bluuebunny/crossref_metadata_2025 huggingface dataset:
Interactions of relativistic electron beams with high atomic-number plasmas
Authors: Mosher David
Published: March 2003

A relativistically correct Fokker–Planck analysis is used to develop fluid equations which model the interaction of relativistic electron beams with high atomic-number plasmas. The derived collision terms can be used to describe scattering and energy loss in materials ranging from the solid to high-temperature plasma forms. The full set of equations discussed can be used to study electron-beam-initiated pellet fusion in a completely self-consistent fashion. Specifically, the model is applicable to study of beam pinching in plasma-filled diodes, the interaction of focused beams with target plasmas, and the transport of high ν/γ beams in high atomic-number plasmas. Although the general equations are amenable to solutions only by computational techniques, analytic solutions describing the time-dependent, collisional interaction of a beam in an infinite plasma and the one-dimensional equilibrium of a beam in a plasma with applied electric field have been obtained.
Cone resonance excited by an alternating point charge in a warm magnetoplasma
Authors: Chasseriaux J. M.
Published: March 2003

Using the quasi-static approximation, the potential created by an alternating point charge in a warm magnetoplasma is studied theoretically. The excitation frequency is assumed to be less than both the plasma frequency and the electron gyrofrequency. An approximate expression for the dispersion relation enables us to obtain an analytical result for the potential, which remains finite on the resonance cone, while an interference structure appears either inside or outside the cone, depending on the excitation frequency.
Resistive instabilities in general toroidal plasma configurations
Authors: Glasser A. H. , Greene J. M. , Johnson J. L.
Published: March 2003

Previous work by Johnson and Greene on resistive instabilities is extended to finite-pressure configurations. The Mercier criterion for the stability of the ideal magnetohydrodynamic interchange mode is rederived, the generalization of the earlier stability criterion for the resistive interchange mode is obtained, and a relation between the two is noted. Conditions for tearing mode instability are recovered with the growth rate scaling with the resistivity in a more complicated manner than η3/5. Nyquist techniques are used to show that favorable average curvature can convert the tearing mode into an overstable mode and can often stabilize it.
Precession of high-intensity elliptically polarized light in a plasma
Authors: Katz Ira , Parks Donald E. , Rotenberg Manuel
Published: March 2003

It is found that the rotation of the polarization ellipse of long-wavelength intense elliptically polarized light in a cold neutral plasma can be described succinctly by the equations of classical mechanics.
Electron thermal conductivity in the trapped electron regime in the FM-1 spherator
Authors: Ejima S. , Okabayashi M.
Published: March 2003

The parametric dependence of electron thermal conductivity was studied in the trapped electron regime by utilizing a localized heating method in a shear stabilizing configuration in the FM-1 spherator. The electron thermal conductivity K⊥ and the particle diffusion coefficient D⊥ show similar dependence on the shear length, Ls, and the electron temperature Te[K⊥ ∼ (1/400 ∼ 1/800)(Ls/a) (kTe/16eB)]. The conductivity was larger when the electron temperature gradient was parallel to the density gradient compared with the antiparallel case. The fluctuations associated with the heat flow are compared with the prediction of the trapped electron particle instability. Relevance to tokamak experiments is discussed.
Instability of the free-convection type in magnetohydrodynamics
Authors: Nedospasov A. V. , Khait V. D.
Published: March 2003

The processes occurring in an electroconductive fluid in a magnetic field and subjected to an electric current flowing through it are discussed. In a fluid whose electrical conductivity rises with temperature, a phenomenon similar to free convection occurs when the entropy drops along the direction of the force j × B. The joint action of this phenomenon and the overheating instability which also stems from the temperature dependence of the electrical conductivity and the effect of electromagnetic braking is considered. In this case, the criterion of stability is obtained. Instability in the form of free convection also appears due to a Hall current jH flowing along the electrodes of a magnetohydrodynamic channel when a high temperature gradient occurs along the direction of the force jH × B. The instability arises near the cathode and the appearance of one is determined by the value of a dimensionless parameter identical to the Rayleigh number Ra = (dlnσ/dT) g̃l4 ‖∇T‖ /νχ where g̃ = jH B/ρ plays the role of the gravitational acceleration and dlnσ/dT plays the role of the expansion coefficient.
Nonlinear analysis of magnetohydrodynamic flow instability
Authors: Kolesnikov V. K. , Nedospasov A. V. , Khait V. D.
Published: March 2003

A nonlinear analysis is given of the oscillations of the magnetohydrodynamic flow instability caused by the dependence of the conductivity on the temperature. The effect of the flow parameters is studied.
Two-dimensional turbulence in inviscid fluids or guiding center plasmas
Authors: Seyler C. E. , Salu Yehuda , Montgomery David , Knorr Georg
Published: March 2003

