bluuebunny/crossref_metadata_2025 huggingface dataset:
Parametric excitation of ion-cyclotron waves by a pump magnetic field in a high-temperature plasma
Authors: Cramer N. F.
Published: March 2003

The growth rate of ion-cyclotron waves, parametrically excited by a pump magnetic field oscillating in time in a hot plasma, is calculated. The process occurs through the excitation of a slow ion-cyclotron wave and a fast wave propagating in opposite directions along the magnetic field, as has been found previously for the case of a cold plasma. The growth rate of the waves is found to vanish at a critical temperature, that temperature being higher for a lower value of the ratio of the pump frequency to the ion-cyclotron frequency. Below the critical temperature the growth rate is always less than the cold plasma growth rate.
Orbit function in the Dupree–Weinstock theory of plasma turbulence
Authors: Pocobelli G.
Published: March 2003

A convergent orbit function within the weak coupling approximation is calculated.
Low-frequency microinstabilities in the PLT tokamak
Authors: Mazzucato E.
Published: March 2003

A turbulence with wavelengths in the range 2–0.2 cm and with a spectrum in the range of frequencies of drift waves has been observed in the PLT discharge with scattering of microwaves. The total density fluctuation was ñe/n̄e≃5×10−3–10−2. It is estimated that this turbulence can cause an anomalous transport much larger than that predicted by neoclassical theory. As the PLT discharge developed a central minimum of the electron temperature, an increase in the turbulence level was observed with a very strong poloidal localization on the outside of the plasma torus.
Numerical study of the Taylor–Green vortices
Authors: Betchov Robert , Szewczyk Albin A.
Published: March 2003

The inviscid flow produced by the initial conditions proposed by Taylor and Green illustrates some basic features of the turbulent flow process, namely, the build-up of the mean square vorticity and the decay of the integral scale. The rate of deformation and the rate of vortex stretching along one direction shows some differences. The deformations occur mostly in lenticular regions. The evolution process of the flow development is discussed.
Kinetic and finite beta effects on the m=1 tearing instability
Authors: Hazeltine R. D. , Strauss H. R.
Published: March 2003

Tearing instabilities with poloidal mode number m=1 are examined by means of a kinetic description of the electron response. At very low beta, the use of a frequency dependent Ohm’s law permits investigation of colllisionless regimes, and new modes are found. At finite beta, variational solution of the eigenmode equation shows that one of these modes remains unstable for quite large beta.
Effects of high-frequency fields on plasma transport coefficients
Authors: Bernstein Ira B. , Max Claire Ellen , Thomson J. J.
Published: March 2003

It is shown that laser fields in plasmas, in addition to the usual ponderomotive force in the center-of-mass momentum equation, give rise to significant modifications of the material stresses and additional terms in the Ohm’s law and equation for the heat flow vector. These are evaluated explicitly for the case of a single geometric optics field assuming that the slowly varying part of the electron distribution function is collision dominated, that the equation for the high frequency part can be linearized, and that the effective charge number Z≫1. The new terms are all roughly proportional to the energy density in the high-frequency field. They are thus comparable in magnitude with conventional ponderomotive forces.
Surface filamentation of a relativistic electron beam in a plasma
Authors: Molvig Kim , Roberson C. W. , Tajima T.
Published: March 2003

The electromagnetic instability of a relativistic electron beam in a plasma that is current and charge neutralized in the beam channel is considered. In addition to the usual filamentary instability an instability that is localized to the surface of the beam is found. The maximum growth rate is ωi =ωbβ/√2γ. The effects of collisions, a conducting wall, magnetic field, hollow beam geometry, and different plasma densities, inside and outside the beam, are calculated.
Heat flux reduction by electromagnetic instabilities
Authors: Ramani A. , Laval G.
Published: March 2003

Heat flux inhibition by microinstabilities in hot and dense plasmas is investigated. Because of the anisotropy induced by the temperature gradient, Weibel-like low frequency electromagnetic modes become unstable. The chaotic magnetic field thus generated effectively reduces the electron mean-free-path. Saturation of these instabilities is expected from mode-mode couplings. With the estimated saturation level, the mean-free-path is self-consistently found to be smaller than the typical gradient length L, thus keeping the heat flux below the free streaming value, with a reduction factor ε′= (c/Lωp)1/3.
Stability of body-centered polygonal configurations of ideal vortices
Authors: Mertz Gordon J.
Published: March 2003

Thomson’s results concerning the stability of regular vortex polygons are generalized to include the case of the polygonal center being occupied by a vortex of arbitrary relative strength. Of most significance is the fact that a strong enough central vortex can stabilize a Thomson polygon consisting of arbitrarily many vortices. The efficacy of the free energy criterion for stability is demonstrated in showing that the Thomson heptagon is stable.
Doppler model for adiabatic toroidal compressor driftwave frequency profiles
Authors: Koch R. A. , Tang W. M.
Published: March 2003

