bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal equilibrium properties of an intense relativistic electron beam
Authors: Davidson R. C. , Uhm Han S.
Published: March 2003

The thermal equilibrium properties of an intense relativistic electron beam with distribution function f0b=Z−1bexp[−(H−βbcPz−ωbPϑ) /T] are investigated. This choice of f0b allows for a mean azimuthal rotation of the beam electrons (when ωb≠0), and corresponds to an important generalization of the distribution function first analyzed by Bennett. Beam equilibrium properties, including axial velocity profile V0zb(r), azimuthal velocity profile V0ϑb(r), beam temperature profile T0b(r), beam density profile n0b(r), and equilibrium self-field profiles, are calculated for a broad range of system parameters. For appropriate choice of beam rotation velocity ωb, it is found that radially confined equilibrium solutions [with n0b(r→∞) =0] exist even in the absence of a partially neutralizing ion background that weakens the repulsive space-charge force. The necessary and sufficient conditions for radially confined equilibria are ω−b<ωb<ω+b for 0⩽ (2ω̂2pb /ω2cb) (1−f−β2b) ⩽1, and 0<ωb<ωcb for (2ω̂2pb/ω2cb) (1−f−β2b) <0. Here, ωcb=eB0/γb mc is the relativistic cyclotron frequency, ωpb= (4πn̂be2/γbm)1/2 is the on-axis (r=0) plasma frequency, f=n0i(r)/n0b(r) = const is the fractional charge neutralization, βbc= (1−1/γ2b)1/2c is the mean axial velocity of the beam, and ω±b= (ωcb/2) {1±[1−(2ω̂2pb/ω2cb) (1−f−β2b)] 1/2} are the allowed equilibrium rotation frequencies in the limit of a cold electron beam(T→0) with uniform density n̂b.
Toroidal equilibria with z asymmetric cross section
Authors: Okada Osami
Published: March 2003

Toroidal equilibria with cross-sectional shapes asymmetric to the plane z =0 are studied analytically. A general solution of the toroidal equilibrium is obtained with an inverse aspect-ratio expansion and the Fourier decomposition as to the poloidal angle of the ideal magnetohydrodynamic equation. In the example of a tear drop rotated around its magnetic axis, the normal tear drop shows the deepest magnetic well, while the depth is only about 70% at 180° rotated ’’Pord-raet’’ position. A proper combination of z-asymmetric deformations, on the other hand, can deepen the well.
Dilute polymer solution effects on bubble growth and collapse
Authors: Chahine G. L. , Fruman D. H.
Published: March 2003

Spark-generated bubble behavior was observed in an unbounded fluid and in the vicinity of a wall, both for water and a polymer solution. The formation of the re-entering jet close to the wall is retarded in the presence of polymer additives.
Detonation velocity transient of Composition B-3 and PBX-9404
Authors: Davis W. C.
Published: March 2003

Experimental measurements of detonation velocity as a function of charge length for Composition B-3 and PBX-9404 are reported. Initation was by a 200-mm-diam baratol lens. A transient decay time of about 10 μsec was observed in Composition B-3; no transient could be measured in PBX-9404.
Electromagnetic emission around the plasma frequency induced by relativistic runaway electrons
Authors: Bornatici M. , Engelmann F.
Published: March 2003

The effects of plasma density inhomogeneity on the electromagnetic emission from a toroidal plasma around the plasma frequency induced by relativistic runaway electrons is considered.
Propagation of a wide ion beam into a magnetic barrier
Authors: Peter William , Ron Amiram , Rostoker Norman
Published: March 2003

A fully relativistic and self-consistent Vlasov equilibrium model is presented and solved for the general problem of the motion of a neutralized ion beam in a transverse magnetic field. The radius of the beam is taken to be much larger than any characteristic length of the system so that the model is, in effect, one-dimensional. The beam has density n0 and velocity v0 and enters a vacuous region with an externally applied transverse magnetic field B0. It is found that the distance that the ions penetrate into the barrier is determined primarily by the longitudinal electric field produced by the electrons, so that their penetration length is much less than the ion gyroradius. In the case v20/c2≪m/M−B20/16πn0Mc2 the model equations can be solved analytically. In this case the injected plasma is quasi-neutral and the ions closely follow the electrons. The penetration length of the plasma is then the geometric mean of the electron and ion gyroradii due to the magnetic field Bc= (B20+16πn0Mv02)1/2. A discussion of the numerical results is included.
Nonlinear Rayleigh–Taylor stability with mass and heat transfer
Authors: Hsieh D. Y.
Published: March 2003

The nonlinear Rayleigh–Taylor stability of a liquid layer over a finite vapor layer is studied using a simplified formulation of the problem. The method of multiple scale expansion is employed for the investigation. It is found that when the heat transfer rate is strong enough, the classically unstable system is stabilized by the nonlinear effect and the effect of mass and heat transfer across the interface. The size of the bubbles detached from the interface can also be estimated. A simple nondimensional parameter is also found to characterize the stability of the system.
Rayleigh–Bénard instability in nonreactive binary fluids. II. Results
Authors: Gutkowicz–Krusin Dina , Collins Michael A. , Ross John
Published: March 2003