Analytic theory for two-dimensional turbulent equilibria for the inviscid Navier–Stokes equation (or the electrostatic guiding center plasma) is tested numerically. A good fit is demonstrated for the approach to a predicted energy per Fourier mode obtained from the two-temperature canonical ensemble of Kraichnan: 〈‖u(k) ‖2〉 = (α+βk2)−1, where k is the wavenumber and α and β are reciprocal energy and enstrophy temperatures. Negative as well as positive temperature regimes are explored. Fluctuations about the mean energy per mode also compare well with theory. In the regime α<0, β≳0, with the minimum value of α+βk2 near zero, contour plots of the stream function reveal macroscopic vortex structures similar to those seen previously in discrete vortex simulations by Joyce and Montgomery. Kraichnan’s assertion that thermodynamic limits exist for the negative temperature states is questioned. Eulerian direct interaction equations, which can be used to follow the approach to inviscid equilibrium, are derived.
Heating of end region plasma in a theta pinch
Authors: Hess Roger A. , Griem Hans R.
Published: March 2003

Rapid heating of the plasma in the end region of a turbulent, collisionless theta pinch has been observed by spectroscopic methods. Nonclassical energy transport from the hot central plasma is the most probable explanation for this heating.
Rayleigh-Taylor instability of a heavy fluid
Authors: Chakraborty B. B.
Published: March 2003

Growth rate of the mode of maximum instability of a heavy, uniform fluid superposed on a lighter one is obtained. The fluids are separated by a layer of transition of finite thickness in which density increases exponentially in the vertical direction.
Nonlinear deep water waves: Theory and experiment
Authors: Yuen Henry C. , Lake Bruce M.
Published: March 2003

The evolution and interaction of nonlinear wavepackets on deep water is studied both theoretically and experimentally. The nonlinear Schrödinger equation, first derived in this context by Hasimoto and Ono, is shown to be a special case of Whitham’s theory. The exact solution to this equation predicts the existence of stable envelope solitons, which is indeed verified by laboratory experiments. A comparison between laboratory data and a numerical solution of the nonlinear Schrödinger equation is also given.
Transport properties of a toroidal plasma at intermediate-to-high collision frequencies
Authors: Rawls John M. , Chu Ming Sheng , Hinton F. L.
Published: March 2003

Neoclassical transport coefficients are computed in a large aspect ratio toroidal magnetic confinement system in order to examine the transition between the plateau and Pfirsch–Schlüter regimes. The calculation employs a hybrid collision operator combining Krook and pitch angle scattering terms with the identical particle collision frequency taken to be a function of velocity which is determined from a fit to known exact results for classical transport. A simple approximate analytic form is presented which incorporates both these results and the results of Hinton and Rosenbluth for lower collision frequencies.
Simulation of turbulent plasma heating by moderately strong oscillating two-stream instabilities
Authors: Katz J. I. , De Groot J. S. , Faehl R. J.
Published: March 2003

Numerical simulations are used to investigate plasma heating by the oscillating, two-stream instability at moderate amplitude. Substantially all the absorbed electromagnetic energy goes into production of a suprathermal electron population. A simple functional form describes the shape of the suprathermal distribution function, which is proportional to v−2 over a wide velocity range. This holds for a wide range of driving field amplitude. The multiplicative constant increases linearly with time within a simulation. The plasma electric field spectrum has a characteristic power law shape, which is interpreted as the result of the waves coming into quasi-thermal balance with electrons near their phase velocity. The results for the electron distribution function are in qualitative agreement with experiments by Dreicer, Ellis, and Ingraham, but they disagree with those of Mizuno and De Groot and of Porkolab.
Plasma heating above the lower hybrid frequency by linear wave absorption
Authors: Schuss J. J.
Published: March 2003

The possibility of heating collisionless toroidal plasmas to high temperatures by means of linear wave absorption above the lower hybrid frequency is discussed. This absorption is mainly due to electron Landau damping and ion damping is neglected. Two methods of heating are considered, propagating a wave across the plasma column and exciting toroidal modes. WKB solutions of the first method show that the incident wave must be within a narrow range of kz for its energy to be uniformly deposited into the plasma. Toroidal mode solutions indicate that this band of kz may be significantly widened by lower kz waves which drive slightly damped toroidal modes. The conditions on kz for accessibility and heating are calculated and the advantages of such an approach are discussed.
Some numerical results for the BGK model: Thermal creep and viscous slip problems with arbitrary accomodation at the surface
Authors: Loyalka S. K. , Petrellis N. , Storvick T. S.
Published: March 2003

Numerically ’’exact’’ results for the thermal creep and viscous slip problems for the BGK model and Maxwellian diffuse specular reflection at the wall are obtained by using equations derived earlier by Cercignani, Loyalka, and Cipolla. Results obtained by the use of both the half range and the ’’full-range’’ expansions are found to be in complete agreement and provide standards of comparison for various approximate methods.
Cold plasma wavebreaking: Production of energetic electrons
Authors: Albritton James , Koch Paul
Published: March 2003

Nonlinear electron plasma oscillations are investigated in the wavebreaking regime where collective energy is converted into random energy. The Lagrangian description of the electrons is extended beyond fluid element orbit crossing, thereby exposing the essential physics of wavebreaking and permitting simple analytical interpretation of it. In driven cold inhomogeneous plasma a region of large resonant oscillations decays by producing energetic electrons which escape into the less dense plasma. The maximum energy of the fast electrons produced during the driver period in which the first wave breaks is much larger than the energy of an electron oscillating freely in the driver field. The total energy of the fast electrons exceeds that supplied the system by the driver in a period and can be a significant fraction of the total energy in the oscillations at the onset of wavebreaking.
Numerical computation of the hypersonic leading edge problem using the Burnett equations
Authors: Tannehill John C. , Eisler Gerald R.
Published: March 2003

