bluuebunny/crossref_metadata_2025 huggingface dataset:
Force on a moving plasma by a finite conductivity wall
Authors: Boozer Allen H.
Published: March 2003

The force on a plasma which is moving relative to a finite conductivity wall is evaluated assuming that the plasma is distorted by a saturated magnetohydrodynamic mode.
Linear mode conversion of upper hybrid waves
Authors: Shoucri Merit , Kuehl H. H.
Published: March 2003

For an extraordinary wave incident on the upper hybrid layer from within an inhomogeneous plasma, the efficiency for mode conversion into a Bernstein wave is derived. Complete mode conversion occurs only if the scale length of the density gradient is large compared with the free-space wavelength.
Interface related velocities in turbulent plane jets
Authors: Oler J. W. , Jenkins P. E. , Goldschmidt Victor W.
Published: March 2003

The velocities of the flow in the vicinity of the interface, of the apparent lateral motion of the interface, and of entrainment are compared for a plane two-dimension jet.
Theory of mode-conversion in weakly inhomogeneous plasma
Authors: Fuchs V. , Ko K. , Bers A.
Published: March 2003

The theory of pair-wise coupled modes excited at a real frequency ω in a weakly nonuniform plasma (coordinate x) is developed on the basis of general local dispersion relations D(k,z) = 0 (such as from the Vlasov equation), which define a many-valued mapping of the real axis x = Rez onto the complex plane of the wavenumber k. Mode coupling, by definition, is the analytical continuation of the branch of the mapping and only occurs at the branch points. This requires that the z plane be cut along contours Cb given by D(kc,Cb) = 0, ∂D(kc,z)/∂k = 0, where z traces a contour passing through the branch points. The coupled modes can be analyzed by expanding the dispersion relation to second order in k around the saddle points and along the lines kc(x), yielding a system of dispersion relations corresponding to unambiguous second-order differential equations, guaranteed to have the right turning point behavior.
Spheromak tilting instability in cylindrical geometry
Authors: Finn John M. , Manheimer Wallace M. , Ott Edward
Published: March 2003

The internal tilting instability in a force-free spheromak plasma in cylindrical geometry is examined. It is found that this instability, originally found in spherical geometry, also occurs in cylindrical geometry. The analysis proceeds by first demonstrating that if no mode rational surface is present in the plasma, a necessary and sufficient condition for ideal magnetohydrodynamic instability is that there exist a solution to ∇×Bm = μmBm, where Bm∼exp(imϑ), with μm<μ0. Solutions to this equation are investigated using two approaches, by a series expansion and by a numerical solution of a modified set of linearized magnetohydrodynamic equations. The eigenvalue for the m = 1 mode satisfies μ1<μ0 for L/a≳1.67. Since no mode rational surface exists for this elongation, an ideal magnetohydrodynamic mode, identified as the tilting mode, is unstable for these parameters. All modes with m≳1 are shown to be stable.
Electromagnetic emission and anomalous resistivity from equal and oppositely directed electron beams
Authors: Alexeff Igor , Roth J. Reece , Birdwell J. Douglas , Mallavarpu Raghuveer
Published: March 2003

The experimental observation and theoretical description of a previously unrecognized mechanism for generating electromagnetic emissions and anomalous resistivity from a beam-plasma interaction which is characteristic of Penning discharges is reported. Very clear emissions were observed from electric field-dominated bumpy torus plasma near the geometric mean plasma frequency. These emissions are inconsistent with familiar physical mechanisms, and occurred in excellent agreement with the theoretical frequency ωgm = 0.537(ωpeωpi)1/2. This frequency was derived from a theory based on the interaction of two opposite, interpenetrating electron beams with a heavy ion plasma. The anomalous resistivity associated with this interaction is predicted to several hundred times that of the familiar Buneman or ’’turbulent’’ resistivity. A perturbation procedure is used to obtain analytic expressions for the emission frequency and the anomalous resistivity in the zero temperature case. These results are extended to include the effects of finite ion temperatures on the dispersive properties of the plasma.
Tokamak microturbulence and the second law of thermodynamics
Authors: Boozer Allen H.
Published: March 2003

The second law of thermodynamics is shown to place interesting limits on fluctuation amplitudes and on the form of interaction of the turbulence with the plasma in large tokamaks.
Variational principle for low-frequency stability of collisionless plasmas
Authors: Antonsen Thomas M. , Lane Barton , Ramos Jesús J.
Published: March 2003

An analysis of the stability of an arbitrary β collisionless plasma to modes with wavelengths greater than the ion gyroradius is presented. The stability of such a plasma to perturbations that grow on the hydrodynamic time scale is determined by the Kruskal–Oberman energy principle. However, a configuration which is predicted to be stable on the basis of this kinetic energy principle may still be unstable to modes that grow with a frequency comparable to the diamagnetic or curvature drift frequency. A new variational principle that gives sufficient conditions for instability of these low- frequency modes is derived. The new principle indicates that two types of instabilities are possible; the first corresponds to the low-frequency electrostatic, trapped particles mode, and the second is the low-frequency limit of magnetohydrodynamic (interchange and ballooning) modes. The kinetic modifications to the interchange (Mercier) criterion are evaluated and the effect of the kinetic terms on ballooning modes is estimated.
Generalized scalar potentials for linearized three-dimensional flows with vorticity
Authors: Hart R. W.
Published: March 2003