The hydrodynamic stability of binary, Boussinesq fluids in Bénard geometry, with both the Soret and Dufour effects included has been studied. For stationary convection, the critical Rayleigh number Rcr, depends only on a single parameter ψ which is proportional to the thermal diffusion ratio and depends on other transport and thermodynamic coefficients. For ψ⩾0 (’’normal’’ Soret effect) the instability sets in only when the fluid is heated from below; for ψ<−1 only when the fluid is heated from above; and for −1<ψ< 0 convection may occur for either sign of the imposed temperature gradient. The critical wave vector kcr becomes vanishingly small in the system with two rigid boundaries; for ψ≳4(ψ<0) when the fluid is heated from below (above). When kcr∼0, Rcr is independent of the Dufour effect and the convective heat flux is proportional to (kcr)2 so that heat flux measurements are impractical in this limit. Oscillatory instability occurs only in fluids with ψ<0 which are heated from below. The dependence of Rcr on the mass density gradient and on the separation of time scales for the relaxation of temperature and concentration fluctiations is discussed.
Lagrangian and Hamiltonian formulations of compressible hydrodynamics
Authors: Wilhelm H. E.
Published: March 2003

A new formulation of compressible hydrodynamics is presented based on the Lagrange and Hamilton densities ℒ (r,t) =ℒ (∂q/∂t,∇∂q) and ℋ (r,t) =ℋ (p,∇⋅q), in which the canonical conjugate variables p and q are given by p=mv and ∂q/∂t=nv [particle mass: m, density field: n (r,t), velocity field: v(r,t)]. Viscous momentum transfer is neglected and conservation of energy is taken into consideration in the polytropic approximation with polytropic coefficient γ〉〈cp/ cV (quasi-perfect gas). The conservation equations for particle density n, momentum density nmv, and energy density 3P/2 of compressible fluids are obtained from a variational principle as functional derivatives of the Lagrange and Hamilton functions L=ℱℱℱℒ (r,t) d3r and H=ℱℱℱℋ (r,t) d3r of the gaseous system of volume Ω=ℱℱℱd3r.
Stability of tokamaks with elongated cross section
Authors: An C. H. , Bateman Glenn
Published: March 2003

Fixed boundary n=1 magnetohydrodynamic instabilities are studied computationally as a function of diamagnetism (βp) and current profile in elongated toroidal equilibria (1<b/a⩽4). It is found that even slightly diamagnetic plasmas with a broad current profile and a highly elongated cross section are subject to a ballooning instability for q values well above unity at the magnetic axis. A peaked current profile in a mildly diamagnetic plasma decreases the elongation of the inner flux surfaces and reduces the marginal q value by suppressing ballooning modes. The maximum stable volume-averaged beta is achieved with a broad current profile and either a paramagnetic plasma (βp<1) with a highly elongated cross section (b/a≳2) or a diamagnetic plasma (βp≳1) with only a mildly elongated cross section (b/a<2).
Equilibria and stability of centrifugal relativistic electron beams
Authors: Benford Gregory
Published: March 2003

Centrifugal equilibria of relativistic beams are distinguished by their high transverse energy. These beams have both azimuthal and axial currents and can produce low net self-forces acting on the particles; i.e., J×B is minimized. The stability properties of these beams using a fully electromagnetic fluid model is calculated. Long wavelength modes resembling the kink are the most easily destabilized. A relatively low applied magnetic field comparable to the beam self-field stabilizes these modes. Uses in the generation of microwave radiation are discussed briefly.
Propagation and plasma heating of the lower hybrid wave in the nonuniform density plasma
Authors: Abe Hirotada , Itatani Ryohei , Momota Hiromu
Published: March 2003

A particle simulation model which treats the wave excitation and propagation in nonuniform density by an external source is applied to the study of the behavior of lower hybrid wave heating. The observed values of the perpendicular wavenumber agree well with those calculated from the WKB approximation. In the case of the large wave amplitude, the following features are observed for the increase in the ion and electron kinetic energies. Ion perpendicular energy distributions are observed to have the components of the high energy tail. These phenomena are explained in terms of the mechanism of trapping and stochastic acceleration of a charged particle in the monochromatic and nearly perpendicular propagating wave with a frequency near cyclotron harmonic. A strong increase in the parallel kinetic energy of the electron is observed near the plasma surface. This is mainly due to the trapped electrons.
Two-dimensional self-modulation of lower hybrid waves in inhomogeneous plasmas
Authors: Leclert G. P. , Karney Charles F. F. , Bers A. , Kaup D. J.
Published: March 2003

For lower hybrid waves in an inhomogeneous plasma, the two-dimensional self-modulation effects due to ponderomotive force are studied under the assumption that the field is electrostatic and has a narrow k spectrum. For a locally linear temperature profile and a broad class of density profiles, exact nonlinear solutions (solitons) are obtained by the inverse scattering method. The solitons decay and spread as they propagate. In addition to the usual area condition on the potential ℱ φ dξ⩾π/2, inhomogeneity introduces a second condition for solitons to occur. It is shown that this second condition is not satisfied in typical tokamak plasmas, i.e., there is no soliton formation, in contrast to the homogeneous case. Furthermore, the scaling of the threshold conditions with density and temperature makes them more difficult to satisfy in larger machines.
Effects of turbulent heating in the Texas turbulent torus
Authors: Gentle K. W. , Bengtson R. , Jancarik J. , Kochanski T. , Patterson D. , Phillips P. , Stinnett R.
Published: March 2003