Microwave and CO2 laser scattering experiments on the ATC adiabatic toroidal compressor tokamak have shown that there exists a spectrum of fluctuations with frequencies ‖f‖≲1 MHz at wavelengths λ∼0.28 cm and with ‖f‖≲400 kHz for λ∼1 cm. However, a typical maximum frequency calculated for given experimental density and temperature profiles is f≲150 kHz for the longer wavelengths and differs from the experimental results by roughly a factor of 2 or 3. At shorter wavelengths the calculated maximum f≲100 kHz, which differs quite substantially from the experimental result. This discrepancy is interpreted as evidence of an E×B Doppler shift from a radial electric field.
Effect of cross-sectional mass dependence in the theory of disparate-mass gas mixtures
Authors: Johnson E. A.
Published: March 2003

Equations previously derived for disparate-mass gas mixtures in the two-temperature regime are generalized to allow for an observed mass dependence of intermolecular forces.
Magnetohydrodynamic instability of quasi-parallel plane jets
Authors: Plaschko P.
Published: March 2003

The spatial stability of jets in homogeneous parallel magnetic fields in analyzed. It is shown that the magnetic stabilization is about proportional to the inverse of the profile gradient and that three-dimensional modes may become more unstable than their two-dimensional counterparts.
Magnetohydrodynamic blast wave in a gravitational field
Authors: Rosenau Philip
Published: March 2003

Exploiting the invariant properties of the first integrals of motion, the closed form solution for the problem of magnetohydrodynamic blast waves in a gravitational field due to a heavy nucleus at the origin is presented.
Trapped electron instability in tokamaks: Analytic solution of the two-dimensional eigenvalue problem
Authors: Catto P. J. , Tsang K. T.
Published: March 2003

The two-dimensional eigenvalue equation for the trapped electron instability in tokamaks is solved analytically by both a perturbation technique and a more exact method of matched asymptotic expansions. The important physical effect is shown to be the radial localization of the trapped electron term caused by the difference between the pitch of the magnetic field and that of the mode. This localization results in a completely new form for the dispersion relation and does not impede magnetic shear stabilization. Coupling of neighboring rational surfaces is shown to result in an increase of only π/2 (at most) in the growth rate.
Equilibrium properties and limiting current behavior of a cusp injected rotating E layer
Authors: Striffler C. D. , Kim Hogil
Published: March 2003

The equilibrium properties of a cusp injected, hollow, rotating E layer are self-consistently calculated by solving the coupled equations representing conservation of energy, canonical angular momentum, and radial force balance. The particles forming the E layer are emitted from an annular knife-edged cathode, accelerated in the cathode-anode gap, pass through a cusped magnetic field, and propagate into a coaxial conducting wall system. The steady-state equilibrium properties including all self-fields are determined for a given choice of diode parameters, applied cusped magnetic fields, and conducting walls. When only an outer solid conducting wall is considered, a limiting current behavior is observed above a critical magnetic field, whereas, below this critical field, the beam is driven to the wall as the beam intensity increases. When an inner squirrel cage and an outer solid conductor are considered, no limiting current behavior occurs, but the beam is driven to the inner squirrel cage as the beam intensity increases. For this case, equilibria are found to exist above the single particle cutoff field.
Two-stream ion-ion instability in an axially bounded ion beam plasma system
Authors: Ohnuma Toshiro , Fujita Takao , Adachi Saburo
Published: March 2003

When ion beams were injected into axially bounded plasmas, ion waves, whose wavelengths were determined by boundaries, were found to be very distinctly excited. The selection of the excited oscillation frequency was determined by the boundaries such that the spacing of the boundaries was approximately an integer times the wavelength of the ion waves. The observed phase velocity was in fairly good agreement with the theoretical velocity.
Numerical simulation of the weak beam-plasma interaction
Authors: Goldstein B. , Carr W. , Rosen B. , Seidl M.
Published: March 2003

The Cerenkov interaction of a weak electron beam with a plasma is studied numerically. Three parts of the nonlinear evolution of the convective instability are discussed. In the first part the understanding of the saturation amplitude of the initial wave and its harmonics is extended. In the second part it is shown that a quasi-linear-like cascade process is responsible for the simutaneous appearance of beam particles and waves which move slower than the original beam velocity. These modes destroy the trapped particle oscillations of the initial wave. The third part of the instability is the development of fast waves whose phase velocities are greater than the original velocity of the beam. It is shown that these waves arise due to a mode coupling mechanism.
High-beta tokamaks surrounded by force-free fields
Authors: D’Ippolito D. A. , Freidberg J. P. , Goedbloed J. P. , Rem J.
Published: March 2003

The sharp-boundary model of ideal magnetohydrodynamics is presented in a form readily applicable to axisymmetric, high-β plasmas of arbitrary cross section. The usual vacuum region outside the plasma is replaced here by a layer of force-free currents, and the influence of force-free currents and cross-sectional shaping on the critical β is studied. Specific results are given for circular, elliptical, and racetrack-like cross sections. A new parameter q* is introduced in place of the Mercier q, and it is shown that q*≈1 is a reasonable estimate of the toroidal current limitation due to external kink modes in high-β plasmas with noncircular cross sections.
Numerical study of an ion acceleration in a z-pinch type plasma focus
Authors: Kondoh Y. , Hirano K.
Published: March 2003