The three-dimensional time-dependence velocity of incompressible fluids satisfying linearized incompressible Navier–Stokes equations can often be expressed in terms of a single h by v = A∇h+B(l̂×∇h)+Cl×(l×∇h), where l is a constant vector and A,B,C are scalar operators. For B,C≠0,curl v≠0.
Appendix: Variational moment solutions to the Grad–Shafranov equation [Phys. Fluids 24, 1431 (1981)]
Authors: Weitzner Harold
Published: March 2003

Appendix to  Variational moment solutions to the Grad–Shafranov equation  (AIP)
Excitation of multiple ion-acoustic shocks
Authors: Chan Chung , Khazei Mehyar , Lonngren Karl E. , Hershkowitz Noah
Published: March 2003

Multiple electrostatic ion-acoustic shock-like density perturbations are observed experimentally to be launched from a large plate in a quiescent collisionless plasma. The formation of the fastest shock is due to ions expelled from the edge of the ’’transient sheath’’ surrounding the plate. The second shock then evolves as a result of the surrounding ions filling in the region of density depression created by the first shock. Reflected ions and turbulent ion-acoustic noise at the shock front and amplitude modulation in the trailing dispersing oscillations are only observed for the leading shock.
Proton beam-target interaction at pellet fusion power densities
Authors: Peleg E. , Zinamon Z.
Published: March 2003

The interaction of proton beams at pellet fusion power densities (∼100 TW/cm2) with initially solid targets is calculated. Radiation losses and conduction are shown to have important effects at these power densities.
Stability properties of azimuthally symmetric perturbations in an intense electron beam
Authors: Uhm Han S. , Lampe Martin
Published: March 2003

The Vlasov–Maxwell equations are used to investigate the stability of azimuthally symmetric perturbations (e.g., sausage and hollowing modes) of an electron or ion beam immersed in a resistive plasma. The perturbed space charge and plasma current are treated self-consistently for any value of the plasma conductivity. A similar analysis of the hose instability is also carried out. It is assumed that ν/γb≪1, where ν is Budker’s parameters and γbmc2 is the characteristic beam electron energy. The analysis is carried out for the ’’loss-cone’’ distribution function in which all of the beam electrons have the same value of energy (in a frame of reference rotating with angular velocity ωb) and the same value of axial canonical momentum. In the high conductivity regime, the system is shown to be strongly destabilized by a sufficiently large value of the fractional current neutralization.
Anomalous absorption of ordinary electromagnetic waves in magnetized plasmas
Authors: Lin A. T. , Lin C. -C.
Published: March 2003

Ordinary electromagnetic waves can be employed to heat electrons in magnetized plasmas through parametric instabilities if the power level exceeds a certain threshold. Around the electron cyclotron second harmonic frequency band, ordinary waves can decay into upper hybrid waves and other ordinary waves with lower frequency and wavenumber. Depending on the pump wavelength and power, both forward and backward scattering processes can take place. The decay waves ultimately fed energy into electrons through turbulent heating. Only bulk heating has been observed in the simulation.
Stochastic instability induced in toroidal plasma by pulsed radio frequency
Authors: Casati Giulio , Lazzaro Enzo
Published: March 2003

It is shown that the interaction of pulse modulated radio frequency waves of suitable amplitude, with the population of trapped particles in a tokamak may develop the features of the so-called stochastic instability, eventually leading to a systematic increase in the energy of the particles and to their detrapping.
Ion cyclotron modes in tokamaks
Authors: Waltz R. E. , Dominguez R. R.
Published: March 2003

A linear theory of electrostatic ion cyclotron normal modes with moderate wavenumber (k⊥ ρi≲1) which can exist in a sheared magnetic field is given. Such modes have been seen in a scattering experiment on the TFR tokamak. A novel mode with fluid electron behavior is found, and the Drummond and Rosenbluth current-driven mode with kinetic electron behavior is recovered. Toroidal effects are considered. The kinetic modes offer the most natural explanation for the experimental frequency spectrum. However, numerical solutions of the dispersion relations predict that current drifts three to ten times larger than those in TFR are needed for instability.
Omnigenous equilibria
Authors: Catto P. J. , Hazeltine R. D.
Published: March 2003

The conditions are obtained for confining a plasma of arbitrary asymmetry, plasma beta, and collisionality, in an equilibrium configuration free of neoclassical transport. Such omnigeneous scalar pressure equilibria are shown to exist if, and only if, the divergence of the parallel current density vanishes, while for an anisotropic pressure other mild restrictions are needed. Explicit constraints are derived for axisymmetric tori and long-thin, low-beta conventional and tandem mirrors.
Rayleigh–Taylor instabilities of an accelerating thin plasma slab
Authors: Tsai Wu-yang , Liskow Dean , Wilcox Thomas
Published: March 2003

Rayleigh–Taylor instabilities of an accelerating plasma sheet are studied by application of normal mode analysis to the one-fluid magnetohydrodynamic equations. The equilibrium unperturbed states are determined by specifying the resistivity law of the current carrying plasma, although resistivity effects are neglected in the developing instabilities. The dispersion curves for the current filamentation and interchange type instabilities are given.
Turbulent solution of the Navier–Stokes equations
Authors: Deissler R. G.
Published: March 2003

