bluuebunny/crossref_metadata_2025 huggingface dataset:
New approach to magnetohydrodynamic stability: II. Sigma-stable diffuse pinch configurations
Authors: Sakanaka P. H. , Goedbloed J. P.
Published: February 2004

On the basis of the theory of σ stability, a classification of high-shear σ-stable diffuse pinch configurations is obtained by numerical solution of the Euler equation corresponding to the modified energy principle. Toroidal effects are introduced by putting a lower bound on the magnitude of the poloidal field in order to assure toroidal equilibrium and by deriving and employing the proper generalization of the Kruskal-Shafranov limit for m = 1 unstable configurations. The classification of high-shear σ-stable configurations consists of five different types, viz., tokamak, Bθ-reversed pinch, screw pinch, combined pinch, Bz-reversed pinch. Among the significant new results are: complete stability of some of the tokamak configurations for β up to 4%, a stable high-β (30%) Bθ-reversed pinch configuration that has not been investigated before, a stable diffuse screw pinch with β = 30% when currents are allowed to flow at the wall and with β = 8% with vanishing current at the wall, the possibility of containing diffuse high-β m = 1 stable plasmas without Bz-field reversal or pressure minimum on axis. Here, σ stability refers to times needed for fusion.
Long-wavelength kink instabilities in low-pressure, uniform axial current, cylindrical plasmas with elliptic cross sections
Authors: Dewar R. L. , Grimm R. C. , Johnson J. L. , Frieman E. A. , Greene J. M. , Rutherford P. H.
Published: February 2004

The magnetohydrodynamic stability of a straight plasma column with elliptic cross section, carrying a uniform axial current, is investigated by extremizing the Lagrangian of the system using a natural coordinate system based on the magnetic field lines. Stability criteria are derived and growth rates are obtained analytically for systems with a uniform mass density inside the plasma. It is shown that the coupling between kink modes and Alfvén waves produced by noncircularity is a destabilizing effect. A technique for solving the problem numerically is also discussed and used to demonstrate the effect of a spatially varying plasma density on the growth rate.
Striated jets due to nonlinear ponderomotive forces in laser produced plasmas at obliquely incident light
Authors: Hora Heinrich
Published: February 2004

An analysis is made of one of the expected nonlinear and anomalous mechanisms and instabilities in the corona of a laser irradiated plasma. As is well known, nonlinear ponderomotive forces generate a net acceleration of the plasma toward lower densities. It is demonstrated that the same forces at oblique incidence of the radiation, can cause a net motion perpendicular to the well-known forces along the density gradient: The standing wave generated that is split into zones (slabs) of the thickness of a quarter of a wave length, where the plasma is moving in the plane of incidence parallel and antiparallel to the slabs. This striated motion can also occur in an underdense plasma, while for the net acceleration toward lower density the strong change of the refractive index near the cutoff density is necessary. The striated parallel and antiparallel motion of the slabs is limited by the mean free path, by the velocity toward lower density and is determined by the condition of laminar and turbulent motion. The time constants on the order of picoseconds and the nonlinear absorption due to the generation of this striated motion are evaluated. Laser intensities exceeding 1013 W/cm2 incident at angles of 25° should build up striated jets with ion energies of a few keV.
Optical frequency mixing near the cyclotron frequency for plasma heating
Authors: Capjack C. E. , James C. R.
Published: February 2004

The nonlinear mixing of two laser beams to drive a mode with a frequency near the cyclotron frequency of either the electrons or ions for plasma heating is investigated. The beat frequency wave that is generated is not required to be a natural mode in the plasma. As a result, the heating scheme is considerably less sensitive to fluctuations in the magnetic field, the plasma density, and in the frequencies of the mixing laser beams than in the case where a natural mode in the plasma is generated. The results that are obtained predict a considerable enhancement in the power absorption by the plasma in a region within the volume of interaction of the two laser beams. The extent of the strongly heated region is determined by the transfer of energy from the higher frequency laser to the lower frequency laser as the two beams propagate through the region of interaction.
Fokker-Planck equation for a plasma in a magnetic field
Authors: Montgomery David , Turner Leaf , Joyce Glenn
Published: February 2004

A convergent Fokker-Planck equation is derived for an electron plasma in a strong dc magnetic field. Conservation laws and an H theorem are proved. The equation is manipulated into a form in which it is straightforward to evaluate magnetic-field-dependent relaxation times in terms of a series of modified Bessel functions.
Rotation of a toroidally confined, collisional plasma
Authors: Hazeltine R. D.
Published: February 2004

Plasma rotation in the collisional regime is considered from the viewpoint of the driftkinetic equation, using orderings which have become standard in neoclassical transport theory. Kinetic arguments require a unique relation between the ion parallel flow U and the radial gradients of density, temperature, and electrostatic potential; this relation is derived and compared to similar relations for collisionless regimes. The off-diagonal stress tensor component, which governs the time evolution of U is also calculated. This component does not resemble a viscous stress, and dominates classical viscosity by roughly the usual Pfirsch-Schlüter factor.
Electron heating due to parametric instability turbulence
Authors: Thomson J. J. , Faehl R. J. , Kruer W. L. , Bodner S.
Published: February 2004

