bluuebunny/crossref_metadata_2025 huggingface dataset:
General realization of N=4 supersymmetric quantum mechanics and its applications
Authors: Ruan Dong , Huang Weicheng
Published: June 2003

Based upon the general supercharges which involve not only generators Cj of the Clifford algebra C(4,0) with positive metric, but also operators of third order, CjCkCl, the general form of N=4 supersymmetric quantum mechanics (SSQM), which brings out the richer structures, is realized. Then from them, a one-dimensional physical realization and a new multidimensional physical realization of N=4 SSQM are respectively obtained by solving the constraint conditions. As applications, N=4 dynamical superconformal symmetries, which possess both the N=4 supersymmetries and the usual dynamical conformal symmetries, are studied in detail by considering two simple superpotentials k/x and ωx, and their corresponding superalgebraic structures, which are spanned by eight fermionic generators and six bosonic generators, are established as well.
Bell inequalities in four dimensional phase space and the three marginal theorem
Authors: Auberson G. , Mahoux G. , Roy S. M. , Singh Virendra
Published: June 2003

We address the classical and quantum marginal problems, namely the question of simultaneous realizability through a common probability density in phase space of a given set of compatible probability distributions. We consider only distributions authorized by quantum mechanics, i.e., those corresponding to complete commuting sets of observables. For four-dimensional phase space with position variables q⃗ and momentum variables p⃗, we establish the two following points: (i) given four compatible probabilities for (q1,q2), (q1,p2), (p1,q2), and (p1,p2), there does not always exist a positive phase space density ρ(q⃗,p⃗) reproducing them as marginals; this settles a long standing conjecture; it is achieved by first deriving Bell-type inequalities in phase space which have their own theoretical and experimental interest. (ii) Given instead at most three compatible probabilities, there always exist an associated phase space density ρ(q⃗,p⃗); the solution is not unique and its general form is worked out. These two points constitute our “three marginal theorem.”
How doping a cholesteric liquid crystal with polymeric dye improves an order parameter and makes possible low threshold lasing
Authors: Araoka Fumito , Shin Ki-Chul , Takanishi Yoichi , Ishikawa Ken , Takezoe Hideo , Zhu Zhengguo , Swager Timothy M.
Published: June 2003

Lasing conditions in a dye-doped cholesteric liquid crystal (ChLC) have been studied in view of optical modes for the light propagating in ChLCs using a polymeric dye with the transition dipole moment parallel to the local director of the ChLC host. We found that lasing always occurs at the lower-energy edge of the photonic gap. This is because that the optical eigen mode at the lower-energy gap is linearly polarized parallel to the director, while it is perpendicular at the higher-energy gap. Because of this well-defined lasing condition, low-threshold lasing was successfully achieved.
Selective ion photodesorption from NO adsorbed on Si(111)7×7 following core excitation
Authors: Hellner L. , Comtet G. , Ramage M. J. , Bobrov K. , Carbone M. , Dujardin G.
Published: June 2003

Selective ion photodesorption from NO adsorbed on Si(111)7×7 has been investigated by core electron excitation. In a first step, the adsorption of nitric oxide on the clean Si(111)7×7 surface has been studied over the temperature range from 15 K to room temperature using ultraviolet photoemission spectroscopy, x-ray photoemission spectroscopy, and photon stimulated desorption of ions. At room temperature, NO was found to react with the surface silicon adatoms to form silicon oxynitride sites (SiNxOy). At low temperature and low coverage, in addition to a permanent dissociative adsorption, a transient molecular adsorption has been observed. At low temperature and high coverage, NO was found to be condensed. In a second step, ion photodesorption induced by core electron excitation of both the adsorbate and the substrate has been studied. Quite interestingly, selective ion photodesorption was observed by core electron excitation of both dissociatively adsorbed NO at room temperature and condensed NO molecules at low temperature. An “ultrafast dissociation” is proposed to explain the results of condensed NO molecules at low temperature.
“Water-free” computer model for fluid bilayer membranes
Authors: Farago Oded
Published: June 2003

We use a simple and efficient computer model to investigate the physical properties of bilayer membranes. The amphiphilic molecules are modeled as short rigid trimers with finite range pair interactions between them. The pair potentials have been designed to mimic the hydrophobic interactions, and to allow the simulation of the membranes without the embedding solvent as if the membrane is in vacuum. We find that upon decreasing the area density of the molecules the membrane undergoes a solid–fluid phase transition, where in the fluid phase the molecules can diffuse within the membrane plane. The surface tension and the bending modulus of the fluid membranes are extracted from the analysis of the spectrum of thermal undulations. At low area densities we observe the formation of pores in the membrane through which molecules can diffuse from one layer to the other. The appearance of the pores is explained using a simple model relating it to the area dependence of the free energy.
Density functional study of hydrogen adsorption at low temperatures
Authors: Gu Chong , Gao Guang-Hua , Yu Yang-Xin
Published: June 2003

