bluuebunny/crossref_metadata_2025 huggingface dataset:
Mesoscopic phenomena in semiconductor nanostructures by quantum design
Authors: Capasso Federico , Faist Jerome , Sirtori Carlo
Published: July 2002

The energy levels, wave functions, optical matrix elements, and scattering rates of electrons can be tailored at will using semiconductor nanostructures as building blocks for practically any kind of potential. This allows the design and experimental realization of new artificial materials and devices, with interesting optical and transport properties arising from quantum confinement, tunneling, and quan- tum coherence on a mesoscopic scale ranging typically from 1 to 100 nm. This approach is illustrated with a number of recent examples based on experiments and calculations, such as resonant tunneling through double barriers, quantum interference phenomena in transport and optical absorption, bound states in the continuum, quantum well ‘‘pseudomolecules’’ with giant nonlinear optical susceptibilities, and quantum cascade lasers.
Symmetries of decoherence functionals
Authors: Schreckenberg S.
Published: July 2002

The basic ingredients of the “consistent histories” approach to quantum theory are a space 𝒰𝒫 of “history propositions” and a space 𝒟 of “decoherence functionals.” In this article we consider such history quantum theories in the case where 𝒰𝒫 is given by the set of projectors 𝒫(𝒱) on some Hilbert space 𝒱. Using an analog of Wigner’s theorem in the context of history quantum theories proven earlier, we develop the notion of a “symmetry of a decoherence functional” and prove that all such symmetries form a group which we call “the symmetry group of a decoherence functional.” We calculate for the case of standard quantum mechanics—when looked at from the perspective of the history program—some of these symmetries explicitly and relate them to some discussions that have appeared previously.
Solution of the Dirac equation in the field of a magnetic monopole
Authors: Torres del Castillo G. F. , Cortés-Cuautli L. C.
Published: July 2002

The Dirac equation for a particle subject to a Coulomb potential, a 1/r scalar potential, and the potential of a magnetic monopole is solved by separation of variables using the spin-weighted spherical harmonics and the bound states are obtained. It is shown that the separation constants are the eigenvalues of the z-component and the square of the total angular momentum, which includes that of the electromagnetic field and the spin of the particle. We find that, under certain conditions, there exist solutions where the spin is in the outward or inward radial direction.
Proof of Polyakov conjecture on supercomplex plane
Authors: Kachkachi M. , Kouadik S.
Published: July 2002

Using Neumann series, we solve iteratively the super Beltrami Equations (SBE) to arbitrary order. Then applying this, we compute the energy momentum tensor and n-points function for generic n starting from WZP action on the supercomplex plane. We solve the superconformal ward identity and we show that the iterative solution to arbitrary order is resumed by WZP action. This proves the Polyakov conjecture on supercomplex plane.
Operator product expansions and stress operators
Authors: Naito Seichi
Published: July 2002

We explain in detail how to derive the operator product expansions (OPEs) among generating functionals of physical vertex operators (GFPVO) of fermionic particles (i.e., GFPVO in the Ramond sector of superstring) and the stress operators. As for OPEs among GFPVO of bosonic particles (i.e., in the Neveu–Schwarz sector of superstring) and the stress operators, they are those simply obtained by super-generalizing OPEs among GFPVO (in bosonic string) and the stress operator.
Wavelet transforms and discrete frames associated to semidirect products
Authors: Aniello Paolo , Cassinelli Gianni , De Vito Ernesto , Levrero Alberto
Published: July 2002

We consider a semidirect product G=Rn×′H and its unitary representations U of the form IndG0G(p0m) where Ind is the unitary induction, p0 is in the dual group of Rn, G0 is the stability group of p0, and m is a unitary representation of G0∩H. We give sufficient conditions such that U defines a wavelet transform and a discrete frame.
Derivative expansion of one-loop effective actions for Yang-Mills fields
Authors: Gargett T. D. , McArthur I. N.
Published: July 2002

Low energy effective actions are computed by integrating out degrees of freedom heavier than some energy scale of physical interest. At the one-loop level, the low energy effective action can be computed in terms of the functional trace of the heat kernel associated with the operator appearing in the part of the action quadratic in the heavy fields. Here, a technique for computing this functional trace is illustrated in the case of heavy scalar fields coupled to a Yang-Mills background. It makes use of the similarity of the functional trace of the heat kernel expressed in momentum space to a Gaussian integral. An explicit computation of the piece of the low energy effective action for the Yang-Mills fields quadratic in derivatives of the field strength is carried out, extending previously known results on the form of the long wavelength limit of the low energy effective action.
Families of dynamical r-matrices and Jacobi inversion problem for nonlinear evolution equations
Authors: Zeng Yunbo , Lin Runliang
Published: July 2002

Three families of dynamical r-matrices are explicitly constructed by means of constrained flows of nonlinear evolution equations (NLEE) associated with polynomial second-order spectral problems. The dynamical classical Yang–Baxter equations for the three linear r-matrix algebras are presented with explicit expression for the extra term. The separation variables and the Jacobi inversion problems for the x- and tn-constrained flow of the NLEEs are found. The factorization of NLEE allows us to obtain the Jacobi inversion problem for the NLEE by combining the above two Jacobi inversion problems. This provides a method of separation of variables to solve the NLEEs.
Quantum superstring field theory in the B0-gauge and the physical scattering amplitudes
Authors: Naito Seichi
Published: July 2002