The hypersonic rarefied flow near the sharp leading edge of a flat plate is computed for the first time using a finite-difference solution of the complete, unsteady Burnett equations. The computation is advanced in time from the initial conditions until the steady-state solution is reached. The computational region extends from the leading edge to the strong-interaction regime. Schamberg’s second-order wall slip and temperature jump boundary conditions are employed at the wall. The numerical results are compared with experimental data, a Monte Carlo simulation, and a finite-difference solution of the complete Navier–Stokes equations. Based on these comparisons, it is evident that the Burnett equations in conjunction with Schamberg’s second-order boundary conditions give a much less accurate description of the rarefied flow field near the leading edge than do the Navier–Stokes equations.
Trapped particle instability
Authors: Franklin R. N. , MacKinlay R. R.
Published: March 2003

A quasi-linear treatment of the time evolution of a large amplitude electron plasma wave following trapped particle orbits shows no instability at wave amplitudes given by eφo/κBTe⩽0.1 in contrast to experimental observations and earlier theoretical results.
Hybrid model studies of ion dynamics and magnetic field diffusion during pinch implosions
Authors: Sgro A. G. , Nielson C. W.
Published: March 2003

A one-dimensional numerical hybrid model (Vlasov ions, fluid electrons) which includes all nontrivial field components has been devised and its predictions have been compared with experimental pinch results. The effect of microscopic electron dynamics is included on the average by the specification of (anomalous) resistivity and thermal conductivity coefficients. The model has reproduced the magnetic field profiles observed during the implosion and post implosion phases of several screw pinch experiments. The behavior of the imploding plasma as various physical parameters are changed is discussed. The foot in the front of an experimentally determined density profile of a high density theta pinch is reproduced and shown to be due to a reflected ion beam. For some conditions the formation of a reflected ion beam is found to be dependent upon whether the bias is parallel or antiparallel to the driving field.
Transport properties of a toroidal plasma in a mixed collisionality regime
Authors: Hirshman S. P.
Published: March 2003

The transport coefficients are calculated for an axisymmetric toroidally confined plasma comprised of main ions in the banana regime and high-Z impurities in the Pfirsch–Schlüter regime. The ambipolar particle diffusion coefficient scales like the Pfirsch–Schlüter value for a collisional plasma. The main ion heat conductivity, however, equals its value in a low collision frequency (banana regime) plasma, thus exceeding the particle diffusion by the factor δ−3/2, where δ<1 is the inverse aspect ratio. A neoclassical current comparable to the banana regime bootstrap current flows in response to the electron and ion gradients.
Spatially unstable disturbances on a fully-developed axisymmetric jet column
Authors: Mattingly G. E.
Published: March 2003

The linearized, inviscid, spatial, stability theory is applied to the fully-developed axisymmetric jet. According to the theory, the helical mode alone is unstable. The characteristics of the most unstable disturbance are presented together with the disturbance velocity field.
Taylor vortices between eccentric cylinders
Authors: Koschmieder E. L.
Published: March 2003

The critical Taylor number and the critical wavelength of Taylor vortices has been measured as a function of the eccentricity. It has been found that in this apparatus the critical Taylor number increases steadily as a function of eccentricity. The critical wavelength was found to remain nearly constant for small ε and to decrease with larger ε. Separated flow, as observed from above, was found to be in qualitative agreement with the prediction of Kamal.
Simple model of convection-diffusion coupling near flames
Authors: Inger George R.
Published: March 2003

A Couette-flame sheet flow model is analyzed to study combined indraft convection-thermal diffusion effects on oxygen distribution near intense fires. These effects enhance the local oxygen concentration, thermal diffusion causing local overshoots relative to ambient conditions.
Determination of intermittency from the probability density function of a passive scalar
Authors: Bilger R. W. , Antonia R. A. , Sreenivasan K. R.
Published: March 2003

The probability density functions of temperature in the intermittent regions of heated jet and wake flows show a strong spike associated with the temperature of the unheated fluid. The fine structure of this spike fits a Gaussian curve quite closely, and the area under this Gaussian gives an accurate measure of 1−γ where γ is the intermittency factor. The standard deviation of the Gaussian is a measure of the noise due to residual temperature fluctuations in the free-stream and the electronic noise in the measurement system. The accuracy with which the intermittency can be determined is limited by the signal-to-noise ratio.
Kinetic theory of turbulent compressible flows and comparison with classical theory
Authors: Tsugé Shunichi , Sagara Kenshi
Published: March 2003

A complete set of turbulent correlations is given in terms of expansion coefficients in a double series of Hermite polynomials of a two-particle correlation in phase space. Only two of these coefficients, corresponding to Reynolds’ stress and turbulent heat flux, are shown to appear in gasdynamic equations of turbulence. This is accomplished by incorporating the phase-space correlation in the collision integral of Boltzmann’s equation, and by deriving generalized Navier–Stokes and Fourier transport relations. In contrast to the classical formalism, the simple expression remains invariant in form whether the flow is compressible or not. Nevertheless, a bilinear transformation of fluctuating quantities shows that the two formalisms are identical with regard to terms of double correlations. The kinetic theory justifies nonexistence of the higher order correlations characteristic of compressible turbulence equations of the classical regime.
Transition regime behavior of supersonic beam skimmers
Authors: Bird G. A.
Published: March 2003