In substitution of path integral isomorphism of the quantum particle, an effective polymer ring model is proposed in the density functional calculation for hydrogen adsorption in single-walled carbon nanotubes. The excess intrinsic Helmholtz energy for quantum particles includes contributions from hard-sphere repulsion, interatomic bonding and soft attraction. The first two contributions are considered through the method developed by Yu and Wu [J. Chem. Phys. 117, 2368 (2002)], and the last contribution is obtained from mean field approximation using Weeks–Chandler–Anderson potential. The theoretical predictions are in good agreement with Monte Carlo simulation data for the density distributions of the hydrogen molecule inside the tube. In addition, the proposed model is applied to the calculation of the adsorption isotherms of hydrogen at 100 and 150 K. The present model is simpler than the current existing theories for quantum fluids.
Irreversible sequential adsorption of k-mers with diffusional relaxation on a one-dimensional lattice
Authors: Lee Jae Woo , Hong Byoung Hee
Published: June 2003

We consider the random sequential adsorption (RSA) of line segments with diffusional relaxation on a one-dimensional lattice by using Monte Carlo method. The line segments with a length k deposit with a probability p or diffuse up to a diffusion length l(l⩽k) with a probability 1−p. We observe a power-law behavior of the coverage fraction θ(t). For the dimer k=2, the empty area fraction decays according to 1−θ(t)=A(l)p0.68(1−p)−0.40(pt)−0.5, regardless of the diffusion length and the adsorption probability. The dynamics of empty area fraction of the dimers is equivalent to the diffusion-limited reaction (DLR), A+A→0, at the long time limits. A single empty site at the RSA corresponds to the reactants A at the DLR. For k⩾4, the empty area fraction decays according to the power law as 1−θ(t)=A(k,l)[(1−p)pt]−α(k,l). For k⩾4, the dynamics of empty area fraction is not interpreted by the kinetics of the diffusion-limited reaction, kA→0. For k⩾3, the model with l>1 stepping corresponds to reactions where the particles (gaps of size l) hop in a correlated way. Thus, our model of l-group-diffusion-limited k-particle reactions is different from those of the ordinary reaction kA→0. We found new power law behavior for l-group-diffusion limited k-particle reactions and the exponents of the power law depend on the hopping length l. We observed a mixed dynamics of the gap creations, splitting, and annihilations for the model at the long time.
Partition function for a simple liquid using cell theory parametrized by computer simulation
Authors: Henchman Richard H.
Published: June 2003

A method is described for directly calculating the partition function of a Lennard-Jones liquid from a single equilibrium computer simulation. The method is a special adaptation of cell theory. The partition function is essentially that of an Einstein crystal, but with assumptions rendering it appropriate for a liquid. The method addresses the three traditional shortcomings of cell theory: namely, how to calculate cell properties, include particle correlations, and account for the communal entropy. A molecular dynamics simulation provides all the necessary parameters to evaluate the partition function. These parameters are the average potential energy and average magnitude of the force acting on each particle. Free energies calculated from the partition function over a range of density and temperature give good quantitative agreement with results from perturbation theory and experiment. The cell properties also yield insight into liquid structure. Prospects for the usefulness of the method for more complex systems are discussed.
Formal study of nucleation as described by fluctuation theory
Authors: MacDowell Luis G.
Published: June 2003

A formal description of the nucleation process with out appeal to any geometrical cluster definition is attempted. This need is avoided by simply specifying the system size and monitoring a global order parameter. Consistent with this assumption, systematic comparison between fluctuation theory and classical thermodynamics leads to the equal-area and equal-height rules for phase coexistence and to a general relation between the surface free energy and fluctuations. An alternative definition for the surface free energy which may be measured by means of a simple thermodynamic integration path arises naturally from the formalism. A proof of the so-called “nucleation theorem” is given. A general expression for the nucleation barrier is obtained, which when applied to a capillary drop model explains a recently observed scaling law. The nucleation barrier as obtained from simulations is seen to be systematically smaller than that predicted by classical nucleation theory. It is argued that a microscopic phase transition, where the homogeneous phase is transformed into an inhomogeneous phase with no free energy cost, is responsible for this behavior.
Verification of generalized Kramers–Kronig relations and sum rules on experimental data of third harmonic generation susceptibility on polymer
Authors: Lucarini Valerio , Peiponen Kai-Erik
Published: June 2003

We present an analysis of harmonic generation data where the full potential of the generalized nonlinear Kramers–Kronig (KK) relations and sum rules is exploited. We consider two published sets of wide spectral range experimental data of the third-harmonic generation susceptibility for different polymers: polysilane (frequency range 0.4–2.5 eV), and polythiophene (frequency range 0.5–2.0 eV). We show that, without extending the data outside their range with the assumption of an a priori asymptotic behavior, independent truncated dispersion relations connect the real and imaginary parts of the moments of the third-harmonic generation susceptibility ω2αχ(3)(3ω,ω,ω,ω),  0⩽α⩽3, in agreement with theory, while there is no convergence for α=4. We report the analysis for ω2α[χ(3)(3ω;ω,ω,ω)]2 and show that a larger number of independent KK relations connect the real and imaginary parts of the function under examination. We also compute the sum rules for the suitable moments of the real and imaginary parts, and observe that only considering higher powers of the susceptibility the correct vanishing sum rules are more precisely obeyed. Our results are in fundamental agreement with recent theoretical findings. Verification of KK relations and sum rules constitutes an unavoidable benchmarks for any investigation that addresses the nonlinear response of matter of radiation over a wide spectral range.
Monte Carlo simulations of conformations of short chains near a cylindrical rod
Authors: Chen Shing Bor , Wang Xiao-Yan , Chiew Y. C.
Published: June 2003