We propose the (BRST-invariant) quantum open superstring field theory in the “B0-gauge,” based on Neveu–Schwarz (NS) strings in 1 picture and Ramond (R) strings in 12 picture. We give the propagators of these open NS and R superstrings. In order to obtain the BRST-invariant interaction terms among these superstrings, we modify the interaction terms among three superstrings (i.e., among NS–NS–NS and R–R–NS) by subtracting the infinite number of counter terms, each of which involves interaction terms among “more than four superstrings.” The modified action can be obtained successively, so that resulting amplitudes in g-loops should become BRST invariant. Thus obtained amplitudes are referred to as the “amputated scatts,” with the help of which the physical scattering amplitudes can be expressed. These physical scattering amplitudes among NB bosonic (NF fermionic) particles are calculated by using the analytic inlint gluing operator (which has already been proposed and used in the quantum bosonic string field theory “in the B0=0 gauge”).
Hamiltonian formalism for the nonlinear Schrödinger equation in physical space–time
Authors: Chen Zhi-De , Chen Xiang-Jun , Huang Nian-Ning
Published: July 2002

Hamiltonian formalism for the nonlinear Schrödinger equation in physical space–time is developed. Owing to the fact that the equation involves the second partial derivative with respect to time, the canonical variables are shown to be u, ū, −ūt, and −ut. The first Lax equation and its variations with respect to canonical variables are very complicated, but the Poisson brackets of transition coefficients are shown to be simple, and thus the Hamiltonian formalism in terms of action-angle variables has been achieved. A peculiarity is that the continuous spectrum consists of real λ as well as pure imaginary λ. In the case of pure imaginary λ the full Jost solutions shall tend to be infinite or vanish as |t|→∞. This problem needs further investigation.
A rigorous solution concept for geodesic and geodesic deviation equations in impulsive gravitational waves
Authors: Kunzinger M. , Steinbauer R.
Published: July 2002

The geodesic as well as the geodesic deviation equation for impulsive gravitational waves involve highly singular products of distributions (θδ,θ2δ,δ2). A solution concept for these equations based on embedding the distributional metric into the Colombeau algebra of generalized functions is presented. Using a universal regularization procedure we prove existence and uniqueness results and calculate the distributional limits of these solutions explicitly. The obtained limits are regularization independent and display the physically expected behavior.
Representations of the cyclically symmetric q-deformed algebra soq(3)
Authors: Havlı́ček M. , Klimyk A. U. , Pošta S.
Published: July 2002

An algebra homomorphism ψ from the nonstandard q-deformed (cyclically symmetric) algebra Uq(so3) to the extension Ûq(sl2) of the Hopf algebra Uq(sl2) is constructed. Not all irreducible representations of Uq(sl2) can be extended to representations of Ûq(sl2). Composing the homomorphism ψ with irreducible representations of Ûq(sl2) we obtain representations of Uq(so3). Not all of these representations of Uq(so3) are irreducible. Reducible representations of Uq(so3) are decomposed into irreducible components. In this way we obtain all irreducible representations of Uq(so3) when q is not a root of unity. A part of these representations turns into irreducible representations of the Lie algebra so3 when q→1. Representations of the other part have no classical analog. Using the homomorphism ψ it is shown how to construct tensor products of finite-dimensional representations of Uq(so3). Irreducible representations of Uq(so3) when q is a root of unity are constructed. Some of them are obtained from irreducible representations of Ûq(sl2) by means of the homomorphism ψ.
Classical mechanics and geometric quantization on an infinite dimensional disc and Grassmannian
Authors: Turgut O. T.
Published: July 2002

We discuss the classical mechanics on the Grassmannian and the disc modeled on the ideal L(2,∞). We apply methods of geometric quantization to these systems. Their relation to a flat symplectic space is also discussed.
Gauge theory of w symmetry
Authors: Zhao Wei-zhong
Published: July 2002

The w∞ algebra is a higher-spin extension of the Virasoro algebra. In this paper, we construct the gauge theory of w symmetry in terms of its representations.
The generation of gravitational waves by the resonant interaction of sound waves
Authors: Anile A. M. , Hunter John K. , Truong Binh
Published: July 2002

We show that the resonant interaction of sound waves is a source of gravitational waves in general relativity. We derive an asymptotic equation that describes this process, and compute the interaction coefficient for the quadratically nonlinear coupling between sound waves and gravitational waves.
Operator representations of a q-deformed Heisenberg algebra
Authors: Schmüdgen Konrad
Published: July 2002

A class of well-behaved  * -representations of a q-deformed Heisenberg algebra previously introduced [Phys. Lett. B 291, 273 (1992); Z. Phys. C 64, 335 (1994)] is studied and classified.
Diffusive energy scattering from weakly random surfaces
Authors: Bal Guillaume , Papanicolaou George , Ryzhik Leonid
Published: July 2002

We derive transport theoretic boundary conditions for acoustic wave reflection at a weakly rough boundary in an inhomogeneous half space. We use the Wigner distribution to go from waves to energy transport in the high frequency limit. We generalize known results on the reflection of acoustic plane waves in a homogeneous medium. We analyze higher order corrections, which include a enhanced backscattering effect in the back direction.
A loop group approach to the C. Neumann problem and Moser–Veselov factorization
Authors: Krešić-Jurić Saša
Published: July 2002