Turbulent heating of a 10 cm radius plasma in a tokamak configuration with densities up to 1013/cm3 produces a strong skin effect. Although the applied electric field at the outside of the column reaches 100 V/cm and the electron drift velocity exceeds the thermal velocity, penetration is slight at these densities during the 1 μsec pulse. The energy dissipated in the skin during the pulse can reach 5 mJ/cm3, the equivalent of 30 keV per electron there, but losses associated with the turbulence are substantial. Average electron energies from the heating larger than 2 keV in the skin and 500 eV overall have not been found.
Maximum constriction phase of a weakly ionized discharge in helium
Authors: Oster Ludwig
Published: March 2003

Available computer results of the time development of a low-ionization discharge in helium are utilized to discuss the radial behavior of the density and temperature profiles as a function of external parameters in detail. It is shown that during the phase of maximum constriction the final radial profile of the electron density is determined. The profile of neutral density and temperature, by contrast, is only established at later times and depends little on external parameters. New model data are then presented which allow us to draw at least qualitative scaling conclusions concerning the dependence of the discharge quantities on external parameters.
Comments on ’’Stability of solitary waves in shallow water’’
Authors: Van Dooren R.
Published: March 2003

It is shown that perturbations of the solitary wave solution of the Korteweg–de Vries equation for the stable case are determinable by a rigorous approach based on a method of Frobenius.
Comments on ’’Adiabatic modifications to plasma turbulence theories’’
Authors: Misguich J. H.
Published: March 2003

It is asserted that, contrary to Catto’s statement, only correct propagator calculations and not improved particle trajectories are involved in Catto’s paper. The consistency of certain terms in Catto’s Eq. (11) is questioned, and also the weak coupling approximation. (AIP)
Numerical studies of current generation by radio-frequency traveling waves
Authors: Karney Charles F. F. , Fisch Nathaniel J.
Published: March 2003

By injecting radio-frequency traveling waves into a tokamak, continuous toroidal electron currents may be generated. This process is studied by numerically solving the two-dimensional Fokker–Planck equation with an added quasi-linear term. The results are compared with the one-dimensional analytic treatment of Fisch, which predicted a reduced plasma resistivity when high-phase-velocity waves are employed. It is shown that two-dimensional velocity space effects, while retaining the predicted scaling, further reduce the ratio of power dissipated to current generated by about 40%. These effects enhance the attractiveness of steady-state tokamak reactors utilizing this method of current generation.
Why is a water wave like a grandfather clock?
Authors: Longuet-Higgins M. S.
Published: March 2003

The orbital motion of particles at the surface of a steep gravity wave consists very nearly of a uniform translation superposed on the backward swing of a pendulum.
Analytic ion self-pinch formulae
Authors: Wright Thomas P.
Published: March 2003

Expressions are derived for the distance over which an ion beam will pinch to its first node for four cases: A—axially injected solid cylindrical beam; B—solid beam with geometric focus; C—hollow cylindrical beam; D—converging disk beam.
Reply to the comments of C. T. Chang
Authors: Lengyel L.
Published: March 2003

In response to preceding comments, it is noted that if any assumptions in the original paper are changed, re-examination of the remaining equations becomes necessary.
Converging shock waves generated by instantaneous energy release over cylindrical surfaces
Authors: Matsuo Hideo
Published: March 2003

Converging shock waves generated by instantaneous energy release over cylindrical surfaces are investigated by an approximate method. The results agree with those of Bach and Lee when the shocks are near the cylindrical surfaces, while they are smoothly continued to Guderley’s solutions near the axis of the cylinder, thus appearing to represent the propagation of shock waves over a wide space in the intermediate region between the wall and the axis where neither Guderley’s solution nor Bach and Lee’s theory can be applied.
Quasi-linear theory of parametric processes in unmagnetized plasma
Authors: Krapchev Vladimir B.
Published: March 2003

Large amplitude, spatially modulated high frequency waves produce a change in the low frequency properties of the plasma. These ponderomotive effects are studied with a quasi-linear theory of the Vlasov equation for general high frequency pump, sidebands, and low frequency waves. A ponderomotive correction to the Maxwellian distribution function is found to second order in the pump field. This ’’renormalized’’ distribution function exhibits the usual density self-modulation and an anisotropic change of temperature. A general dispersion relation is derived, which contains all previously known parametric processes and is correct to second order in the pump amplitude. The modifications in the stability analysis for the case of electron plasma wave scattered off an ion acoustic wave are examined.
Finite Larmor radius effects in the absorption of electromagnetic waves around the electron cyclotron frequency
Authors: Bornatici M. , Engelmann F. , Lister G. G.
Published: March 2003

The role of finite Larmor radius effects in the absorption of the extraordinary and ordinary mode at frequencies around the electron cyclotron frequency by a weakly relativistic thermal plasma of finite density is investigated. An inconsistent approximation regarding the absorption of the extraordinary mode at perpendicular propagation is corrected.
Generalized lower-hybrid-drift instability
Authors: Hsia J. B. , Chiu S. M. , Hsia M. F. , Chou R. L. , Wu C. S.
Published: March 2003