The turbulent electron heating due to laser-plasma instabilities at the critical density (laser frequency equals plasma frequency) is considered. In the regime where the laser energy is much less than the plasma thermal energy, simulations show that the wave energy spectrum takes on approximate k−2 shape concomitant with the formation of a suprathermal electron tail. Test particle calculations demonstrate that these tails are produced by velocity space diffusion due to the plasma waves. Quasilinear theory predicts a linear heating rate and an exponential shape for the electron tail, in agreement with the simulation result. The fluid equations, including mode coupling terms, are solved, and it is found that the instability saturation level and k−2 spectrum are due to mode coupling. Using the resulting fields, the electron distribution function is evolved, giving reasonable heating rates and suprathermal tail formation. Calculations in the underdense region (laser frequency greater than plasma frequency) show that the heated distribution function has fewer high energy electrons. Finally, an approximate analysis of heating in a finite interaction region is given.
Test wave coexisting with a large amplitude electron plasma wave
Authors: DeNeef Peter
Published: February 2004

When a small test wave is launched near the frequency of a large amplitude electron plasma wave, the behavior of the test wave is determined by the nonlinear dynamics of the electrons that are trapped by the large amplitude wave. Consequently, the amplitude of the test wave oscillates coherently with the trapping oscillations in the amplitude of the main wave. The behavior of a small, launched, test wave at frequency ω is observed as a function of its frequency separation from a large amplitude electron plasma wave at frequency ω0. The initial damping and subsequent amplitude oscillations of the test wave are compared with a calculation in which the test wave is treated as a slow modulation of the amplitude and phase of the main wave. Test wave experiments agree with the calculation when ω0 − 4π/T < ω < ω0 + π/T, where T is the transit time of the main wave through the experiment. When the spontaneously unstable frequency of the lower sideband is within this range, the slow amplitude oscillations of the sideband agree with the calculation. When the frequency of the test wave is sufficiently far below ω0 − 4π/T, the test wave damps according to linear theory. The phase velocity at which the test wave behaves essentially linearly determines the velocity of the fastest electrons that interact strongly with the wave.
Enhancement of plasma direct currents by intense alternating current fields
Authors: Lin A. T. , Dawson J. M.
Published: February 2004

Instabilities in a plasma containing electrons drifting relative to the ions and subjected to an intense ac electric field of frequency ω are investigated. The beat disturbance produced by the interaction of the driving field and ion density fluctuations of wavenumber ki accelerates electrons of velocity ω/ki. If this is larger than the electron drift velocity, the acceleration enhances the current, while the recoil momentum imparted to the ion fluctuation can cause it to grow. The process has been simulated on a one-dimensional plasma model and it was found that the small amplitude growth is in agreement with a theory which is a minor modification of that for the anomalous high-frequency resistivity. Nonlinear effects ultimately saturate the growth of the instability and the current enhancement, and some discussion of these is given.
Interaction between the ocean surface and underwater spherical blast waves
Authors: Ballhaus William F. , Holt Maurice
Published: February 2004

The object of this analysis is to obtain the solution for the flow field resulting from an explosion released at a small depth beneath the ocean surface. At time t = 0, the explosion produces a spherical blast wave. When the blast wave reaches the surface, a shock wave is transmitted into the atmosphere and an expansion wave is reflected back into the water region. The solution for the flow variables is given by Taylor series expansions in the three independent variables: r, distance in the radial direction; z, distance in the axial direction; and time, t − t0. The series expansions are different in each of the following flow regions: (1) the air region disturbed by the transmitted shock wave, (2), the water region between the expansion wave and the ocean surface, and (3) the expansion region. Coefficients for the series expansions in region 3 are determined by introducing a family of surfaces z = (r, t, N0) expanded in series for r and (t − t0) with parameter N0. The coefficients of the series expansions for the flow variables along the surfaces are determined by the integration across the expansion wave of a system of differential equations obtained from wave relations and the equations of motion. Numerical results are obtained for the case of a pressurized sphere of gas with an initial radius to depth ratio of 13 and an initial pressure of 9000 atm.
Aerodynamic torques on rotating oblate spheroids
Authors: Kry P. R. , List Roland
Published: February 2004

Aerodynamic torques about the vertical major axis of each of three rotating oblate spheroids (axis ratios 0.50, 0.67, and 0.79) with smooth surfaces were measured in a horizontal wind tunnel as a function of Reynolds number (4 × 104 < Re < 3 × 105) and rotation rate. Rotations were either about the vertical axis or the minor axis which was held inclined to the mean air flow at several fixed angles. Spin about a minor axis only shifted critical Reynolds numbers to lower values. Spin rates corresponding to Strouhal numbers less than 0.1 at Reynolds numbers less than 1.5 × 105 had no effect on the aerodynamic restoring torque. Each of the three spheroids autorotated at frequencies with Strouhal numbers of approximately 0.15. For rotations at Strouhal numbers less than 0.04, the average nonconservative torque was less than 10% of the maximum static torque. Hence, these experiments establish the range of applicability of a quasistatic approximation for the aerodynamic torques on smooth oblate spheroids. They also give necessary basic data for the general treatment of aerodynamic motions of this type of body in free fall.
Simulation of the two-stream convective instability
Authors: Busnardo-Neto J. , Rowe J. E.
Published: February 2004