A geometrical description of continuous and discrete versions of the Neumann oscillator in terms of a loop group framework is investigated. It is shown that the continuous Neumann oscillator can be integrated by the Riemann–Hilbert factorization on the “twisted” loop group of O(3), LO(3). The solution of the problem is given in terms of a special class of flows on the quotient space LO(3)/LO(3)+ where LO(3)+ is a subgroup of positive loops in LO(3). It is also shown that the Moser–Veselov algorithm for integrating a discrete version of the Neumann oscillator (Heisenberg XYZ chain) is induced by a discrete flow in this space. The flow can be explicitly integrated by solving the matrix Riccati equation. In both cases, discrete and continuous, conservation laws are derived from time invariance of a relation that holds for coefficients of the Fourier expansion of the flows.
Qualitative analysis of early universe cosmologies
Authors: Billyard Andrew P. , Coley Alan A. , Lidsey James E.
Published: July 2002

A qualitative analysis is presented for a class of homogeneous cosmologies derived from the string effective action when a cosmological constant is present in the matter sector of the theory. Such a term has significant effects on the qualitative dynamics. For example, models exist which undergo a series of oscillations between expanding and contracting phases due to the existence of a heteroclinic cycle in the phase space. Particular analytical solutions corresponding to the equilibrium points are also found.
Linearization stability of the Einstein equation for Robertson–Walker models. II
Authors: Bruna Lluı́s , Girbau Joan
Published: July 2002

In a previous paper (referred to here as paper I) we showed that the Einstein equation is linearization stable when a Robertson–Walker model of curvature K=0 is considered. For that purpose, a slightly different definition of linearization stability was introduced. In this paper we show that in case the curvature K is equal to 1 the Einstein equation G(g)=χT is not linearization stable at the Robertson–Walker metric.
Multidimensional integrable Schrödinger operators with matrix potential
Authors: Chalykh O. A. , Goncharenko V. M. , Veselov A. P.
Published: July 2002

The Schrödinger operators with matrix rational potential, which are D-integrable, i.e., can be intertwined with the pure Laplacian, are investigated. Corresponding potentials are uniquely determined by their singular data which are a configuration of the hyperplanes in Cn with prescribed matrices. We describe some algebraic conditions (matrix locus equations) on these data, which are sufficient for D-integrability. As the examples some matrix generalizations of the Calogero–Moser operators are considered.
Elliptic Calogero–Moser systems and isomonodromic deformations
Authors: Takasaki Kanehisa
Published: July 2002

We show that various models of the elliptic Calogero–Moser systems are accompanied with an isomonodromic system on a torus. The isomonodromic partner is a nonautonomous Hamiltonian system defined by the same Hamiltonian. The role of the time variable is played by the modulus of the base torus. A suitably chosen Lax pair (with an elliptic spectral parameter) of the elliptic Calogero–Moser system turns out to give a Lax representation of the nonautonomous system as well. This Lax representation ensures that the nonautonomous system describes isomonodromic deformations of a linear ordinary differential equation on the torus on which the spectral parameter of the Lax pair is defined. A particularly interesting example is the “extended twisted BCl model” recently introduced along with some other models by Bordner and Sasaki, who remarked that this system is equivalent to Inozemtsev’s generalized elliptic Calogero–Moser system. We use the “root-type” Lax pair developed by Bordner et al. to formulate the associated isomonodromic system on the torus.
Existence and multiplicity results for massive particles trajectories in a universe with boundary
Authors: Germinario Anna , Giannoni Fabio
Published: July 2002

In an open time-convex region Λ of a strongly causal Lorentzian manifold (M,g), we consider an event p and a timelike, injective curve γ. We look for geodesics connecting p and γ in Λ and satisfying the conservation law g(z)[ż,ż]=−E for a fixed E>0. It is already known that such geodesics are the stationary points of the arrival time functional τ. Our main result is to prove the existence of a decreasing flow for τ, by means of a shortening procedure. This makes possible to apply to τ global variational methods obtaining existence and multiplicity results (using the Ljusternik–Schnirelmann category theory) and also to develop a Morse theory.
Towards the canonical tensor operators of uq(3). II. The denominator function problem
Authors: Ališauskas Sigitas
Published: July 2002

The explicit denominator (normalization) function of the canonical tensor operators of the quantum algebra uq(3), corresponding to the maximal null space case is derived ab initio in terms of double basic hypergeometric series, which cannot be obtained as any q-extension of the SU(3) denominator polynomial Gb″1(Δ,x) in terms of multiple (double or triple) balanced hypergeometric series, introduced by Biedenharn, Louck, and their collaborators (although their q=1 versions are shown being equivalent). The corresponding orthonormal seed isoscalar factors of the coupling (Wigner–Clebsch–Gordan) coefficients of uq(3) and SU(3) with multiple irreducible representations are presented. Conjectured expression of the q-polynomials [which ratios appear in the uq(3) and (new) SU(3) denominator functions for an arbitrary value of the canonical multiplicity label t of the repeating irreducible representations] in terms of multiple partition dependent q-series (extension of the maximal and minimal null space versions) is presented and considered.
Quasispin graded-fermion formalism and gl(m|n)↓osp(m|n) branching rules
Authors: Gould Mark D. , Zhang Yao-Zhong
Published: July 2002