The theory of lower-hybrid-drift instability is extended to include a finite k∥ (the component of wave vector k parallel to the ambient magnetic field B0) so that the analysis bridges the usual lower-hybrid-drift instability of flute modes and the modified-two-stream instability. The present theory also includes electromagnetic and ambient magnetic field-gradient effects. It is found that in the cold-electron limit the density and magnetic gradients can qualitatively modify the conclusion obtained in the early theory of the modified-two-stream instability. For example, even if the relative drift far exceeds the Alfvén speed of the plasma, the instability may still persist. This result is in contrast to that established in the literature. When the electron temperature is finite, the problem is complicated. Numerical solutions are obtained for a number of cases. Results indicate that when k∥≠0, the growth rate is not always reduced.
Oscillating two-stream instability of ion cyclotron waves
Authors: Tripathi V. K. , Liu C. S.
Published: March 2003

It is shown that a high power electrostatic pump around ion cyclotron frequency is unstable for a purely growing short wavelength (k≫k0) perturbation, viz., oscillating two-stream instability. For typical PLT parameters, the instability is excited when the electric field amplitude E0 exceeds 0.2 esu (i.e., the power ≳200 kW). When the pump is a Bernstein eigenmode (ω0≲ωci, k0zve<ω0), the instability occurs over a wide range of k values and the growth rate is large (of the order of 10−4 sec−1). For ω0≳ωci, the instability has a large growth rate only when the frequency shift is large, i.e., the pump is not an eigenmode. In the case of an ion cyclotron eigenmode, the instability occurs only for restricted k values and pump powers.
Relativistic cylindrical shock propagation through a magnetic field
Authors: Chakraborty T. K.
Published: March 2003

Similarity solutions for the propagation of cylindrical relativistic shock waves in the presence of a constant axial magnetic field for the medium, where the nucleon number density is uniform are obtained. The shock surface moves with constant velocity and the total energy of the disturbance is dependent on time. The solutions are applicable only to an isothermal medium or a cold gas.
Velocity Fourier transform solution of a model collision operator
Authors: Catto Peter J.
Published: March 2003

A model collision operator similar to the one first introduced by Chandrasekar is employed to obtain a kinetic equation for waves in a magnetized plasma that can be solved via a velocity Fourier transform technique.
Impurity effects on ion-drift-wave eigenmodes in a sheared magnetic field
Authors: Tang W. M. , White R. B. , Guzdar P. N.
Published: March 2003

The stability of ion-drift-wave eigenmodes in a slab geometry with a sheared magnetic field is investigated. It is found that in contrast to the case of universal and dissipative electron-drift-wave eigenmodes, unstable impurity-driven normal modes can appear if specific conditions are satisfied. In addition, the influence of impurities on unstable ion-temperature-gradient-driven drift eigenmodes is also studied. It is found that, if their density profile is inwardly peaked, the impurities can exert a strong stabilizing influence on these modes.
Linear amplitude oscillation of a whistler wave excited by high power microwaves
Authors: Sugai H. , Takeda S.
Published: March 2003

Large-amplitude whistler waves launched from an open-waveguide antenna are found to exhibit amplitude oscillation as if due to trapped-particle effects. However, the possibility of such nonlinear effects has been excluded by propagation measurements of the small-amplitude test wave. Two-dimensional ray tracing has revealed that the amplitude oscillation observed along lines of force is closely related to snakelike motions of whistlers in an inhomogeneous plasma. The ray trajectory is calculated in a simple geometry, and the results are in good agreement with the experimental observations.
Note on the ballooning criterion for multipoles
Authors: Adler E. A. , Lee Y. C.
Published: March 2003

An equation giving the critical pressure gradient for stability to ballooning modes is derived directly from the energy principle by specializing to displacements that do no bulk compression.
Nonparallel stability of two-dimensional nonuniformly heated boundary-layer flows
Authors: Nayfeh Ali H. , El-Hady N. M.
Published: March 2003

An analysis is presented for the linear stability of water boundary-layer flows over nonuniformly heated flat plates. Included in the analysis are disturbances due to velocity, pressure, temperature, density, and transport properties as well as variations in the liquid properties with temperature. The method of multiple scales is used to account for the nonparallelism of the mean flow. In contrast with previous analyses, the nonsimilarity of the mean flow is taken into account. No analysis agrees, even qualitatively, with the experimental data when similar profiles are used. However, both the parallel and nonparallel results qualitatively agree with the experimental results of Strazisar and Reshotko when nonsimilar profiles are used.
Surface modes in magnetized fully ionized plasma
Authors: Waldron W. L. , Shohet J. L. , Hopps J. H.
Published: March 2003

Density fluctuations in a semi-infinite fully ionized plasma in the presence of a uniform magnetic field are investigated using a direct variational principle. ’’Two-stream’’ distribution functions are included to allow for the expected discontinuity in velocity space at the boundary. The microscopic boundary conditions incorporate both specular reflection and diffuse scattering effects. The shape of the density fluctuation spectrum is very dependent on the orientation of the wave vector (k) with respect to the direction of the magnetic field. The spectrum also shows evidence of both ion and electron surface effects which become enhanced with the increase in diffuse scattering contributions at the boundary.
Oscillating two-stream and parametric decay instabilities in a weakly magnetized plasma
Authors: Freund H. P. , Papadopoulos K.
Published: March 2003

