bluuebunny/crossref_metadata_2025 huggingface dataset:
Kink instabilities in the belt pinch
Authors: Marder B. M.
Published: February 2004

The stability with respect to kink modes of a high β straight screw pinch with elliptical cross section is examined using sharp boundary theory. No restriction is placed on the ellipticity or β. It is found that the critical q needed for stability is no longer unity but is a strongly increasing function of ellipticity. There are indications that large ellipticity in toroidal systems is too strongly destabilizing to allow such equilibria to be useful; however, small ellipticity may be useful for achieving higher β.
Infrared radiation from the dense plasma focus
Authors: Post Richard S. , Marshall T. C.
Published: February 2004

Experimental observations of infrared emission (2-10.6 μm) from a dense plasma focus have been made, along with the standard diagnostics of neutrons, x rays, and visible light. The thermal bremsstrahlung spectrum has been observed over the range 2 μm ≲ λ ≲ 6.5 μm. Occasional bursts of strong, nonthermal infrared occur for λ ≳ 5 μm with enhancements up to 106 over thermal radiation level. At a filling pressure of 1.6 Torr D2, the enhanced radiation occurs during the dense pinch stage of the discharge; however, at lower pressure (1.1 Torr), the maximum emission occurs during and shortly after the breakup of the dense pinch.
Two propagating modes of low-frequency waves in a single-ended Q machine
Authors: Sato N. , Sugai H. , Sasaki A. , Hatakeyama R.
Published: February 2004

Two propagating modes of low-frequency perturbations are excited by applying oscillating currents to a small coil surrounding a plasma column in a single-ended Q machine. One of them has the same phase velocity and damping factor as grid-excited waves, in spite of quite different exciting mechanisms. The other is observed to propagate only when the exciting frequency is higher than the frequency slightly above the ion cyclotron frequency. Its phase velocity increases with an increase in the magnetic field. This mode follows a dispersion relation of electrostatic ion cyclotron waves propagating along a magnetized plasma column.
Theory of microwave generation by an intense relativistic electron beam in a rippled magnetic field
Authors: Manheimer Wallace M. , Ott Edward
Published: February 2004

The stability of a waveguide enclosed relativistic electron beam in a rippled magnetic field has been theoretically investigated. The presence of the ripple can couple negative energy beam modes to positive energy waveguide modes to produce instability and thereby generate microwaves. In the experiment, the thickness of the beam is small compared with all other relevant lengths. Therefore, the nonlinear dynamics of an infinitesimally thin sheet beam are analyzed. The system is described by the orbit equations for the particles, Maxwell's equations, a set of nonlinear boundary conditions across the moving surface, and a continuity equation for the moving surface.
Thermonuclear burn characteristics of compressed deuterium-tritium microspheres
Authors: Fraley G. S. , Linnebur E. J. , Mason R. J. , Morse R. L.
Published: February 2004

The phenomenology of thermonuclear burn in deuterium-tritium microspheres at high densities is described, and numerical results characterizing the burn for a broad range of initial conditions are given. The fractional burnup, bootstrap-heating, and depletion of the DT fuel, its expansive disassembly, and thermonuclear ignition by propagating burn from central hot spots in the microspheres are discussed. Extensive numerical results from a 3 T Lagrangian simulation code are presented. The yields Y0 from uniform 10, 1, and 0.1 μg microspheres with densities ρ = 1 to 4 × 104 g/cm3 and temperatures Te = Ti = 1.8 to 100 keV are given. It is shown that Y0 ∼ ρR, ρR < 0.3 (R is the microsphere radius) or, equivalently, Y0 ∼ ρ2/3 for spheres of fixed mass m. The gain-factor G0 ≡ Y0/mI0 (I0 is the internal energy) is shown to measure burn efficiency in uniform microspheres. More than a four-fold increment in the gain factor is shown to derive from apportionment of the internal energy in a central hot spot. The limiting effects of electron degeneracy on the gain factor are outlined. As a guideline, the experimental observation of 1013 neutrons/kJ of input laser energy is established as proof of good absorption; 1015/kJ will imply yields exceeding break even.
Space charge dynamics of viscous liquids
Authors: Zahn Markus , Sojka Richard J.
Published: February 2004

A general set of relations, useful in the analysis of the propagation and instability characteristics of small signal space charge and polarization interfacial waves, are derived for field and flow variables on the perturbed surfaces of a uniformly charged, incompressible, viscous prototype layer.
Expansion of partially ionized argon through a supersonic nozzle
Authors: Maxwell Barry R. , Wessling F. C.
Published: February 2004

A theoretical study is made of the nonequilibrium quasi-one-dimensional expansion of partially ionized argon through a supersonic nozzle of known geometry. The nozzle exit plane properties are plotted as a function of upstream conditions of pressure and temperature.
Properties of the Vlasov phase in plasma turbulence theory
Authors: Skadron G. , Jones M. E.
Published: February 2004

While the Vlasov phase, [Xv(t, t0), Vv(t, t0)], can be identified as a perturbed particle trajectory in the variable t0, the time-reversed Vlasov phase may be identified as the phase space stream of test particles at the fixed time t0 which emanates from [x, v].
Coils and grids as ion-wave launchers
Authors: Hirshfield J. L. , Mussetto Michael S.
Published: February 2004