The graded-fermion algebra and quasispin formalism are introduced and applied to obtain the gl(m|n)↓osp(m|n) branching rules for the “two-column” tensor irreducible representations of gl(m|n), for the case m⩽n(n>2). In the case m<n, all such irreducible representations of gl(m|n) are shown to be completely reducible as representations of osp(m|n). This is also shown to be true for the case m=n, except for the “spin-singlet” representations, which contain an indecomposable representation of osp(m|n) with composition length 3. These branching rules are given in fully explicit form.
Algebraically special, expanding and twisting gravitational fields with vanishing Newman–Unti–Tamburino parameter
Authors: Ivanov B. V.
Published: July 2002

The system of Einstein–Maxwell equations for fields mentioned in the title is simplified. Known pure radiation solutions are systematized and new solutions are given by separating the variables.
Quantum fields in nonstatic background: A histories perspective
Authors: Anastopoulos C.
Published: July 2002

For a quantum field living on a nonstatic space–time no instantaneous Hamiltonian is definable, for this generically necessitates a choice of inequivalent representation of the canonical commutation relations at each instant of time. This fact suggests a description in terms of time-dependent Hilbert spaces, a concept that fits naturally in a (consistent) histories framework. Our primary tool for the construction of the quantum theory in a continuous-time histories format is the recently developed formalism based on the notion of the history group. This we employ to study a model system involving a 1+1 scalar field in a cavity with moving boundaries. The instantaneous (smeared) Hamiltonian and a decoherence functional are then rigorously defined so that finite values for the time-averaged particle creation rate are obtainable through the study of energy histories. We also construct the Schwinger–Keldysh closed-time-path generating functional as a “Fourier transform” of the decoherence functional and evaluate the corresponding n-point functions.
Quantum interaction :φ44:, the construction of quantum field defined as a bilinear form
Authors: Osipov Edward P.
Published: July 2002

We construct the solution φ(t,x) of the quantum wave equation □φ+m2φ+λ:φ3:=0 as a bilinear form which can be expanded over Wick polynomials of the free in-field, and where :φ3(t,x): is defined as the normal ordered product with respect to the free in-field. The constructed solution is correctly defined as a bilinear form on Dθ×Dθ, where Dθ is a dense linear subspace in the Fock space of the free in-field. On Dθ×Dθ the diagonal of the Wick symbol of this bilinear form satisfies the nonlinear classical wave equation.
Monopole Skyrmions
Authors: Kleihaus B. , Tchrakian D. H. , Zimmerschied F.
Published: July 2002

A systematic numerical study of the classical solutions to the combined system consisting of the Georgi–Glashow model and the SO(3) gauged Skyrme model is presented. The gauging of the Skyrme system permits a lower bound on the energy, so that the solutions of the composite system can be topologically stable. The solutions feature some very interesting bifurcation patterns, and it is found that some branches of these solutions are unstable.
Polyakov conjecture on the supertorus
Authors: Kachkachi M. , Dafounansou O. , Nazah M.
Published: July 2002

We prove the Polyakov conjecture on the supertorus (ST2): We determine an iterative solution at any order of the superconformal Ward identity and we show that the Polyakov action that describes the (1,0) 2D(two-dimensional)-supergravity, resums this perturbative series. The resolution of the super-Beltrami equation for the Wess–Zumino field from which the Polyakov action is expressed, is done by using on the one hand the Cauchy kernel techniques on ST2 defined in H. Kachkachi and M. Kachkachi, Class. Quantum Grav. 11, 493 (1994) and on the other hand, the formalism developed in M. Kachkachi and S. Kouadik, J. Math. Phys. 38, 4336 (1997). Hence, we determine the n-points Green functions from the Polyakov action expressed as a functional integral of the Beltrami superfield μ̂.
The scaling limit of the incipient infinite cluster in high-dimensional percolation. II. Integrated super-Brownian excursion
Authors: Hara Takashi , Slade Gordon
Published: July 2002

For independent nearest-neighbor bond percolation on Zd with d≫6, we prove that the incipient infinite cluster’s two-point function and three-point function converge to those of integrated super-Brownian excursion (ISE) in the scaling limit. The proof is based on an extension of the new expansion for percolation derived in a previous paper, and involves treating the magnetic field as a complex variable. A special case of our result for the two-point function implies that the probability that the cluster of the origin consists of n sites, at the critical point, is given by a multiple of n−3/2, plus an error term of order n−3/2−ε with ε>0. This is a strong version of the statement that the critical exponent δ is given by δ=2.
Resonances for laterally coupled quantum waveguides
Authors: Frolov S. V. , Popov I. Yu.
Published: July 2002

A system of two waveguides coupled laterally through a small window is considered. The asymptotics (in the width of window) of resonance (quasibound state) close to the second threshold is obtained. The cases of two different and two identical waveguides are considered. The technique is matching the asymptotic expansions of the solutions.
Effect of pressure gradients on Stokes flows over cavities
Authors: Higdon J. J. L.
Published: July 2002

Prior studies of Stokes flow over cavities have been limited to simple shear and simple stagnation point flows. In the present work, it is shown that the presence of a transverse pressure gradient has a dramatic effect on the character of the flow, eliminating the separated flow region in many cases. Consequences of this phenomenon for mass transfer are discussed.
Some limitations of two-dimensional unbounded Stokes flow
Authors: Smith S. H.
Published: July 2002