The effects of a weak ambient magnetic field on the oscillating two-stream and parametric decay instabilities, with particular emphasis on the dependence of the angular variation of the instability thresholds and growth rates on the magnetic field, are considered. A dispersion relation is derived in the limit in which ωe≳≳Ωe (where ωe and Ωe are the electron plasma and cyclotron frequencies, respectively), and is solved for dipole and monochromatic pump spectra. The analysis shows that the presence of a magnetic field can substantially enhance thresholds and reduce growth rates for waves propagating at an oblique angle with respect to the ambient magnetic field and k2λ2e∼Ω2e/ω2e (where k is the wave vector of the perturbation and λe is the Debye length). Thus, the magnetic field has a stabilizing influence on the off-parallel propagating modes.
Modified Korteweg–de Vries solitary wave in a slowly varying medium
Authors: Ko K. , Kuehl H. H.
Published: March 2003

A solitary wave solution of the modified Korteweg–de Vries equation with slowly varying coefficients is derived for a soliton initial condition. It is shown that a shelf is generated behind the main peak, and that an irreversible transfer of energy occurs from the main body of the solitary wave to the shelf.
Higher-order Chapman–Enskog theory for electrons
Authors: Hassam A. B.
Published: March 2003

Fluid equations for electrons are obtained correct to second order in the inverse of the collision frequency by employing a Chapman–Enskog-type expansion. These equations are an order more accurate than those of Braginskii, and should be especially useful for physical situations, linear and nonlinear, in which the electrons behave adiabatically.
Distribution of electromagnetic waves in an inhomogeneous plasma containing random irregularities
Authors: Yuan C. P. , Liu C. H.
Published: March 2003

When an electromagnetic wave propagates in a turbulent, inhomogeneous plasma, interactions of the waves with the random irregularities in the electron density will modify the field structure of the wave. The effects of multiple scattering have been taken into account in deriving equations for the coherent wave field. Numerical examples are presented to indicate the change in the field distribution and the decrease in the amplification factor due to multiple scattering. Generalization of the results to more complicated situations is discussed.
Statistical analysis of hydrodynamic cavitation events
Authors: Gimenez G. , Sommer R.
Published: March 2003

The frequency (number of events per unit time) of pressure pulses produced by hydrodynamic cavitation bubble collapses is investigated using statistical methods. The results indicate that this frequency is distributed according to a normal law, its parameters not being time-evolving.
Annular pipe flow subject to axial motion of the inner boundary
Authors: Shands Jay , Alfredsson Henrik , Lindgren E. Rune
Published: March 2003

This is an initial study concerning the stability of annular flow and the establishment of fully developed turbulent flow under conditions of various axial velocities of the inner surface. Both laminar and turbulent flow are characterized experimentally and theoretically.
Fully nonlinear ion-acoustic solitary waves in a magnetized plasma
Authors: Yu M. Y. , Shukla P. K. , Bujarbarua S.
Published: March 2003

Fully nonlinear planar ion-acoustic solitary waves moving obliquely to an external magnetic field are studied.
Bremsstrahlung spectra associated with anomalous electron thermal conduction
Authors: Wiley J. C. , Hinton F. L.
Published: March 2003

A steady-state model of the linearized Fokker–Planck equation has been solved numerically for two types of anomalous electron transport. Electron distributon functions which consistently describe both the thermal and runaway regimes and the soft x-ray spectra computed from them are given. The effect of the anomalous transport on the x-ray spectra is compared with the effect of an electric field. Due to the simplicity of the analytic model and the significant enhancement of the soft x-ray spectra predicted, this type of calculation provides a useful tool for analysis of the anomalous electron transport from observed x-ray spectra.
Curvature and gradient drift effects on trapped-electron modes
Authors: Crystal T. L. , Denavit J.
Published: March 2003

Computer simulations of local trapped-electron modes in toroidal plasmas, including curvature and gradient drift effects, are presented. These simulations are based on the linearized electron drift-kinetic equation, Fourier transformed with respect to the poloidal and toroidal angles. No à priori distinction is made between trapped and circulating particles, and collisions are represented by a Lorentz model giving pitch-angle diffusion. A series of computations shows the dependence of the growth rates on ρe/r and on νef/ω* (ρe is the thermal electron gyroradius, r is the flux surface minor radius, νef is the effective collision frequency, and ω* is the drift wave frequency). For νef≲0.5 ω*, strong drift resonance effects are observed, but these are destabilizing only for ρe/r below a critical value. These growth rates decrease rapidly for collision frequencies νef≳ω*. For νef≳≳ω*, the dissipative trapped-electron instability occurs. In this regime, curvature and gradient drifts are stabilizing; Landau damping due to resonant circulating electrons reduces the growth rates and significantly modifies the mode structure of the dissipative trapped-electron instability.
Ion temperature drift instabilities in a sheared magnetic field
Authors: Lee W. W. , Tang W. M. , Okuda H.
Published: March 2003

Results from the first particle code simulations of the ion-temperature-gradient-driven instabilities in a sheared slab geometry are reported. In the linear stage of the instability, the results are in very good agreement with the theoretical calculations of the mode frequency, growth rate, and radial mode structure. Ion energy transport caused by the instability is found to be the process primarily responsible for nonlinear saturation. Enhanced fluctuations associated with marginally stable eigenmodes have been observed.
Effects of multiple ion species on two-dimensional trapped-electron modes
Authors: Rewoldt G. , Tang W. M. , Frieman E. A.
Published: March 2003