To study the nonlinear physics of incompressible turbulent flow, the unaveraged Navier–Stokes equations are solved numerically. Initial three-dimensional cosine velocity fluctuations and periodic boundary conditions are used. No mean gradients are present. The three components of the mean-square velocity fluctuations are equal for the initial conditions chosen. The resulting solution shows characteristics of turbulence, such as the nonlinear excitation of small-scale fluctuations. For the higher Reynolds numbers the initially nonrandom flow develops into an apparently random turbulence. Thus, randomness or turbulence can apparently arise as a consequence of the structure of the Navier–Stokes equations.
Two-dimensional evolution of packets of short water waves in systems of finite depth
Authors: Laedke E. W. , Spatschek K. H.
Published: March 2003

The evolution of packets of water waves described by the long-wave limit of the Davey–Stewartson equations is considered. The stationary one-dimensional kink solutions are analyzed with respect to transverse perturbations. They are shown to be stable when surface tension can be neglected. To demonstrate this, the two-dimensional inverse scattering transform found by Anker and Freeman is applied. The present stability analysis supplements previous investigations in the long-wavelength limit of water waves where finite depth effects have been ignored.
Theory of the renormalized dielectric for electrostatic drift wave turbulence in tokamaks
Authors: Diamond P. H. , Rosenbluth Marshall N.
Published: March 2003

A theory of collisionless electrostatic drift wave turbulence in a circular cylinder with shear is presented. A renormalized electron drift kinetic equation which is consistent with conservation of energy is derived. For low levels of turbulence, a perturbative solution indicates that the turbulence has a stabilizing effect and that total mode spectrum energy decreases. For strongly turbulent regimes, results quantitatively but not qualitatively different from those of Hirshman and Molvig are found. In particular, additional stabilizing terms lead to a lower saturation amplitude, but the basic picture of turbulent destabilization competing against linear and nonlinear shear damping persists.
Physical mechanism of wave-particle resonances in an inhomogeneous magnetic field. I. Linear theory
Authors: Huba J. D. , Drake J. F.
Published: March 2003

A physical description is given of the wave-particle resonance which can occur when particles undergoing a ∇ B drift are in phase with a wave propagating across the magnetic field (i.e., ω ∼ k⋅V∇ B, where V∇ B is the ∇ B drift velocity). Specifically, the physics of the energy exchange mechanism is discussed and a general equation for the wave damping/growth rate is derived based upon physical arguments. The theory is applied to the lower-hybrid-drift instability and collisionless trapped electron instability.
Microwave heating of the ELMO Bumpy Torus relativistic electron ring
Authors: Hamasaki S. , Klein H. H. , Krall N. A. , McBride John B. , Sperling J. L.
Published: March 2003

A model for microwave heating of electron rings in the ELMO Bumpy Torus configuration is analyzed using a relativistically correct quasi-linear formulation. The spatial locations of heating by the different electron-cyclotron harmonics are calculated. The steady-state ring energy and the microwave power required to sustain the rings are determined by balancing the line-averaged heating rate against classical collisional and radiative energy loss processes. Although ring formation is generally attributed to the second harmonic electron-cyclotron resonance, the calculations show that fundamental heating also plays a critical role in ring start-up and steady state. The model predicts ring power requirements for EBT which are consistent with previous estimates.
Comment on ‘‘Adiabatic modifications to plasma turbulence theories’’
Authors: Weinstock J. , Catto P. J.
Published: March 2003

Comment on ’’adiabstic modifications to plasma turbulence theories’’ is made. (AIP)
Comments on ‘‘Viscous buckling of thin fluid layers’’
Authors: Bejan Adrian
Published: March 2003

Comments on viscus buckling of thin fluid layers are pretented. (AIP)
Reply to the comments by A. Bejan
Authors: Munson B. R.
Published: March 2003

Reply to the comments on viscons buckling of fluid layers is made. (AIP)
Analytic field-reversed equilibria
Authors: Berk Herbert L. , Hammer James H. , Weitzner Harold
Published: March 2003

Several families of analytic equilibria for field-reversed plasma are obtained for arbitrary internal pressure and toroidal field.
Thermal equilibrium and stability of an Ohmically heated plasma
Authors: Rosenau Philip
Published: March 2003

Steady-state temperature profiles in a magnetically confined tokamak type plasma are derived by balancing Ohmic power input, thermal diffusion, and radiation. A comprehensive study is presented of the impact that different electron conductivities, K⊥ boundary conditions, and radiation may have on thermal stability. In particular, their influence on the bifurcation in the position of the minor radius as a function of the temperature at the center Tm is considered. Points of bifurcation correspond to marginally stable equilibria. However, it is also possible to have both branches without marginally stable equilibrium. Critical values of parameters that cause the onset of a new branch or instability are determined. Growth rates are not calculated, but domains of stabilty of all possible equilibria are determined. It is shown that Ohmically heated plasma in the classical scaling is thermally unstable to convective boundary conditions or if the plasma is cold at the edge. It is shown that a finite temperature at the edge will generate a stable, lower branch, but the upper branch will be unstable as long as p<0.5, where K⊥(T)∼Tp.
Nonlinear evolution of lower-hybrid drift instability
Authors: Ishihara Osamu , Hirose Akira
Published: March 2003