Motions of ions in the plasma focus are investigated theoretically using a model for a z-pinch type plasma focus. Macroscopic radial motions of plasma are calculated numerically using the snowplow model, the Leontovich–Osovets’ equation, and a circuit equation. The equations of motion of ions are solved in the presence of fields induced in the pinched phase of the macroscopic motion. It is found that in the collapse phase there appears a betatron-like acceleration process of ions with negligible drift velocity. It is also shown that a strong free-streaming acceleration process leading to high, axial velocity of ions in the direction of current flow appears in the expansion phase.
Differential equation for Alfvén ion cyclotron waves in finite-length plasma
Authors: Watson Duncan C. , Fateman Richard J. , Baldwin David E.
Published: March 2003

The fourth-order differential equation describing an Alfvén ion-cyclotron wave propagating along a magnetic field of varying intensity is found. The equation is self-adjoint and possesses nontrivial turning points.
Stability of displacement of a cold fluid by a hot fluid in a porous medium
Authors: Bachu S. , Dagan G.
Published: March 2003

The stability of nonisothermal flow through porous media is investigated, when both density and viscosity variations with temperature are present. The instability phenomena are due to the buoyancy effect of a density gradient directed upward, and to the fingering effect of the displacement of a more viscous fluid by a less viscous one. Small perturbations are superimposed on the basic flow, and their development is investigated in order to establish the criteria of flow stability. The flow variables are expanded in a series of eigenfunctions, and the ensuing system of ordinary differential equations is solved numerically. Criteria of flow stability and parameters affecting flow conditions are studied.
Model of the distribution function for source flow expansion
Authors: Nanbu K.
Published: March 2003

A simple model of the distribution function has been obtained by examining the Willis–Hamel–Lin solution of the BGK equation. This model is an extension of the ellipsoidal model to a large translational nonequilibrium. Once the perpendicular temperature Tp and the number density n in the ellipsoidal model are replaced by σTp and C00 n, respectively, the model immediately results. Two parameters σ and C00 are given as functions of Tp/Tr for various values of an exponent of a power law viscosity-temperature relationship. The model has been shown to be a valid approximation except for the tail of the distribution function.
Effect of spatial turbulence on parametric instabilities
Authors: Williams E. A. , Albritton J. R. , Rosenbluth M. N.
Published: March 2003

Three-wave backscattering instabilities are investigated in a plasma slab with stationary density fluctuations. The noise is of sufficient amplitude to induce random variation in the phase of the coupled waves. The analysis is formulated in terms of the Nyquist theorem. The ensemble average number and distribution of the zeroes of the exact dispersion relation are obtained from the solution of a Fokker–Planck/Boltzmann equation for the probability density of the phase angle of the dispersion relation. Threshold lengths and growth rates obtained are less optimistic for stability than those found in previous random phase investigations. The stabilizing influence of inhomogeneity is weaker in turbulent plasmas than in nonturbulent ones. The analytic results are confirmed in detail by direct numerical simulation of the fundamental equations.
One-dimensional motion of collisionless particles in gasdynamic approximation
Authors: Zeldovich Ya. B.
Published: March 2003

It is shown that one-dimensional motion of collisionless particles with a step distribution function can be exactly described by gasdynamics.
Nonlinear Landau damping in mirror plasmas
Authors: Nicholson Dwight R. , Aamodt R. E. , Liu C. S.
Published: March 2003

The well-known drift cyclotron loss cone mode is shown to couple nonlinearly to a low frequency stable Rayleigh–Taylor mode through the process of nonlinear Landau damping. When the drift cyclotron loss cone mode is linearly marginally stable, this coupling leads to an explosive instability, the time scale for which is in some agreement with experimental time scales.
Wave reflection from the lower hybrid surface: A toroidal effect
Authors: Ott Edward , Wersinger Jean-Marie , Bonoli Paul T.
Published: March 2003

In tokamaks, the equilibrium magnetic field does not lie in the lower hybrid surface. As a result, cold lower hybrid waves are reflected there rather than encountering a resonance. For high temperatures, however, mode conversion occurs before the wave can bounce.
Interaction of a high frequency magnetic field with the drift-cyclotron loss-cone mirror instability
Authors: Shaing Ker-Chung , Kesner Jay , Conn Robert W.
Published: March 2003

The effect of a small amplitude, high frequency field on drift-cyclotron loss-cone instability is investigated. With B1/B0=5% and ωce/ω0=80, the critical characteristic length of plasma density gradient reduces dramatically and is comparable to the finite β stabilization effect.
Radio frequency electric fields in ion cyclotron excitation of multispecies plasma
Authors: Tang J. T. , Stenzel R. L. , Kim H. C.
Published: March 2003

The self-consistent rf electric field in ion cyclotron excitation of a multispecies plasma is measured and compared with linear plasma theory. For wave propagation perpendicular to the magnetic field Bz (kz=0), the rf electric field has minima at major and minor ion cyclotron frequencies f1, f2, respectively. Near fα, where fα is the ion cyclotron frequency of species α, the field is proportional to Δf=f−fα. The line width about fα is proportional to rα ≡ the ratio of the ion concentration nα to the total ion density n0. As the concentration of minor ion species decreases (r2 ≲ 10%), the field at frequencies near f2 increases sufficiently to accelerate the minor ions to high energy (≳ 100 eV).
Two-dimensional magnetic flux shell model for magnetohydrodynamic simulations
Authors: McMullin J. N. , Milroy R. D. , Capjack C. E.
Published: March 2003