Off-lattice Monte Carlo simulations are employed to study the behavior of short chain molecules near a long cylindrical rod. The molecules are modeled by freely jointed hard sphere chains. The emphasis is placed on the chain and bead distributions as well as the location dependence of the chain conformation and anisotropy. The simulation results show that at a given low chain concentration, the surface curvature of the rod gives rise to a slight increase in the bead concentration within the depletion layer. As the separation distance from the rod decreases, the chains first contract slightly and exhibit weak anisotropy in favor of an orientation parallel to the rod axis. With further increase in the closeness, to the contrary, the chains elongate and adopt a conformation that tends to wrap around the rod. This intriguing behavior is attributed primarily to the effect of the cylindrical surface.
Interplay between hydrodynamic and direct interactions using liposomes
Authors: Haro-Pérez C. , Quesada-Pérez M. , Callejas-Fernández J. , Casals E. , Estelrich J. , Hidalgo-Álvarez R.
Published: June 2003

This work deals with the short-time effective diffusion coefficient of charged and uncharged liposomes, measured (as a function of the volume fraction) using fiber optic dynamic light scattering. Particularly, we are interested in the interplay between electrostatic and hydrodynamic interactions on the diffusion of these lipid vesicles. Regarding the charged liposome, it has been found that the effective diffusion coefficient can be theoretically justified for volume fractions not exceeding certain critical value. In applying the theoretical approach, a surface charge has been obtained which is consistent with the electrokinetic characterization of the liposome. Regarding the uncharged liposome, the hard-sphere model seems to account for reasonably well the self-diffusion data. In addition, comparing the measurements of the short-time self-diffusion coefficient for both liposomes, we conclude that strong electrostatic forces (direct interactions) slow down diffusion processes.
The properties and structure of a plasma non-neutral shock
Authors: Yemin Hu , Xiwei Hu
Published: June 2003

A non-neutral shock wave in fully ionized plasma is investigated. The effects of the plasma electric characters (current, field and charge) on the shock jump relations and front constructions are considered emphatically. The Hugoniot relations of velocities and temperatures, and the critical up-stream Mach number Mc for the plasma shock existence depend on the current passed through the shock front J0, the electric potential difference between the up- and downstream of shock Δφ and the ion charge number Z. The numerical results of shock front show that a weak current carried by the shock can strengthen or weaken the non-neutral shock distinctly.
A numerical assessment of the Lundquist number requirement for relaxation current drive
Authors: Izzo V. A. , Jarboe T. R.
Published: June 2003

Numerical simulations of a decaying, unstable spheromak equilibrium are conducted with the resistive magnetohydrodynamic code NIMROD [A. H. Glasser et al., Plasma Phys. Controlled Fusion 41, A747 (1999)] in a “bowtie” flux conserver geometry. The magnetic Lundquist number, S, is varied over one order of magnitude and the minimum value needed for relaxation current drive is identified, based on poloidal flux generation results. The results can be understood as a two-stage relaxation process with two governing time scales—the Alfvén time governing the growth of the unstable mode, and the Sweet–Parker reconnection time governing the relaxation toward the Taylor state. An analytic energy cascade model based on helicity conservation explains the NIMROD results. Implications for relaxation current drive in sustained spheromaks are discussed.
Electron acceleration by cylindrical upper hybrid oscillations trapped in density irregularities in the ionosphere
Authors: Istomin Ya. N. , Leyser T. B.
Published: June 2003

A powerful electromagnetic wave of ordinary mode polarization in the ionosphere creates filamentary density depletions in the upper hybrid resonance region. These striations have small scales across the ambient geomagnetic field but are stretched along the field. By scattering off these irregularities, the electromagnetic pump wave generates cylindrical upper hybrid oscillation with azimuthal wave numbers that are trapped in the density depletions. It turns out that the azimuthal component of the electric field of such cylindrical upper hybrid oscillations rotates in the direction of the gyromotion of the electrons. This leads to the acceleration of electrons transverse to the geomagnetic field and the formation of a power-law tail in the distribution function of the electrons. These fast electrons can excite, e.g., oxygen atoms and nitrogen molecules, which produce the enhanced optical emissions observed in high frequency pump–ionosphere interaction experiments at high latitudes.
Three-dimensional electron magnetohydrodynamic reconnection. I. Fields, currents, and flows
Authors: Stenzel R. L. , Griskey M. C. , Urrutia J. M. , Strohmaier K. D.
Published: June 2003

In a large laboratory plasma, reconnection of three-dimensional (3-D) magnetic fields is studied in the parameter regime of electron magnetohydrodynamics. A reversed magnetic field topology with two 3-D null points and a two-dimensional (2-D) null line is established, and its free relaxation is studied experimentally. Major new findings include the absence of tilting instabilities in an unbounded plasma, relaxation times fast compared to classical diffusion times, dominance of field line annihilation at the 2-D current sheet versus reconnection at 3-D null points, conversion of magnetic energy into electron thermal energy, and excitation of various microinstabilities. This first of four companion papers focuses on the magnetic field topology and dynamics.
Three-dimensional electron magnetohydrodynamic reconnection. II. Tilt and precession of a field-reversed configuration
Authors: Griskey M. C. , Stenzel R. L. , Urrutia J. M. , Strohmaier K. D.
Published: June 2003