The direct simulation Monte Carlo method is applied to typical skimmer flows associated with the production of molecular beams from a supersonic stream. Attention is concentrated on the skimmer interference arising from intermolecular collisions when the mean free path in the stream is of the same order as the diameter of the skimmer entrance. The effects of skimmer geometry, Knudsen number, molecular model, speed ratio, and surface temperature have been investigated. It is found that the onset of skimmer interference is best correlated by a modified Knudsen number based on the collision cross section at the stagnation temperature, rather than the cross section for the undisturbed stream. The interference becomes serious at modified Knudsen numbers of order unity. There are qualitative differences between the flows in slender and wide angle skimmers, the most striking effect being a very sudden breakdown of the flow in a slender skimmer.
Diffusion in velocity space associated with nonadiabatic changes in the magnetic moment of a charged particle
Authors: Bernstein Ira B. , Rowlands G.
Published: March 2003

A kinetic equation is derived which includes velocity space diffusion effects due to nonadiabatic jumps in the magnetic moment. This extra diffusion can be comparable to classical diffusion in experimental situations of interest.
Investigation of plasma turbulence by modified analysis of scattered laser light
Authors: Maurmann S. , Finken K. H. , Kunze H.-J.
Published: March 2003

It is suggested, that the mean square deviation of measured values of the spectrum of scattered light from the best fit (Gaussian) curve is correlated with the level of plasma turbulence. Results indicate that after excitation an ion acoustic turbulence decays on a time scale of ion–ion collisions.
Nonlinear theory of stimulated backscattering in a bounded dissipative plasma
Authors: Fuchs Vladimir
Published: March 2003

The anomalous reflectivity, k2, of a bounded plasma, dissipative for the excited electrostatic wave, is investigated. Quantitatively, the phenomenon is controlled by three characteristic lenghts: L, the length of the plasma, La, the longitudinal absorption length, and L0, the basic gain length. When the parametric decay instability is convective, L0/La≡β⩾2, Tang’s approximation is shown to apply. With α2=2LLa/L02, and ε2= (radiation noise/incident signal), it is found that when Γ=ε2 exp(α2) ≲0.1, k2 is negligible. When Γ≳0.1, then k2≃1−α−2 ln(1/4ε2). In the regime of absolute instability, β<2, with zero noise, it is found that the reflectivity in implicit form is κL/L0=F (π/2, k)+(1/2) F (tan−1 A, k). F is the elliptic integral of the first kind, κ2=1−β2/4 kc2, kc2=1−k2, A=2B/kc(1−B2), B=β/2kcκ. As a function of L/L0, the reflectivity saturates at 1−β2/4.
Damped nonlinear Schrödinger equation
Authors: Nicholson Dwight R. , Goldman Martin V.
Published: March 2003

High frequency electrostatic plasma oscillations described by the nonlinear Schrödinger equation in the presence of damping, collisional or Landau, are considered. At early times, Landau damping of an initial soliton profile results in a broader, but smaller amplitude soliton, while collisional damping reduces the soliton size everywhere; soliton speeds at early times are unchanged by either kind of damping. For collisional damping, soliton speeds are unchanged for all time.
Relativistic effects in resonance absorption
Authors: Drake J. F. , Lee Y. C.
Published: March 2003

The role of the relativistic-electron-mass variation in the generation of plasma waves by the linear mode conversion of intense electromagnetic waves is investigated. The increase in the electron mass in high intensity regions of the mode-converted wave reduces the local plasma frequency and thereby strongly modifies the plasma-driver resonance. A spatial discontinuity in the structure of the mode-converted wave results and causes the wave to break. Under rather modest restrictions, the wave breaking resulting from these effects occurs before the wave amplitude is limited either by thermal convection or by breaking caused by previously investigated nonrelativistic effects. Consequently, the amplitude of the mode-converted plasma wave should saturate at a much lower level than previously predicted. For simplicity, the analysis is limited to the initial stages of mode conversion where the ion dynamics can be neglected. The validity of this approximation is discussed.
Internal m=1 kink modes in tokamaks
Authors: Pao Young-ping
Published: March 2003

A normal mode analysis is developed for m=1 kink modes in tokamaks with large aspect ratio and circular section. The result is applied to the internal kink modes where the q=1 surface is near the minor axis. It is shown that the m=k=1 internal kink modes, which are unstable in the screw pinch model, are also unstable in the toroidal geometry with even greater growth rates.
Nonlinear analysis of Görtler vortices
Authors: Aihara Yasuhiko
Published: March 2003

An integral method of analysis is applied to investigate the Görtler vortices in the nonlinear region, and the following results are obtained: (1) The neutral stability diagram obtained for small amplitude vortices shows reasonable agreement with the results of linearized theory by Görtler, Hämmerlin, and Smith. (2) A possible analytical prediction of unsteady meandering motion of vortices is discussed. (3) The stable finite amplitude of Görtler vortices is achieved associated with some distortion of waveform from its original sinusoidal pattern. The results obtained by this analysis are not contradictory to experimental evidence.
Influence of heat transfer on the stability of parallel flow between concentric cylinders
Authors: Choo Y. K. , Potter M. C.
Published: March 2003