The basic approach toward a theoretical understanding of slow viscous flows in two dimensions is through solutions of the biharmonic equation; however, when the fluid is unbounded some of the solutions corresponding to locally generated flows lead to paradoxical behavior (e.g., Jeffery [Proc. R. Soc. London Ser. A 101, 169 (1922)]). Here one case in detail (the source–sink flow in front of a circular cylinder) is described, and then whether such a flow is possible as either (a) the limit of a bounded flow in two dimensions as the radius of the outer boundary grows without bound, or (b) the limit of an unbounded three-dimensional flow as lengths in the third dimension grow without bound, or (c) the limit of an impulsively started two-dimensional unbounded flow as time grows without bound is considered. In each case it is found that the formal limit does exist, but that the error is only as small as O[(ln μ)−1] when the appropriate parameter μ→∞. This indicates that such locally generated unbounded flows are not realistically attainable.
Transport in a confined compressible fluid under time-dependent volumetric heat sources
Authors: Zappoli B. , Bailly D.
Published: July 2002

The response of a confined compressible perfect gas to an uneven time-dependent volumetric heat source is studied. The low Mach number compressible Navier–Stokes equations are solved numerically by means of the pressure implicit with splitting of operators (P.I.S.O.) algorithm in the case where the characteristic time of the thermal perturbation is small compared to the diffusion time and large compared to the acoustic time. A comparison is made with first-order asymptotic results previously obtained. The asymptotic analysis is then carried out up to the second order in the bulk. It is shown that: (a) a flow is generated from one side of the cavity to the other, confirming the asymptotic results previously obtained; (b) a flow towards the walls is found in thermal boundary layers because of a sink effect due to the lower temperature in these regions; (c) comparison with analytical results in the bulk is quite satisfactory except for the velocity where some differences are shown; (d) the second-order asymptotic analysis shows that this approximation in the bulk is a mechanical perturbation caused by the contraction of the fluid layers near the boundaries; (e) the matching between analytical results and numerical results is improved by more than 50% when considering a second-order solution; (f) this analysis validates both numerical code and scaling laws.
Description of transient states of von Kármán vortex streets by low-dimensional differential equations
Authors: Ohle F. , Lehmann P. , Roesch E. , Eckelmann H. , Hübler A.
Published: July 2002

Aperiodic time series of hot-wire signals can be described as trajectories in a state space representation. The flow vector field is calculated by numerical differentiation of these trajectories and then each component of the flow vector field is approximated by a polynomial of order p. This approximation provides a model for the dynamics of the von Kármán vortex street by a low-dimensional system of ordinary differential equations. At a Reynolds number of 114 a compact description of the complex dynamics of the vortex street by a set of only ten parameters can be obtained. It will be shown that these parameters are independent of the probe position for distances greater than two-and-one-half cylinder diameters.
Effect of rise time and pulse width on the transport and interaction of a 1 MeV, 15 kA relativistic electron beam in low pressure argon and hydrogen
Authors: Iyyengar S. K. , Rohatgi V. K.
Published: July 2002

A numerical study of the effect of rise time (10–30 nsec) and pulse width (30–100 nsec) on the transport and interaction of a 1 MeV, 15 kA relativistic electron beam (REB) in argon and hydrogen in the pressure range 0.05–1.0 Torr is reported. The computations have been carried out taking into account charge and current neutralization effects, plasma heating by return current, and two-stream instabilities. The results of the study show that charge transport increases for short rise times and longer pulse widths at the optimum pressure in the range 0.1–0.2 Torr. With a rise time of 30 nsec and a pulse width of 100 nsec, the 1 MeV, 15 kA REB generates a plasma with density 1–10×1021 m−3, an electron temperature of 4–20 eV, and transports with 90% efficiency at the optimum pressure.
Filamentation instability of electromagnetic waves in magnetized plasmas
Authors: Shukla P. K. , Stenflo L.
Published: July 2002

The filamentation instability of electromagnetic electron and ion-cyclotron waves is investigated by including the combined effect of relativistic electron mass variation as well as static density and field-aligned magnetic field perturbations that are created by the radiation pressure. Analytical expressions for the critical power at which the instability starts are presented. The relevance of this investigation to radio-frequency wave heating of fusion plasmas is pointed out.
Electrostatic ion-cyclotron waves in a plasma with negative ions
Authors: Song Bin , Suszcynsky D. , D’Angelo N. , Merlino R. L.
Published: July 2002

Electrostatic ion-cyclotron (EIC) waves have been investigated in plasmas containing K+ positive ions, electrons, and SF−6 negative ions. Two EIC wave modes are generally present, the K+ and SF−6 modes. Their frequencies increase with increasing ε, the percentage of negative ions, while the critical electron drift velocities for excitation of either mode decrease with increasing ε. The observations are discussed on the basis of available theories.
Anomalous transport in strongly inhomogeneous systems. I. A kinetic theory of nonlocal hydro- and plasma dynamics
Authors: Belyi V. V. , Demoulin W. , Paiva-Veretennicoff I.
Published: July 2002