Similarities between results of ion-wave propagation on a single-ended Q machine using either grid or coil excitation are shown to be not inconsistent with the notion that free-streaming ion motions dominate both cases, contrary to recent claims of Sato et al.
Pressure perturbation of a turbulent boundary layer
Authors: Blackwelder R. F. , Woo H. H. W.
Published: February 2004

A novel pressure perturbation was applied in the irrotational region outside of a turbulent boundary layer to simulate the natural pressure disturbance created by a free-stream flowing over the turbulent bulges at the interface. Conditional sampling was used to reveal the perturbation and its effect on the boundary layer. The natural mean bursting frequency scaled with the outer variables in agreement with the theoretical and experimental results reported previously in the literature. The mean frequency of the bursting phenomenon in the wall region during the disturbance was independent of the pressure perturbation frequency.
Upper bound on the solute flux in doubly diffusive convection
Authors: Straus Joe M.
Published: February 2004

The properties of doubly diffusive convection of large amplitude are investigated using the upper bounding method. The specific problem treated is the thermohaline instability in a horizontal layer of fluid containing temperature and solute concentration increasing in the direction opposite to that of gravity. For large values of the solute and thermal Rayleigh numbers, R and Ra, a boundary-layer analysis is used to calculate an upper bound on the solute flux. This upper bound is found to be f*(R/Ra)Ra11/8, where the function f* is a monotonically increasing function of R/Ra. Thus, for large values of Ra, the solute flux may be very large even when R/Ra is only slightly in excess of unity.
Magnetic compression and electron cyclotron heating of a low temperature, lithium plasma
Authors: Kim J. , Lieberman M. A.
Published: February 2004

Magnetic mirror compression and electron cyclotron heating have been investigated in a high field, simple mirror, compression device (midplane field rises from 200 G to 50 kG in 0.5 msec, mirror ratio = 1.4), using a contact ionization lithium source (n ≈ 108−1010 cm−3, Te = Ti ≈ 0.2 ev) to produce the initial plasma. Experimental results are: (1) For magnetic mirror compression, the plasma is macroscopically unstable, and, although Ti ≈ 10 eV, confinement is destroyed with ∼200 μsec, for all ranges of initial plasma density and neutral pressure. A set of rate equations for electron and ion density and temperature and ambipolar potential predicts classical confinement times of the order of milliseconds. (2) For short pulse, electron cyclotron heating (250 kW, 0.25 μsec, 8.95 GHz pulse) followed by magnetic compression, Te ≈ 45 keV, Ti ≈ 10 eV and the plasma is stably confined, provided the neutral gas pressure exceeds ∼2 × 10−5 Torr. The observed stability is in rough agreement with the Guest-Beasley criterion for stabilization of flute modes by flow of cold plasma to the conducting chamber walls. The confinement time is in agreement with previous rate equation calculations of hot electron plasma confinement in magnetic mirrors.
Interaction of a plasma flow with a magnetic dipole field
Authors: Oberth Ronald C.
Published: February 2004

The interaction of a streaming plasma with a magnetic dipole field is studied in the framework of a linearized, two-fluid continuum description. For the case of low-density flows, in which the pressure gradients are small in comparison to magnetic and electric forces, it is possible to extend the solution beyond the first-order one, which gives the distribution of induced current in the azimuthal direction, and calculate space-charge density and plasma potential distributions, along with the Hall current components in a restricted spatial region. The quantities of second-order scale directly with the appropriate Cowling number, whereas the azimuthal current density increases with the square root of this ratio. It is also shown that the Hall current densities and potential variation increase rapidly with increasing plasma density, while the normalized space charge density scales with the square of the plasma velocity. Moreover, the theory predicts a significant decrease in plasma potential in the vicinity of the dipole; a result which tends to agree with recent experimental indications.
E
-Layer trapping in astron by resistor interaction: Theory and experiment
Authors: Stallard B. W. , Fessenden T. J.
Published: February 2004

The interaction of a moving E layer with the resistor structures that line the walls of the Livermore astron apparatus are studied theoretically and experimentally. It is shown that for a weak interaction no change in mean layer radius results from the energy loss in the resistors. Using the approximation of a long thin layer in axisymmetric geometry, curves are given for calculating the energy dissipated in the resistors per meter traveled or, equivalently, the axial force on the moving layer. Results of experiments are reported showing transport of the incoming layer in the astron tank and trapping in the magnetic mirrors. Measurements of the damping of E-layer axial motion in several resistor geometrics show typical damping times of 0.5 μsec. Comparison of experiment and theory show agreement within about a factor of 2.
Current-driven collisional drift instability
Authors: Ellis R. F. , Motley R. W.
Published: February 2004