A ring/disk model is used in numerical experiments to investigate the two-stream convective instability in a cylindrically symmetric system with finite transverse dimensions. The spatial growth rates obtained in the linear region agree well with the predictions of the linear theory. The development of a vortex structure in velocity-phase space is associated with the saturation of the instability. Generation and amplification of harmonics occur abundantly as expected. The two electron streams exchange kinetic energy over a very short distance and become thoroughly mixed and randomized (thermalized). Due to the choice of geometry, no coherent oscillations are established in the transverse plane, and although they increase, the radial and angular kinetic energies remain much less than the axial.
Stability of an annulus of rotating liquid to plane disturbances
Authors: Ross Dieter K.
Published: February 2004

The stability to plane disturbances of a column of inviscid liquid which rotates with a surrounding inviscid liquid of finite radius is studied. It is found that the system is stable to disturbances which are confined to cross-sectional planes if the coefficient of surface tension T > (ρ1 − ρ2) ω2a3/3 > 0, where ρ1 and ρ2 are the densities of the inner and outer liquids with radii a and b, respectively, and ω is the angular speed of the system in the steady state. For T < (ρ1 − ρ2) ω2a3/6, the system is always unstable and, in the intermediate range, some modes which are stable when b = ∞ are unstable when b is small (b > a) provided that ρ1 > ρ2 > 0. When the outer medium is the denser (i.e., ρ2 > ρ1 ≥ 0), the system is stable, a result in agreement with Taylor.
Effects of evaporation and diffusion on an oscillating bubble
Authors: Wang Tunglu
Published: February 2004

The effects of the diffusion process, due to the dissolved gas in liquid, and the evaporation process, due to the liquid-vapor phase transformation, on the motion of an oscillating bubble are studied. It is found that while the effect of gas diffusion alone is significant only when the diffusion length is large compared with the size of the bubble, evaporation effects can produce some interesting features. In particular, a second resonance is found for bubbles in superheated liquid. The stability of the linear motion of the bubble is also better understood with the inclusion of evaporation and diffusion effects. Attenuation of sound waves in an incompressible liquid due to the presence of a single bubble is also calculated.
On third-order mixed moments
Authors: Lumley John L.
Published: February 2004

It is shown that, for third-order mixed moments of two quantities (of zero mean), four sets of orthogonal axes exist (rotated 12π from each other) in which both moments involving odd powers of one of the variables vanish. The mixed moments in an arbitrary coordinate system are characterized by two real, positive numbers, and the angle from the principal axes. If one of the eigenvalues is larger than the other, the moments involving odd powers of the same variable will always have the same sign. Such distributions, termed “simple” have third-order mixed moments obeying certain inequalities. This is applied to the mixed moments of the temperature and velocity gradients in turbulent flows. Where these have been measured, the distributions are simple; where incomplete measurements exist, they satisfy the subsidiary inequalities derived for simple distributions. If the distribution of such quantities is always simple, a rather tight bound is provided for the temperature gradient production term.
Wiener-Hermite expansion and the inertial subrange of a homogeneous isotropic turbulence
Authors: Wang J. C. T. , Shu S. S.
Published: February 2004

The two-term truncated three-dimensional Wiener-Hermite expansion is applied to the study of the inertial subrange energy spectrum of a homogeneous isotropic turbulence. It is found that this expansion, up to the second term, will predict Kolmogoroff's inverse five-thirds law if the relaxation time is modified according to Kolmogoroff's second hypothesis. It is found that in the inertial subrange the energy spectrum of the non-Gaussian part is much smaller than that of the Gaussian part.
Transport equation in modified Eulerian coordinates
Authors: Wienke B. R.
Published: February 2004

The Boltzmann equation is formulated in a hydrodynamic representation (modified Eulerian) in terms of velocities relative to an accelerated medium. Treating the target particles as fixed in moving hydrodynamic zones, or cells, and employing a representation in relative velocities gives a well-defined cross section and permits use of the standard set of velocities and cross sections for computational purposes. Specific one-dimensional forms for the transport equation are also given in plane and spherical geometries.
On Stokes' problem in kinetic theory
Authors: McLennan J. A. , Chiu S. C.
Published: February 2004

The stationary drag on a sphere is calculated using vector spherical harmonics. It is shown that for small Knudsen numbers, the slip coefficient for Couette flow can be inserted into this problem and reasonable agreement with the Knudsen-Weber formula can be obtained. The nonstationary drag problem for the Boltzmann equation is formulated in terms of the normal solutions.
Rarefied gas acoustics in the noble gases
Authors: Schotter Roland
Published: February 2004