Further observations are presented on a reconnection experiment involving a three-dimensional magnetic field reversed configuration (FRC) in the parameter regime of electron magnetohydrodynamics (EMHD). The stability of the FRC that relaxes in a large ambient plasma free of boundary effects is investigated. No destructive instabilities are observed. However, the EMHD FRC performs a precession around the axis given by the ambient magnetic field after a tilt develops. The precession velocity corresponds to the electron drift velocity of the toroidal current. The phenomenon is explained by the convection of frozen-in field lines in a rotating electron fluid. It is a new phenomenon in EMHD plasmas.
Three-dimensional electron magnetohydrodynamic reconnection. III. Energy conversion and electron heating
Authors: Urrutia J. M. , Stenzel R. L. , Griskey M. C. , Strohmaier K. D.
Published: June 2003

Further observations are presented of a magnetic reconnection experiment with three-dimensional fields in the parameter regime of electron magnetohydrodynamics. The initial magnetic configuration is imposed via a Helmholtz coil, whose field is added to or subtracted from a uniform background magnetic field. Energy is transferred from the coil’s external power supply into thermal energy of electrons and kinetic energy of ions via the decay of the imposed magnetic field configuration. For the case when the Helmholtz coil field opposes the background field, thus creating a field-reversed configuration, the magnetic energy convects in the whistler mode and dissipates over large distances resulting in negligible heating. For the case when the Helmholtz coil field is added to the background field, magnetic field annihilation leads to strong localized electron heating and acceleration of unmagnetized ions via space-charge electric fields. The energy conversion to electron heat is observed in regions away from magnetic nulls and a new mechanism for breaking the frozen-in condition is proposed.
Three-dimensional electron magnetohydrodynamic reconnection. IV. Instabilities, fluctuations, and emissions
Authors: Stenzel R. L. , Griskey M. C. , Urrutia J. M. , Strohmaier K. D.
Published: June 2003

Further observations are presented on a reconnection experiment involving three-dimensional magnetic fields in the parameter regime of electron magnetohydrodynamics. The focus is on current-driven instabilities in the magnetic neutral sheet. Density fluctuations are observed in the neutral sheet and identified as current-driven ion sound turbulence. No lower hybrid turbulence or Buneman instabilities are detected. Enhanced thermal fluctuations are measured in the range of the electron plasma frequency. Microwave radiation is emitted from the plasma and explained by mode conversion of plasma waves on density gradients. The role of these instabilities in the conversion of magnetic energy and energy and transport is discussed.
Wave driven fast ion loss in the National Spherical Torus Experiment
Authors: Fredrickson E. D. , Cheng C. Z. , Darrow D. , Fu G. , Gorelenkov N. N. , Kramer G. , Medley S. S. , Menard J. , Roquemore L. , Stutman D. , White R. B.
Published: June 2003

Spherical tokamaks have relatively low toroidal field which means that the fast-ion Larmor radius is relatively large (ρfi>0.04 ap) and the fast ion velocity is much greater than the Alfvén speed (Vfi>2 VAlfvén). This regime of large Larmor radius and low Alfvén speed is a regime in which fast ion driven instabilities are potentially virulent. It is therefore an important goal of the present proof-of-principle spherical tokamaks to evaluate the role of fast ion driven instabilities in fast ion confinement. This paper presents the first observations of fast ion losses in a spherical tokamak resulting from energetic particle driven modes. Two classes of instabilities are responsible for the losses. Multiple, simultaneously bursting modes in the toroidal Alfvén eigenmode frequency gap cause neutron drops of up to 15%. A bursting, chirping mode identified as precession and/or bounce resonance fishbone also causes significant neutron drops. Both modes are usually present when the losses are observed.
The stability of steady magnetohydrodynamic flows with current-vortex sheets
Authors: Ilin K. I. , Trakhinin Y. L. , Vladimirov V. A.
Published: June 2003

The stability of steady magnetohydrodynamic flows of an inviscid incompressible fluid with current-vortex sheets to small three-dimensional perturbations is studied. The energy method of Frieman and Rotenberg is extended to the case of steady flows with surfaces of tangential discontinuities across which the tangent velocity or the tangent magnetic field or both of them have jump discontinuities. Sufficient conditions for linear stability of some classes of steady flows with parallel velocity and magnetic field are obtained. Also, a sufficient condition for instability of a tubular current-vortex sheet is given.
Higher order trace formulas of the Buslaev–Faddeev-type for the half-line Schrödinger operator with long-range potentials
Authors: Belov S. M. , Rybkin A. V.
Published: June 2003

We deal with trace formulas for half-line Schrödinger operators with long-range potentials. We generalize the Buslaev–Faddeev trace formulas to the case of square integrable potentials. The exact relation between the number of the trace formulas and the number of integrable derivatives of the potential is also given. The main results are optimal.
On neutral wind and blob motion in linear devices
Authors: Krasheninnikov S. I. , Smolyakov A. I.
Published: June 2003