A magnetic flux shell model is described which is suitable for numerical simulations of cylindrically symmetric plasmas. The magnetohydrodynamic equations in magnetic field line coordinates are derived including the effects of finite electrical conductivity and anisotropic heat conductivity. Subsequently, the equations of motion of coaxial plasma shells of constant density, temperature, axial velocity, and axial magnetic field are derived including (a) full radial dynamics and (b) radial pressure balance. Sample simulations of a laser heated solenoid plasma and a ϑ-pinch reactor are described.
Equilibrium of low-aspect-ratio plasma configurations and implications on stability
Authors: Morikawa George K.
Published: March 2003

Nonlinear effects on the stationary equilibrium of spheroidal low-aspect-ratio plasma shapes with vacuum boundaries are considered mainly using appropriate linear methods. Simple analyses of both magnetohydrodynamic and guiding center fluids with anisotropic pressures p⊥ and p∥ nearly equal to the scalar pressure p are presented. Results concerning the necessary amount of axial current I0 required for equilibrium are given and their implications for stability are described.
Interpretive method for studying effects of strong magnetic shear on plasma equilibrium and stability
Authors: Mynick Harry E.
Published: March 2003

A graphical technique is developed which is useful for understanding the effects of magnetic shear on particle orbits and plasma stability. This technique is, in principle, as precise as its algebraic counterpart, but its chief advantage lies in enabling one to develop qualitative expectations for the mathematical results, and to discern their physical meaning. Several effects on individual particle motion and collective phenomena are discussed, among them the modification by shear of the particle gyrofrequency, and a generalized expression for the diamagnetic drift frequency.
Dynamic interaction of intense microwaves with plasma
Authors: Mizuno K. , DeGroot J. S.
Published: March 2003

The ponderomotive force of the parametrically excited electron plasma waves drastically modifies the density profile. The asymptotic density profile has a subcritical density plateau followed by a density jump to supercritical densities which reduces the parametric instabilities, as observed in particle simulation calculations.
Ion temperature and neutral density measurements in the direct current octopole by induced optical fluorescence
Authors: Lipson J.
Published: March 2003

A continuous wave tunable dye laser, operating with a broadband (0.5 Å bandwidth) or with a locked single mode output (10−4 Å bandwidth) was used to investigate the local density and velocity distribution of sodium metal neutrals present in a magnetically confined laser produced sodium metal plasma. With the broadband input, the intensity of fluorescence is proportional to the local neutral density. From the temporal evolution of this quantity, it is possible to evaluate the importance of resonance charge exchange in establishing ion energy balance, and also the effectiveness of the limiters in retaining neutralized ions. With the locked single mode input, the structure of the velocity distribution is accessible. Specifically, when the plasma is seeded with additional sodium neutrals from an external oven source, the charge exchange products achieve sufficient concentration for the neutral Doppler profile to acquire recognizable wings. The ion temperature is readily obtained from the width of these wings.
Resonant absorption due to dc magnetic fields parallel to the density gradient
Authors: Woo Wee , DeGroot J. S.
Published: March 2003

A new resonant absorption mechanism of an electromagnetic wave incident on a magnetized plasma is investigated. A dc magnetic field along the density gradient couples the incoming electromagnetic wave to electromagnetic waves in other directions. These electromagnetic waves drive electrostatic waves which results in resonant absorption of the incident electromagnetic wave. This indirect process can be well separated from the direct process in the s polarization case in which a maximum absorption of 90% is obtained. For completeness, the total directly and indirectly driven absorptions due to perpendicular, parallel, and azimuthal magnetic fields are obtained.
Elongated field-reversed plasma equilibria
Authors: Kadish Abraham
Published: March 2003

A simple analysis of field-reversed equilibria is presented which includes toroidal effects. The location of elongated sharp boundary plasma columns is determined as a function of the ratio of open to closed magnetic fluxes and the location of material boundaries.
Transport and radiation studies of belt pinches and high-beta tokamaks
Authors: Byrne R. N. , Chu C. K.
Published: March 2003

Transport and radiation effects on eliptical cross-section pinch machines have been performed using the G2m code. Profile effects are shown to be small for machines of the general parameters of Torus I at Columbia and significant for those like Torus II. An explanation of toroidal paramagnetism is advanced.
Deceleration of a rotating disk in a viscous fluid
Authors: Watson Layne T. , Wang Chang-Yi
Published: March 2003

A disk rotating in a viscous fluid decelerates with an angular velocity inversely proportional to time. It is found that the unsteady Navier–Stokes equations admit similarity solutions which depend on a nondimensional parameter S =α/Ω0, measuring unsteadiness. The resulting set of nonlinear ordinary differential equations is then integrated numerically. The special case of S =−1.606 699 corresponds to the decay of rotation of a free, massless disk in a viscous fluid.
Relations between point sources buoyant convection phenomena
Authors: Shlien D. J.
Published: March 2003

