the overflow case the local densimetric Froude number Fd of the current is shown to be a constant and a similarity solution is found in the far field behind the headwave giving a universal result for the density and velocity structure in the vertical for the range of parameters explored.
Convergent kinetic equations in the theory of transport properties in multicomponent ionized gas mixtures
Authors: Luchina A. A.
Published: March 2003

The classical unified theory of relaxation phenomena in hot fully ionized gases is applied to multicomponent gas mixtures composed of electrons and several types of ions. The theoretical expressions containing exact numerical factors in the arguments of Coulomb logarithms are developed for the bracket integrals needed in the computations of the third approximations to the thermal and the electrical conductivities, and the diffusion coefficients of multicomponent gas mixtures at intermediate and full ionization within the framework of the Chapman–Enskog–Burnett method.
Analysis of spherically imploding shocks
Authors: Fujimoto Y. , Mishkin E. A.
Published: March 2003

The self-similar solution of spherically imploding shock waves is derived analytically for a perfect gas with a constant ratio γ =cp/cv. The basic conservation equations are reduced to a first-order differential equation in the x- y plane. The requirement of a maximum for the pressure curve dictates the values of the self-similar exponent αm. These values are compared with the previously derived numerical values of αm. When γ=2+√3, the maximum of the pressure occurs at the shock front. The pressure curve then decreases monotonically.
Pellet ablation in hot plasmas and the problem of magnetic shielding
Authors: Lengyel L. L.
Published: March 2003

Shock wave analyses and shielding models pertaining to pellet ablation phenomena are reviewed. Some inconsistencies are shown to exist in some of the studies available. Models are developed and estimates are given for pellet ablation rates in hot plasmas with and without magnetic fields present. The possible existence of a self-regulating ablation mechanism is indicated.
Ion sound turbulence in a magnetoplasma
Authors: Gekelman W. , Stenzel R. L.
Published: March 2003

An experimental investigation of current-driven ion sound turbulence in a collisionless magnetized plasma column is presented. Frequency and wave vector spectrum of the saturated instability are analyzed. The cross-power spectral density of probe signals shows that waves are localized in k space both in the electron drift direction and along the instability cone of angle ϑ=arc cos(cs/vd) ≲90°. In spite of good plasma uniformity, azimuthal asymmetries in wave propagation are noticed. The self-consistent electron distribution function deviates from a shifted Maxwellian.
Dynamics of test particles in a turbulent magnetoplasma
Authors: Stenzel R. L. , Gekelman W.
Published: March 2003

Small diameter, low energy test electron and ion beams are injected into a collisionless magnetoplasma in which current-driven ion sound turbulence is generated independently. The spatial diffusion coefficient of electrons across B0 is measured and found to exhibit Bohm scaling. Electrons are strongly scattered in velocity space from short wavelength fluctuations. Electron heating does not arise from parallel electric fields and anomalous resistivity but from randomizing the injection energy acquired at a sheath potential drop. Test ion diffusion in real and velocity space is strongly enhanced at the wave-particle resonance. Fast ion tails in the background distribution are formed.
Electron energy distribution of a mirror confined relativistic plasma inferred from synchrotron radiation measurements
Authors: Tsakiris G. D. , Boyd D. A. , Hammer D. A. , Trivelpiece A. W. , Davidson R. C.
Published: March 2003

Properties of a relativistic electron plasma confined in a magnetic mirror field are investigated by measuring the synchrontron radiation emitted in the 12.4–18.0 GHz frequency range. The measured spectra are recorded in a sufficiently short interval of time so that the confining magnetic field can be regarded as constant. The spectra are unfolded to obtain the electron energy distribution f (γ) during the decay of the confining magnetic field. The energy distribution obtained in this manner is compared with that calculated from a theoretical model that utilizes a self-consistent equilibrium distribution function f0e(x,p). This model takes into account the influence of strong spatial inhomogeneities and large Larmor orbits on the emission spectrum. The comparison between theory and experiment yields information about the evolution of such quantities as the radial electron density profile, ne0(r). An analysis of the data shows that n0e(r) evolves from a relatively thin E layer to a diffuse profile with density buildup on axis.
Boundary value problems for three-dimensional plasmas
Authors: Guernsey Ralph L.
Published: March 2003