Previous calculations for the two-dimensional spatial structure of drift and trapped-electron modes in tokamaks are generalized to include an arbitrary number of ion species. Thus, it is possible to determine the influence of light or heavy impurity ions, and of multiple hydrogen isotopes, on these instabilities. As an example, results are presented for the case of a single light impurity species. Here, the effect is found to be either stabilizing or destabilizing, depending on specific parameters such as the equilibrium density profiles. Moreover, if a sufficiently idealized model is adopted, beam ion effects can also be studied. In the case considered, corresponding to the neutral-beam-heated Princeton Large Torus, these effects are found to be stabilizing.
Necessary and sufficient magnetohydrodynamic stability criterion for rotating multipoles and mirrors
Authors: Spies G. O.
Published: March 2003

For arbitrary axisymmetric isentropic equilibria with a purely toroidal rigid mass flow and a purely poloidal magnetic field whose field lines are either closed (as in multipoles) or periodic (as in linked mirrors), the magnetohydrodynamic stability problem is reduced to the determination of the lowest two eigenvalues of an ordinary differential operator of second order. Application to low beta spherators shows that rotation can stabilize an equilibrium with unfavorable magnetic curvature, provided the interior conductor is placed so that the magnetic field is weak at the inner side of the torus, but strong at its outer side.
Linear kinetic theory of high-m tearing modes
Authors: Rosenberg M. , Dominguez R. R. , Pfeiffer W. , Waltz R. E.
Published: March 2003

A linear electromagnetic kinetic theory of high-m tearing modes, for frequencies less than or comparable to the electron-ion collision frequency, is presented. A pitch-angle scattering Fokker–Planck operator is used to model electron-ion collisions. In the presence of an electron temperature gradient, a high-m tearing mode instability occurs over a broad range of tokamak parameters. Electrostatic effects are vital in obtaining these unstable modes.
Nonparallel stability analysis of axisymmetric stagnation-point flow
Authors: Grabowski Walter J.
Published: March 2003

The method of multiple scales has been used to extend linear-stability theory to nonparallel axisymmetric boundary-layer flow in the neighborhood of the stagnation point on a blunt body of revolution. The extended theory includes nonparallel planar effects as well as the effects of such possibly destabilizing three-dimensional mechanisms as the stretching of vortex filaments in the rapidly diverging boundary-layer flow. These mechanisms have not been previously incorporated into stability theory. Stability predictions based on the extended theory are found to be in close agreement with predictions of parallel-flow stability theory based on the Orr–Sommerfeld equation; axisymmetric and planar nonparallel effects are concluded to be of negligible importance in the axisymmetric stagnation-point boundary layer.
Soliton perturbations in a model equation for resonant interaction between long and short waves
Authors: Lisak M.
Published: March 2003

A variational perturbation method is used to study the evolution of a single soliton solution in the presence of perturbations in a system describing the interaction between long and short waves when they are resonantly coupled. Adiabatic evolution equations for the soliton parameters are derived to first order in the perturbation, including the effects of shape modifications of the soliton. The results are applied to the interaction system modified by next order contributions in the weakly nonlinear limit.
Ponderomotive force of an ion cyclotron wave in a two-ion species plasma
Authors: Festeau-Barrioz M. C. , Weibel E. S.
Published: March 2003

The ponderomotive force experienced by an ion in a left circularly polarized wave changes sign as the frequency increases from below to above the ion cyclotron frequency. If the wave frequency is chosen to lie between the ion cyclotron frequencies of two different isotopes, then the ponderomotive force tends to separate the two species in space. As a result, the index of refraction is modified. Self-consistent solutions of the nonlinear wave equation taking into account both effects are obtained analytically and numerically. The ratio of the densities of the two ions is proportional to exp[mE2(z)/4γ(1−γ)αB20kTi], where E(z) is the amplitude of the wave, B0 is the magnetic field, and Ti is the temperature of the ions, m=2m1m2/(m1+m2), α=(m1−m2)/(m1+m2), and γ=(ω−Ω2)/(Ω1−Ω2).
Self-consistent Vlasov description of the free electron laser instability
Authors: Davidson Ronald C. , Uhm Han S.
Published: March 2003

A self-consistent description of the free electron laser instability is developed for a relativistic electron beam with uniform density propagating through a helical wiggler field B0=−B̂ cosk0zêx−B̂ sink0zêy. The analysis is carried out for the class of solutions to the Vlasov–Maxwell equations described by fb(z,p,t)=n0δ(Px)δ(Py)G(z,pz,t), where Px and Py are the exact canonical momenta invariants perpendicular to the beam propagation direction. The linearized Vlasov–Maxwell equations lead to an exact matrix dispersion relation which is valid for perturbations about general beam equilibrium G0(Pz) and which includes coupling to arbitrary harmonic number (n) of the fundamental wiggler wavenumber k0. No à priori restriction is made to low beam density (as measured by ω2P/c2k20) or small wiggler amplitude (as measured by ω̂c/ck0=eB̂/γ̄mc2k0). Moreover, no assumption is made that any off-diagonal elements in the matrix dispersion relation are negligibly small. A detailed numerical analysis of the exact dispersion relation is presented for the case of a cold electron beam described by G0(Pz) =δ(pz−p0). It is shown that the instability bandwidth increases rapidly with increasing wiggler amplitude ω̂c/ck0. Moreover, except for very modest values of wiggler amplitude, it is shown that the growth rate calculated from an approximate version of the dispersion relation can be in substantial error for large values of (k+nk0)/k0. Preliminary estimates of the influence of beam thermal effects are also presented.
Cyclotron harmonic waves detected in the direction parallel to the magnetostatic field
Authors: Lembege B.
Published: March 2003