An experimental and theoretical study of the current-driven collisional drift instability is reported. This very strong [Im(ω) ∼ Re(ω)], low-frequency (ω ≪ Ωi) instability was observed in a current-carrying collision dominated, cesium plasma. Positive instability identification is based on a detailed comparison of experimental wave parameters with a linearized two-fluid theory which includes the effects of electron heat flow, electron temperature fluctuations, parallel resistivity, finite ion Larmor radius and transverse ion viscosity. Theory and experiment are in agreement on: (1) the strong destabilizing effect of axial current; (2) the magnitude of the instability frequency and its parametric dependence on magnetic field, azimuthal mode number, and axial current; (3) the qualitative features of the axial structure and their variation with axial current; (4) the magnitude of the critical current for excitation and its variation with magnetic field and density; (5) the relative stability of the different azimuthal modes; (6) the variation with current, magnetic field, and density of the relations between fluctuating density and fluctuating floating potential. In addition, large wave induced plasma losses occurring with instability onset could be explained on the basis of the measured wave parameters.
Nonlinear Landau damping in a radially inhomogeneous cylindrical plasma
Authors: Hewett D. W. , Armstrong T. P.
Published: February 2004

The nonlinear Vlasov equation is solved numerically as an initial value problem for an electrostatically confined cylindrical plasma with a Gaussian density profile. Electrostatic perturbations are excited by imposing a small sinusoidal density variation in the axial direction. The resulting oscillations of the axial and radial components of the electric field are studied to determine approximate frequencies and damping decrements from the first few oscillations. As the width of the Gaussian profile is decreased, making the plasma more inhomogeneous, the oscillation frequencies decrease and the damping decrements increase. Nonlinear distortions of the distribution function in the neighborhood of vz = vph are observed.
Instabilities and growth rates of low shear guiding center plasma pinches
Authors: Pao Young-ping
Published: February 2004

Some instabilities and their growth rates are examined for low shear guiding center plasma pinches. Relations between these instabilities and the Suydam-type instability are also discussed in terms of their growth rates.
New ion acoustic instability
Authors: Leprince P. , Peyraud J.
Published: February 2004

In the presence of a quasiresonant high frequency field, a new type of ion acoustic instability is described. In using the macroscopic equations, it is possible to show that an ion acoustic wave can be unstable when the high frequency is close to the resonance frequency. The experiment is performed on an afterglow discharge; the secondary (or Dättner) resonance is excited and when the incident power increases, the reflected microwave is modulated by a low frequency corresponding to the frequency of the ion-acoustic oscillation.
Linear sidebands
Authors: Morales G. J. , Malmberg J. H.
Published: February 2004

The existence of a new mechanism by which waves at nearby frequencies can be excited when a small amplitude, monochromatic, electron plasma wave is launched in a collisionless plasma is reported. The amplitude of these excited sidebands depends linearly on the amplitude of the launched wave, hence they have been named linear sidebands. A striking feature of linear sidebands is that their amplitude exhibits large spatial oscillations, while the amplitude of the wave exciting them damps monotonically according to the linear theory of Landau. Linear sidebands arise from the interaction of the launched wave with pre-existing low-frequency, streaming perturbations in the electron distribution function having the functional form: g(ω, ν) exp[iω(t − x/υ)]. The existence of a continuous spectrum of streaming perturbations in a collisionless plasma has been established by identifying the excited plasma wave echoes that appear when a heavily damped wave is launched. A generalization of the echo theory predicts the existence of linear sidebands and is in good quantitative agreement with the experimental observations of the linear sideband properties. It is experimentally observed that the well-known trapped-particle sidebands can evolve continuously from the linear sidebands as the amplitude of the launched wave is increased.
Nonlinear stabilization and nonrandom behavior of macroinstabilities in plasmas. I. Theory
Authors: Sato Tetsuya
Published: February 2004

Nonlinear mass transport associated with the Hall motion of particles coherent with a wave field is studied for electrostatic instabilities, which are described by the magnetohydrodynamic equations. It is shown that the nonlinear transport causes a modification of the density distribution and/or the drift velocity, leading to stabilization of the unstable waves in both cases. It is also shown that fluid elements (particles) move in the Hall direction in a nonrandom manner under the action of a coherent wave electric field. Consequently, the density distribution is modified in an oscillatory way, thus giving rise to a modulation in amplitude.
Nonlinear stabilization and nonrandom behavior of macroinstabilities in plasmas. II. Numerical verification
Authors: Sato Tetsuya , Ogawa Tadahiko
Published: February 2004

To verify the nonlinear theory of electrostatic macroinstabilities in magnetized plasmas, with special emphasis on the amplitude oscillation, numerical calculations were made for a two-dimensional, weakly ionized plasma with a density gradient and crossed electric and magnetic fields (cross-field instability), which is found to be a suitable plasma to yield an amplitude oscillation. It is shown that, on the average, the unstable mode is stabilized by the reduction of the density gradient but, in detail, exhibits an oscillation in amplitude in conjunction with oscillation in density and potential distributions. It is also shown that nonlinear higher modes excited by the dominant mode suffer strong amplitude oscillations. Theoretical interpretation of such strong amplitude oscillations is considered.
Kink instabilities in arbitrary cross-section plasmas
Authors: Marder B. M.
Published: February 2004

A numerical method is presented to study the thin skin magnetohydrodynamic stability to kink modes of arbitrary cross section two-dimensional plasmas. Only long wavelength perturbations are considered but no other restrictions are assumed. Laplace's equation is solved for the perturbed fields by using a variation of Green's third formula.
Peak emission from second harmonic generation at the upper hybrid layer
Authors: Cotsaftis Michel
Published: February 2004