It is shown that asymmetry of neutral components going to and from the wall results in a net force, inducing blob plasma polarization and radial blob motion. This mechanism may explain experimental observations of coherent plasma density structures in linear devices. Estimates of the radial blob velocity are in agreement with experimental data.
Numerical optimization of a picosecond pulse driven Ni-like Nb x-ray laser at 20.3 nm
Authors: Lu X. , Zhong J. Y. , Li Y. J. , Zhang J.
Published: June 2003

Detailed simulations of a Ni-like Nb x-ray laser pumped by a nanosecond prepulse followed by a picosecond main pulse are presented. The atomic physics data are obtained using the Cowan code [R. D. Cowan, The Theory of Atomic Structure and Spectra (University of California Press, Berkeley, CA, 1981)]. The optimization calculations are performed in terms of the intensity of prepulse and the time delay between the prepulse and the main pulse. A high gain over 150 cm−1 is obtained for the optimized drive pulse configuration. The ray-tracing calculations suggest that the total pump energy for a saturated x-ray laser can be reduced to less than 1 J.
Foldy–Wouthuysen transformation for relativistic particles in external fields
Authors: Silenko Alexander J.
Published: June 2003

A method of Foldy–Wouthuysen transformation for relativistic spin-1/2 particles in external fields is proposed. It permits the determination of the Hamilton operator in the Foldy–Wouthuysen representation with any accuracy. Interactions between a particle having an anomalous magnetic moment and nonstationary electromagnetic and electroweak fields are investigated.
Special solution of the inhomogeneous Bloch equation
Authors: Kobayashi M.
Published: June 2003

A solution of the inhomogeneous Bloch equation is given for a class of three-dimensional time-varying magnetic fields by finding the fundamental system in terms of a set of the three independent solutions of the homogeneous Bloch equation. This class is distinguished by requiring a nonlinear relation between one of the magnetic field components and the other two components and their derivatives. A brief discussion of the magnetic field class characteristics and an illustrative example are given.
Exact duality transformations for sigma models and gauge theories
Authors: Pfeiffer Hendryk
Published: June 2003

We present an exact duality transformation in the framework of statistical mechanics for various lattice models with non-Abelian global or local symmetries. The transformation applies to sigma models with variables in a compact Lie group G with global G×G-symmetry (the chiral model) and with variables in coset spaces G/H and a global G-symmetry [for example, the nonlinear O(N) or RPN models] in any dimension d⩾1. It is also available for lattice gauge theories with local gauge symmetry in dimensions d⩾2 and for the models obtained from minimally coupling a sigma model of the type mentioned above to a gauge theory. The duality transformation maps the strong coupling regime of the original model to the weak coupling regime of the dual model. Transformations are available for the partition function, for expectation values of fundamental variables (correlators and generalized Wilson loops) and for expectation values in the dual model which correspond in the original formulation to certain ratios of partition functions (free energies of dislocations, vortices or monopoles). Whereas the original models are formulated in terms of compact Lie groups G and H, coset spaces G/H and integrals over them, the configurations of the dual model are given in terms of representations and intertwiners of G and H. They are spin networks and spin foams. The partition function of the dual model describes the group theoretic aspects of the strong coupling expansion in a closed form.
Evolution of magnetic flux in an isolated reconnection process
Authors: Hornig Gunnar , Priest Eric
Published: June 2003

A realistic notion of magnetic reconnection is essential to understand the dynamics of magnetic fields in plasmas. Therefore a three-dimensional reconnection process is modeled in a region of nonvanishing magnetic field and is analyzed with respect to the way in which the connection of magnetic flux is changed. The process is localized in space in the sense that the diffusion region is limited to a region of finite radius in an otherwise ideal plasma. A kinematic, stationary model is presented, which allows for analytical solutions. Aside from the well-known flipping of magnetic flux in the reconnection process, the localization requires additional features which were not present in previous two- and 2.5-dimensional models. In particular, rotational plasma flows above and below the diffusion region are found, which substantially modify the process.
Magnetic helicity balance in the Sustained Spheromak Plasma Experiment
Authors: Stallard B. W. , Hooper E. B. , Woodruff S. , Bulmer R. H. , Hill D. N. , McLean H. S. , Wood R. D. ,   SSPX Team
Published: June 2003

The magnetic helicity balance between the helicity input injected by a magnetized coaxial gun, the rate-of-change in plasma helicity content, and helicity dissipation in electrode sheaths and Ohmic losses have been examined in the Sustained Spheromak Plasma Experiment (SSPX) [E. B. Hooper, L. D. Pearlstein, and R. H. Bulmer, Nucl. Fusion 39, 863 (1999)]. Helicity is treated as a flux function in the mean-field approximation, allowing separation of helicity drive and losses between closed and open field volumes. For nearly sustained spheromak plasmas with low fluctuations, helicity balance analysis implies a decreasing transport of helicity from the gun input into the spheromak core at higher spheromak electron temperature. Long pulse discharges with continuously increasing helicity and larger fluctuations show higher helicity coupling from the edge to the spheromak core. The magnitude of the sheath voltage drop, inferred from cathode heating and a current threshold dependence of the gun voltage, shows that sheath losses are important and reduce the helicity injection efficiency in SSPX.
Simulation of intermittent beam ion loss in a Tokamak Fusion Test Reactor experiment
Authors: Todo Y. , Berk H. L. , Breizman B. N.
Published: June 2003