The propagation of plane pressure waves in rarefied He, Ne, Ar, and Kr has been investigated for frequencies up to 80 times the collision rate (corresponding to pressures of roughly 0.003 Torr at the experimental frequency of 0.975 MHz) along distances extending four “mean wavelengths” 2πcm/ω into the interior of the gas. This large range was obtained by the use of high Q barium titanate sandwich transducers and narrow-band phase-sensitive signal detection. For small transmitter-receiver distances standing waves were observed at all pressures, i.e., even for very long mean free paths, as the result of incomplete accommodation of the atoms at the transducer surfaces. For large distances and small pressures the experiment resembles the free molecule propagation characteristics. While increasing the pressure, the influence of binary collisions is first recognized in the attenuation, which increases. Only for higher pressures does the phase velocity change toward lower values. Apart from the standing wave region the experiment fits the theory of J. K. Buckner and J. H. Ferziger [Phys. Fluids 9, 2315 (1966)] in an excellent way.
Diaphragm opening process in shock tubes
Authors: Rothkopf E. M. , Low W.
Published: February 2004

An experimental study of the diaphragm opening process for various types of diaphragms and shock tube configurations is presented. A qualitative description of the opening process is given. A normalized curve is presented which permits prediction of the functional dependence of the diaphragm opening aperture with time for different experimental conditions.
New Rankine-Hugoniot relation for transport shock embedded in two-temperature ionizing gas
Authors: Clarke Joseph H.
Published: February 2004

Recently established was the existence of a new Rankine-Hugoniot relation across the transport shock embedded within a two-temperature, multilevel ionized gas. The traditional statement of no electron temperature change across the transport shock is replaced with an electron energy balance between elastic, heating collisions and inelastic, cooling collisions. In the present study two independent upstream properties are varied systematically and the values of downstream properties are evaluated by the old and new method; the difference can be large.
Axially symmetric magnetohydrodynamic equilibria with free-boundaries and arbitrary cross section
Authors: Chu M. S. , Dobrott D. , Jensen T. H. , Tamano T.
Published: February 2004

An iterative method is used to solve the magnetohydrodynamic equations of free-boundary, axially symmetric equilibria with arbitrary cross section. The method is applied numerically to the study of the plasma equilibrium. The limiter creates a vacuum region outside the plasma. It is shown that the current density profile has a strong effect on the equilibrium. Topologically different equilibria may be obtained by changes in the parameters which determine the current profile. The method is also applied to generate elliptic, D-shape, doublet, and other shapes of equilibria maintained by coil systems.
Nonlinear magnetohydrodynamic stability and plasma containment with closed field lines
Authors: Spies G. O.
Published: February 2004

Previous formulations of the nonlinear energy principle of ideal magnetohydrodynamics in toroidal geometry cease to be relevant for stability if all magnetic field lines are closed. On the other hand, nonlinear stability is more vital in this degenerate case because the conservation laws cease to prevent plasma from touching the wall. The appropriate formulation of the nonlinear energy principle is given for this case, and from this the necessary and sufficient condition is derived for stability to finite line-preserving perturbations. Apart from the well known requirement of stability to infinitesimal interchanges and flutes deducible from the linear theory, this condition contains the additional requirement that the level surfaces of the quantities q =  ∮  dl/ B, I =  ∮  dl B, and the pressure p, coincide globally. It is further shown that nonlinear stability is compatible with containment only if the (purely geometrical) quantity Λ = Iq attains its minimum at the wall. The entire analysis is completely general and fully nonlinear.
Compression of matter to superhigh densities by an accelerating heat wave
Authors: Mikoshiba S. , Ahlborn B.
Published: February 2004

A one-dimensional analytical model is presented for the compression of matter (e.g., thermonuclear fusion fuel to densities of more than 103 times the solid density) by an accelerating subsonic heat wave. The heat wave, driven possibly by the absorption of a temporally tailored laser pulse, launches a large number of successive weak shock waves which compress and heat the target quasiadiabatically in order to keep the energy expenditure at a minimum. The net power to drive this heat wave must have a stepwise increase in time approximated by W = 98ρ0c03K2/τ2, where K = Dfρf/D0ρ0 is the fraction of the initial target mass (of density ρ0 and thickness Df) which reaches the final state (of ρf and Df. The adiabaticondition sets the requirement that K should be much smaller than one. The time t is scaled as τ = 1 − t/t8, where t8 = D0/c0 and c0 is the initial sound speed. The sound speed in the compressed matter, from which pressure and density can be obtained using the adiabatic equations of state, will increase approximately as c0(K/τ)1/4. Half of the total driving energy is expended by the time tf[τf = (Df/D0) (ρ0/ρf)1/3], from which time the power has to be held constant at Wf = 98(ρf/ρ0)8/3ρ0c03 until time t8.
Stimulated scattering of electromagnetic ordinary waves from electron plasma waves at the upper hybrid frequency
Authors: Lee Kai Fong
Published: February 2004

Stimulated scattering of electromagnetic waves of ordinary polarization incident on a magnetized plasma from electrostatic waves propagating normal to an external magnetic field at the upper hybrid frequency is studied. The analysis is based on a multiple-time-scale perturbation expansion of the fluid equations, incorporating the effects of temperature, collisions, and the spatial variation of the pump wave. The threshold intensity required for the process and the growth rate above threshold are calculated.
Microwave scattering from an overdense turbulent plasma
Authors: Attwood David
Published: February 2004