The stability of the parallel flow of water between concentric cylinders at different temperatures is investigated for infinitesimal velocity and pressure disturbances. Primary interest is in the effect of heat transfer and the radius ratio a/b on the critical point of the neutral stability curve. The results indicate a strong dependence of the critical eigenvalues on both the heat transfer and the radius ratio. The critical Reynolds number of the nonisothermal flow appears to approach a finite value as the inner radius approaches zero (pipe flow) by showing an inflection point on the curve Rc vs a/b.
Interaction effects in turbulent premixed flames
Authors: Bray K. N. C. , Libby Paul A.
Published: March 2003

The Bray–Moss model for turbulent, premixed combustion is applied to plane, oblique combustion waves. The analysis takes into account the influence of turbulence and inhomogeneity on the effective rate of heat release, and also the competing effects of dilatation and turbulent production due to shear in the turbulent kinetic energy balance. Predictions are made of the flame speed and the structure of the reaction zone in cases where turbulent mixing is rate limiting. Qualitiative agreement is found with relevant experimental data.
Effect of anisotropic pressure on the localized magnetohydrodynamic interchange modes in an axisymmetric torus
Authors: Connor J. W. , Hastie R. J.
Published: March 2003

The familiar q≳1 criterion (where q is the safety factor) for the stability of tokamak equilibria against localized interchanges, was derived for an isotropic pressure toroidal plasma. The present importance of neutral injection techniques and also the evidence of significant numbers of runaway electrons in some experiments both lead to an interest in plasmas with anisotropic pressure. The stability criterion appropriate to such a plasma in a general axisymmetric toroidal geometry is developed basing the analysis on the kinetic energy principle. The general result is applied to a discussion of perpendicular and parallel neutral injection in a large aspect ratio torus and also to the effect of runaway electrons.
Fourth approximation to the viscosity of a multicomponent ionized gas
Authors: Bonnefoi Cl. , Fauchais P.
Published: March 2003

Some missing elements necessary for the fourth approximation to the viscosity of a multicomponent plasma have been calculated and some features of the thermal conductivity have been pointed out.
Nonlinear Landau damping of electrostatic waves in an electron beam-plasma system
Authors: Sugaya R. , Sugawa M. , Nomoto H.
Published: March 2003

The nonlinear Landau damping and growth of electrostatic waves in an electron beam-plasma system in a magnetic field has been observed experimentally. The space charge wave of the beam decays into the Trivelpiece mode, which is amplified exponentially by increasing the amplitude of the pump wave.
High-beta, three-dimensional mirror equilibria
Authors: Kadish Abraham
Published: March 2003

Curvature-free minimum-B mirror geometries are constructed. The macroscopic pressure balance equations are solved for plasmas with two-pressure stress tensors subject to the condition that the plasma pressure vanish on a prescribed bounding surface. It is shown that the resulting configurations are stable.
Destabilization of hydromagnetic drift-Alfvén waves in a finite pressure, collisional plasma
Authors: Tang J. T. , Luhmann N. C.
Published: March 2003

The hydromagnetic drift mode of the coupled drift-Alfvén wave is destabilized as a standing wave in a dense, current-free plasma in the presence of a density gradient. When an axial electron current is drawn, a localized Alfvén mode propagating against the current is destabilized, in addition to the unstable drift mode now propagating along the current. The measured wave properties, dispersion, and dependence on plasma parameters are found to agree with the theory derived for a finite β, collisional plasma.
Frequency shift of a nonlinear plasma wave and its initial damping
Authors: Canosa José
Published: March 2003

For large wave amplitudes, the frequency shift of a nonlinear plasma wave and its initial exponential damping are found to be approximately proportional to the square of the initial wave amplitude. Extensive Vlasov computations are in essential agreement with recent experimental results for wavenumber shifts and initial nonlinear dampings obtained at large amplitudes.
Stability of oblique modulation on an ion-acoustic wave
Authors: Kako Masashi , Hasegawa Akira
Published: March 2003

Modulation instability is shown to be a general property of a wave in a nonlinear and dispersive medium when the modulation is allowed in the direction oblique to that of the wave phase velocity. As an example a modulation on an ion-acoustic wave is shown to be unstable even if this wave is modulationally stable in the case of parallel or perpendicular modulation.
Nonlinear effects on mode-converted lower-hybrid waves
Authors: Kuehl H. H.
Published: March 2003

Nonlinear ponderomotive force effects on mode-converted lower-hybrid waves are considered. The nonlinear distortion of these waves is shown to be governed by the cubic nonlinear Schrödinger equation. The threshold condition for self-focusing and filamentation is derived.
Harmonic generation in a radially limited unstable beam-plasma system
Authors: Weinfeld M.
Published: March 2003

Harmonic generation by a three wave coupling mechanism has been studied in an unstable beam-plasma system, whose dispersion is small at low frequencies due to its finite geometry. This mechanism has been observed in the case of resonant coupling (nondispersive mode), and in the case of quasi-resonant coupling (weakly dispersive mode). The experimental results give fair agreement with hydrodynamic theory.
Transit-time magnetic pumping of an electron beam in the Proto-Cleo stellarator
Authors: Golovato S. N. , Shohet J. L.
Published: March 2003