Recurrent bursts of toroidicity-induced Alfvén eigenmodes (TAE) are studied using a self-consistent simulation model. Bursts of beam ion losses observed in the neutral beam injection experiment at the Tokamak Fusion Test Reactor [K. L. Wong et al., Phys. Rev. Lett. 66, 1874 (1991)] are reproduced using experimental parameters. It is found that synchronized TAE bursts take place at regular time intervals of 2.9 ms, which is close to the experimental value of 2.2 ms. The stored beam energy saturates at about 40% of that of the classical slowing down distribution. The stored beam energy drop associated with each burst has a modulation depth of 10%, which is also close to the inferred experimental value of 7%. Surface of section plots demonstrate that both the resonance overlap of different eigenmodes and the disappearance of KAM surfaces in phase space due to overlap of higher-order islands created by a single eigenmode lead to particle loss. Only co-injected beam ions build up to a significant stored energy even though their distribution is flattened in the plasma center. However, they are not directly lost, as their orbits extend beyond the outer plasma edge when the core plasma leans on a high field side limiter. The saturation amplitude is δB/B∼2×10−2, which is larger than would appear to be compatible with experiment. Physical arguments are presented for why the stored energetic particle response observed in the simulation is still plausible.
Regularity for Lorentz metrics under curvature bounds
Authors: Anderson Michael T.
Published: June 2003

Let (M, g) be an (n+1)-dimensional space–time, with bounded curvature, with respect to a bounded framing. If (M, g) is vacuum, or satisfies a weak condition on the stress-energy tensor, then it is shown that (M, g) locally admits coordinate systems in which the Lorentz metric g is well-controlled in the (space–time) Sobolev space L2,p, for any p<∞. This result is essentially optimal. The result allows one to control the regularity of limits of sequences of space–times, with uniformly bounded curvature, and has applications to the structure of boundaries and extensions of space–times.
Resolvent convergence in norm for Dirac operator with Aharonov–Bohm field
Authors: Tamura Hideo
Published: June 2003

We consider the Hamiltonian for relativistic particles moving in the Aharonov–Bohm magnetic field in two dimensions. The field has δ-like singularity at the origin, and the Hamiltonian is not necessarily essentially self-adjoint. The self-adjoint realization requires one parameter family of boundary conditions at the origin. We approximate the point-like field by smooth ones and study the problem of norm resolvent convergence to see which boundary condition is physically reasonable among admissible boundary conditions. We also study the effect of perturbations by scalar potentials. Roughly speaking, the obtained result is that the limit self-adjoint realization is different even for small perturbation of scalar potentials according to the values of magnetic fluxes. It changes at half-integer fluxes. The method is based on the resolvent analysis at low energy on magnetic Schrödinger operators with resonance at zero energy and the resonance plays an important role from a mathematical point of view. However it has been neglected in earlier physical works. The emphasis here is placed on this natural aspect.
Coherent acceleration of magnetized ions by electrostatic waves with arbitrary wavenumbers
Authors: Strozzi D. J. , Ram A. K. , Bers A.
Published: June 2003

This paper studies the coherent acceleration of ions interacting with two electrostatic waves in a uniform magnetic field B0. It generalizes an earlier analysis of waves propagating perpendicularly to B0 to include the effect of wavenumbers along B0. The Lie transformation technique is used to develop a perturbation theory describing the ion motion, and results are compared with numerical solutions of the complete equations of motion. Coherent energization occurs when the Doppler-shifted wave frequencies differ by nearly an integer multiple of the ion cyclotron frequency. When the difference in the parallel wavenumbers of the two waves is increased the coherent energization of ions is limited to a small part of the phase space. The energization of ions and its dependence on wave parameters is discussed.
Oscillatory modes of magnetized grains in a plasma
Authors: Vladimirov S. V. , Morfill G. E. , Yaroshenko V. V. , Cramer N. F.
Published: June 2003

It is demonstrated that new modes of particle oscillations, associated with magnetic properties, can exist in a one-dimensional chain of charged magnetized particles in a plasma. The stability of equilibria, transitions between the different equilibria, and a critical dependence on the external fields and plasma parameters are investigated.
Isotope and crystal orientation effects in low-energy H/D blistering of Si
Authors: Moutanabbir O. , Terreault B. , Ross G. G.
Published: June 2003

In this letter we report a giant isotope effect in silicon blistering induced by low-energy (5 keV) H or D ion implantation and annealing. Atomic force microscopy and thermal desorption spectroscopy revealed abundant blistering and exfoliation with a D fluence of 6×1016 D cm−2, whereas no blistering was observed with a H fluence up to 1×1017 H cm−2. This is accompanied by premature H2 release, and the evidence suggests that inefficient defect trapping is the cause. The blister density and the degree of exfoliation also depend strongly on the crystal orientation.
Scaling of saturated stimulated Raman scattering with temperature and intensity in ignition scale plasmas
Authors: Kirkwood R. K. , Berger R. L. , Geddes C. G. R. , Moody J. D. , MacGowan B. J. , Glenzer S. H. , Estabrook K. G. , Decker C. , Landen O. L.
Published: June 2003