The nonlinear evolution of the lower-hybrid instability is studied analytically for the cross-field electron drift velocity much larger than the ion thermal velocity (hydrodynamic regime). A nonlinear dispersion relation is derived, in which the frequency as well as growth rate modulation is taken into account, and the ion heating and ion drift motion accompanied by the growth of the instability are renormalized in the ion susceptibility. The dispersion relation determines self-consistently, in a quasilinear approximation, the time variation of the complex frequency Ωk(t) = ωk(t)+iγk(t). Numerical solution of the dispersion relation reveals that the growth rate of the most unstable mode becomes ∼0.1γ0 (γ0 is the initial growth rate) after several growth periods.
Convective Brillouin amplification in drifting plasmas
Authors: Mitchel G. R. , Johnston T. W. , Grek B.
Published: March 2003

Previous work on the absolute instability of Brillouin scatter in drifting plasmas is extended to the case of convective amplification. It is found that, similar to temporal growth rates for the absolute instability, forward oblique scatter has the highest spatial gain, with backscatter near a minimum. To agree with experimental results on outward scattered light, source terms are required which must be many orders of magnitude above thermal. Although in the heavy ion damping regime self-limiting via ion heating decreases the sensitivity of the final reflectivity to the source strength, there is no evidence of a scattering limit when pump depletion is small (the normal experimental situation).
Destabilization of the electron Bernstein modes by runaway electrons
Authors: Hitchcock D. A. , Mahajan S. M.
Published: March 2003

It is shown that the electromagnetic finite k∥ electron Bernstein mode can be destabilized by the runaway electron distribution which results from the quasilinear action of the magnetized plasma oscillation. This mechanism is shown to yield growth rates of the order of 108 sec−1 and is suggested as a mechanism for the enchanced cyclotron harmonic emission in the presence of runaway electrons.
Onset of convection in impulsively heated or cooled fluid layers
Authors: Neitzel G. P.
Published: March 2003

Energy stability theory is employed to determine lower bounds on onset times and global stability bounds for initially isothermal fluid layers subjected to impulsive changes in surface temperature. Various combinations of rigid and free boundary conditions and heating or cooling are considered.
Wave-wave interaction and the self-focusing of Langmuir waves
Authors: Weatherall J. C.
Published: March 2003

A perturbation theory describes the exchange of energy between modes with nearly the same linear frequency. A distinction is made between this interaction, which is apparently associated with the initiation of collapse, and the exponentially growing modulation instability.
Investigation of the frozen-turbulence hypothesis for temperature spectra in a convectively mixed layer
Authors: Deardorff J. W. , Willis G. E.
Published: March 2003

Taylor’s frozen turbulence hypothesis is investigated in a laboratory free-convection mixed layer which can simulate buoyancy-driven turbulence in an atmospheric mixed layer (of height h) for mean wind speeds of up to several meters per second. For large turbulence intensities the temperature spectra at the height 0.1h are found to be spuriously enhanced at higher wavenumbers based on the frozen turbulence hypothesis, as deduced theoretically by previous investigators. The excess is borrowed from spectral intensities within the energy-containing range. A theory based on the concept of longitudinal-temporal isotropy, after proper scaling of the coordinates, is shown to predict a simple shift of the entire spectrum toward higher wavenumbers with increasing turbulence intensity. The failure of the observed spectra to behave this simply is associated with a complicated structure of the correlation coefficient as a function of longitudinal-temporal lag coordinates when the former is measured relative to a frame moving with the mean flow speed. The temperature spectrum based on the frozen-turbulence hypothesis appears to be a satisfactory representation of the true spectrum in wavenumber space, in tubulence dominated by thermal convection, if the mean wind speed exceeds 2.7–3.6 times the root-mean-square horizontal velocity fluctuation.
Static and dynamic impulses generated by two-phase detonations
Authors: Eidelman Shmuel , Sichel Martin
Published: March 2003

The influence of the mixture density and the reaction zone length on the static and dynamic impulse of the detonations through wheat dust, RDX dust, and decane droplet air mixtures was studied. A numerical solution of the detailed model of the two-phase detonation initiation and development in the medium, provided the basis for the study. Mixtures with a higher average density were found to produce a significantly greater static impulse, but a reduced dynamic impulse. The reasons for this behavior were discussed.
Free expansion and diffusion in a laser-produced plasma
Authors: Segal D. , Avivi P.
Published: March 2003

A diffusion effect has been measured on a time-of-flight velocity distribution measurement of a laser-produced plasma. After allowing for this effect, a good fit to a nondisplaced Maxwellian is obtained. The fit was made to the total ion signal. Retarding voltage measurements show that most of the ions are triply ionized.
Kelvin–Helmholtz instability for parallel flow in porous media: A linear theory
Authors: Bau Haim H.
Published: March 2003

Two fluid layers in fully-saturated porous media are considered. The lighter fluid is above the heavier one so that in the absence of motion the arrangement is stable and the interface is flat. It is shown that when the fluids are moving parallel to each other at different velocities, the interface may become unstable (the Kelvin–Helmholtz instability). The corresponding conditions for marginal stability are derived for Darcian and non-Darcian flows. In both cases, the velocities should exceed some critical values in order for the instability to manifest itself. In the case of Darcy’s flow, however, an additional condition, involving the fluids’ viscosity and density ratios, is required.
The nonunique rate of spread of the two-dimensional mixing layer
Authors: Weisbrot I. , Einav S. , Wygnanski I.
Published: March 2003

