bluuebunny/crossref_metadata_2025 huggingface dataset:
Unifying scheme for generating discrete integrable systems including inhomogeneous and hybrid models
Authors: Kundu Anjan
Published: September 2003

A unifying scheme based on an ancestor model is proposed for generating a wide range of integrable discrete and continuum as well as inhomogeneous and hybrid models. They include in particular discrete versions of sine-Gordon, Landau–Lifshitz, nonlinear Schrödinger (NLS), derivative NLS equations, Liouville model, (non-)relativistic Toda chain, Ablowitz–Ladik model, etc. Our scheme introduces the possibility of building a novel class of integrable hybrid systems including multicomponent models like massive Thirring, discrete self-trapping, two-mode derivative NLS by combining different descendant models. We also construct inhomogeneous systems like Gaudin model including new ones like variable mass sine-Gordon, variable coefficient NLS, Ablowitz–Ladik, Toda chains, etc. keeping their flows isospectral, as opposed to the standard approach. All our models are generated from the same ancestor Lax operator (or its q→1 limit) and satisfy the classical Yang–Baxter equation sharing the same r-matrix. This reveals an inherent universality in these diverse systems, which become explicit at their action-angle level.
Resistive wall modes in the EXTRAP T2R reversed-field pinch
Authors: Brunsell P. R. , Malmberg J.-A. , Yadikin D. , Cecconello M.
Published: September 2003

Resistive wall modes (RWM) in the reversed field pinch are studied and a detailed comparison of experimental growth rates and linear magnetohydrodynamic (MHD) theory is made. RWM growth rates are experimentally measured in the thin shell device EXTRAP T2R [P. R. Brunsell et al., Plasma Phys. Controlled Fusion 43, 1 (2001)]. Linear MHD calculations of RWM growth rates are based on experimental equilibria. Experimental and linear MHD RWM growth rate dependency on the equilibrium profiles is investigated experimentally by varying the pinch parameter Θ=Bθ(a)/〈Bφ〉 in the range Θ=1.5–1.8. Quantitative agreement between experimental and linear MHD growth rates is seen. The dominating RWMs are the internal on-axis modes (having the same helicity as the central equilibrium field). At high Θ, external nonresonant modes are also observed. For internal modes experimental growth rates decrease with Θ while for external modes, growth rates increase with Θ. The effect of RWMs on the reversed-field pinch plasma performance is discussed.
Transport threshold model of subsonic neoclassical tearing modes in tokamaks
Authors: Mikhailovskii A. B. , Shirokov M. S. , Tsypin V. S. , Konovalov S. V. , Ozeki T. , Takizuka T. , Galvão R. M. O. , Nascimento I. C.
Published: September 2003

A transport threshold model of subsonic neoclassical tearing modes (NTMs) in tokamaks is developed. The basic procedure is to include the velocity-dependent term into the single-fluid heat-conductivity equation and to complement this equation with the single-fluid parallel plasma motion equation. These equations permit the determination of the perturbed plasma temperature and the bootstrap current drive of NTMs, for both strong and weak perpendicular heat transport, which is the precondition for developing the above model. It is shown that the subsonic NTMs transport threshold model can be more realistic than the standard transport model of NTMs suggested by Fitzpatrick [Phys. Plasmas 2, 825 (1995)].
Banded frequency structure from linear mode conversion in inhomogeneous plasmas
Authors: Willes A. J. , Cairns Iver H.
Published: September 2003

Linear mode conversion of unmagnetized Langmuir waves into transverse electromagnetic waves in an inhomogeneous plasma is investigated numerically. It is shown that the presence of a tunneling region and density well near the mode conversion region can significantly influence the mode conversion efficiency. The density cavity acts as a resonator, such that the mode conversion efficiency shifts from zero to a local maximum (up to 100% efficiency) with variation of the cavity width on scales of order the Langmuir wavelength. In this way, Langmuir waves with a smooth (structureless) frequency dependence can be selectively mode converted to produce narrow frequency bands of electromagnetic radiation. Applications are discussed to banded frequency fine structure in electromagnetic emissions at the electron plasma frequency in Earth’s foreshock and the solar wind, type III solar radio bursts, and lower ionospheric auroral roar emissions.
Model validation, dynamic edge localized mode discrimination, and high confidence resistive wall mode control in DIII-D
Authors: Fransson C. M. , Edgell D. H. , Humphreys D. A. , Walker M. L.
Published: September 2003