A traveling wave was launched around the Proto-Cleo stellarator to attempt transit-time magnetic pumping of a pulsed electron beam moving along the magnetic field lines. An apparent loss of the beam was seen when transit-time magnetic pumping was applied. A random walk diffusion of the beam with a step size determined by the radial E×B drift in the wave poloidal electric field agrees well with the experimental results.
Anomalous absorption near the lower-hybrid frequency
Authors: Fidone I. , Granata G.
Published: March 2003

Turbulent absorption of a wave with a frequency near or above the lower-hybrid frequency in a parametrically unstable plasma is investigated. The analysis is restricted to the transitory quasi-linear stage of the development of the instability. Within the quasi-linear framework, the effect of the driven turbulence on the spatial damping of the pump wave and the mode conversion efficiency at the lower-hybrid resonance is discussed. It is found that, at a moderate level of the turbulent noise (W/n0Te ≃10−6), the pump wave experiences an appreciable dissipative effect.
Energy lost by a relativistic electron beam propagating along an external magnetic field
Authors: Thode Lester E. , Godfrey Brendan B.
Published: March 2003

The nonlinear interaction between a relativistic electron beam and a homogeneous, magnetized plasma is discussed. The plasma heating as a function of guide magnetic field strength is obtained by comparing three two-dimensional, fully electromagnetic numerical simulations. The interaction involves a (γ0−1)mc2=1.5 meV monoenergetic beam with a beam-to-plasma density ratio of nb/ne=10−1. The zero and moderate magnetic field interactions are strongly two-timensional in character, in agreement with theory. The strong magnetic field case is similar to a one-dimensional interaction. The presence of the magnetic field appears to reduce high energy tail formation perpendicular to the beam. Nonlinear Landau damping is observed to be an important process in two-dimensional space.
Nonlinear theory of rf heating at cyclotron harmonics
Authors: Schmitt J. P. M.
Published: March 2003

The nonlinear interaction of a single particle with an electromagnetic wave at a cyclotron harmonic is studied. Emphasis is on the large wavelength limit (fast wave). The cases of a coherent wave particle interaction and of an incoherent interaction are treated. In both cases explicit expressions for the temporal evolution of the particle perpendicular energy distribution function are presented. The heating is efficient at the first two harmonics. The formation of a suprathermic tail is predicted at the second and higher harmonics.
Effect of particle and heat sources on impurity transport in tokamak plasmas
Authors: Burrell Keith H.
Published: March 2003

Local particle injection or heating can affect the transport of impurities. Proper source configurations can oppose the natural inward impurity drift, thus providing a means for controlling impurity influx.
Linear response theory of a turbulent plasma
Authors: Nambu Mitsuhiro
Published: March 2003

The linear response theory of a turbulent plasma is presented. The procedure of obtaining the dielectric constant of a turbulent plasma is presented using quasi-linear techniques. The principal result of the theory is the electron orbit modification due to the steady Langmuir turbulence fields. The collisional dissipative parametric destabilizing effect of the Langmuir turbulence fields on the ion sound waves appears. A steady turbulent state is maintained by the competing processes between the linear Landau damping effect and the collisional dissipative parametric destabilizing effect of the Langmuir turbulences. It is suggested that the generalized parametric resonance effect is effective for ion heating through linear Landau resonance. The critical Langmuir wave fluctuation level is given in terms of the ion-to-electron temperature ratio and wavelength. The steady plasma turbulence theory is applicable to plasma far from the thermal equilibrium state.
Comparison of unstable modes and growth rates in ideal magnetohydrodynamics and guiding center plasmas
Authors: Weitzner Harold
Published: March 2003

Unstable modes and growth rates are compared for helically symmetric equilibria based on the models of ideal magnetohydrodynamics and guiding center plasmas. After appropriate expansions and approximations, it is shown that any unstable mode in ideal magnetohydrodynamics is present in exactly the same form and with the same growth rate in a guiding center plasma. Except for a small class of modes whose existence is doubted but cannot be proved with the analysis given, the converse statement also holds.
Unstable electrostatic ion cyclotron waves excited by an ion beam
Authors: Michelsen P. , Pécseli H. L. , Rasmussen J. Juul , Sato N.
Published: March 2003

Electrostatic ion cyclotron waves were observed in a quiescent cesium plasma into which a low-energy beam of sodium ions was injected. The instability appeared when the beam velocity was above 12 times the ion thermal velocity. The waves propagated along the magnetic field with a velocity somewhat smaller than that of the beam. The dispersion relation was in good agreement with theory.
Turbulent fluctuations in the hypersonic boundary layer over an adiabatic slender cone
Authors: Laderman A. J. , Demetriades A.
Published: March 2003

Static temperature fluctuations are shown to be strongly dependent on wall temperature so that at high Mach numbers excessive fluctuation intensities are encountered in the adiabatic case.
Destabilization of the trapped-electron mode by magnetic curvature drift resonances
Authors: Adam J. C. , Tang W. M. , Rutherford P. H.
Published: March 2003