The rate of spread of a plane, incompressible, turbulent shearlayer was determined experimentally. The velocity ratio was constant, while the actual velocities were altered. It was established that the divergence of the flow with downstream distance was not uniquely determined by the velocity ratio in the range of variables considered. It is believed that an instability is responsible for this behavior.
Stability of an expanding cylindrical plasma envelope: Rayleigh–Taylor instability
Authors: Han S. J.
Published: March 2003

The stability of a cylindrically symmetric plasma envelope driven outward by blast waves is considered. The plasma fluid is assumed to be a compressible, isentropic gas describable as an ideal gas ( p = aργ, γ≳1). The stability problem of such an envelope undergoing self-similar motion is solved by considering the initial-value problem. It is shown that in the early phase of an expansion, the envelope is unstable to Rayleigh–Taylor modes which develop at the inner surface. In the later phase of the expansion, the Rayleigh–Taylor modes are weakened due to the geometrical divergence effect. The implications of the time-dependent behavior of the Rayleigh–Taylor instability for plasma switches are discussed.
Mechanism of atomization of a liquid jet
Authors: Reitz R. D. , Bracco F. V.
Published: March 2003

In the atomization regime of a round liquid jet, a diverging spray is observed immediately at the nozzle exit. The mechanism that controls atomization has not yet been determined even though several have been proposed. Experiments are reported with constant liquid pressures from 500 psia (33 atm) to 2500 psia (166 atm) with five different mixtures of water and glycerol into nitrogen, helium, and xenon with gas pressures up to 600 psia (40 atm) at room temperature. Fourteen nozzles were used with length-to-diameter ratios ranging from 85 to 0.5 with sharp and rounded inlets, each with an exit diameter of about 340 μm. An evaluation of proposed jet atomization theories shows that aerodynamic effects, liquid turbulence, jet velocity profile rearrangement effects, and liquid supply pressure oscillations each cannot alone explain the experimental results. However, a mechanism that combines liquid–gas aerodynamic interaction with nozzle geometry effects would be compatible with our measurements but the specific process by which the nozzle geometry influences atomization remains to be identified.
Bipolar model for traveling-wave induced nonequilibrium double-layer streaming in insulating liquids
Authors: Ehrlich R. M. , Melcher J. R.
Published: March 2003

A model is proposed for the time evolution of ion concentrations in a thin charge layer near an interface between an insulating solid and a semi-insulating bipolar liquid, subjected to an applied electric field. Given the specific case of a traveling-wave applied field of peak magnitude E0 and planar geometry, solutions for the charge density and electric field in the layer are used to calculate the time-average stress moment and, hence, the pumping velocity of the liquid. Analytic solutions, valid in the regimes of small applied field magnitude (E0LD/Vt≪1, where L0 and Vt are the Debye length and thermal voltage, respectively) or frequency (ωε/σ≪1, ω the angular frequency and ε and σ the permittivity and equilibrium conductivity, respectively), predict charge layers with a characteristic dimension of the Debye length and fluid pumping in the direction of propagation of the traveling wave (forward). Numerical solutions, in the regime of large magnitude fields with ωε/σ∼1, predict either forward or backward pumping, as well as a charge layer with thickness on the order of a migration length (L = 2πbE0/ω, where b is the ion mobility). Parameters such as ion mobility, thermal generation rate, and level of ionization in the liquid are important in determining the rate (and even direction) of the pumping.
Hamiltonian formulation of guiding center motion and of the linear and nonlinear gyrokinetic equation
Authors: Wong H. Vernon
Published: March 2003

This derivation of the gyrokinetic equations is based on the Hamiltonian formulation of the guiding center motion. The transformation to guiding center variables is accomplished by a sequence of canonical transformations. The kinetic equation is determined by Liouville’s equation. This equation is then ordered in accordance with the gyrokinetic ordering, and analyzed order by order to obtain the linear and nonlinear gyrokinetic equations.
Finite-β stabilization of the universal drift instability: Revisited
Authors: Huba J. D. , Gary S. Peter
Published: March 2003

The stabilization of the universal drift instability due to finite β effects (i.e., electromagnetic coupling and ∇B orbit modifications) is studied numerically and a marginal stability curve (as a function of β and k) is presented. It is found that the most difficult modes to stabilize have arbitrarily small wavenumbers and the critical value of β is βcr ≃0.135 for Te = Ti.
Beat excitation of whistler waves
Authors: Shoucri Merit M. , Morales G. J. , Maggs J. E.
Published: March 2003

A detailed calculation is made of the nonlinear excitation of a low-frequency whistler due to the beat of two high-frequency electromagnetic waves. The whistler is excited near the reflection layers of the high-frequency pumps where an effective antenna is generated by the beat ponderomotive force acting on electrons. Results relevant to ionospheric and laboratory experiments are obtained.
Nonlocal aspects of electrostatic current-driven ion cyclotron instability due to magnetic shear
Authors: Ganguli G. , Bakshi P.
Published: March 2003