Starting from the Fokker–Planck or Boltzmann type of linearized kinetic equation, and using a projection operator technique, a general evolution equation is derived for the hydrodynamical component of the distribution function with a renormalized collision operator providing extra dissipation mechanisms. Generalized Fourier and Newtonian laws are derived leading to nonlocal transport in time and space. Explicit evaluation of the transport coefficients is performed after a discussion of various truncation procedures. The results are applied to the study of dispersion and damping of sound in a rarefied one-component gas. A comparison with experimental results shows that a 14-moment approximation is very satisfactory.
The effects of plasma flow on thermal and ponderomotive light filamentation
Authors: Schmitt Andrew J.
Published: July 2002

The effects of flowing plasma on laser light filamentation is reexamined [Phys. Fluids 25, 2302 (1982)] and extended to the thermal-conduction-driven filamentation mechanism. Formulas with a broad range of applicability are developed to predict filamentation growth lengths, thresholds, and fastest growing modes. Transverse flow velocities that are of order Cs are found to have large effects on the filamentation growth rates and thresholds. Maximum growth rates are typically increased by a factor of 10 for thermal filamentation, and a factor of 100 for ponderomotive filamentation, when compared to zero-flow conditions. These fastest growing modes have much shorter perturbation wavelengths than those found in the zero-flow case.
Toroidal ion-pressure-gradient-driven drift instabilities and transport revisited
Authors: Biglari H. , Diamond P. H. , Rosenbluth M. N.
Published: July 2002

A unified theory of ion-pressure-gradient-driven drift wave instabilities and transport is presented, which ties the long-wavelength trapped-ion mode to the moderate-wavelength hydrodynamic mode in toroidal geometry. An analytic dispersion relation that retains ion drift resonances, and keeps the leading-order contribution from finite Larmor radius effects and parallel compressibility, is derived. Results indicate that the slab and toroidal branches of these instabilities are of comparable importance, and are both strong candidates to explain the observed anomalous ion loss in toroidal fusion devices. However, it is concluded that in the limit of flat-density profiles characteristic of H-mode discharges, the stabilizing influence of perpendicular compressibility is insufficient to corroborate an improvement, if any, in ion confinement quality. Mixing-length expressions for the fluctuation amplitudes and both electron and ion transport coefficients are derived. Results also indicate that the heretofore experimentally observed favorable current scaling of the energy confinement time may saturate in low ion-collisionality discharges. Finally, it is shown that a population of energetic trapped particles, such as those that may be produced during radio frequency or perpendicular neutral beam heating, can significantly exacerbate the instability. Several suggestions for experiments are made to help in differentiating among various anomalous transport scenarios.
Magnetohydrodynamics equilibrium of a self-confined elliptical plasma ball
Authors: Wu Han-ming , Oakes M. E.
Published: July 2002

A variational principle is applied to the problem of magnetohydrodynamics (MHD) equilibrium of a self-contained elliptical plasma ball, such as elliptical ball lightning. The principle is appropriate for an approximate solution of partial differential equations with arbitrary boundary shape. The method reduces the partial differential equation to a series of ordinary differential equations and is especially valuable for treating boundaries with nonlinear deformations. The calculations conclude that the pressure distribution and the poloidal current are more uniform in an oblate self-confined plasma ball than that of an elongated plasma ball. The ellipticity of the plasma ball is obviously restricted by its internal pressure, magnetic field, and ambient pressure. Qualitative evidence is presented for the absence of sighting of elongated ball lightning.
High-Q plasmas in the TFTR tokamak
Authors: Jassby D. L. , Barnes C. W. , Bell M. G. , Bitter M. , Boivin R. , Bretz N. L. , Budny R. V. , Bush C. E. , Dylla H. F. , Efthimion P. C. , Fredrickson E. D. , Hawryluk R. J. , Hill K. W. , Hosea J. , Hsuan H. , Janos A. C. , Jobes F. C. , Johnson D. W. , Johnson L. C. , Kamperschroer J. , Kieras-Phillips C. , Kilpatrick S. J. , LaMarche P. H. , LeBlanc B. , Mansfield D. K. , Marmar E. S. , McCune D. C. , McGuire K. M. , Meade D. M. , Medley S. S. , Mikkelsen D. R. , Mueller D. , Owens D. K. , Park H. K. , Paul S. F. , Pitcher S. , Ramsey A. T. , Redi M. H. , Sabbagh S. A. , Scott S. D. , Snipes J. , Stevens J. , Strachan J. D. , Stratton B. C. , Synakowski E. J. , Taylor G. , Terry J. L. , Timberlake J. R. , Towner H. H. , Ulrickson M. , von Goeler S. , Wieland R. M. , Williams M. , Wilson J. R. , Wong K.-L. , Young K. M. , Zarnstorff M. C. , Zweben S. J.
Published: July 2002