Electron curvature drift resonances, ignored in earlier work on the trapped-electron modes, are found to exert a strong destabilizing influence in the lower collision frequency range of these instabilities. Effects arising from ion temperature gradients, shear, and finite ion gyroradius are included with these ∇B drifts in the analysis, and the resultant eigenvalue equation is solved by numerical procedures rather than the commonly used perturbation techniques. For typical tokamak parameters the maximum growth rates are found to be increased over earlier estimates by roughly a factor of 4, and requirements on magnetic shear strength for stabilization are likewise more severe and very difficult to satisfy. For inverted density profiles, this new destabilizing effect is rendered ineffective, with the result that the modes can be stabilized for achievable values. of shear provided the temperature gradients are not too severe. Estimates of the particle and thermal energy transport are given for both normal and inverted profiles.
Modulational instability of a finite amplitude Alfvén wave
Authors: Lashmore-Davies C. N.
Published: March 2003

Conditions are derived for the break-up of a finite amplitude Alfvén wave into upper and lower sideband waves and a longitudinal disturbance. This instability can occur over a much wider range of conditions than the decay instability. The longitudinal disturbance is only nonoscillatory when dissipation is neglected.
Excitation of lower hybrid waves in a plasma by electron beams
Authors: Papadopoulos K. , Palmadesso P.
Published: March 2003

The linear theory of excitation of electrostatic lower hybrid waves by electron beams is presented. The importance of such waves in tokamaks with runaway electrons is discussed.
Conditional (point averaged) temperature and velocities in a heated turbulent plane jet
Authors: Jenkins P. E. , Goldschmidt V. W.
Published: March 2003

The conditional (point-averaged) velocity and temperature profiles in a plane jet of air were measured. The conditional point averages of the mean temperature and velocity were found with respect to the moving interface for five intermittences: γ=0.1, 0.2, 0.3, 0.4, and 0.5, at axial stations of x/D=35, 45, and 50. The results suggest coincidence of the interfaces and a flatter temperature profile within the fully turbulent flow.
Optical heterodyne test of perturbation expansions for the Taylor instability
Authors: Gollub J. P. , Freilich Michael H.
Published: March 2003

The velocity field for the Taylor instability in a rotating fluid has been studied in order to test detailed theoretical predictions based on perturbation expansions about the critical point. Optical heterodyne methods were used to measure the spatial variation (along the axis of symmetry z) and time evolution of the local radial velocity component Vr(ε,z,t), where ε= (f−fc)/fc is a measure of the difference between the rotation rate f and the critical value fc. Measurements of the steady state spatial Fourier coefficients Ap(ε) of Vr are presented as a function of ε in order to determine both the asymptotic power laws and the correction terms which are necessary for large ε. Measurements of the time dependence of A1 after a sudden change in rotation rate are consistent with a heuristically useful analogy between hydrodynamic instabilities and certain second-order phase transitions.
Smooth transition of neoclassical diffusion from the banana to Pfirsch–Schlüter regime
Authors: Tsang K. T. , Callen J. D.
Published: March 2003

It is shown that neoclassical transport previously obtained by numerical evaluation of variational procedures can be reproduced analytically by taking account of the energy dependence of the collision and bounce frequencies through the separation of velocity space into banana, plateau, and Pfirsch–Schlüter regimes.
Low-frequency stability of high-current particle rings
Authors: Lovelace R. V.
Published: March 2003

A theoretical study is made of the low-frequency magnetohydrodynamic stability of high-current particle rings embedded in a dense plasma. Two configurations are investigated in detail: astron geometry where there is no toroidal magnetic field, and tokamak geometry where a strong toroidal field exists. For an astron, a sufficient condition for stability of the kink modes (m=±1, n≠0) (excluding the n=1 precession mode) is found to be βe<2/g2; where βe is the ratio of the directed beam kinetic energy density to the energy density of the external magnetic mirror field with βe⩾ (2/πg)(R/a)2 required for field cancellation at the torus center; g is a numerical factor of order unity; m (n) is the mode number for the minor (major) circumference; and R/a is the aspect ratio of the torus. For a tokamak, it is found that stability conditions for the modes (m≠0, n≠0), with n2≪ (R/a)2 m2, are the same as the stability conditions for these modes in a conventional plasma pinch with isotropic pressure p (r) = (1/2) nbmbu2z≡ (B2z/8π) βt, where βt is the ratio of the directed beam kinetic energy density to the energy density of the toroidal magnetic field (Bz).
A BBGKY framework for fluid turbulence
Authors: Montgomery David
Published: March 2003

A kinetic theory for fluid turbulence is developed from the Liouville equation and the associated BBGKY hierarchy. Real and imaginary parts of Fourier coefficients of fluid variables play the roles of ’’particles.’’ Closure is achieved by the assumption of negligible five-coefficient correlation functions. Probability distributions of Fourier coefficients, rather than moments, are the basic variables of the theory. Neglect of the correlation functions does not necessarily imply a cumulant discard hypothesis or a quasi-normal assumption. However, a later additional approximation leads to a closed moment description similar to the so-called eddy-damped Markovian approximation. A kinetic equation is derived for which conservation laws and an H theorem can be rigorously established. In the absence of viscosity and external driving forces, the H theorem implies relaxation to the absolute equilibrium of Kraichnan. The equation can be cast in the Fokker–Planck form, and relaxation times estimated from its friction and diffusion coefficients. An undetermined parameter in the theory, about which significant assumptions have to be made, is the free decay time for triplet correlations. Some attention is given to the inclusion of viscous damping and external driving forces.
Upper-hybrid solitons and oscillating-two-stream instabilities
Authors: Porkolab Miklos , Goldman Martin V.
Published: March 2003