The full three-dimensional Maxwell–Vlasov system is solved as a boundary value problem for systems contained by plane, perfectly reflecting boundaries. The spatial behavior of the fields seems to contradict some commonly made assumptions. In particular, for low frequency, ω≪ωp, and typical plasma densities, all components of the electric and magnetic fields decay to zero on a scale which is no larger and 0.05 cm.
Bernstein waves, parametric instabilities, and magnetic shear
Authors: Sperling J. L.
Published: March 2003

The effect of magnetic shear on electrostatic Bernstein waves is investigated. It is shown that shear leads to nonlocal eigensolutions and the convective damping of the Bernstein waves. The threshold for the parametric instability of a magnetosonic wave into two Bernstein waves in a multispecies plasma is increased by shear. For a magnetosonic heating experiment conducted on a tokamak comparable to the Doublet III device at General Atomic, the parametric instability may still be excited despite the plasma inhomogeneities provided the pump wave amplitude exceeds a critical value to be estimated in this paper.
Ergodic behavior of lower hybrid decay wave ray trajectories in toroidal geometry
Authors: Wersinger Jean-Marie , Ott Edward , Finn John M.
Published: March 2003

In cylindrical geometry, as a result of both magnetic shear and density gradient there exist radially trapped lower hybrid decay waves bouncing back and forth in the low density region of the plasma. If this situation persists in toroidal geometry, it could have a severely destabilizing effect on the nonresonant parametric decay of an externally launched lower hybrid heating wave. However, it is shown here that weak toroidicity causes some of these waves to follow ergodic ray trajectories, and hence to be detrapped and to reach their lower hybrid resonance. The fraction of waves which shows ergodic behavior increases as the aspect ratio R0/a decreases. For realistic aspect ratios, i.e., R0/a≲5, nearly all the rays are ergodic and energy flows toward the resonance. The consequences for lower hybrid wave heating are discussed.
Universal drift instability from single-particle approach
Authors: Chan V. S. , Wong Seung Kai
Published: March 2003

An exact evaluation of the universal drift instability growth rate in a magnetic field with zero shear is presented. It is based on an asymptotic expansion of the energy equation for large time, in which the change in the kinetic energy of the plasma due to interaction with the wave is obtained from a single particle approach.
Small Reynolds number nearly isotropic turbulence in a straight duct and a contraction
Authors: Bennett J. C. , Corrsin S.
Published: March 2003

Measurements have been made of nearly isotropic, low Reynolds number, grid-generated turbulence. The decay results agree with the predictions for ’’final period’’ isotropic turbulence decay (in time) by the linear approximation of von Kármán and Howarth, and Batchelor and Townsend. This agreement occurs in spite of the fact that at the smallest turbulence Reynolds number attained, Rλ≈4, the inertial (triple velocity correlation) term in the double velocity correlation equation is not negligible as assumed in the theoretical estimates. As in experiments of Batchelor and Stewart, the turbulence shows appreciable departure from isotropy, indicated by component energy inequality growth downstream. It is also shown by nonzero velocity skewness, not reported heretofore at small Rλ. Measurement of the effect of a secondary contraction on small Reynolds number turbulence indicates that the contraction has less effect than at larger Reynolds numbers.
On inertial motion
Authors: Faller Alan J.
Published: March 2003

For a medium whose motion is described by v̇+B×v=0, where B is perpendicular to the two-dimensional velocity v, the trajectory of each element of the medium is a circle that is determined by the initial value of v. Through a transformation of coordinates the differential equation for the (transformed) velocity derivative matrix is U̇+U2=−I, a special Ricatti equation for which the solution is known. This allows the determination of ∇⋅v, ∇×v, and other functions of the velocity derivatives until the time of formation of a shock.
Theory of the classical electron gas
Authors: Guernsey Ralph L.
Published: March 2003