Experimental results of microwave scattering from a turbulent plasma are presented. For underdense values of mean and fluctuation electron density, scattering is similar to that noted by several other groups, following Born predictions for very weak scattering and saturating as the critical point is approached. Near the critical point for average electron density, a crossover from volume to surface scattering is observed. For sufficiently overdense values, scattering resembles that from a reflecting surface of appropriate shape and statistics, mean density distribution notwithstanding. Scattering in this latter regime is used as a diagnostic tool to determine the probability distribution function for orientation fluctuations displayed by the overdense thrashing plasma column.
Spectrum of turbulence at a magnetic neutral point
Authors: Baum P. J. , Bratenahl A.
Published: February 2004

The spectral density of plasma waves generated at the x-type magnetic neutral point of a laboratory device known as the double inverse pinch has been measured using a double probe technique devised by Hamberger and Jancarik. The spectra peak at low frequencies and have no components above the ion plasma frequency. This is in general agreement with the ion-acoustic wave spectrum of Kadomtsev. No contribution is seen at frequencies characteristic of the two-stream instability. The plasma wave amplitude is estimated to be sufficient to produce the anomalous resistivity which has been observed in this device. A knowledge of the resistivity mechanism is essential in understanding neutral point phenomenon as the resistivity controls “the reconnection rate” or more precisely the flux transfer rate. Flux transfer is almost certainly a key element of solar flares and geomagnetic substorms. The flux transfer process also occurs in many laboratory plasma experiments.
Computer simulated finite-length turbulent heating experiment
Authors: Jones Walter W. , Krall N. A. , Klein H. H.
Published: February 2004

A computer code has been used which was designed to allow for finite length effects found in real plasmas in order to study turbulent heating in a plasma where boundary conditions might be important. An electric field was applied to an initially quiescent plasma, and it was found that the final energy distribution (after saturation occurs) favors ions and electrons equally (Ti≃Te). This is in contrast to the infinite length simulations where the electrons become much hotter than the ions Ti≃(me/mi)1/3Te. It was also found that the saturation level depends critically upon the length of the system as well as the mass of the ions and the applied electric field.
Effect of toroidal gradient drifts on the dissipative trapped-ion instability
Authors: Tang W. M.
Published: February 2004

Conditions for the onset of the dissipative trapped-ion instability in tokamaks with elliptic and circular cross sections are determined. Toroidal gradient drifts, ignored in earlier calculations, are included in the analysis and found to give rise to significant stabilizing effects. In particular, the results show that the ions trapped in regions of good gradient (dB/dρ > 0) contribute to the Landau damping of the unstable waves, and that ion collisional damping is also enhanced when the drifts are taken into account. Since vertical ellipticity increases the region of good gradient, these stabilizing effects are further enhanced in elliptical cross-section tokamaks. It is also shown that previously calculated restrictions on the allowable magnitude of temperature gradients for favorable damping can be relaxed. Results of the analysis are applied to expected parameters for the Princeton Large Torus experiment and growth rate estimates given for conditions violating the stability criteria.
Viscous stress tensor effects in low-pressure toroidal plasma confinement
Authors: Hellberg M. A. , Winsor N. K. , Johnson J. L.
Published: February 2004

Calculations employing a numerical magnetohydrodynamic toroidal plasma simulation model show that contributions to the viscous stress tensor in the momentum balance equation, which are associated with bulk viscosity and magnetic field line curvature, are as important as the usual approximation, a term proportional to ∂2υb/∂l2 with υb and l directed along the field.
“Pressure” balance in pulsed plasmas with large self-fields
Authors: Hammer D. A.
Published: February 2004

Momentum and flux conservation laws are combined for a cylindrically symmetric magnetically confined, pulsed electron beam (or plasma) to obtain a generalized “pressure balance” equation. This equation is useful for interpretation of magnetic probe signals in intense electron beam experiments, in which large self-electric and magnetic fields are present.
Theory of magnetic insulation
Authors: Lovelace R. V. , Ott Edward
Published: February 2004

An investigation is made of the behavior of a high voltage diode for the situation where the cathode-anode gap is initially filled with a transverse magnetic field. An exact relativistic self-consistent equilibrium is found for the electron sheath which is expected to form under the condition where the applied magnetic field is sufficiently strong to prevent electrons from flowing between the electrodes. The condition on the magnetic field for “insulation” is found to be (eBy0d/mc2)2 > 2|eV0/mc2| + (eV0/mc2)2, where By0 is the applied magnetic field, V0 is the voltage across the diode, d is the cathode-anode separation in the x direction, and —e and m are the electron charge and rest mass, respectively.
Electric field and potential near the plasma resonance cone
Authors: Kuehl H. H.
Published: February 2004