The gross convection velocities of various simple point source convective phenomena in an unstratified stationary fluid can be related to each other through empirical constants by using Turner’s model of the starting plume cap. Considered here are ’’weak’’ (Rayleigh number approaching zero), laminar, and turbulent regimes of the phenomena, the thermal, the starting plume cap, and the steady plume. Thus, by determining an empirical constant a, for either the thermal or the starting plume cap, the convection velocity of the other phenomenon can be estimated. Here, a is defined in terms of the thermal, a≡zt2/ktAm, where zt is the thermal height above the buoyancy source at time t, k is a molecular diffusivity, A is the effective Rayleigh number, and m=1/2, 1, or 2 depending on the flow regime. The dependence of a on the Prandtl number Pr is presently unknown. For experimental verification of the model, new measurements of the laminar and of the turbulent starting plume are presented. The constant a, determined independently for the thermal and for the starting plume cap was within 20% of the mean value of 0.038 for the laminar case, while for the turbulent case the constant was within 13% of the mean value of 4.2. The new experimental data further reveals that a change in Prandtl number from 21 to 7 results in a 50% increase in a for the laminar case.
Poloidal mode ballooning of trapped electron instability
Authors: Pandey S. R. , Ross David W.
Published: March 2003

The effect of the magnetic moment dependence of the bounce averaged toroidal drift velocity on the eigenvalues and poloidal structure of the trapped electron mode is investigated in the radially local model. It is found that eigenvalues from the magnetic moment dependent dispersion relation deviate significantly from those of the constant drift velocity approximation for negative and large positive shear values. However, for shear ranging from rq−1 dq/dr=0.5 to 1.5, the trapped electron magnetic drift frequency can be approximated by ωdew (0.4 + 0.8rq−1dq/dr), where ωde is a constant, w is the particle kinetic energy, and q is the safety factor.
Skewness of spatial derivatives of temperature in a turbulent boundary layer
Authors: Antonia R. A. , Van Atta C. W.
Published: March 2003

A simple model based on a geometrical property of the organized large scale motion is used to predict the relative magnitudes and signs of odd moments of the components of the temperature gradient in turbulent boundary layers.
Viscous flow in oscillatory spherical annuli
Authors: Munson B. R. , Douglass R. W.
Published: March 2003

Theoretical and experimental results are presented describing viscous incompressible flow in spherical annuli. The character of the flow depends strongly upon the dimensionless frequency of oscillation and the amplitude ratio of the oscillations of the bounding spherical surfaces. The secondary flow can be either ’’inward’’ or ’’outward’’ centrifuging, depending on the values of the parameters.
Breakup of a liquid jet: Third perturbation Cosserat solution
Authors: Bogy D. B.
Published: March 2003

The straightforward third perturbation solution is derived for a time harmonic disturbance applied at the nozzle. The problem formulation sets two boundary conditions at the nozzle and downstream radiation conditions. Numerical results are presented for parameters appropriate to ink-jet printers that show the jet radius near the breakup point. In a certain frequency range good quantitiative agreement with experiment is obtained for satellite drop behavior as regards forward or backward merging with the main drops.
Distribution functions in plasmas generated by a volume source of fission fragments
Authors: Deese Jerry E. , Hassan H. A.
Published: March 2003

The role played by fission fragments and electron distribution functions in nuclear pumped lasers is considered and procedures for their calculations are outlined. The calculations are illustrated for a 3He–Xe mixture where fission is provided by the 3He(n,p) 3H reaction. Because the dominant ion in the system depends on the Xe fraction, the distribution functions cannot be determined without the simultaneous consideration of a detailed kinetic model. As is the case for wall sources of fission fragments, the resulting plasmas are essentially thermal but the electron distribution functions are non-Maxwellian.
One-dimensional kinetic beam-plasma instability in a fluctuating plasma
Authors: Escande D. F.
Published: March 2003

The one-dimensional kinetic beam-plasma instability in a fluctuating plasma is theoretically studied within both the linear and nonlinear framework. Starting with the wave action conservation equation, and using the Bourret approximation, previous results for the linear development of the one-dimensional kinetic beam-plasma instability in the presence of random static fluctuations are recovered in a more compact form. The meaning of the small Kubo number assumption is also made more precise. These results are generalized to the case of static nonrandom fluctuations. In both cases a strong modification of the growth rate is found to occur even for small density fluctuations. The one-dimensional kinetic beam-plasma instability saturation in the presence of space time dependent density fluctuations is then studied in the limit where the group velocity of the unstable modes is much greater than the phase velocity of the density fluctuation modes. Previous results obtained for the case of static density fluctuations are recovered : some of the beam particles are accelerated, and the turbulence level is lowered.
Microstability of a focused ion beam propagating through a z-pinch plasma
Authors: Ottinger P. F. , Mosher D. , Goldstein Shyke A.
Published: March 2003

A beam-plasma system consisting of a focused light ion beam propagating through a z-pinch plasma is analyzed for microinstabilities. Two instabilities are discussed, one driven by the relative streaming between beam ions and electrons and the other driven by streaming between plasma ions and electrons. Conditions for stability of both modes are derived and are used to demonstrate that ion beams appropriate for use in a pellet fusion device can be propagated to the pellet through a z-pinch plasma without disruptive microturbulence.
Excitation of plasma waveguide modes at high power levels
Authors: Ferrari L. A.
Published: March 2003