It is shown that the apparent divergences in the Meeron expansion for the properties of the classical equilibrium electron gas, suggested by Cohen and Murphy, can be resolved by a more careful treatment of the region of small particle separation. Explicit expressions are given for the ε4 (lnε)2 and ε4 lnε corrections to the equation of state.
Quantum plasmas. II: The high frequency conductivity of a magnetized plasma
Authors: Jones Roger D.
Published: March 2003

The high frequency conductivity of a magnetoplasma is calculated from a fully convergent quantum mechanical kinetic equation. The frequency of the perturbing field is not restricted to frequencies low in comparison with the plasma frequency nor is the temperature of the unperturbed plasma restricted to values low in comparison with a Rydberg.
l=1,2 high-beta stellarator
Authors: Bartsch R. R. , Cantrell E. L. , Gribble R. F. , Klare K. A. , Kutac K. J. , Miller G. , Siemon R. E.
Published: March 2003

The final scyllac experiments are described. These experiments utilized a feedback-stabilized, l=1,2 high-beta stellarator configuration and like the previous feedback-stabilization experiments were carried out in a toroidal sector, rather than a complete torus. The energy confinement time, obtained from excluded flux measurements, agrees with a two-dimensional calculation of particle end loss from a straight theta pinch. Because simple end loss was dominant, the energy confinement time was independent of whether equilibrium adjustment or feedback stabilization fields were applied. The dynamical characteristics of the toroidal equilibrium were improved by elimination of the l=0 field used previously, as expected from theory. A modal rather than local feedback control algorithm was used. Although feedback clearly decreased the m=1 motion of the plasma, the experimental test of modal feedback, which is expected from theory to be superior to local feedback, is considered inconclusive because of the limitations imposed by the sector configuration.
Thermal and field-aligned-drift effects near the lower oblique resonance
Authors: Storey L. R. O. , Thiel J.
Published: March 2003

A rapid method is used to find the least-damped root of the dispersion equation for electrostatic waves in a Maxwellian magnetoplasma, including the effects of field-aligned drift; the low-temperature and low-drift approximations are avoided. Calculations are made of the potential created by an alternating point charge at a frequency less than both the plasma and the electron cyclotron frequencies, neglecting collisions, forced ion motion, and the contributions of higher-order roots. A comparison of the numerical results with the approximate expressions previously published shows that the latter are inadequate for diagnostic purposes, i.e., for deducing electron density, temperature, and drift velocity from measurements of the potential.
Experimental demonstration of E×B plasma divertor
Authors: Strait E. J. , Kerst D. W. , Sprott J. C.
Published: March 2003

The E×B drift due to an applied radial electric field in a tokamak with poloidal divertor can speed the flow of plasma out of the scrape-off region, and provide a means of externally controlling the flow rate and thus the width of the density fall-off. An experiment in the Wisconsin levitated toroidal octupole, using E×B drifts alone, demonstrates divertor-like behavior, including 70% reduction of plasma density near the wall and 40% reduction of plasma flux to the wall, with no adverse effects on confinement of the main plasma.
Theory of electron cyclotron maser interaction in a cavity at the harmonic frequencies
Authors: Chu K. R.
Published: March 2003

A theory of the cyclotron maser interaction between an annular electron beam and the standing electromagnetic wave in a cavity structure is formulated on the basis of the relativistic Vlasov equation and the Maxwell equations. Detailed analytical expressions for the beam-wave coupling coefficient, beam energy gain, and threshold beam power have been derived for the fundamental and higher cyclotron harmonics. Physical interpretations of these results and comparison with cyclotron maser interactions in a waveguide structure are presented. Methods of parameter optimization and their applications to experiments are illustrated through numerical examples.
Deflection of a viscous liquid curtain
Authors: Lin S. P. , Krishna M. V. G.
Published: March 2003