The effect of the magnetic shear on the current-driven ion cyclotron instability has been studied. Taking into account the asymmetry introduced by the external current, an analytical theory to study the nonlocal behavior of this instability is given. The main consequences of the magnetic shear are to (i) localize the instability in space and (ii) reduce the growth rates in general. The damping influence of shear arises in two distinct ways; (a) a damping rate directly proportional to the shear strength, and (b) a damping rate (due to the nonlocal nature of the dispersion relation) not explicitly dependent on shear which can be quite strong for above marginal currents. Shear makes this instability more coherent by reducing the band of the perpendicular wavelengths which is unstable. The general physics of this instability and the parametric dependences of the growth rates are studied and marginal stability curves given.
Fluctuation spectra of a drift wave soliton gas
Authors: Meiss J. D. , Horton W.
Published: March 2003

A theory of drift wave turbulence is presented based on a low-density gas of drift wave solitons. The Gibb’s ensemble for the ideal gas is used to calculate the dynamical scattering form factor S(k,ω). In contrast to renormalized turbulence theory, the spectrum has a broad frequency component with Δω proportional to the fluctuation level δne/n0 at fixed k and peaks at a frequency ω≳kyvde.
Enhanced growth of tearing modes due to turbulent dissipation induced by a stochastic magnetic field
Authors: Kleva Robert G.
Published: March 2003

The effect of a stochastic magnetic field on the evolution of a long wavelength tearing mode is investigated analytically. A near Gaussian statistical closure approximation is used to obtain renormalized statistical equations from the fluid equations. The stochastic magnetic field is found to induce a turbulent electron dissipation. For typical tokamak discharge parameters, this turbulent dissipation both broadens the current layer of the mode and leads to a growth rate which, for fluctuation levels 〈(δB/B)2〉 as small as 10−8, is significantly larger than the classical resistive growth rate.
Coalescence of spheromaks
Authors: Reiman Allan
Published: March 2003

The coalescence of two spheromaks is described using the quasi-ideal model of reconnection. Nonaxisymmetric effects are found to play an important role in general. Possible applications of repeated coalescence are studied, including heating the spheromak plasma, building up a large spheromak from smaller ones, and maintaining a spheromak in steady state. The analysis suggests that coalescence experiments could also provide a valuable method for studying magnetic field relaxation.
Transport of neutrals in a multicomponent cool plasma mantle
Authors: Tendler M. , Chhabra R. S.
Published: March 2003

Transport of neutrals in a plasma, consisting of two species of ions and neutrals, across a plane plasma slab bounded between the wall and hot plasma is investigated using a kinetic approach. Analytical expressions for the neutral density profile and the velocity distribution functions have been obtained. For impurity elements like He, Ne, and Ar for temperatures T<10 eV, the neutral transport is controlled jointly by electron ionization and charge exchange and the penetration depth for neutral atoms of these elements is found to be somewhat larger than the penetration depth for neutral hydrogen atoms. In the temperature range 20 eV<T<100 eV the penetration of both the neutral species is governed mainly by electron ionization and the penetration depth for neutral hydrogen atoms is found to be nearly equal to that for neutrals of these elements. It is also noted that the impurity content in the plasma phase affects the transport of impurity neutrals weakly when 20 eV<T<100 eV and strongly for T<10 eV.
Radial transport in the central cell of the tandem mirror experiment
Authors: Drake R. P. , Hooper E. B. , Karmendy C. V. , Allen S. L. , Casper T. A. , Clauser J. F. , Coensgen F. H. , Cohen R. H. , Correll D. L. , Davis J. C. , Foote J. H. , Futch A. H. , Goodman R. K. , Grubb D. P. , Gryczkowski G. E. , Hallock G. A. , Hunt A. L. , Nexsen W. E. , Pickles W. L. , Pontau A. E. , Poulsen P. , Simonen T. C. , Strand O. T. , Wampler W. R.
Published: March 2003

An experimental study of radial transport in the Tandem Mirror Experiment is reported here. Plasma parameters were measured in a series of well-diagnosed plasma discharges. A negative electric current (80±40 A within a 30-cm radius) flowed to the end wall, implying an equal radial loss of plasma ions. The axial losses of plasma ions were 100 A from the same volume. The nonambipolar radial ion flux was of the same order as the flux resulting from resonant-neoclassical and ion-neutral transport, but the uncertainties are large. The ambipolar radial transport (of both ions and electrons) was investigated by comparing the observed end losses with calculations of the plasma fueling by gas penetration and neutral beams. The ambipolar radial losses are probably smaller than the loses through other processes and may be as small as the classical losses resulting from Coulomb collisions.
Flux-trapping during the formation of field-reversed configurations
Authors: Armstrong W. T. , Harding D. G. , Crawford E. A. , Hoffman A. L.
Published: March 2003

Flux-trapping during the early formation phases of a field-reversed configuration has been studied experimentally on the field-reversed theta-pinch TRX-1. An annular z-pinch preionizer was employed to permit ionization at high values of reverse-bias flux. Contrary to previous analysis, the rate of flux loss was not governed exclusively by inertially limited plasma convection to the tube walls. At high reverse flux levels, a pressure bearing sheath was observed to form at the tube walls and the flux loss was restricted by resistive diffusion across this sheath. The characteristic time for flux loss was 0.08rt (cm) μsec, independent of the bias field and independent of the fill pressure for fill pressures above 15 mTorr D2. Octopole barrier fields were found to be effective in limiting the inertially governed flux loss at very early times before the wall sheath formed.
Kinetic analysis of evaporation and condensation in a vapor-gas mixture
Authors: Soga Takeo
Published: March 2003