The radiation pattern of a very short antenna is studied in the electron cyclotron harmonic wave regime, ωc<ω<2ωc, ωp≳≳ωc, where ωp, ωc, and ω are, respectively, the plasma, cyclotron, and wave frequencies. Experimental data show an interference pattern of the potential in the direction of detection parallel to the magnetostatic field B0, and this interference pattern is explained. Axial dispersion curves are deduced from the experimental data and are presented. These curves are seen to be sensitive to the bulk drift motion of the plasma along the field B0. For particular cases of transmitter frequencies near gyroharmonics, the parallel wavenumber measured along B0 is observed to tend toward zero.
Whistler wave trapping in a density crest
Authors: Sugai H. , Niki H. , Takeda S. , Inutake M.
Published: March 2003

The linear trapping of whistler waves in a field-aligned density crest is investigated experimentally and theoretically below ω=ωc/2 (half gyrofrequency). An experiment has been performed on antenna-excited whistler waves in a large magnetized plasma with a density crest. The phase and amplitude profiles of the whistler wave are measured along and across the crest. The results are compared with predictions based on ray theory. Laboratory observations have verified the characteristic behavior of crest trapping.
Relativistic dispersion relation for electron Bernstein waves
Authors: Lazzaro E. , Orefice A.
Published: March 2003

The relativistic electrostatic dispersion relation for a magnetized plasma is obtained and analyzed in the case of electron cyclotron waves traveling quasi-perpendicularly to the magnetic field.
Transport fluxes and currents in a multispecies tokamak plasma with external sources
Authors: Stacey W. M.
Published: March 2003

Momentum balance, including external sources and drags, is used to uniquely determine the lowest order fluxes and the radial potential gradient in a multi-species tokamak plasma, from which transport fluxes and currents can be constructed.
A confinement theorem for nonneutral plasmas
Authors: O’Neil T. M.
Published: March 2003

A plasma consisting solely of particles of a single species is initially in the shape of a long column. It is confined by an axial magnetic field in a region of space bounded by a perfectly conducting and perfectly absorbing cylindrical wall. Conservation of angular momentum and conservation of energy are used to place an upper bound on the fraction of electrons that can ever reach the wall.
Particle and energy end loss from a collisionless plasma
Authors: Klevans Edward H. , Gary S. Peter
Published: March 2003

A one-dimensional free-flow kinetic model is used to study the axial ion losses from a linear theta pinch under collisionless conditions. The effects of a simple mirror model are included. The loss due to ion thermal flux is shown to be much smaller than the total ion kinetic energy flux loss, thereby indicating that it is appropriate to neglect ion thermal conduction in numerical simulations of the Scylla IV-P experiment.
Finite bandwidth induced stochasticity in a magnetic mirror
Authors: Menyuk C. R. , Lee Y. C.
Published: March 2003

The electrostatic fluctuation spectrum in a magnetic mirror always has some finite bandwidth. The role of a finite bandwidth in destroying the superadiabatic motion of ions has been explored. It is found that virtually any bandwidth is sufficient to destroy the resonant island regions in velocity space; however, to destroy all of phase space, so that ions may move freely, requires a bandwidth on the other of an inverse bounce time in the mirror. Assuming such a bandwidth, the diffusion rate in the velocity space is calculated.
Drift-wave eigenmodes in toroidal plasmas
Authors: Chen Liu , Cheng C. Z.
Published: March 2003

The eigenmode equation describing ballooning drift waves in toroidal plasmas is investigated both analytically and numerically. Two branches of eigenmodes are identified. One is slab-like and the other is a new branch induced by finite toroidal coupling. The slab-like eigenmodes correspond to unbounded states and experience finite shear damping. The toroidicity-induced eigenmodes, however, can become local quasi-bounded states with negligible shear damping. Both branches of eigenmodes may exist simultaneously. The corresponding analytical theories are also presented.
Stability of rotation-modified plane Poiseuille flow
Authors: Gusev Anatolij , Bark Fritz H.
Published: March 2003

The linear stability problem for the steady shear flow between two parallel planes, which rotate with the same angular velocity around a common axis, is considered. The critical Reynolds number Rc depends on the Taylor number T, which is a measure of the ratio between the Coriolis force and the viscous forces. The parameter range 1⩽t≃100 is studied. It is shown that the critical Reynolds number has a minimum value Rc?31 for T?9.5. It is also shown that, for large values of T, the most unstable mode approaches the most unstable mode associated with the Ekman layer. For 1.75≲T≲3, the theoretical results agree qualitatively with experimental results obtained by other investigators. The disagreement between experiment and theory for smaller values of T is presumably due to inlet effects in the experimental apparatus.
Radiation damping of long, finite-amplitude internal waves
Authors: Pereira N. R. , Redekopp L. G.
Published: March 2003

Numerical solutions of a damped, nonlinear wave equation are presented. The equation describes the propagation of waves in a narrow thermocline or inversion which lose energy by exciting internal waves in the weakly stratified ambient environment. The results provide estimates for the persistence of finite-amplitude internal waves propagating in a thermoclinic waveguide.
Simulations of the runaway electron distributions
Authors: Wiley J. C. , Choi Duk-In , Horton Wendell
Published: March 2003