It is suggested that the self-ducting observed in a laboratory experiment may be due to the excitation, at high power levels, of plasma-waveguide modes. The field patterns of these modes are calculated and found to resemble, the observed intensity distributions quite closely.
Collision effects on light scattering by plasmas containing ionized impurities
Authors: Theimer O. , Sandalov A. N.
Published: March 2003

A high temperature fusion plasma is considered containing fully ionized impurities, e.g., 5% oxygen or 1% molybdenum. Evan’s treatment of such systems as collision-free is generalized to include collisions and it is shown that, because of the large charges involved, collision effects can be significant. A general theory of light scattering by many-component plasmas is presented and numerical results for the scattering spectrum are given which demonstrate the practical importance of impurity-enhanced collision effects.
Magnetohydrodynamics of nearly cylindrical configurations with fixed internal currents
Authors: Miller Guthrie
Published: March 2003

A theta pinch plasma with perturbing magnetic fields produced by fixed internal currents is considered. The constant pressure model is used and stability is calculated for k=0 modes, which are neutrally stable in the unperturbed situation. The approach is very similar to that used for the high-beta stellarator. The field perturbations produced by internal windings are found to be stabilizing whereas they are destabilizing for the high-beta stellarator with external windings.
Finite amplitude localized whistler waves
Authors: Spatschek K. H. , Shukla P. K. , Yu M. Y. , Karpman V. I.
Published: March 2003

The localization of wave fields arising from modulation and filamentation of large amplitude whistler waves propagating nearly parallel to the external magnetic field are considered. The low-frequency modulations are allowed to be fully nonlinear, so that large density variations as often observed in the experiments are included. In the expression for the ponderomotive force, the contribution of the time-dependent polarization current has been accounted for. It is shown by means of the Sagdeev potential analysis that both sub- and supersonic solitary wave/filaments can exist, depending on the frequency regime of the whistler waves. The relationship between the speed, the maximum electric field, and the density variation of a solitary wave/filament is investigated.
Universal formula for quasi-static density perturbation by a magnetoplasma wave
Authors: Kaufman A. N. , Cary J. R. , Pereira N. R.
Published: March 2003

The general expression for the ponderomotive Hamiltonian is used to obtain the quasi-static quasi-neutral density change caused by the ponderomotive force of a cold magnetoplasma wave of arbitrary frequency and polarization: δn (x) =−[‖E(x) ‖2−‖B(x) ‖2] /4π (Te+Ti).
Scaling laws and asymptotic states for ion acoustic turbulence
Authors: Horton Wendell , Choi Duk-In , Koch R. A.
Published: March 2003

The scaling laws predicted by renormalized plasma turbulence theory are obtained for current-driven ion acoustic turbulent heating using the mode simulation technique.
Radioactivity enhanced mass transfer in xenon gas at pressures near one atmosphere
Authors: Benenson R. E.
Published: March 2003

A radioactivity-related increase in the rate of drift of xenon tracer isotopes in xenon gas was observed while measuring the coefficient of self-diffusion. The effect occurred at pressures near one atmosphere and room temperature. Some auxiliary experiments are described.
Analysis of particle orbits in an ultra-high-current plasma column
Authors: Gratreau P. , Robouch B. V.
Published: March 2003

Electron collisionless motion in an infinite plasma column is studied under the conditions of relaxed Bennet equilibrium in order to understand the macroscopic structure of the equilibrium, and serve as a preliminary step in an expanded study aimed at determining the relative importance of drift reversed currents. The model assumes, in the framework of the Vlasov theory, a Bennett equilibrium released of the constraint of a constant transverse temperature, a constant macroscopic speed of the charged particles with a constant ratio of their densities; the particles, however, are not required to be monoenergetic, which leads to a diffuse plasma edge. The results, in graphical form, define the values of the parameters for which drift reversals occur, and the conditions under which variations of the parameter values do not affect drift reversals, thus suggesting simplifications in the parametric study of particle trajectories.
Temperature field measurement of an axisymmetric laminar plume
Authors: Shlien D. J. , Boxman Raymond L.
Published: March 2003

The temperature field of axisymmetric laminar plumes generated in water from a small heat source located in a large horizontal plane was measured interferometrically for heat injection rates of 1.5 and 0.72 cal/sec at heights of up to 19 cm above the source. For a height of 19 cm and heat injection rate of 1.5 cal/sec, steady state was reached within 5 sec of the passage of the starting cap; an axial temperature of 3.1° C above ambient was measured, and the diameter at half that temperature was 4 mm. The experimental results were compared with previous analytic solutions for plumes generated from ideal isolated point sources. Good agreement was obtained if the concept of an apparent source is utilized.
Beam-driven instabilities in a field-reversed ion layer
Authors: Gerver M. J. , Sudan R. N.
Published: March 2003