Using a parabolic approximation for the propagation index of the electric field around the existing minimum of the upper hybrid curve, a closed and finite expression for the value of the peak energy radiated to infinity from the second harmonic generation in the hybrid layer is given and compared with the ST tokamak experiment. This calculation shows reasonable agreement with the observed value, indicating that in this case the peak is probably due to the second harmonic generation.
Quasi-one-dimensional solution for the power of CO2 gasdynamic lasers
Authors: Lee George
Published: February 2004

A theory has been developed for calculating the laser power of CO2 gasdynamic lasers. A three-mode vibrational gas model was assumed and the coupled rate and one-dimensional conservation equations were solved by the time-dependent technique. The results were compared with experimental data and the agreement was good.
Tall Taylor cells in polyacrylamide solutions
Authors: Beavers Gordon S. , Joseph Daniel D.
Published: February 2004

The behavior of Taylor cells in a polyacrylamide solution contained between rotating cylinders is described. As the rotational speed increases, the cell aspect ratio changes from about 1 to 4. Hysteresis of the 4-cell configuration is observed.
Remarks on the decay of homogeneous turbulence from a given state
Authors: Deissler R. G.
Published: February 2004

A previous theory which did not require a usual closure assumption required three or more initial spectra. By allowing a simple physical assumption (a modification of Kovasznay's hypothesis), the required number of spectra is reduced to two. Agreement with experiment is good.
Variation of the magnetic moment in nonneutral electron plasmas
Authors: Kapetanakos C. A. , Striffler C. D.
Published: February 2004

Exact and approximate expressions are obtained for the magnetic moment of a charged particle, under conditions pertinent to nonneutral electron plasma experiments.
Transverse dynamic stabilization of a screw pinch
Authors: Lister G. G. , Troyon F. S. , Weibel E. S.
Published: February 2004

An oscillating axial current can stabilize a weak screw pinch (Bθ ≪ Bz). The minimum aspect ratio for a stabilized toroidal screw pinch is the same as for a dynamically equilibrated theta pinch.
Rotational stabilization of a metallic liner
Authors: Book D. L. , Winsor N. K.
Published: February 2004

Taylor instability of the imploded metallic liner used in axial flux compression experiments can be stabilized by linear rotation. One can either remove the instability or limit its amplitude by choosing the rotation speed. The cost (in field compression efficiency) of stabilization is calculated.
Effects of an air stream on turbulent diffusion of a helium jet from a small nozzle
Authors: Aihara Yasuhiko , Koyama Hisao , Morishita Etsuo
Published: February 2004

In a round helium jet with a small nozzle, and a Reynolds number of 2.95 × 103, with and without an air stream, mean profiles, instantaneous fluctuations, and correlations of velocity and matter are investigated using the hot-wire technique. The characteristic difference in the behavior of the jet due to the presence of an air stream is extensively studied and summarized as follows: (1) Similarity in mean profiles is not reached at least in terms of r/z and the spreading and decay of the jet follow some slower laws, and (2) lateral turbulent diffusion is reduced while active axial turbulent diffusion is induced in the middle of the distribution of the jet. The correlations between fluctuations are established as a whole, but those between concentration and velocity fluctuations are reduced in the lateral direction. It seems that the turbulent motion of large eddies plays an important role in the transport mechanism of the flow field.
Turbulent transport of mean kinetic energy in countergradient shear stress regions
Authors: Wilson D. J.
Published: February 2004

Transport of mean flow kinetic energy by turbulent interactions has been measured in the inner region of a plane wall jet, where turbulent shear stress opposes mean velocity gradient. Energy transport by Reynolds stresses dominates, with loss to production of turbulence playing a secondary role.
Models for viscous dissipation of energy obtained from the Lagrangian form of the equations of motion
Authors: Attermeyer Mary
Published: February 2004

Elementary analytic functions that exactly satisfy the Lagrangian form of the Navier-Stokes equations have been found by using guessed solutions to the Lagrangian form of the continuity equation for an incompressible fluid. These functions depict the viscous dissipation of energy in unbounded and semi-infinite fluids. The equations of motion are presented in a form that describes the hydrodynamic pressure field. The trajectories of “labeled” fluid particles given by these functions are found to be straight lines in some instances and curved lines in others. Projections of the distortion experienced by a fluid element in the flow regimes represented by these functions are given.
Radiative relaxation behind high-speed shock waves in air
Authors: Chan S. K. , Glass I. I.
Published: February 2004

Some new results are reported on the radiative relaxation times (nonequilibrium emission coefficient) of high-speed shock waves (0.6−1.2 cm/μsec) in air at p1 = 1 Torr. The relaxation times are shown to be due to molecular processes for shock velocities below 0.93 cm/μsec and are caused by ionization beyond 0.95 cm/μsec.
Collisional generation of precursor ions by laser-produced plasma expanding in a gas
Authors: Goforth R. R. , Koopman David W.
Published: February 2004