Evaporation and condensation of vapor-gas mixture is studied on the basis of the kinetic BGK–Morse model equation. The linearized kinetic model equation is solved using the half-range Hermite polynomials and various slip coefficients are obtained. The obtained slip coefficient of vapor pressure is insensitive to the variation in concentration of a noncondensable gas. When the mean concentration of noncondensable gas is very small, an exponential distribution of noncondensable gas is obtained and a set of nonlinear equations is transformed to that of linear equations for pure vapor. It is found from the linear and nonlinear solutions that the impedance of mass flux in the two-surface problem is composed of surface and induced resistances and that the latter is proportional to the total amount of the noncondensable gas rather than the mean concentration of it.
Elementary derivation of Poisson structures for fluid dynamics and electrodynamics
Authors: Kaufman Allan N.
Published: March 2003

The canonical Poisson structure of the microscopic Lagrangian is used to deduce the noncanonical Poisson structure for the macroscopic Hamiltonian dynamics of a compressible neutral fluid and of fluid electrodynamics.
Stability of a thick two-dimensional quasineutral sheet
Authors: Lembège B. , Pellat R.
Published: March 2003

The stability of a two-dimensional magnetic model of a thick quasineutral sheet including a small but finite normal magnetic field component is studied in a collisionless plasma. Such a magnetic configuration allows an adiabatic motion for electrons which are trapped in good agreement with the thick sheet model. A detailed kinetic study of the energy balance shows that the ion linear tearing mode instability is suppressed by the interaction between the perturbed electromagnetic field and the adiabatic electron motion; this interaction leads to a ‘‘compressibility’’ effect which prevents the instability onset. The connection with the magnetohydrodynamic energy principle for stability is demonstrated. A general formalism is developed for any magnetic configuration and applied to a parabolic and a magnetic island topology. Some conclusions concerning the nonlinear tearing mode behavior (explosive phase) are drawn.
An energy loss coefficient in fluid buckling
Authors: Cruickshank J. O. , Munson B. R.
Published: March 2003

A jet of viscous fluid falling against a flat plate may become unstable and buckle. The buckling process is postulated as a discontinuity, and a simple model is developed that indicates a loss of energy in the fluid buckling. Experimental values of the energy loss coefficient are presented.
Anomalous frequency spectrum of inertial waves in a finite, rotating, sectored cylinder
Authors: Scott W. E.
Published: March 2003

It is shown that an inviscid, incompressible liquid completely filling a finite, sectored, rapidly rotating cylinder, possesses a continuous inertial wave frequency spectrum rather than the usual denumerably infinite set of frequencies! A physical argument for this unusual phenomenon is presented along with reference to some confirmatory experiments.
The stability of swirling flows at large Reynolds number when subjected to disturbances with large azimuthal wavenumber
Authors: Stewartson K.
Published: March 2003

An asymptotic theory is developed to describe the stability characteristics of a swirling axial flow at high Reynolds number R when subject to disturbances with a large azimuthal wavenumber n. It is based on an earlier study by Leibovich and Stewartson of the corresponding inviscid problem. The essence of the theory is to exploit the fact that the disturbance is concentrated on a narrow band at a finite distance from the axis decaying exponentially on either side. As an example to illustrate the theory, the stability characteristics of a trailing vortex is examined. A comparison with computed values of the neutral curves for n=1,2,3 shows that even at such low values of n the theory is generally qualitatively correct and in some respects is remarkably accurate. UFoff
Continuous temporal eigenvalue spectrum of an Ekman boundary layer
Authors: Spooner George F.
Published: March 2003

It is demonstrated that the perturbation equation governing small disturbances in an Ekman boundary layer possesses a double branched, continuous spectrum of temporal eigenvalues. The nature of these eigenvalues and their associated eigenfunctions is discussed and compared with that of the temporal spectrum of the Blasius boundary layer.
Collisional drift waves in a spheromak geometry
Authors: Marchand R. , Guzdar P. N.
Published: March 2003

An eigenmode equation for collisional electrostatic drift waves in general axisymmetric toroidal geometry is derived and solved numerically for a low-β spheromak. In the calculation of the density responses, the ions are treated as a cold fluid, and the electrons are assumed to be isothermal. The electron–ion collision operator is approximated by a friction term in the parallel component of the electron momentum equation, and the perturbation analysis includes the self-consistent equilibrium electron current dynamics. Large toroidal mode numbers are assumed and use is made of the simplifying ballooning mode representation. The main destabilizing mechanism found here comes from electron–ion collisions. For the parameters considered, the mode frequency and growth rate are hardly affected by the equilibrium current driving terms.
Flute instability in axisymmetric mirrors
Authors: Adler E. A.
Published: March 2003

The Kruskal–Oberman energy principle is used to calculate the stability to flutes of an axisymmetric mirror. Marginally stable pressure profiles are calculated for the Lamex device.
Free-boundary high-beta tokamaks. II. Mathematical intermezzo: Hilbert transforms and conformal mapping
Authors: Goedbloed J. P.
Published: March 2003