An infinitely long, thin, field-reversing ion layer immersed in a much denser, cooler background plasma is examined for instabilities driven by the velocity difference between the layer ions and the background plasma, taking into account the radial mode structure, as well as Landau damping by the background plasma. The only instability is the low frequency (ω≪Ωi) magnetosonic mode; the worst mode has growth rate γ∼ω∼vA/a, and k--∼k⊥∼a−1, where a is the width of the layer. This mode might be stabilized by electron Landau damping and transit-time magnetic damping, when the temperature of the layer ions is comparable to their energy.
Microwave emission from pulsed, relativistic e-beam diodes. I. The smooth-bore magnetron
Authors: Orzechowski T. J. , Bekefi G.
Published: March 2003

Measurements of intense magnetron oscillations in pulsed, field-emission diodes (∼350 kV, 30 nsec) subjected to crossed externally applied fields (≲16 kG) are reported. The oscillations set in as soon as the magnetic field exceeds the critical field necessary for cutting off the diode current. The oscilations are diagnosed by the microwave emission which is studied in the range from 7 to 40 GHz. The radiation is emitted in broad frequency bands, it is strongly polarized, and can be tuned by the magnetic field; the power levels are typically 1 to 5 kW. The observations are consistent with the onset of the slipping stream instability in the Brillouin space charge flow of the electron cloud.
Microwave emission from pulsed, relativistic e-beam diodes. II. The multiresonator magnetron
Authors: Palevsky A. , Bekefi G.
Published: March 2003

The design and operating characteristics of relativistic, electron beam magnetrons are described. The magnetrons are comprised of a pulsed field-emission cathode (∼360 kV, ∼15 kA, ∼30 nsec) and several coupled resonators embedded in the anode block. The tubes are designed to work at fixed frequency, in the range from 2.3 to 5 GHz. The peak powers generated are typically 500 to 1000 MW.
Damping of solitary waves
Authors: Miles John W.
Published: March 2003

The damping of a solitary wave due to weak dissipation is calculated for any process for which the damping of a monochromatic wave would be proportional to some power of the frequency. The result for bottom scattering by small inhomogeneities differs from that given by Ostrovsky.
Finite amplitude electrostatic ion cyclotron modes
Authors: Ray Dipankar
Published: March 2003

Using the small amplitude approximation, some steady state nonsinusoidal solutions for an obliquely traveling electrostatic wave in a collisionless magnetoplasma, have been given by Chaturvedi [Phys. Fluids 19, 1064 (1976)]. The present note makes a more rigorous study.
Astron type equilibrium in the absence of an applied magnetic field
Authors: Kapetanakos C. A.
Published: March 2003

It is shown that the Vlasov–Maxwell equations predict the existence of rotating layer equilibria (rigid-rotor) in the absence of an external magnetic field, provided that the density of the layer exceeds a critical density.
Nonlinear interaction of tearing modes in highly resistive tokamaks
Authors: Waddell B. V. , Carreras B. , Hicks H. R. , Holmes J. A.
Published: March 2003

A mechanism for the major disruption in tokamaks is proposed involving the nonlinear destabilization of tearing modes by the m=2, n=1 tearing mode. A three-dimensional cylindrical nonlinear code based on a set of equations valid in the limit of low β and large ratio of the toroidal and poloidal magnetic fields has been constructed. The essential result is that for safety factor profiles flat in the plasma core the 2/1 mode significantly destabilizes other modes, particularly odd modes such as the 3/2 mode, before the 2/1 island in the single-pitch limit has expanded to its maximum width. Many magnetic islands of different pitch are produced and the corresponding deformation of the toroidal current density is more severe than in the two-dimensional case. The magnetic islands generated can extend across the plasma cross section; presumably, the corresponding ergodic magnetic fields can result in the escape of particles and heat from the plasma core. An analytic model in agreement with these results is also presented.
Circuit related instability of a plasma discharge
Authors: Jensen T. H. , Moeller C. P. , Freeman R. L.
Published: March 2003

Electrical circuits involving gas discharges may be unstable because the resistance of the gas discharge tends to decrease with increasing current. A semiquantitative treatment of these instabilities, relevant to tokamak, reversed Z pinch, and similar plasma physics devices, is provided.
Investigation of the diffusion of impurity atoms in plasmas by laser fluorescence
Authors: Meng H. C. , Kunze H.-J.
Published: March 2003

A pulse of aluminum atoms was injected into hydrogen gas and plasma by focusing a TEA CO2-laser beam onto a solid target. The propagation along the axis of the target was investigated by measuring the local atomic densities using dye laser excited fluorescence. A diffusion model allowed the derivation of diffusion coefficients as well as of the rate coefficient for ionization of the Al atoms from the observations.
Invariance of turbulent closure models
Authors: Speziale Charles G.
Published: March 2003

The invariance of second moment turbulent closure under a change of frame is examined. It is shown that the Reynolds stresses and the higher turbulence correlations based on an ensemble mean are frame-indifferent while the Reynolds stress transport equations are frame dependent. As a result of this incompatibility, second moment closure cannot form a general foundation for the study of turbulence. Alternative approaches that are properly invariant are discussed.
Velocity space ring-plasma instability, magnetized, Part I: Theory
Authors: Lee Jae Koo , Birdsall C. K.
Published: March 2003