The electric field and potential at and close to the resonance cone of an oscillating point charge and dipole in a warm magnetized plasma are investigated theoretically, neglecting ion motion. Approximate expressions are derived for both a drifting and a stationary Maxwellian plasma. The shift in angle of the maximum potential due to plasma drift is shown to be small and dependent on both drift and thermal velocities if the drift velocity is much less than the thermal velocity. For a stationary plasma, a comparison of the potential of a point charge with its electric field and with the potential and field of an arbitrarily-oriented dipole shows that the potential of the point charge has the following distinguishing characteristics: The maximum lies closest to the cold-plasma resonance cone; the angular location of this maximum is least dependent on damping mechanisms in the plasma; the interference structure is the largest. The approximate expression for potential yields results in good agreement with existing experimental results and more rigorous calculations. From the multipole expansion of an arbitrary charge distribution in a stationary Maxwellian plasma, it is shown that higher-order multipole contributions are small if the characteristic source dimension is small compared with the spatial separation between two successive interference maxima.
Parametric instabilities in a plasma-beam system
Authors: Khan T. P.
Published: February 2004

The excitation of electromagnetic transverse waves, cyclotron waves, and Ĉerenkov waves by a beam of charged particles moving through a plasma immersed in a crossed electric and magnetic field with a constant uniform velocity parallel to the direction of the external magnetic field has been considered.
Synchrotron radiation spectrum for an intense relativistic electron ring
Authors: Davidson R. C. , Mahajan S. M. , Schwartz M. J.
Published: February 2004

The synchrotron emission spectrum is calculated for a thin, mirror-confined, relativistic electron ring including self-field effects. Since individual electrons execute betatron oscillations about a mean radius R0, the single-particle emission spectrum is modified from the conventional (Schott-Trubnikov) result. The spectrum of radiation emitted by all electrons in the ring is obtained by averaging the single-particle spectrum over the distribution function, fe0(H, pθ), that self-consistently generates the ring equilibrium.
Plasma confinement in multiple-mirror systems. I: Theory
Authors: Makhijani A. , Lichtenberg A. J. , Lieberman M. A. , Logan B. Grant
Published: February 2004

For an intermediate mean free path regime where λ ≪ L, the system length, but where λ ≫ lm, the scale length of the magnetic field variation, it is found that the confinement time τmm of ions in a multipole mirror system scales quadratically with the system length. When either inequality is not satisfied, a transition is found to a scaling which is more closely proportional to L. For the high density regime this corresponds to magnetohydrodynamic flow. By comparison with numerical and experimental results a criterion is found for the transition from the quadratic to the linear scaling. The value of τmm = ML2/(2lcν¯) found from diffusion theory is in good agreement with a more accurate analytic treatment which is valid in the limit of λ/M ≪ lc, where M is the mirror ratio, Lc is the cell length, and ν is the average ion velocity. Good agreement is also obtained with a self-consistent numerical computation.
Plasma confinement in multiple mirror systems. II. Experiment and reactor calculation
Authors: Logan B. Grant , Brown I. G. , Lichtenberg A. J. , Lieberman M. A.
Published: February 2004

A multiple mirror experiment confirms the predictions of the theory that the axial confinement time exceeds that of a single mirror of the same length, and that the confinement scales as L2, where L is the system length. The experiment indicates that the improved confinement occurs in an intermediate mean free path regime in which the mean free path for scattering out of a loss cone is of the order of a cell length. The absolute value of the axial confinement is smaller than the optimum confinement predicted from the theory by a factor between two and three, which is accounted for by the deviation of experimental parameters from optimum conditions. The scaling of the confinement time with mirror ratio is also investigated. A reactor calculation using the multiple mirror confinement time gives QE = 2 for a 400-m system with 3000-MW(e) output.
Plasma experiments on the linear scyllac theta pinch
Authors: Thomas K. S. , Harris H. W. , Jahoda F. C. , Sawyer G. A. , Siemon R. E.
Published: February 2004

Experiments on a 5-m-long theta pinch both with and without strong magnetic mirrors (R ≈ 2.5) are reported. When the experiment is operated without magnetic mirrors, the particle loss rate is found to scale from shorter theta-pinch experiments directly as the length and inversely as the ion thermal velocity. The electron temperature scales with length (l2/5) as predicted by a theory which accounts for thermal conduction to the ends. Addition of the magnetic mirrors increases plasma confinement time from 11.5 to 18.9 μsec. a smaller increase than predicted by available theories, and also produces an m = 1, k ≈ 0 instability which is moderated under certain conditions by “line tying” effects.
High power fundamental and harmonic resonant ion cyclotron heating in a mirror machine
Authors: Clark R. W. , Swanson D. G. , Korn P. , Sandel F. , Robertson S. , Wharton C. B.
Published: February 2004

Radio frequency heating at powers up to 1 MW and pulse widths of ∼700 μsec was applied to a turbulently preheated hydrogen plasma in a large pulsed mirror machine. Energy analysis of charge exchange neutrals indicates that resonant heating occurred when the radio frequency matched either the ion cyclotron frequency or one of its harmonics. The behavior of the induced rf fluctuations in the plasma was observed by means of microwave scattering. These measurements show resonance phenomena and the presence of rf fluctuations at harmonics of the rf heating frequency. Diamagnetic loop measurements indicate that 310 ≤ (Te+Ti) ≤ 380 eV as a result of the heating, while measurements of the ion energy distribution by charge exchange energy analysis shows the ion energy distribution to be non-Maxwellian with a low temperature component of Ti ∼ 320 eV. Microwave interferometer measurements indicate densities of ∼2 to 3 × 1013 cm−3.
Stability of turbulent jets and wakes
Authors: Lessen Martin , Singh Pawan Jit
Published: February 2004