The time evolution of the electron distribution function is followed from an initial Maxwellian to the quasi-steady-state runaway distribution as a function of E/ED and Z using a new two-dimensional Fokker–Planck code. The electron distributions are used to determine the runaway production rate, the current density along with the fraction of Ohmic power directed to the runaways, and the perpendicular and parallel temperatures of the high energy distributions. A simple parameterization of the high energy distribution is given and used to investigate the high frequency runaway instability for the infinite uniform plasma.
Wave modulation in a nonlinear dispersive medium
Authors: Kim Y. C. , Khadra L. , Powers E. J.
Published: March 2003

A model describing the simultaneous amplitude and phase modulation of a carrier wave propagating in a nonlinear dispersive medium is developed in terms of nonlinear wave-wave interactions between the sidebands and a low frequency wave. It is also shown that the asymmetric distribution of sidebands is determined by the wavenumber dependence of the coupling coefficient. Digital complex demodulation techniques are used to study modulated waves in a weakly ionized plasma and the experimental results support the analytical model.
Self-modulation of ion Bernstein waves
Authors: Myra J. R. , Liu C. S.
Published: March 2003

A self-modulation equation for coherent ion Bernstein waves is derived by a multiple-time-scale, perturbative expansion of the Vlasov equation. The dominant nonlinearity acting on the waves is shown to be the nonlinear ion gyrofrequency shift. The waves obey a version of the nonlinear Schrödinger equation with the dispersive terms in the three spatial directions having, in general, differing signs. If the modulation is independent of one spatial variable, the elliptic or hyperbolic two-dimensional nonlinear Schrödinger equation results. In contrast to the elliptic case which exhibits collapse, wave energy always disperses if initially localized in the hyperbolic case.
A two-term approximation for growth rates of a guiding center screw pinch
Authors: Cayton Thomas E. , Vahala George , Barnes D. C.
Published: March 2003

The guiding center plasma description of an isotropic, collisionless plasma is used to study the linear stability of the diffuse screw pinch in the special case when the poloidal magnetic field component is small compared with the axial magnetic field component. A two-term approximation for growth rates is derived from the linearized guiding center plasma equations by straightforward asymptotic expansion in terms of a small parameter that is proportional to (Bϑ/rBz)‖r=0. The two-term approximate solution is compared with exact solutions and the range of validity of the approximations is examined. The result obtained from the guiding center plasma model is compared and contrasted with that from ideal magnetohydrodynamics. It is shown that the isotropic guiding center plasma may be more unstable or less unstable than ideal magnetohydrodynamics for the same configuration, depending on the parameters.
Local instability near the vortex point of a field-reversed mirror
Authors: Newcomb William A.
Published: March 2003

A study is made of the curvature-driven magnetohydrodynamic instability in the neighborhood of the vortex point of a simple field-reversed magnetic-mirror system, with a purely poloidal magnetic field. The linearized magnetohydrodynamic equation of motion for localized modes in that neighborhood is found to be completely solvable. Two independent sets of modes are found, axial and radial, with the same spectrum of eigenfrequencies. Each set of modes, axial and radial, includes exactly one exponentially growing mode, of which the growth rate is found to be Ω, where 2πΩ−1 is the time required for one complete traversal of a closed magnetic flux line by an Alfvén-wave signal.
Heating of a toroidal plasma by a nonuniform radio frequency field
Authors: Amagishi Y. , Hirose A. , Skarsgard H. M.
Published: March 2003

Nonuniform electric fields created by an oscillating (1.8 MHz) dipole magnetic field are applied to a preformed, argon plasma in a torus with major radius R=19 cm, minor radius a=2.5 cm, and a toroidal magnetic field Ba=0.3 T. The induced rf plasma current flows in opposite toroidal directions in the outer (larger major radius) and inner regions of the plasma. Spatially and temporally resolved measurements are made of the electron density and temperature as well as the induced electric field and current density. Heating of both the electrons and the ions is observed. Maximum temperatures Te∼100 eV and t→Ti∼35 eV are found at a density of 1018 m−3. Rapid electron heat conduction toward the plasma center occurs, with a characteristic time of several μsec. The ion heating rate correlates with the growth rate for ion acoustic waves, calculated from measured plasma parameters.
Thermal and radiation losses in a linear device
Authors: Rosenau Philip , Degani David
Published: March 2003

An analysis is presented of the electron temperature in a linear device which includes the effect of thermal conduction, heat flux limit, radiation, and end plugs. It is found that the thermal conduction and the heat flux limit are dominant in the initial phase of cooling, while the later phase is almost completely controlled by radiation that spatially homogenizes the temperature distribution. In the case of bremsstrahlung, within the frame of the present model, the temperature decays to zero in a finite time. This process takes the form of a cooling wave that moves from the ends of the column to the center. Impurities cause a milder, exponential decay, which is still much faster than the algebraic conduction decay. The thermal effectiveness of the end plugs is described by a convective transfer coefficient hp. Its scaling law (in terms of the coupled plamsa-plug system) reveals that a very high plug-plasma density ratio provides a simple way to significantly retard the cooling.
Necessary magnetohydrodynamic stability criterion for rotating plasmas
Authors: Spies G. O. , Hellsten T. A. K.
Published: March 2003

A stability criterion is derived for axially symmetric equilibria with a purely toroidal rigid mass rotation, a purely poloidal magnetic field, and constant entropy along the field lines. If this criterion is violated, unstable eigenvalues accumulate at the harmonics of the rotation frequency.