Surface tension and shear stress are shown to cause a viscous liquid film falling from the edge of an inclined plane to deflect toward the underside of the plane.
Quasi-linear diffusion and particle transport in inhomogeneous plasmas
Authors: Sperling J. L.
Published: March 2003

A general dispersion relation and quasi-linear diffusion operator for electrostatic turbulence in strongly magnetized but inhomogeneous plasmas are derived. Wave induced particle transport rates across the gradients and criteria for their applicability are then deduced. The theory is applied to assess enhanced transport associated with high-power lower-hybrid heating of toroidally confined plasmas.
Moment equation approach to neoclassical transport theory
Authors: Hirshman Steven P.
Published: March 2003

The neoclassical cross-field fluxes for a toroidally confined, axisymmetric plasma are calculated in terms of the thermodynamic forces from the fluid continuity and momentum balance equations. This macroscopic formulation of neoclassical transport theory unifies the numerous complex expressions for the transport coefficients, previously obtained by solving the Fokker–Planck equation, and elucidates their physical basis. In the large aspect ratio limit, the continuous transition in the scaling of the diffusion coefficient throughout various collisionality regimes is shown to depend on the ratio of parallel viscosity coefficients of the plasma species. Comparison of the present results with the kinetic theory expressions for the neoclassical fluxes determines the parallel viscosity coefficients for a multispecies plasma in the long-mean-free-path regime.
Anomalous transport effects in magnetically-confined plasma columns
Authors: Steinhauer Loren
Published: March 2003

The evolution of density structure in a magnetized plasma column is analyzed accounting for anomalous diffusion due to the lower hybrid drift instability. The plasma column is found to be divided into regions of classical, anomalous, and intermediate diffusivity. The bulk behavior, described in terms of radial confinement time, depends most sensitively upon the particle line density (ion/cm). For broad plasmas (large line density), the transport is characteristic of classical diffusion, and for slender plasmas (small line density) the transport is characteristic of anomalous diffusion. For intermediate line densities, the transport undertakes a rapid transition from classical to anomalous. Correlations between the theoretical results and past experiments are described.
Nonlinear self-modulation of ion-acoustic waves
Authors: Ikezi H. , Schwarzenegger K. , Simons A. L. , Ohsawa Yukiharu , Kamimura T.
Published: March 2003

The nonlinear evolution of an ion-acoustic wave packet is studied. Experimentally, it is found that (i) nonlinear phase modulation develops in the wave packet; (ii) the phase modulation, together with the dispersion effect, causes expansion and breaking of the wave packet; (iii) the ions trapped in the troughs of the wave potential introduce self-phase modulation; and (iv) the ion-acoustic wave is stable with respect to the modulational instability. Computer simulations have reproduced the experimental results. The physical picture and the model equation describing the wave evolution are discussed.
Threshold behavior of the three-wave parametric-decay interaction in bounded inhomogeneous plasmas
Authors: Fuchs V. , Beaudry G.
Published: March 2003

The three-wave parametric-decay absolute instability in a bounded inhomogeneous plasma, as a function of the plasma length L, the basic gain length L0, and the wavenumber mismatch gradient κ is examined numerically and analytically. The stability boundary in the (Λ,α) plane, with Λ=L/L0 and α=κ L20, is found to be composed of a seesaw structure of branches merging at common values of α and of the product wave frequency shift. As Λ increases, the stability boundary degenerates into the α=8/π line, the plasma tends to perform the wave conversion in a zone of width 4/κ L0, and the best-matched point shifts to within a distance of 2/κ L0 from the boundary of pump incidence. Finally, a novel integral representation of the wave-coupling problem is formulated which allows straightforward application of asymptotic methods under long plasma and/or strong pump conditions.
Stability of settling of suspended sediments
Authors: Thacker W. C. , Lavelle J. W.
Published: March 2003