A fast ion precursor is observed to propagate ahead of a laser-produced plasma expanding into a partially ionized background gas. The ions are identified to be of the background species, and their absolute energy distribution has been measured. Comparison of the data with detailed models suggests that the precursor ions arise from violent charge-transfer collisions between laser-target ions and background neutrals.
Fluid theory of reflected particles in ion-acoustic shocks
Authors: Manheimer Wallace M. , Haber Irving
Published: February 2004

The time-independent equation of motion for a one-dimensional ion fluid of velocity ν and temperature T in an electric field E is dν/dx = (eE/Mν)/(1 − 3T/Mν2). This equation has a singularity at Mν2 = 3T. This singularity is of crucial importance in any shock whose downstream state satisfies 3T > Mν2. Assuming a square (waterbag) ion distribution function, one shows that the singularity occurs where the first ion is reflected. By adding the presence of a second (reflected) fluid, it is possible to join these two fluids to form a single fluid beyond the singularity. Using this technique the structure of ion acoustic shocks containing reflected particles is found, and it is shown that the solutions are identical to direct solutions of the Vlasov equation. The advantage of the fluid formulation is that one can investigate the effect of anomalous friction and energy exchange between incident and reflected beams.
Interpretation of ion-acoustic wave propagation experiments by the multiple-water-bag model
Authors: Buzzi J. M.
Published: February 2004

Theoretical and experimental results concerning the linear ion-acoustic wave propagation in the low-density range (∼ 108 cm−3) for a single-ended Q device are presented. For plasma densities less than 109 cm−3, the ions have a beam-like distribution. This allows one to observe two ion waves traveling in the direction of the plasma flow. Observed phase velocities and damping lengths are in good agreement with the theory if the actual ion distributions are taken into account in calculating the plasma response. The multiple-water-bag model presented allows one to compute the plasma response using the measured ion distribution. In the high-frequency range of measurements (0.5 ≲ ω0/ωpi ≲ 1) the beating between the fast and slow ion waves is in agreement with the multiple-water-bag predictions where the excitation is described classically by oscillating charge sheets. In contrast to the experiments carried out at higher densities, it can be demonstrated that the macroscopic plasma response is clearly collective.
Continuum theory of spherical electrostatic probes in a stationary, moderately ionized plasma
Authors: Barad Michael S. , Cohen Ira M.
Published: February 2004

A theory is developed for spherical electrostatic probes in a stationary, collision-dominated plasma in which the ratio of charge-charge to charge-neutral collision frequencies may range between zero and unity. The former limit corresponds to the usual “weakly ionized” condition of earlier probe analyses, while for non-zero values of this ratio, transport coefficients must be assumed to vary with position in the plasma. Electron temperature variation is allowed for through the consideration of electron energy conservation and transport. Quasilinearization is used to solve the equations numerically, and an orthonormalization technique is developed to overcome the “ill-conditioning” problem which often occurs in the solution of linear two-point boundary value problems. Plasma property profiles in the vicinity of the probe, for several values of collision frequency ratio and a wide range of probe potentials, are investigated. A few representative current-voltage characteristics are calculated. The effects of including variable transport coefficients in the formulation are discussed. It is found that including charge-charge collisions increases the effective positive bias of an electron-attracting probe, and of a probe at plasma potential, and more effectively shields an electron-retarding probe of low potential. For more strongly retarding probes, this trend reverses and shielding is decreased (although very slightly). For strongly retarding probes, there is no apparent difference between the behavior of weakly and moderately ionized gases. A systematic procedure is developed by which experimentally obtained probe characteristics may be interpreted.
Theory and simulation of collisional damping of longitudinal waves in a two-dimensional plasma
Authors: Klein H. H. , Krall Nicholas A. , Orens Joseph H.
Published: February 2004

The collisional damping of plasma oscillations is studied by numerical simulation techniques. The results agree with the theoretical calculation of collisional damping in a two-dimensional plasma, resolving discrepancies which had previously existed between analytic and simulation approaches to this problem.
Nonlinear stochastic theory for a plasma driven by strong high-frequency electric fields
Authors: Bona G. di , Masselot C.
Published: February 2004

The interaction of an electron-ion plasma with a strong high-frequency electromagnetic field is studied by means of the Stratonovitch stochastic method. The hierarchy of equations obtained is broken by means of an expansion in power of a small dimensionless parameter. The solution of this set of equations leads to the computation of density fluctuations spectral densities, dynamical friction, and diffusion terms of the evolution equation of the one-particle distribution function.
Lagrangian formulation of the one-dimensional Vlasov equation
Authors: Lewak G. J.
Published: February 2004

A new formulation of the one-dimensional Vlasov equation is derived which is analogous to the Kalman-transformed cold-plasma equations. The equations are shown to yield nonsecular, nonlinear approximations to a source or boundary-value problem. It is suggested that the formulation may have other applications in nonlinear plasma theory.
Absorption of laser radiation in a H-He plasma. I. Theoretical calculation of the absorption coefficient
Authors: Stallcop James R.
Published: February 2004