The mean flow of rotationally symmetric turbulent jets and wakes is postulated as marginally stable. The angles of spread of turbulent jets and wakes can be estimated as being those of the laminar flows at their critical Reynolds numbers.
Solution of a generalized Korteweg—de Vries equation
Authors: Tagare S G. , Chakrabarti A.
Published: February 2004

The solitary-wavelike solution of the generalized Korteweg-de Vries equation with mixed nonlinearity is obtained. Two asymptotic cases of the solution have been discussed and solitary wave solutions have been derived.
Shock wave structures in binary gas mixtures with regard to temperature overshoot
Authors: Abe Kanji , Oguchi Hakuro
Published: February 2004

Shock wave structures in argon-helium mixtures are numerically investigated with special regard for the temperature overshoot. Comparison with Harnett and Muntz' experiment is made. The argon temperature overshoot is expected to occur for a sufficiently small mole fraction of argon.
Population inversion of CO2 by free expansion
Authors: Wasserstrom E. , Stricker J.
Published: February 2004

Population inversion achieved by a one-dimensional unsteady sudden expansion of a hot mixture of CO2 − N2 − He into vacuum is investigated. Numerical calculations show that for appropriate conditions a positive gain can be achieved. Results of preliminary experiments have not been conclusive.
Imbibition in the flow of two immiscible fluids with magnetic field
Authors: Mishra S. K. , Verma A. P.
Published: February 2004

The physical phenomenon of imbibition due to relative wettability of flowing fluid in double phase flow through homogeneous porous media is discussed. The injected liquid is conducting while the native liquid is nonconducting, and the effect of a variable magnetic field is considered.
Suppression of ionization waves by hydrodynamic turbulence
Authors: Attwood David
Published: February 2004

Microwave scattering from density fluctuations in a dc discharge tube indicates that striations can be eliminated by hydrodynamic turbulence.
Stimulated Brillouin scattering of electromagnetic circularly polarized waves in a magnetized plasma
Authors: Lee Kai Fong
Published: February 2004

Stimulated scattering of electromagnetic waves of circular polarization incident on a magnetized plasma from ion waves propagating parallel to the external magnetic field is studied. The relevance of the process to ionospheric modification experiments is discussed.
Further applications of hot-wire anemometry to turbulence measurements in helium-air mixtures
Authors: Stanford Richard A. , Libby Paul A.
Published: February 2004

The extension of the Way-Libby probe to permit the measurement of two velocity components u and υ in the usual notation, and the mass fraction c of helium in turbulent flows involving helium-air mixtures is described. The accuracy of the technique, especially the sensitivity to flow deflection, is carefully assessed. Interesting results obtained in applying the new probe show, inter alia, highly skewed probability density functions of helium concentration in an internal flow.
Inertial oscillations and multiple boundary layers in an unsteady rotating flow
Authors: Debnath Lokenath , Mukherjee Sukla
Published: February 2004

An asymptotic analysis is made of the unsteady boundary layer flow generated impulsively in an incompressible homogeneous viscous fluid bounded by an infinite porous plate with uniform suction or blowing to describe the manner of the transient approach to the ultimate steady state. It is shown that the initial motion for small times describes the general features of the unsteady boundary-layer flow and consists of three boundary layers on the plate which are unaffected by rotation. In subsequent large times, the effect of rotation manifests itself through inertial oscillations of frequency 2Ω and the generation of diffused waves propagating outward from the plate with velocity 2(Ων)1/2a1. It is found that the final steady boundary layers are established in a dimensional time (4/Ω) (S4/4E2 + 4)−1/2 which decreases with an increase in the suction parameter. Several limiting cases of interest are recovered from this analysis.
Thermal force on aerosol particles
Authors: Cha C. Y. , McCoy B. J.
Published: February 2004

With a method previously applied to thermal transpiration and planar radiometric force, the force on a spherical aerosol particle in a gas which sustains a temperature gradient is analyzed. Expressions for thermal force and thermal velocity span all values of the particle Knudsen number and show the effect of imperfect accommodation. The results are compared with other theories and with experimental data.
Effects of nonadiabatic transitions on invariants of the motion
Authors: Aamodt R. E. , Jaeger E. F.
Published: February 2004

A computer study is made of the change in adiabatic invariant for a plane pendulum when a slow variation in the pendulum length forces the pendulum to change from circularly rotating motion to an oscillating state. The numerical results are shown to be in good agreement with a simply derived analytic expression which itself is generalizable to calculations of nonadiabatic transitions in other problems.
Stability of filamentary structures
Authors: Valeo Ernest
Published: February 2004

Isolated, one-dimensional channels of electromagnetic radiation in a plasma are shown to be unstable to bending perturbations. Let l be the wave vector of the perturbation along the channel, k be that of the radiation, and C8 be the sound speed. Then, the growth rate γ ∼ lC8 for l/k ≪ 1.
Influence of ion tail formation and ion resonance broadening on the dynamical behavior of a current-carrying plasma
Authors: Caponi M. Z. , Davidson R. C.
Published: February 2004