A warm two-fluid theory of soliton formation near the upper-hybrid frequency is developed. Several forms of the nonlinear Schrödinger equation are obtained, depending on whether the electric field is completely perpendicular to the dc magnetic field or whether it has an additional small component parallel to the magnetic field. For the perpendicular case, the character of the soliton depends on its scale length, L, and on β. For low β, when L<c/ωpe, stationary envelope and hole solitons are found, whereas in the limit L≳c/ωpi the super-Alvénic solitons described magnetohydromagnetically by Kaufman and Stenflo are obtained. However, the case E∥≠0 may be of more interest, since it couples the pump to the excited waves more efficiently. In the limit of linearization about an infinite wavelength pump, the nonlinear Schrödinger equations yield purely growing (oscillating-two-stream) instabilities in both cases.
Low-frequency waves in a rotating magnetoplasma
Authors: Uberoi C.
Published: March 2003

The phenomena of polarization reversal and intermode coupling of magnetic and inertial modes of propagation in a rotating magnetoplasma across the crossover frequency, which arises mainly due to the presence of Coriolis force and ion-cyclotron effects, are discussed.
Electrostatic trapping and the linear and nonlinear evolution of dissipative trapped electron instabilities
Authors: Ott Edward , Manheimer Wallace M.
Published: March 2003

Three problems related to the effect of electrostatic trapping on dissipative trapped electron instabilities are investigated: (a) the linear theory of the dissipative trapped electron mode for the case in which there is both a magnetic well and an electric well (or anti-well); (b) the nonlinear stability of a drift wave (in a straight constant magnetic field) whose amplitude is large enough to trap electrons; and (c) the nonlinear saturation of the dissipative trapped electron mode in a tokamak-type magnetic well via the mechanism of electric trapping and detrapping by wave electrostatic potential perturbations along B.
Profile of an anisentropic nitrogen nozzle expansion
Authors: Lewis J. W. L. , Williams W. D.
Published: March 2003

Hypersonic N2 flow fields were produced using a conical nozzle of 1.04 mm throat diameter and an exit plane area ratio of 13.4. The reservoir pressure was varied over the range of 1.93 to 13.6 atm at the reservoir temperature of 285 K, and the reservoir conditions were such that both isentropic and anisentropic conditions existed within the axial region investigated. The N2 number density and rotational temperature axial and radial profiles were measured using laser Raman scattering, and comparisons are presented with the method of characteristics isentropic prediction. The onset of condensation and subsequent cluster growth were observed using laser Rayleigh scattering and depolarization measurements as well as photographic recording. The Rayleigh and Raman scattering data were used to obtain estimates of the axial variation of the cluster size as well as the variation of the depolarization ratio with the mean number of molecules of the cluster.
Effects of a magnetic field gradient on the lower hydrid drift instability
Authors: Huba J. D. , Wu C. S.
Published: March 2003

The effect of a magnetic field gradient on the lower hydrid drift instability is examined in the low drift velocity regime (i.e., of the order of the ion thermal velocity). The theoretical model includes density and temperature gradients, and considers only waves propagating perpendicular to the ambient magnetic field with wavelengths of the order of the electron Larmor radius. It is found, for the case of finite βe, that a magnetic gradient drift-wave resonance can be important and is stabilizing or destabilizing depending upon the physical conditions. Substantial plasma heating and a large anomalous resistivity can also occur.
Ion-streaming instabilities: Electromagnetic and electrostatic
Authors: Perkins F. W.
Published: March 2003

Electromagnetic effects are shown to reduce the threshold velocity (relative to electrostatic calculation) for ion-beam instabilities in plasmas where the beam velocity, taken parallel to the magnetic field, becomes a modest fraction of the Alfvén velocity. The most unstable mode occurs for frequencies in the ion-cyclotron frequency range and is caused by an interaction of the beam with a type of electromagnetic ion-cyclotron wave. Applications of the theory range from basic research experiments, to collisionless shocks and two-component thermonuclear burning devices.
Excitation and propagation of lower-hybrid waves in a bounded, inhomogeneous plasma
Authors: Colestock P. L. , Getty W. D.
Published: March 2003

The excitation and propagation of lower-hybrid waves in an inhomogeneous, cylindrical plasma is studied theoretically for finite-length electrostatic sources. The boundary-value problem for the electrostatic potential in a cold, inhomogeneous plasma is solved numerically as a superposition of the radial eigenmodes excited by a finite-length source. Radial eigenmodes are found numerically by an algorithm which includes the case where the lower-hybrid resonance layer occurs in the plasma. The eigenmode superposition is carried out for several phased-ring sources. The plasma response is found to be composed of resonance-cone surfaces along which the potential is a maximum. When the resonance layer does not occur in the plasma, the resonance-cone surfaces reflect from the column axis and at the plasma boundary. For the case when the resonance layer does occur, the resonance-cone surfaces become asymptotic to the resonance layer and do not penetrate to the center. The presence of damping causes the resonance-cone singularities to dissolve axially leaving the lowest-order radial mode excited by the source.