In the Tokamak Fusion Test Reactor (TFTR) [Plasma Phys. Controlled Fusion 26, 11 (1984)], the highest neutron source strength Sn and D–D fusion power gain QDD are realized in the neutral-beam-fueled and heated ‘‘supershot’’ regime that occurs after extensive wall conditioning to minimize recycling. For the best supershots, Sn increases approximately as P1.8b. The highest-Q shots are characterized by high Te (up to 12 keV), Ti (up to 34 keV), and stored energy (up to 4.7 MJ), highly peaked density profiles, broad Te profiles, and lower Zeff. Replacement of critical areas of the graphite limiter tiles with carbon-fiber composite tiles and improved alignment with the plasma have mitigated the ‘‘carbon bloom.’’ Wall conditioning by lithium pellet injection prior to the beam pulse reduces carbon influx and particle recycling. Empirically, QDD increases with decreasing pre-injection carbon radiation, and increases strongly with density peakedness [ne(0)/〈ne〉] during the beam pulse. To date, the best fusion results are Sn=5×1016 n/sec, QDD=1.85×10−3, and neutron yield=4.0×1016 n/pulse, obtained at Ip=1.6–1.9 MA and beam energy Eb=95–103 keV, with nearly balanced co- and counter-injected beam power. Computer simulations of supershot plasmas show that typically 50%–60% of Sn arises from beam–target reactions, with the remainder divided between beam–beam and thermonuclear reactions, the thermonuclear fraction increasing with Pb. The simulations predict that QDT=0.3–0.4 would be obtained for the best present plasma conditions, if half the deuterium neutral beams were to be replaced by tritium beams. Somewhat higher values are calculated if D beams are injected into a predominantly tritium target plasma. The projected central beta of fusion alphas is 0.4%–0.6%, a level sufficient for the study of alpha-induced collective effects.
Resistive wall modes in a reversed field pinch with interchangeable shells
Authors: Greene Philip , Barrick Greg , Robertson Scott
Published: July 2002

Resistive wall modes have been investigated in a reversed field pinch (Reversatron IIi [IEEE Trans. Plasma Sci. PS-16, 667 (1988)]) operated with three different boundary conditions: (1) a copper shell having a magnetic penetration time τs comparable to the discharge duration, (2) a brass shell having τs comparable to the setting-up time, and (3) no shell, which gives τs much shorter than the setting-up time. The brass shell is found to impede the growth of the m=1, n=−6 ‘‘on-axis’’ mode observed to grow in the setting-up phase of no-shell discharges. In the sustainment phase, there is a higher level of m=1 modes than with the copper shell and the discharge duration, ion temperature, and plasma current are reduced. The mode spectrum is broad in the sustainment phase and the degradation in discharges cannot be attributed to any single mode. There is evidence for transient mode locking resulting in a slinky mode in copper-shell discharges.
Role of compressibility on driven magnetic reconnection
Authors: Sato T. , Hayashi T. , Watanabe K. , Horiuchi R. , Tanaka M. , Sawairi N. , Kusano K.
Published: July 2002

Whether it is induced by an ideal (current driven) instability or by an external force, plasma flow causes a change in the magnetic field configuration and often gives rise to a current intensification locally, thereby a fast driven reconnection being driven there. Many dramatic phenomena in magnetically confined plasmas such as magnetospheric substorms, solar flares, magnetohydrodynamic (MHD) self-organization, and tokamak sawtooth crash, may be attributed to this fast driven reconnection. Using a fourth-order MHD simulation code it is confirmed that compressibility of the plasma plays a crucial role in leading to a fast (MHD time scale) driven reconnection. This indicates that the incompressible representation is not always applicable to the study of a global dynamical behavior of a magnetically confined plasma.
Computer studies on development of the fast reconnection mechanism for different resistivity models
Authors: Ugai M.
Published: July 2002

Computer simulations systematically study how the fast reconnection mechanism involving standing switch-off shocks can be established and sustained in a large-scale current sheet system. Initiated by a small disturbance, all the phenomena spontaneously grow from near the origin and propagate outward. Under the same initial boundary conditions, different resistivity models are assumed, where the resistivity is self-consistently determined by macroscopic quantities in the system. It is found that the reconnection process is strongly controlled by the resistivity model. Only when the resistivity is locally enhanced near an X-type neutral point in accordance with the global reconnection flow, the fast reconnection mechanism can rapidly build up and be sustained steadily. The steady fast reconnection mechanism works as an engine that drastically drives the overall system into catastrophe. Since this mechanism depends on the resistivity parameter very weakly, it may be applicable to large dissipative events in space plasmas. It is argued that local conditions near an X neutral point should be fundamental for the fast reconnection mechanism to be realized.
Temperature dependence of synchrotron radiation current drive in inhomogeneous tokamak plasmas
Authors: Fidone I.
Published: July 2002

Current drive by asymmetric synchrotron radiation in high-temperature inhomogeneous tokamaks is discussed and the global normalized efficiency as a function of the peak density and temperature and profile indices is obtained.
Loss of equilibrium and reconnection in tearing of two-dimensional equilibria
Authors: Finn John M. , Guzdar Parvez N.
Published: July 2002

Two-dimensional tearinglike behavior is studied in reduced resistive magnetohydrodynamics (MHD) with flux conserving boundary conditions on a rectangular box. The tearinglike perturbations do not destroy the symmetries of the initial state, either discrete or continuous. In such cases, in which the perturbation does not break a symmetry of the equilibrium, linear instability is typically not directly observed. However, there can be a loss of equilibrium associated with the existence of a tearing unstable state. These ideas are illustrated with three examples: a very elongated tokamak, a tokamak with pinching coils to elongate its flux surfaces, and a model for the magnetotail or for solar arcades. The loss of equilibrium is demonstrated by means of a nonlinear energy functional. The importance of the fact that the dynamics shows a loss of equilibrium is that a large amount of free energy can be released, in the form of reconnection, and that there is a possibility of hysteresis.
Conservation of canonical circulation and its relation to finite Hall term magnetohydrodynamics
Authors: Bellan P. M.
Published: July 2002