The influence of ion tail formation on the dynamical behavior and anomalous resistivity of a current-carrying plasma is studied within the context of a quasilinear model that includes ion resonance broadening as a possible quasi-saturation mechanism for the ion acoustic instability. Although the detailed time development of macroscopic plasma parameters depends on nh/ni (the ratio of ion tail density to total ion density), the value of anomalous resistivity at quasi-saturation is found to be relatively insensitive to the formation of a low-density high-energy ion tail. For example, if nh/ni = 0.2, the anomalous resistivity is lowered by 15% relative to its value in the absence of an ion tail.
Plasma heating by spatial resonance of Alfvén wave
Authors: Chen Liu , Hasegawa Akira
Published: February 2004

Heating of a collisionless plasma by utilizing the spatial resonance of shear Alfvén waves is proposed and application to toroidal plasmas is discussed. The resonance exists due to the nonuniform Alfvén speed. This heating scheme is analyzed in one dimension including the effects of a shear magnetic field and plasma compressibility. For plasmas with smooth nonuniformities (| k⊥l | ≫ 1, k⊥ is the wavenumber prependicular to the ambient magnetic field and the nonuniformity direction, and l is the scale length of the nonuniformity), the energy absorbed per unit surface area per driving cycle is [b02(μ0k⊥)−1]. Here, b0 is the flux density of the driving magnetic field evaluated at the resonant point. With sharp nonuniformities (| k⊥l | ≪ 1), absorption is large if the surface eigenmode is excited. The corresponding value is [b02(μ0k⊥)−1(k⊥l)−1]. Otherwise, it is [b02(μ0k⊥)−1(k⊥l)].
Stability test for strongly inhomogenous plasmas through Nyquist diagrams
Authors: Bloomberg H. W.
Published: February 2004

The stability of inhomogeneous plasma equilibria in the water bag approximation is discussed by means of Nyquist diagrams. A function suitable for a Nyquist diagram is constructed, and the method is applied to demonstrate the instability of the electron sheath configuration. The behavior of the Nyquist diagram shows directly that instabilities occur near multiples of the bounce frequency of the innermost sheath contour in phase space.
Microwave emissions from turbulent plasmas generated in a fast, high voltage theta pinch
Authors: Chin-Fatt C.
Published: February 2004

Intense, and evidently nonthermal, bremsstrahlung has been observed from turbulent helium plasmas that were generated in a large, high voltage theta pinch operated in two different experimental configurations. The emissions were in the wavelength range 1 mm ≲ λ ≲ 16 mm, and are identified as collective bremsstrahlung, originating from the interaction of longitudinal modes of the turbulent plasmas by wave-wave scattering.
Parametric instabilities induced by the coupling of high and low frequency plasma modes
Authors: Manheimer Wallace M. , Ott Edward
Published: February 2004

A general dispersion relation is derived for parametric instabilities caused by a large amplitude pump wave which couples high and low frequency modes of a magnetized plasma. The nonlinear effects coupling the high and low frequency waves are: (1) the low-frequency pondermotive force due to the coupling of the pump with the high frequency perturbations, and (2) the high frequency nonlinear source current density produced by coupling of the pump with the low frequency perturbations. The dispersion relation contains decay instabilities, purely growing instabilities, modulational instabilities, self-focusing and nonlinear Landau damping. As examples the dispersion relation is applied to self-focusing, magnetosonic decay and purely growing instabilities, whistler decay and nonlinear Landau dumping of electron plasma waves and transverse electromagnetic waves.
Experimental determination of the rate of slowing of fast ions in a dense plasma in a magnetic field
Authors: Burke R. J. , Post R. F.
Published: February 2004

An experiment to measure the energy loss rate of fast ions moving in a dense magnetized plasma is described. In the experiment, proton and deuteron test particles lose energy predominantly to plasma electrons of comparable thermal speed. Interaction of the test particles with the plasma is limited to a defined path between two charge changing reactions. The time of interaction is determined from the cyclotron frequency of the test ions and the entrance and exit angles of the test particles. The observed energy losses are compared to the Spitzer formula and to more recent theoretical calculations. It is concluded that the Spitzer formula underestimates the energy loss by about a factor of 2; the disagreement with the more recent calculations amounts to about a factor of 3. It is proposed that the observed discrepancies may arise from cooperative particle-wave energy transport effects in the magnetized plasma.
Theory and simulation of higher-order cyclotron damping
Authors: Gitomer S. J. , Forslund D. W.
Published: February 2004

The infinity of roots for real wavenumber k and complex frequency ω of the dispersion relation for transverse electromagnetic waves propagating in a thermal plasma parallel to an applied magnetic field B are studied theoretically and observed in numerical simulations. In addition to the usual weakly damped whistler and ion cyclotron roots, there are infinitely many more heavily damped electron (ion) roots characterized by real frequency near the gyrofrequency and damping rate proportional to the wavenumber. The electron modes have been observed in a thermal electromagnetic numerical simulation plasma and their dispersion agrees well with finite temperature linear theory. These modes may be observable experimentally.