Measurements show the scaling of stimulated Raman scattering (SRS) with laser intensity and plasma electron temperature under the conditions expected in ignition experiments. The scaling of the scattered energy with each parameter follows a power law with a small exponent (of order 1). Comparison with simulations suggests SRS is nonlinearly saturated in these cases. Further experiments with high Z dopants showed that the effect of electron-ion collisions on the measured SRS is primarily due to the inverse bremsstrahlung absorption of the scattered light.
The internal magnetic field structures and current density profiles in the Helicity Injected Spherical Torus plasma driven by coaxial helicity injection
Authors: Nagata Masayoshi , Kanki Takashi , Fukumoto Naoyuki , Uyama Tadao
Published: June 2003

In the Helicity Injected Spherical Torus device [Nagata et al., Proceedings of the 17th International Atomic Energy Agency Fusion Energy Conference, Yokohama, 1998 (International Atomic Energy Agency, Vienna, 1998) CD-ROM, EXP4/10], internal magnetic field and current density structures of spherical torus (ST) plasmas sustained by coaxial helicity injection (CHI) have been revealed via intensive internal magnetic measurements. The internal magnetic configuration of the ST plasma formed by CHI is in good agreement with the results of numerical equilibrium fitting calculations. The generation of closed poloidal flux of ST has been verified by varying the external toroidal field strength in the same device. Interestingly, the transition of the current profile from hollow to peaked has been observed during the sustainment phase, which could be explained by inductive effects of currents on open field lines winding the central conductor.
Simulation of electromagnetically and magnetically induced transparency in a magnetized plasma
Authors: Hur M. S. , Wurtele J. S. , Shvets G.
Published: June 2003

Electromagnetically induced transparency (EIT), a phenomenon well known in atomic systems, has a natural analogy in a classical magnetized plasma. The magnetized plasma has a resonance for right-hand polarized electromagnetic waves at the electron cyclotron frequency Ω0, so that a probe wave with frequency ω1=Ω0 cannot propagate through the plasma. The plasma can be made transparent to such a probe by the presence of a pump wave. The pump may be an electromagnetic wave or magnetostatic wiggler. Simulations and theory show that the physical reason for the transparency is that the beating of the probe wave with the pump wave sets up a plasma oscillation, and the upper sideband of the pump wave cancels the resonant plasma current due to the probe. The theory of plasma EIT derived here extends that found in the earlier work to include the effects of the lower sideband of the pump and renormalization of the plasma frequency and an analysis of the transient response. A detailed comparison of theory to one-dimensional particle-in-cell simulations is presented and estimates for the performance ion accelerator using the EIT interaction are given. The dispersion relation and estimates for the phase velocity and amplitude of the plasma wave are in good agreement with particle-in-cell simulations.
Towards the complete classification of homogeneous two-component integrable equations
Authors: Foursov Mikhail V.
Published: June 2003

In this article we suggest an improved method for classifying general two-component integrable evolution equations, homogeneous in a given weighting scheme. This method relies on linear changes of variables and on an appropriate splitting of the solution space. To illustrate the method, we implement the classification of coupled KdV-type equations. We show that there are five nontriangular systems possessing higher order generalized symmetries. One of these systems is previously unknown. This seems to be the first classification of coupled integrable equations homogeneous in a given weighting scheme, without any restrictions on the form of the main matrix.
A space–time in toroidal coordinates
Authors: Krisch J. P. , Glass E. N.
Published: June 2003

We present an exact solution of Einstein’s field equations in toroidal coordinates. The solution has three regions: an interior with a string equation of state; an Israel boundary layer; and an exterior with constant isotropic pressure and constant density, locally isometric to anti–de Sitter space–time. The exterior can be a cosmological vacuum with negative cosmological constant. The size and mass of the toroidal loop depend on the size of Λ.
Weakly two-dimensional modulated wave packet in dusty plasmas
Authors: Duan Wen-shan
Published: June 2003

The higher order transverse perturbations for modulated wave packets in a dusty plasma are investigated. A Davey–Stewartson equation is obtained for this system. The instability for small amplitude linear transverse perturbations are investigated.
Optical properties of highly compressed polystyrene using laser-driven shockwaves
Authors: Koenig Michel , Philippe Franck , Benuzzi-Mounaix Alessandra , Batani Dimitri , Tomasini Micaela , Henry Emeric , Hall Tom
Published: June 2003

Plastic is a common material used for laboratory astrophysics and inertial confinement fusion. Experimental measurements of the optical properties of shock compressed polystyrene in the strongly coupled and correlated regime (0.7 Mbar<P<1.7 Mbar; 0.5<T<1.3 eV) are reported. A VISAR (Velocity Interferometer System for Any Reflector) system was used in addition to self-emission recording on a streak camera. This allowed a simultaneous access to reflectivity, instantaneous shock velocity and temperature. Mean ionization and conductivity of the material have then been deduced through the Drude model. The values found are more than an order of magnitude greater than published ones in this temperature domain.
Bursting events in zonal flow-drift wave turbulence
Authors: Manfredi G. , Roach C. M.
Published: June 2003