A linear model for feedback stabilization of n=1 resistive wall modes (RWMs) in the DIII-D [T.C. Simonen, J. Fusion Energy 11, 79 (1992)] tokamak is presented and validated with recent experimental data. The model uses a toroidal current sheet to represent the plasma surface and “picture frame” currents to represent the conducting structure. Since the model does not account for plasma rotation, recent low rotation DIII-D discharges are vital for validation. It is shown that edge localized modes (ELMs) cause the system to become unstable in DIII-D by affecting the magnetic field sensor measurements, and thus, exciting the active coils even though the RWM is already stabilized. Two procedures for discriminating ELMs from the sensor signals are suggested and by combining the two approaches, the ELM contributions in the closed loop can be removed almost completely. Filtered sensor signals and a validated closed loop model facilitates high confidence RWM feedback stabilization. Controllers with high stability robustness and low sensitivity to noise are designed, and achievable closed loop performance for different sensor configurations in DIII-D are compared.
Physics of pedestal density profile formation and its impact on H-mode density limit in burning plasmas
Authors: Mahdavi M. A. , Maingi R. , Groebner R. J. , Leonard A. W. , Osborne T. H. , Porter G.
Published: September 2003

Based on semianalytic modeling of experimental H-mode density profiles, a pedestal density limit is computed for a prototypical next generation burning plasma. For a range of input assumptions, the projected limit lies near or above Greenwald density limit [M. Greenwald, J. L. Terry, S. M. Wolfe, S. Ejima, M. G. Bell, S. M. Kaye, and G. H. Neilson, Nucl. Fusion 28, 2199 (1988)]. Two separate models are developed and utilized: the first model determines the edge density profile from consideration of cross-field transport in the steep gradient region and the distribution of fueling sources. It is shown that the observed shape of the density profile in H-mode can be explained with constant particle diffusivity within the separatrix. The second model determines the separatrix density above which the conduction limited scrape-off layer (SOL) transport is no longer sustainable. These results imply that further increases in pedestal density (while maintaining separatrix density below the power balance limit) are achievable through control of the fueling profile, e.g., with shallow pellets from the high-field side and divertor pumping.
Three regimes of intense laser beam propagation in plasmas
Authors: Sharma Ashutosh , Prakash Gyan , Verma M. P. , Sodha M. S.
Published: September 2003

The nature of propagation of an intense laser beam in a plasma depends on the power and width of the beam and Ω, the ratio of plasma frequency and wave frequency. In this paper, for a given value of Ω (<1) three regimes have been obtained in the beam power-beam width plane, characterizing the nature of propagation as follows: (i) steady divergence (the beam keeps on diverging as it propagates in the plasma); (ii) oscillatory divergence (as the beam propagates in the plasma, the beamwidth oscillates between the original beamwidth and a maximum value); and (iii) self-focusing (as the beam propagates in the plasma the beam width oscillates between the original beam width and a minimum value). Ponderomotive force, collisions, and relativistic dependence of mass on quiver velocity have been considered to be the mechanisms of nonlinearity in the effective dielectric constant.
Prototype system for superconducting quantum interference device multiplexing of large-format transition-edge sensor arrays
Authors: Reintsema Carl D. , Beyer Jörn , Nam Sae Woo , Deiker Steve , Hilton Gene C. , Irwin Kent , Martinis John , Ullom Joel , Vale Leila R. , MacIntosh Mike
Published: September 2003

We discuss the implementation of a time-division superconducting quantum interference device (SQUID) multiplexing system for the instrumentation of large-format transition-edge sensor arrays. We cover the design and integration of cryogenic SQUID multiplexers and amplifiers, signal management and wiring, analog interface electronics, a digital feedback system, serial-data streaming and management, and system configuration and control. We present data verifying performance of the digital-feedback system. System noise and bandwidth measurements demonstrate the feasibility of adapting this technology for a broad base of applications, including x-ray materials analysis and imaging arrays for future astronomy missions such as Constellation-X (x-ray) and the SCUBA-2 instrument (submillimeter) for the James Clerk Maxwell Telescope.
Study of He clusters by means of a compact time-of-flight detector for atom scattering
Authors: Pedemonte L. , Tatarek R. , Bracco G.
Published: September 2003