The theory for calculating the absorption of laser radiation by hydrogen is outlined for the temperatures and pressures of common laboratory plasmas. Nonhydrogenic corrections for determining the absorption by helium are also included. The coefficients for the absorption of He-Ne laser radiation at the wavelengths of 0.633, 1.15, and 3.39 μm in a H plasma is presented for temperatures in the range 10 000-40 000°K and electron number densities in the range 1015−1018 cm−3. The total absorption of a H-He plasma calculated from this theory is compared with the measured absorption. The theoretical composition of the H-He absorption is analyzed with respect to the significant absorption processes, inverse bremsstrahlung, photoionization, resonance excitation, and photodetachment.
Absorption of laser radiation in a H-He plasma. II. Experimental measurement of the absorption coefficient
Authors: Billman Kenneth W. , Rowley Paul D. , Stallcop James R. , Presley Leroy
Published: February 2004

The absorption coefficients of 0.633-, 1.15-, and 3.39-μm laser radiation for a homogeneous H-He plasma have been measured in the temperature range of 12.2 to 21.7 (× 103 °K) and in the electron number density range 0.45 to 6.5 (× 1017 cm−3). Good agreement is found between the experimentally determined total absorption for each of the wavelengths and that calculated from theory. Furthermore, because the 3.39-μm absorption is dominated by inverse bremsstrahlung while the 0.633-μm absorption is dominated by photoionization and resonance absorption, the experiment indicates a correct assessment by the theory of these individual absorption mechanisms.
Parametric instabilities of electromagnetic waves in plasmas
Authors: Drake J. F. , Kaw P. K. , Lee Y. C. , Schmid G. , Liu C. S. , Rosenbluth Marshall N.
Published: February 2004

A simple formalism for the parametric decay of an intense, coherent electromagnetic wave into an electrostatic wave and scattered electromagnetic waves in a homogeneous plasma is developed. Various instabilities including Brillouin and Raman scattering, Compton scattering, filamentational and modulational instabilities are derived and discussed in a systematic manner. Growth rates as a function of the incident pump power are shown.
New electron-wave amplitude oscillation due to an initial spatial disturbance
Authors: Sugihara Ryo , Kamimura T.
Published: February 2004

When an initial disturbance in a plasma is so strong that f0(λ) [f0(ν): unperturbed distribution, λ: phase velocity] and ĝ(λ) cos kx [ĝ(λ) cos kx: disturbance ] are of the same order, the spatial inhomogeneity represented by the latter causes a new type of amplitude oscillation while the usual amplitude oscillation predicted by O'Neil is not sensitive whether ĝ(λ) = 0 or not. This is due to the fact that the initial spatial disturbance survives around λ unsubjected to phase mixing for some time and causes a finite shift of the real part of the frequency which modifies the pattern of the trapping region. The most remarkable feature of this oscillation is that the amplitude almost always remains larger than the initial one. The maximum amplitude of the electric field E is E0[1 + O(ĝ2(λ)/k4E02)], where ĝ(λ), k, and the initial field E0 are normalized with (n0/νth), the Debye shielding constant and the square root of the kinetic energy (4πn0 Te)1/2, respectively.
Large amplitude steady-state harmonic cyclotron waves
Authors: Aamodt R. E.
Published: February 2004

The spatial dependence of an electron plasma-harmonic ion cyclotron amplifying wave is derived for a steady-state loss-cone simulated system. Amplitude saturation is accomplished when the ion field energy density is balanced by the electron field energy density. For low-density systems this implies saturation amplitudes much less than the available free ion energy, while for high densities, essentially all of the initial free energy goes into the field. Wave damping finally occurs over long distances because nonlinearities cause ion resonance with the parallel wave motion, and the induced acceleration heats the ions along the direction of the external magnetic field.
Measurements of electron-cyclotron heating rates
Authors: Barter J. D. , Sprott J. C. , Wong K. L.
Published: February 2004

Electron-cyclotron heating rates have been measured for plasmas in a toroidal octupole magnetic field over a wide range of magnetic field strength, electric field strength, plasma density, and neutral density. The results agree with single-particle heating theories at low densities but show a decreased heating rate as the density increases.
Interaction of a rotational relativistic electron beam with a magnetized plasma
Authors: Chu K. R. , Rostoker N.
Published: February 2004

In the presence of a uniform magnetic field, it is possible to form a hollow rotational relativistic electron beam which gyrates as a whole about its axis while propagating axially along the magnetic field. Here, the interaction of a rotational beam front with a dense magnetized plasma is studied. Starting from the two-fluid equations for the plasma, it is shown that under the conditions a2 − a1 ≫ λ, Ωe ≫ νe, and Ωi ≪ νi, where a2 − a1 is the beam thickness, λ is the plasma skin depth, Ω is the gyro frequency, and ν is the momentum transfer collision frequency, the beam current will not only be axially neutralized as usual but also angularly neutralized by a drift plasma current. The subsequent decay of these counter currents will in return induce upon the beam an axial retarding force capable of dissipating most of the beam axial energy in a few nsec. In addition to Ohmic heating the plasma electrons, a significant portion of the beam axial energy lost in the above manner will be transformed into ion energies through the action of a current sustained radial electrostatic field. Possible applications to plasma heating and beam trapping in astron type machines are discussed.
Axial deceleration and focusing of an unneutralized electron layer by helical resistors
Authors: Lauer Eugene J.
Published: February 2004