The solution to the equations of two-phase flow which describes hindered settling is unstable to small perturbations.
Preliminary study of mutual slip-through of a pair of vortices
Authors: Yamada Hideo , Matsui Tatsuya
Published: March 2003

Mutual slip-through of a pair of vortices was successfully accomplished in an experiment, and its result was found to show good agreement with the theoretical result based on the Biot–Savart law.
On the equilibrium solution of the Boltzmann equation
Authors: Sone Yoshio
Published: March 2003

It is proved that the continuous, nonnegative equilibrium solution of the Boltzmann equation never vanishes unless it is identically zero.
Statistical theory of vortex merger in the two-dimensional mixing layer
Authors: Takaki Ryuji , Kovasznay Leslie S. G.
Published: March 2003

The phenomenon of vortex merging in a two-dimensional mixing layer is treated statistically by introducing the probability density of spacings between neighboring vortices. The rate of merging is the other statistical variable and is a function of the spacing. The mixing layer is assumed to be statistically uniform along the streamwise coordinate and not to change with time. The following further assumptions were made: no correlation between adjacent spacings, similarity of the probability density, etc., to all times, and that the rate of merging for a single pair of vortices is inversely proportional to the square of their distance. The probability density was obtained by solving the governing equation. The result agrees well with that data measured by Brown and Roshko.
Modeling methods in physical and spectral space
Authors: Jeandel D. , Brison J. F. , Mathieu J.
Published: March 2003

A model of turbulence including a Reynolds-stress-mean velocity relation is developed. The functional nature of this relationship is presented and expressions are given for the unknown terms that can be derived from spectral information. With some modifications, inhomogeneous turbulent fields in which shear effects prevail can be pretty well predicted.
Stability of ablation and combustion fronts
Authors: Baker L.
Published: March 2003

An analytic model is developed to examine the stability of ablation fronts (as in laser and particle beam produced implosions) and combustion fronts.
Mode crossing in a Lagrangian system
Authors: Rosenbluth Marshall N.
Published: March 2003

By use of the Lagrangian formalism a simple criterion is derived for the stability of a mode crossing in a slightly nondegenerate fluid, or Vlasov plasma.
Modification of Pfirsch–Schlüter transport by poloidally asymmetric sources
Authors: Wong Seung Kai
Published: March 2003

Modification of particle and heat fluxes in Pfirsch–Schlüter regime due to the presence of poloidally asymmetric particle and energy sources is found for a multispecies plasma in an arbitrary axisymmetric magnetic field. The results can be obtained from those of the source-free theory via a simple substitution.
Plasma wave reflection from sharp density gradients
Authors: Vidmar Paul J.
Published: March 2003

Electrostatic wave reflection from density gradients is studied using an expansion in the ratio of the time an electron spends in the gradient to the wave period. The reflection coefficient is of order unity under rather general conditions.
Observations of relativistic electron beam surface envelopes and angular velocities
Authors: Mahaffey R. A.
Published: March 2003

The surface envelopes and rotation velocities of relativistic electron beams propagating through a background gas are observed to vary in a spatially-periodic manner. In the fast mode of rotation it is found that when the beam radius decreases, the beam rotation velocity increases and vice versa.
Fast expansions of laser-heated plasmas
Authors: Felber F. S. , Decoste R.
Published: March 2003

New analytic solutions describe ambipolar acceleration of fast ions from a steep, localized density gradient with a high electron temperature. A scaling law and estimates for the peak energy of ion species are presented.
Response of a nonlinear dumbbell with varying frictional coefficient in a pseudo-turbulent flow field
Authors: Phan-Thien N. , Tanner R. I.
Published: March 2003

The response of a nonlinear dumbbell with varying frictional coefficient in a pseudo-turbulent flow field is examined. It is shown that in such flows, the dumbbells will be able to maintain their highly dissipative extended configurations even though the mean flow is weak.
One-dimensional outgassing problem
Authors: Cong T. Tran , Bird G. A.
Published: March 2003