The design of a time-of-flight detector for energy resolved He atom scattering experiments is discussed in detail. The project has aimed at realizing a high efficiency detector combining an ionization region with length of ∼4 mm and a quadrupole mass filter with mass resolution M/ΔM∼10 for helium. The detector performances have been tested using a supersonic helium atom source cooled down to ∼20 K. Measurements performed at the helium mass show that the requirements concerning the mass resolution, the sensitivity, and the response time of the detection system have been fulfilled. Helium clusters have been detected within the supersonic beam tuning the filter on mass 8 a.m.u. An intriguing behavior of the dimer ion velocity is pointed out. Moreover, the evolution of the helium and the dimer ion signal with the source pressure is investigated at different source temperatures. The data are interpreted suggesting that clusters of increasing size condense within the beam.
Acoustoelectric probe for d33 measurement on piezoelectric thin films
Authors: Verardi P. , Craciun F.
Published: September 2003

An acoustoelectric probe capable of measuring the d33 constant of piezoelectric thin films is presented. The principle used is the direct piezoelectric effect: a mechanical stress is applied to the film surface and the subsequent voltage generated is measured and compared with a reference. The mechanical stress consists of a rf acoustic longitudinal wave generated by a piezoelectric plate in a metallic rod and through this applied to the film free surface. The probe is mounted in a classical electrical probe in order to easily position and perform reliable measurements. The instrument permits the exploration and mapping of the piezoelectric properties of the deposited thin film without any need for a top electrode deposition. This allows an easy mapping of the film properties in a nondestructive way. A sensitivity of 1 pC/N has been estimated. Measurement of piezoelectric properties under a dc bias field, as required for relaxor thin films, are also possible. The structure and the design of the probe, as well the complete experimental setup, are presented. Some results of measurements made on different materials are reported.
Novel frictionless approach mechanism for a scanning tunneling microscope
Authors: Guha A. , Kim S. , de Lozanne A. L.
Published: September 2003

A novel coarse approach mechanism for a scanning tunneling microscope (STM) is described. Any approach mechanism, which brings a tip close to the sample, suffers from dry frictional force, which makes positioning of the tip over the sample rather difficult. In this unique design, we have reduced the friction to a minimum by oscillating the normal force on the sliding sapphire surfaces. This technique allows us to precisely position the tip over the sample after traveling a distance greater than 100 μm while maintaining a compact STM design. This technique of reducing friction is also very useful in an automatic inertial approach mechanism (or “stick–slip” motor), where the motion often becomes clamped due to excessive friction. We believe that this technique will be extremely useful for applications where high precision positioning is required.
Testing of an edge thermal instability model for the high-to-low mode power threshold
Authors: Stacey W. M. , Petrie T. W.
Published: September 2003

A test of a new model for the high-to-low (H–L) mode power threshold, based on the destabilization of edge thermal instabilities, is made by comparison with a set of DIII-D [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] discharges in which increasing radiative power leads to a H–L transition. Agreement is found between the measured power crossing the separatrix just prior to the H–L transition and the predicted power threshold for the onset of transport enhancing thermal instabilities.
Effects of dipole perturbation on the stochastic layer and magnetic footprint in single-null divertor tokamaks
Authors: Punjabi Alkesh , Ali Halima , Boozer Allen
Published: September 2003

In this paper, the method of maps is used to calculate the effects of high toroidal and poloidal mode number perturbation on the trajectories of magnetic field lines in a single-null divertor tokamak. First, a simplified derivation of the dipole map from the Hamiltonian mechanics of magnetic field is given. This map represents the effects of an externally located current carrying coil on the motion of field lines. The unperturbed magnetic field topology of a single-null divertor tokamak is represented by the symmetric simple map. The coil is placed across from the X-point on the line joining the X-point and the O-point at a fixed distance from the last good confining surface. The effects of coil on the stochastic layer and magnetic footprint are calculated using the symmetric simple map and the dipole map. Self-similarities, singularities, and topological equivalences in the pattern of physical parameters are found that characterize the stochastic layer and the magnetic footprint. The dipole perturbation increases the area of footprint, drastically reduces the fraction of heat flux escaping the stochastic layer, disperses the heat flux more evenly over a wider area, and reduces number of hotspots on the collector plate.
Analysis of three-dimensional photoacoustic imaging of a vascular tree in vitro
Authors: Pilatou Magdalena C. , Voogd Nico J. , de Mul Frits F. M. , Steenbergen Wiendelt , van Adrichem Leon N. A.
Published: September 2003