The interaction of magnetized monoenergetic ions (a ring in velocity space) with a homogeneous Maxwellian target plasma is studied numerically using linear Vlasov theory. The ring may be produced when an energetic beam is injected perpendicular to a uniform magnetic field. In addition to yielding the previously known results, the present study classifies this flute-like instability into three distinct regimes based on the beam density relative to the plasma density, where many features such as physical mechanisms, dispersion diagrams, and maximum growth rates are quite different. The effects of electron dynamics, plasma or ring thermal spread, the ratio of ωp/ωc for plasma ions, and electromagnetic modifications are also considered.
SF6 condensation in supersonic nozzle expansions
Authors: Fisher Sam S.
Published: March 2003

The condensation of SF6 in a dilute mixture with either Ar or He as a carrier gas when quickly expanded in a small, adjustable nozzle is investigated. Condensation is observed by monitoring the disappearance of individual rotational-state lines in the SF6 ν4 absorption band. For this, a diode-laser spectroscopy system is employed, the nozzle is two dimensional, and the flows are short-duration pulses. The gas density at which condensation onset occurs is measured as a function of local gas temperature (30°–100° K), local expansion rate, and SF6 mole fraction (0.18%–3.4%). The onset density depends strongly on the local temperature and expansion rate and not at all on the mole fraction. For the SF6/Ar data, Ar co-condensation appears to reduce the SF6 onset density level at the lowest mole fractions, and SF6 vibrational lag appears to increase the onset density level at the highest mole fractions. A simple ’’trimers-critical’’ model for condensation onset is derived, and with this model reasonable correlation of much of the onset data is obtained. From this correlation, an effective dimer binding energy and trimer formation probability are extracted.
Influence of energy and axial momentum spreads on the cyclotron maser instability in intense hollow electron beams
Authors: Uhm Han S. , Davidson R. C.
Published: March 2003

The influence of energy and axial momentum spreads on the cyclotron maser instability in an intense hollow electron beam propagating parallel to a uniform axial magnetic field B0êz is investigated. The stability analysis is carried out within the framework of the linearized Vlasov–Maxwell equations. It is assumed that ν/γ̂≪1, where ν is Budker’s parameter and γ̂mc2 is the characteristic electron energy. Stability properties are investigated for the choice of electron distribution function in which all electrons have a step-function distribution in energy (H=γmc2) and a step-function distribution in axial momentum (pz). The instability growth rate is calculated including the important stabilizing influence of energy spread (ε=Δγ) and axial momentum spread (Δ=Δpz). It is shown that a modest energy spread (ε≈ a few percent) is sufficient to stabilize perturbations with high magnetic harmonic number (s⩾2). Moreover, a relatively small axial momentum spread (Δ/mc≈0.1) can easily stabilize perturbations with axial wavenumber satisfying ‖kc/ωc‖≳0.2, for typical beam parameters of experimental interest.
Comments on ’’Pellet ablation in hot plasmas and the problem of magnetic shielding’’
Authors: Chang C. T.
Published: March 2003

Clarifications are provided concerning the consistency of a previously formulated magnetic nozzle model in connection with pellet ablation.
Energy of waves in a plasma
Authors: Auerbach Steven P.
Published: March 2003

A formula is given for the energy of an arbitrary electrostatic or electromagnetic wave in a plasma which may be magnetized or unmagnetized, collisional or collisionless, and homogeneous or weakly inhomogeneous. The formula relates the energy of the wave to the magnitude of the electric and magnetic fields of the wave and derivatives of the frequency of the wave with respect to wavenumber and plasma parameters. This formula makes it possible to determine the energy of wave from its dispersion relation (and the magnitude of the fields). The derivation rests on a simple invariance property, related to dimensional analysis, of the Fokker–Planck equation, together with well-known results from the theory of dispersive media.
Suprathermal field fluctuations and high energy electrons in a low density plasma: A spectroscopic investigation
Authors: Pal Rabindranath , Griem Hans R.
Published: March 2003

An oscillating magnetic field produces a hollow cylindrical helium plasma in the presence of a slowly varying bias field. The field penetrates to the center in the first quarter cycle, but is then shielded by a current layer without significant compression. The plasma is observed end-on in the helium I lines λ 4471.48 Å (23P←43D) and λ 4921.93 Å (21P←41D) and their nearby forbidden components at λ 4470.04 Å and λ 4920.59 Å, respectively. During the early phases of the discharge the forbidden components have intensities in the central, low density region much higher than those expected in a thermal plasma, indicating the presence of microinstabilities which cause suprathermal electric field fluctuations. The nonthermal or turbulent state of this low temperature (∼1 eV) plasma is consistent with the presence of an appreciable number of high energy (∼600 eV) electrons, indicated primarily by the spectroscopic investigations and verified by x-ray measurements.
Initial-value problem for boundary layer flows
Authors: Gustavsson L. Håkan
Published: March 2003

The behavior of small disturbances in a boundary layer flow is studied. The initial-value problem is solved formally with Fourier–Laplace transforms, and an expression for the development of the velocity component normal to the wall is obtained. It is found that a disturbance evolves not only as discrete waves of the Tollmien–Schlichting type, but also has a portion described by a continuous spectrum. This portion is associated with a branch cut of the solution in the complex plane of the Laplace transform variable.