Mathematical techniques are described that facilitate the reduction of the stability problem of a toroidal free-boundary high-β tokamak equilibrium with skin currents to one that is basically one-dimensional. This includes the conformal mapping of the simply connected plasma region onto a circular disk and the conformal mapping of the doubly connected vacuum region onto an annulus by means of the Theodorsen and Garrick nonlinear integral equations. Henrici’s method of constructing the discretized Hilbert transforms for periodic functions on the boundaries of these domains provides both the basis for constructing the mappings and the tool for the study of the perturbations. The methods are applied to problems of two-dimensional potential flow with a discontinuity of which the stability of sharp-boundary high-β tokamaks is just a special case.
Free-boundary high-beta tokamaks. III. Free-boundary stability
Authors: Goedbloed J. P.
Published: March 2003

Using the techniques of Hilbert transforms and conformal mapping, the stability problem of a toroidal free-boundary high-β tokamak equilibrium with a skin current is reduced to a one-dimensional problem for which a new variational principle is derived. The minimization is carried out numerically and a complete scan of parameter space is carried out. The stability limit is qualitatively different from the one obtained in the usual fixed-boundary model without a wall. Rather than a more severe, a less severe limitation on the plasma current is obtained. It is shown that the Kruskal–Shafranov limit may be surpassed when the value of β is sufficiently high and the wall is sufficiently close to the plasma.
Stability properties of an intense relativistic non-neutral electron ring in a modified betatron accelerator
Authors: Davidson Ronald C. , Uhm Han S.
Published: March 2003

Equilibrium and stability properties of an intense electron ring located at the midplane of an externally applied mirror field are investigated within the framework of the linearized Vlasov–Maxwell equations, including the important influence of equilibrium self-fields and an applied field Bext0θ in the toroidal direction. It is assumed that the ring is thin and that ν/γb≪1, where ν is Budker’s parameter and γbmc2 is the characteristic electron energy. Equilibrium and stability properties are calculated for the choice of equilibrium distribution function in which all electrons have the same value of energy in a frame of reference rotating with angular velocity ωb in the minor cross section of the ring, and a Lorentzian distribution in canonical angular momentum Pθ. Negative-mass and resistive-wall stability properties are calculated, and a closed dispersion relation is obtained for the case where the ring is located inside a toroidal conductor with finite resistivity and minor radius ac much less than the major radius R0. One of the most important features of the stability analysis is that the negative-mass instability in a high-current ring can be stabilized by equilibrium self-field effects in circumstances where the self-fields are sufficiently intense. Moreover, a modest spread Δ in canonical angular momentum can stabilize the resistive-wall instability.ufoff
Transition from single to multiple double layers
Authors: Chan Chung , Hershkowitz Noah
Published: March 2003

It is shown that laboratory double layers become multiple double layers when the ratio of Debye length to system length is decreased. This result exhibits characteristics described by boundary layer theory.
Evolution of groups of gravity waves with moderate to high steepness
Authors: Su Ming-Yang
Published: March 2003

Experimental measurements of evolution of a deep-water wave group are described. Wave groups are found to change rapidly over a few tens of wavelengths when the initial steepness 0.09≤a0k0≤0.28. The transition creates envelope solitons composed of waves with smaller steepness and lower carrier frequency than the initial state. The carrier frequencies of the envelope solitons can be downshifted as much as 25%. The transition process is irreversible, but does not lead to total randomness.
Small-amplitude waves produced by a submerged vorticity distribution on the surface of a viscous liquid
Authors: Prosperetti A. , Cortelezzi L.
Published: March 2003

The small-amplitude waves generated by a submerged vorticity distribution on the surface of a viscous fluid are studied. The linearized initial-value problem is considered, and a closed-form solution for each monochromatic component is obtained. The results of the theory are illustrated by a numerical synthesis of these components for the case of a vortex filament in water.
Kinetic theory, transport, and hydrodynamics of a high-Zplasma in the presence of an intense laser field
Authors: Jones Roger D. , Lee K.
Published: March 2003

A systematic treatment of collisional kinetic theory and transport for a high-Z plasma in the presence of an intense laser field is presented. The time-averaged electron kinetic equation is obtained in three ways. Collisionally induced harmonics of the laser frequency in the electron distribution function examined. In the case of high and low laser intensities, the kinetic equation is shown to possess self-similar solutions. In the low field limit, the solution found earlier by Langdon is recovered. In the high field limit, under special conditions, the solution is shown to be a Maxwellian. Monte Carlo calculations are found to corroborate these findings. In the low field limit, it is shown that the anisotropic part of the distribution follows the isotropic part adiabatically. An expression for the anisotropic part is obtained. The inverse bremsstrahlung heating rate is derived and shown to agree with Monte Carlo results. Memory effects in transport are discussed. The bremsstrahlung emission rate and the electron pressure tensor are derived. The thermoelectric transport efficients are calculated. And finally, the electron fluid equations are obtained.
Model of resonance absorption with profile modification
Authors: Kruer W. L.
Published: March 2003

A capacitor model for resonance absorption in a weakly driven, convective regime is presented. The steepening of the plasma density profile and the amplitude of the resonantly generated wave are self-consistently determined.