We used photoacoustics in order to image a vasculature cast, which was obtained from a Wistar rat. The main objective was to investigate the imaging quality and the performance of the beamforming algorithm. For these purposes, the specimen was measured in several Intralipid™ 10% solutions and it was scanned with scanning steps of 100, 200, and 300 μm. The measurements were performed with a disk-shaped detector, with PVDF as an active material and four fibers for the light delivery. From the recorded signals, three-dimensional images of the cast were constructed.
A cryogenic radiometer for absolute neutron rate measurement
Authors: Chowdhuri Z. , Hansen G. L. , Jane V. , Keith C. D. , Lozowski W. M. , Snow W. M. , Dewey M. S. , Gilliam D. M. , Greene G. L. , Nico J. S. , Thompson A. K. , Wietfeldt F. E.
Published: September 2003

We detail the design and operation of an electrical substitution radiometer, which measures the absolute fluence of thermal neutron beams based on neutron absorption in a Li6-rich metallic alloy. We demonstrate that the device possesses a linear response to electrical power in the 50–500 nW range with better than 0.1% absolute accuracy and negligible zero offset. We show the response of the radiometer to a 3 meV neutron beam. We compare the noise of the radiometer to the noise observed upstream in a thin rate monitor and show that the radiometer noise is understood quantitatively. We establish that the radiometer measures neutron rates above 105 s−1 to an absolute accuracy of 0.1%.
Development of phosphor scintillator-based detectors for soft x-ray and vacuum ultraviolet spectroscopy of magnetically confined fusion plasmas
Authors: Soukhanovskii V. A. , Regan S. P. , May M. J. , Finkenthal M. , Moos H. W.
Published: September 2003

Specialized soft x-ray and vacuum ultraviolet (VUV) diagnostics used to monitor impurity emissions from fusion plasmas are often placed in a very challenging experimental environment. Detectors in these diagnostics must be simple; mechanically robust; immune to electromagnetic interference, energetic particles, and magnetic fields up to several tesla; ultra-high-vacuum compatible; and able to withstand bakeout temperatures up to 300 °C. The design and the photometric calibration of a detector consisting of a P45 phosphor (Y2O2S:Tb), two incoherent fiber-optic bundles coupled with a vacuum feedthrough fiber-optic faceplate, and a photomultiplier tube (PMT) are reported. We have successfully operated the detectors of this type in novel soft x-ray and VUV diagnostics on several fusion plasma facilities. Measurements of the visible photon throughput of the silica/silica incoherent fiber-optic bundle, and the light loss associated with the coupling of the two fibers with the faceplate are presented. In addition, improved absolute measurements of the conversion efficiency of the P45/PMT photodetector based upon the use of a PMT with a bialkali photocathode instead of a multialkali one are presented for the soft x-ray and VUV range of photon wavelengths. The conversion efficiency is defined as the ratio of the photoelectrons ejected from the photocathode of a visible detector, which are excited by the scintillated photons that are emitted from the phosphor in a solid angle of 2π, to the number of soft x-ray photons incident on the phosphor. Sensitive electronic gain measurements of the PMT using the visible scintillated light from the P45 phosphor are compared with the gain measurements supplied by the manufacturer of the PMT, which were performed with a tungsten filament lamp operated at 2856 K.
He
3
maser for earth magnetic field measurement
Authors: Gilles Hervé , Monfort Yves , Hamel Joseph
Published: September 2003

We describe the realization of a He3 Maser operating as an Earth magnetic field magnetometer. Preliminary experiments in order to optimize the device are first presented and finally the He3 Maser is used in the Earth magnetic field and compared with a He4 magnetometer.
Solvable models of Bose–Einstein condensates: A new algebraic Bethe ansatz scheme
Authors: Zhou Huan-Qiang , Links Jon , Gould Mark D. , McKenzie Ross H.
Published: September 2003

A new algebraic Bethe ansatz scheme is proposed to diagonalize classes of integrable models relevant to the description of Bose–Einstein condensation in dilute alkali gases. This is achieved by introducing the notion of ℤ-graded representations of the Yang–Baxter algebra.
Double warped space–times
Authors: Ramos M. P. M. , Vaz E. G. L. R. , Carot J.
Published: September 2003

An invariant characterization of double warped space–times is given in terms of Newman–Penrose formalism and a classification scheme is proposed. A detailed study of the conformal algebra of these space–times is also carried out and some remarks are made on certain classes of exact solutions.
Potential and field singularity at a surface point charge
Authors: Silbergleit Alexander , Mandel Ilya , Nemenman Ilya
Published: September 2003