The axisymmetric, compressible visco-resistive two-fluid plasma equations are examined under the constraint that the current is purely poloidal and the pressure is a function of density only (‘‘barotropic’’). For ideal plasmas (zero resistivity and zero viscosity) the Kelvin circulation theorem of fluid mechanics and the concept of frozen-in field lines turn out to be limiting cases of a more general concept, namely, that the canonical circulation Sσ=∮ (mσuσ+qσA) ⋅dl of a toroidal fluid element, is exactly conserved as the toroidal element convects and/or is compressed. Appropriate linear combinations of the electron and ion fluid equations give a magnetohydrodynamic vorticity transport equation and an induction equation with a nonlinear Hall term. The finite Hall term is identical to the source term in the vorticity transport equation [P. M. Bellan, Phys. Rev. Lett. 69, 3515 (1992)], except for a constant factor related to the ion collisionless skin depth.
Magnetohydrodynamic ballooning instabilities excited by energetic trapped particles
Authors: Weiland J. , Chen L.
Published: July 2002

A new branch of magnetohydrodynamic ballooning modes is shown to be destabilized by energetic trapped particles. Both the real frequencies and growth rates of the instabilities are comparable to the trapped-particle precession frequencies. The theoretical results are also shown to be consistent with the high-frequency (∼100 kHz) oscillations observed during the high-power beam-injection experiments in the tokamak experiment PDX.
The whistler mode in a Vlasov plasma
Authors: Tokar Robert L. , Gary S. Peter
Published: July 2002

In this study, properties of small-amplitude parallel and oblique whistler mode waves are investigated for a wide range of plasma parameters by numerically solving the full electromagnetic Vlasov dispersion equation. To investigate the cold-plasma and electrostatic approximations for the whistler mode, the results are compared with results obtained using these descriptions. For large wavelengths (kc/ωi≲100), the cold-plasma description is often accurate, while for short wavelengths (kc/ωi≳100) and sufficiently oblique propagation, the electrostatic description is often accurate. The study demonstrates that in a Vlasov plasma the whistler mode near resonance has a group velocity more nearly parallel to the magnetic field than that predicted by cold-plasma theory.
Direct conversion of a fast wave into ion Bernstein modes caused by density fluctuations
Authors: Morales G. J. , Antani S. N. , Fried B. D.
Published: July 2002

An analytical study is presented of the interaction between a fast Alfvén wave having a frequency larger than the ion-cyclotron frequency, and low frequency density fluctuations. When appropriate k, ω matching conditions are satisfied, the interaction results in a beat current that acts as an in-situ antenna, exciting ion Bernstein modes resonantly. Since such modes have relatively small damping for large parallel phase velocities, their excitation can significantly enhance the damping of fast waves having small k∥, particularly in those regions of the plasma where the temperature is relatively low. The interaction with coherent, as well as with broad band density fluctuations is investigated, and the role of plasma nonuniformities is examined. Specific features of relevance to ion-cyclotron range of frequency heating of tokamak plasmas are considered.
Kinetic theory of resistive ballooning modes
Authors: Diamond P. H. , Similon P. L. , Hender T. C. , Carreras B. A.
Published: July 2002

A linear and nonlinear kinetic theory of resistive ballooning modes that includes diamagnetic drifts and finite Larmor radius effects is presented. The linear stability of resistive ballooning modes is examined analytically and numerically. A renormalized resistive ballooning equation is derived, and the saturation level of the instabilities is analytically calculated. Finally, a calculation of the electron thermal conductivity for the large ω* regime is presented.
Generalized Kirchhoff vortices
Authors: Polvani L. M. , Flierl G. R.
Published: July 2002

A family of exact solutions of the Euler equations is presented: they are generalizations of the Kirchhoff vortex to N confocal ellipses. Special attention is given to the case N=2, for which the stability is analyzed with a method similar to the one used by Love [Proc. London Math. Soc. 1, XXV 18 (1893)] for the Kirchhoff vortex. The results are compared with those for the corresponding circular problem.
Effect of impurity particles on the finite-aspect ratio neoclassical ion thermal conductivity in a tokamak
Authors: Chang C. S. , Hinton F. L.
Published: July 2002

The effect of finite-aspect ratio on the impurity contribution to neoclassical ion thermal conductivity is studied. A simple modification to the pure-ion case is obtained with the assumption that the single heavy impurity species is in the Pfirsch–Schlüter regime. It is found that the impurity contribution is larger than the usual approximation: Zeff times the pure ion thermal conductivity.
Structure of weak shocks in fluids having embedded regions of negative nonlinearity
Authors: Cramer M. S.
Published: July 2002

The dissipative structure of weak shock waves in fluids in which the fundamental derivative is negative for a finite range of pressures and temperatures has been examined. Conditions under which the shock thickness increases with strength rather than decreases are delineated. Nonclassical features of the entropy distribution and variation of local Mach number are also described.
The tokamak equilibrium profile
Authors: Hsu J. Y. , Chu M. S.
Published: July 2002

The fully relaxed magnetohydrodynamic (MHD) equilibrium is obtained by imposing nonideal MHD perturbations constrained by the total plasma current. The minimum energy state governed by Δ*ψ+CF exp(ψ/λ)+CpR2 exp(5ψ/4λ) =0 reveals properties of profile consistency, bifurcated solutions, and a loss of equilibrium condition. It predicts the transport coefficient peaked at the plasma edge and a unique current profile for given q0 and ql.