A predominantly numerical study, using the direct simulation Monte Carlo method, of the flow from outgassing surfaces with plane, cylindrical, or spherical geometry is presented. The numerical results for the plane flow case are compared with existing theoretical and experimental results, and also with a new formulation of the jump conditions across the Knudsen layer between the surface and the continuum outflow. This outflow is sonic for the free expansion case, but subsonic in the presence of back-pressure effects. The self-scattered return flux is 19% of the outgassed flux in the sonic outflow case and increases at lower Mach numbers. Thermal accomodation and reflection of this return flux produces an outgassing cooling effect. The cylindrical and spherical geometries introduce an additional Knudsen number defined by the ratio of the mean free path in the effusing gas to the radius. The plane flow results apply when this Knudsen number is less than 0.001 and, when it is of order unity or above, the return flux is inversely proportional to it.
Partially averaged field approach to cosmic ray diffusion
Authors: Jones Frank C. , Birmingham Thomas J. , Kaiser Thomas B.
Published: March 2003

The kinetic equation for particles interacting with turbulent fluctuations is derived by a new nonlinear technique which successfully corrects the difficulties associated with quasi-linear theory. In this new method the effects of the fluctuations are evaluated along particle orbits which themselves include the effects of a statistically averaged subset of the possible configurations of the turbulence. The new method is illustrated by calculating the pitch angle diffusion coefficient Dμμ for particles interacting with ’’slab model’’ magnetic turbulence, i.e., magnetic fluctuations linearly polarized transverse to a mean magnetic field 〈B〉. Results are compared with those of quasi-linear theory and also with those of Monte Carlo calculations reported in a companion paper. The major effect of the nonlinear treatment in this illustration is the determination of Dμμ in the vicinity of 90° pitch angles where quasi-linear theory breaks down. The spatial diffusion coefficient κ∥ parallel to 〈B〉 is evaluated using Dμμ as calculated by our technique. It is argued that the partially averaged field method is not limited to small amplitude fluctuating fields and hence is not a perturbation theory.
Computer simulation of the velocity diffusion of cosmic rays
Authors: Kaiser Thomas B. , Birmingham Thomas J. , Jones Frank C.
Published: March 2003

Monte Carlo simulation experiments have been performed in order to study the velocity diffusion of charged particles in a static turbulent magnetic field. By following orbits of particles moving in a large ensemble of random magnetic field realizations with suitably chosen statistical properties, a pitch-angle diffusion coefficient is derived. Results are presented for a variety of particle rigidities and rms random field strengths and compared with the predictions of standard quasi-linear theory and the nonlinear partially averaged field theory.
Nonlinear wave and soliton propagation in media with arbitrary inhomogeneities
Authors: Chen H. H. , Liu C. S.
Published: March 2003

Asymptotic solutions of nonlinear wave propagation in media with gentle, but otherwise arbitrary density inhomogeneities, are discussed. In the adiabatic approximation, a nonlinear Schrödinger equation is derived for media with linear, but time-dependent density gradients. The resulting extra term can be eliminated by going to an accelerated reference frame, which makes this modified nonlinear Schrödinger equation completely integrable by the inverse scattering method. Multi-solitons are therefore still the asymptotic states of waves propagating in media with arbitrary inhomogeneities.
One-dimensional inhomogeneous Vlasov equilibria
Authors: Crownfield F. R.
Published: March 2003

Bernstein, Greene, and Kruskal showed how, given the electrostatic potential as a function of position, the entire distribution function for ions, and the distribution function for untrapped electrons in a one-dimensional, two-species Vlasov plasma, one could determine the distribution function for the trapped electrons as the solution of an Abel integral equation. This result is generalized by replacing the statements about the distribution functions with the specification of the velocity space distribution functions of both species at a single position in the plasma. Limiting cases are shown to correspond to the earlier treatment, and the applicability of the theory to experiment is discussed.