An analysis is made of the interaction between an unneutralized, relativistic, cylindrical electron layer and resistive conductors that have a coaxial, helical geometry. It is assumed that the current per unit length varies slowly in the axial direction. There is an average axial decelerative force on the layer and, if the pitch angle of the helix is greater than a critical value, the axial force is inward (focusing) on electrons at both ends of the layer.
Multipoint distribution calculation of the isotropic turbulent energy spectrum using self-consistent initial conditions
Authors: Fox Ronald L.
Published: February 2004

The prediction of the decay of the energy spectrum obtained by a solution of the multipoint equations is improved by introducing a self-consistent initial condition in order to eliminate the previously required truncated series expressions for the initial distributions.
Parametric instability thresholds and their control
Authors: Thomson J. J. , Kruer W. L. , Bodner S. E. , DeGroot J. S.
Published: February 2004

It is shown that the “swelling” of the laser electric field must be included in threshold estimates for the electrostatic instabilities excited by a laser near the critical density. Random amplitude modulation of the laser is found to lead to an increased instability threshold.
Turbulent quenching of the drift-dissipative mode in a Q Machine: Theory and experiment
Authors: Thomson J. J. , Benford Gregory , Rynn N. , Williamson W. S.
Published: February 2004

Current-generated broadband turbulence can appear to individual particles as a diffusive damping, leading to saturation of low-frequency modes in steady-state experiments. Mode saturation occurs when the linear growth γ = k⊥2D⊥, the diffusive damping. As long as mode frequency ω > k⊥2D⊥, the mode is well defined. When k⊥2D⊥ > ω, the mode loses meaning and should disappear. The turbulent damping k⊥2D⊥ is interpreted as an upper bound on the linewidth of the wave. As current increases, frequency falls and linewidth increases. The mode is quenched when damping exceeds the mode frequency. Agreement with experiment is good.
Angular distribution function from axial density measurements in a mirror confinement experiment
Authors: Hall Laurence S. , Simonen T. C.
Published: February 2004

The angular distribution of particle velocities in a magnetized plasma can be uniquely determined by measurement of the variation of density along a magnetic field line. From measurements on the 2XII mirror experiment, it is determined that the angular distribution of ions is monotonic and very closely approximates sin2aθ, where a = 2.25 and θ is the pitch angle at the center. Particles with sin θ < 0.72 communicate with the region outside the mirrors and comprise approximately 5% of the total density at the center.
Whistler decay instability in three dimensions
Authors: Wright Thomas P.
Published: February 2004

A generalized treatment of the three-wave decay of oblique whistler/electron cyclotron waves into other whistler/electron cyclotron waves is presented which clarifies the three-dimensional aspects of the process. The generalized expression for the growth rate is given and several special cases are considered, establishing the existence of a strong instability. It is shown that there is no instability when the three wavenumber axes are coplanar with the background magnetic field in the plane except for the special case when one of the waves propagates along the background magnetic field.
Stimulation of the Harris instability in the ionosphere
Authors: Benson Robert F.
Published: February 2004

Satellite soundings of the topside ionosphere reveal diffuse signals on the low frequency side of nfH when nfH < fT, where n is an integer and fH and fT are the electron cyclotron and upper hybrid frequencies, respectively. They extend no further than the midway point between (n − 1)fH and nfH. The present observing conditions allow detection up to n = 10. The origin of the signals is attributed to the Harris instability of longitudinal plasma waves when T⊥/T‖ > 2n, where T⊥ and T‖ refer to the temperature corresponding to the electron motion perpendicular and parallel to the earth's magnetic field, respectively. The large anisotropies are caused by collisionless cyclotron damping of energy from the high power sounder pulse. This energy is absorbed in a region which extends radially from the antenna, a distance which is small compared with the antenna length but large compared with the antenna sheath region.
Momentum of photons and the nonlinear force of laser-plasma interaction
Authors: Hora Heinrich
Published: February 2004

The momentum of photons in a collisionless plasma reproduces the Fresnel formulas only if the energy exchange with electrons is included. The transferred momenta correspond exactly to those derived from the theory of the nonlinear force of a laser-plasma interaction.
Electron scattering by enhanced fluctuations in quiescent mirror machines
Authors: Aamodt R. E. , Baldwin D. E.
Published: February 2004

Enhanced electron scattering induced by the Rosenbluth-Post convective loss-cone instability could reduce electron Landau damping and produce a highly unstable configuration. The effect is calculated and shown to be unimportant for fusion devices.
Comments on “Stability limits for longitudinal waves in ion beam-plasma interactions”
Authors: Imre Kaya , Özizmir Ercüment
Published: February 2004

It is shown that electron dynamics significantly alters the stability limits of the ion-acoustic waves in a plasma-ion beam system even when phase velocity is much smaller than the electron thermal velocity.
Approach of axisymmetric turbulence to isotropy
Authors: Herring J. R.
Published: February 2004