The generation of zonal flows and their interplay with drift wave turbulence is studied numerically using a model based on the Hasegawa–Mima equation, with an electron response depending only on the fluctuating part of the electrostatic potential. In regimes dominated by the diamagnetic velocity, large-amplitude nonlinear oscillations are observed in the time history of the zonal flow and drift wave spectra. Such oscillations have also recently been detected in toroidal gyrokinetic simulations, and could be important in determining the transport behavior in experimental devices.
Computational model for a low-temperature laser-plasma driver for shock-processing of metals and comparison to experimental data
Authors: Colvin J. D. , Ault E. R. , King W. E. , Zimmerman I. H.
Published: June 2003

Few-joule table-top lasers can generate pressures up to the 100 kbar range in solid materials by propagating a low-intensity beam through a transparent dielectric, which confines the ablation pressure, onto an ablation layer in contact with the material of interest. This technique has application in studies of material dynamic behavior and material processing. Development and application of physically based models of this process have lagged experiment. In this article the particulars of a detailed computational model incorporated into a two-dimensional radiationhydrodynamics code are presented. The model accounts for the initial absorption onto a metal surface, low-intensity photoionization absorption in neutral vapor, collisional ionization, recombination, dielectric breakdown, band gap collapse, electron conductivity, thermal transport, and constitutive properties of the materials. The model shows that most of the laser energy is absorbed in the dielectric tamper, not the ablator. Good agreement is found between simulated and measured pressure histories for materials irradiated with several tens of joules using a single-beam neodymium-glass laser at the Lawrence Livermore National Laboratory.
Exponentially accurate error estimates of quasiclassical eigenvalues. II. Several dimensions
Authors: Toloza J. H.
Published: June 2003

We study the behavior of truncated Rayleigh–Schrödinger series for low-lying eigenvalues of the time-independent Schrödinger equation, in the semiclassical limit ℏ↘0. In particular we prove that if the potential energy satisfies certain conditions, there is an optimal truncation of the series for the eigenvalues, in the sense that this truncation is exponentially close to the exact eigenvalue. These results were already discussed for the one-dimensional case in a previous article. This time we consider the multi-dimensional problem, where degeneracy plays a central role.
Entropic repulsion for a Gaussian lattice field with certain finite range interaction
Authors: Sakagawa Hironobu
Published: June 2003

Consider the centered Gaussian field on Zd, d⩾2l+1, with covariance matrix given by (∑j=lKqj(−Δ)j)−1 where Δ is the discrete Laplacian on Zd, 1⩽l⩽K and qj∈R,l⩽j⩽K are constants satisfying ∑j=lKqjrj>0 for r∈(0,2] and a certain additional condition. We show the probability that all spins are positive in a box of volume Nd decays exponentially at a rate of order Nd−2l log N and under this hard-wall condition, the local sample mean of the field is repelled to a height of order log N. This extends the previously known result for the case that the covariance is given by the Green function of simple random walk on Zd (i.e., K=l=1,q1=1).
Scaling behavior and parasitic series resistance in disordered organic field-effect transistors
Authors: Meijer E. J. , Gelinck G. H. , van Veenendaal E. , Huisman B.-H. , de Leeuw D. M. , Klapwijk T. M.
Published: June 2003

The scaling behavior of the transfer characteristics of solution-processed disordered organic thin-film transistors with channel length is investigated. This is done for a variety of organic semiconductors in combination with gold injecting electrodes. From the channel-length dependence of the transistor resistance in the conducting ON-state, we determine the field-effect mobility and the parasitic series resistance. The extracted parasitic resistance, typically in the MΩ range, depends on the applied gate voltage, and we find experimentally that the parasitic resistance decreases with increasing field-effect mobility.
Weakly turbulent electron cloud transport in a plasma with an external electric field
Authors: Kontar E. P. , Mel’nik V. N.
Published: June 2003

The propagation of a fast electron cloud in a relatively cold and dense plasma in an electric field is investigated in the framework of weak turbulence theory. The dynamics of an electron cloud in the external electric field is studied both analytically and numerically. It is shown that electrons propagate as a beam–plasma structure and that the structure becomes accelerated. For propagation along the field the structure loses particles and the velocity of the structure declines whereas propagation against the field leads to structure acceleration and a high level of plasma waves behind the structure.
Observation of and model for nonlinear mode conversion in a non-neutral plasma
Authors: Hart Grant W. , Spencer Ross L. , Peterson Bryan G.
Published: June 2003

The nonlinear interaction of the two lowest Trivelpiece–Gould modes in a non-neutral plasma has been observed. Because of coupling in the nonlinear terms of the continuity and momentum equations, the two modes can exchange energy and convert one to the other. This can be modeled using the cold fluid equations and the averaging method. Experimentally, this process always stops with the lower frequency mode dominating the final state. Numerical integration of the model suggests that this occurs because the higher frequency mode is more strongly damped than the lower frequency mode.