The approach of axisymmetric, homogeneous turbulence to isotropy using the direct interaction approximation is investigated. The turbulence is characterized by two parameters, the spectral variance transverse and parallel to the direction of axisymmetry. The dependence of these energy components on wave vector orientation is developed into a spherical harmonic expansion, and only low order terms are examined in detail. In terms of this characterization of the theory, the general qualitative nature of the relaxation to isotropy is discussed and numerical results for the energy spectrum and transfer functions are presented. It is shown that the simplest characterization of the theory leads to an almost linear relaxation to isotropy. The numerical results at moderate Reynolds numbers are compared to the phenomenological theory of Rotta [J. C. Rotta, Z. Physik 129, 547 (1951)]. A simple analytic estimate of the Rotta relaxation rate is also presented.
Temperature and intermittency in the turbulent wake of a heated cylinder
Authors: LaRue John C. , Libby Paul A.
Published: February 2004

An experimental investigation of the form of the temperature structure in the slightly heated plane wake and its relationship to the intermittency and interface structure is described. No evidence is found of periodic interface motion. Furthermore, it is shown that the large scale structures of the interface modulations with wavelengths greater than 10% of the wake width are highly correlated with the large scale temperature structure within the wake and hence that the interface is related primarily to the large scale structure of the flow field.
Viscous stability of parallel streams of superposed fluids
Authors: Hayakawa Norio , Unny T. E.
Published: February 2004

Viscous linear stability analysis of half-jet flows of superposed, immiscible fluids with small density difference is presented. For small values of wavenumber α and Reynolds numbers, series solution is used to obtain the effect of density difference on the neutral stability curve.
Linear viscous stability analysis of the stratified Bickley jet
Authors: Gage K. S. , Miller J. R.
Published: February 2004

The stability of the stably stratified Bickley jet to small disturbances in a viscous, heat conducting fluid is explored by numerical integration of the governing differential equation. Curves of neutral stability are presented in the α-R plane and the parametric dependence of these curves upon Richardson number and Prandtl number is examined. The results show a curious bimodal behavior of the curve of neutral stability for small Richardson numbers. In addition, closed neutral curves are found for Richardson numbers in excess of the critical value for the inviscid flow. The unstable regions in the interior of these curves increase with decreasing Prandtl number. Energy balances are computed which show the relative magnitude of the Reynolds stress production, buoyancy dissipation, and viscous dissipation terms across the flow. As the thermal diffusivity becomes large compared with the kinematic viscosity, the buoyancy term is suppressed and the thermal stratification becomes irrelevant.
Side-band instability of shallow water waves
Authors: Baker R. L.
Published: February 2004

The linear instability of small but finite amplitude cnoidal waves on shallow water is examined. A new set of equations valid under the shallow water approximation is used to derive periodic wavetrains and to study the behavior of small perturbations. A resonance condition k2 = k1 + 2k, similar to that used by other authors, is required to hold between the side-band perturbations with wavenumbers k1 and k2, and the main wave with wavenumber k. It is also necessary for the perturbations to have a specific nonzero frequency Ω, measured with respect to the main wave which is stationary in a wave frame. In the region 0 < F2 < 1, where F is a Froude number of the flow underlying the cnoidal wave, all wavetrains are unstable to these side-band perturbations. Like all other parametric instabilities, the instability is due to the resonant transfer of energy from the main wave to the perturbing waves.
Temperature jump in a gas mixture
Authors: Loyalka S. K.
Published: February 2004

The problem of temperature jump in a multicomponent gas mixture is considered and a variational result valid for the Boltzmann equation and arbitrary gas surface interaction law is given. From this general result, a particularly useful expression for the monatomic binary gas mixtures and Maxwellian diffuse specular reflection is deduced. Explicit results for the He-Ar mixture are given by using the Lennard-Jones potential. Generalizations to the polyatomic gases are also discussed.
Experimental study of the shock-induced unsteady laminar boundary layer on a flat plate
Authors: Cook William J.
Published: February 2004

The behavior of the unsteady laminar boundary layer induced by the incident shock wave passing over a flat plate mounted in a shock tube has been experimentally studied for shock speeds ranging from 2.35 to 7.34 km/sec by measuring unsteady heat transfer rates to the plate using thin-film heat-flux gages. Theoretical heat-transfer rates were predicted from analytical solutions in the literature which describe the unsteady flat plate boundary layer development for equilibrium real-gas flows. Experimental results obtained for both air and nitrogen were found to be in good agreement with the theoretical predictions.
New approach to magnetohydrodynamic stability: I. A practical stability concept
Authors: Goedbloed J. P. , Sakanaka P. H.
Published: February 2004

An equilibrium is called σ stable if growth faster than exp (σt) does not occur. On the basis of this definition a modified energy principle is obtained by means of which the stability of plasma confinement systems can be tested for times of thermonuclear interest, instead of the infinitely long times which are pertinent to the usual stability analysis. The theory is applied to the diffuse linear pinch, a theorem for σ stability is derived, and the connection with the normal-mode analysis is shown to be given with the Sturmian property, which holds for the unstable side of the spectrum, whereas the stable side consists of Sturmian and anti-Sturmian point spectra separated by continuous spectra. Growth rates and eigen-functions of Suydam modes are numerically calculated, and it is shown that violation of Suydam's criterion in the high and intermediate shear case leads to nonlocalized rapidly growing m = 1 modes. Consequently, this criterion obtains new relevance in the σ-stability analysis for this regime.