The behavior of the magnetic potential near a point charge (fluxon) located at a curved regular boundary surface is shown to be essentially different from that of a volume point charge. In addition to the usual inverse distance singularity, two singular terms are generally present. The first of them, a logarithmic one, is axially symmetric with respect to the boundary normal at the charge location, and proportional to the sum of the two principal curvatures of the boundary surface at this point, that is, to the local mean curvature. The second term is asymmetric and proportional to the difference of the two principal curvatures in question; it is also bounded at the charge location. Both terms vanish, apparently, if the charge is at a planar point of the boundary, and only in this case. The field in the charge vicinity behaves accordingly, featuring generally two singular terms proportional to the inverse distance, in addition to the main inverse distance squared singularity. This result is significant, in particular, for studying the interaction of magnetic vortices in type II superconductors.
Numerical simulation of the heat transfer in amorphous silicon nitride membrane-based microcalorimeters
Authors: Revaz B. , Zink B. L. , O’Neil D. , Hull L. , Hellman F.
Published: September 2003

Numerical simulations of the two-dimensional (2D) heat flow in a membrane-based microcalorimeter have been performed. The steady-state isotherms and time-dependent heat flow have been calculated for a wide range of sample and membrane thermal conductivities and heat capacities. In the limit of high internal thermal conductivity and low membrane heat capacity, the sample heat capacity determined using the relaxation method with a single time constant is shown to be exact. The fractional contribution of the square 2D membrane border to the total heat capacity is calculated (∼24%). Analysis of the steady-state isotherms provide the 2D geometric factor (10.33) linking membrane thermal conductance to thermal conductivity, allowing extraction of the thermal conductivity of either the membrane itself or a sample deposited everywhere on the membrane. For smaller internal thermal conductivity and/or larger membrane heat capacity, systematic errors are introduced into the determination of heat capacity and thermal conductivity of a sample analyzed in the standard (single time constant) relaxation method, as has been previously shown for one dimension. These errors are due to both the changing contribution of the membrane border and to deviations from the ideal semiadiabatic approximation of the relaxation method. The errors are here calculated as a function of the ratios of thermal conductivity and heat capacity of sample and membrane. The differential method of measurement in which the sample heat capacity is taken as the difference between a relaxation method measurement with and without the sample is shown to give significantly smaller errors than the absolute errors of a single measurement. Under standard usage, high internal thermal conductivity is guaranteed by use of a thermal conduction layer such as Cu. The systematic error in this case is an underestimate of true sample heat capacity by less than 2%. The simulation was extended to thermal conditions where a single time constant relaxation approximation cannot be used, specifically, for a sample with low thermal conductivity. Because of the highly precise geometry of these micromachined devices, a comparison between measured and simulated steady-state and time-dependent temperatures is demonstrated to allow extraction of the heat capacity and thermal conductivity of this sample with less uncertainty due to elimination of the Cu heat capacity.
Numerical study of collisional ripple diffusion in a tokamak plasma
Authors: Park Gunyoung , Chang C. S.
Published: September 2003

A comprehensive numerical study of collisional ripple diffusion of hot ions is performed based upon a well-established banana tip map in a tokamak plasma. New nonlinear resonances are found at inverse-integer harmonics, in addition to the well-known integer number harmonics. It is found that the new nonlinear resonances, when they exist in multiple harmonic numbers, significantly enhance the global collisional diffusion rate in the transition region between the collisional and stochastic diffusion regimes. Much below the stochastic diffusion regime, although the localized collisional ripple diffusion rate at isolated precessional resonances is found to be significantly faster than the previously known rates, its contribution to the radially averaged diffusion is negligible, to reproduce a previously known analytic rate [P. N. Yushmanov, Nucl. Fusion 23, 1599 (1983)]. A simple unified analytic formula to model collisional, transitional and stochastic ripple diffusion rates is suggested.
Dust-acoustic instability in inhomogeneous complex plasmas
Authors: Yaroshenko Victoria V. , Verheest Frank , Hellberg Manfred A.
Published: September 2003

Modification of the dust-acoustic mode in a weakly inhomogeneous plasma due to spatial gradients of dust charge, plasma densities, and a discharge electric field are considered. It is shown that the dust-acoustic mode can be subjected to a specific gradient instability, the criterion for which has been derived. It is possible that this instability explains experimentally observed spontaneous excitation of the dust density perturbations in laboratory complex plasmas.
Experimental studies of electrostatic confinement on the intense neutron source-electron device
Authors: Park J. , Nebel R. A. , Rellergert W. G. , Sekora M. D.
Published: September 2003

Theoretical works by Barnes and Nebel [R. A. Nebel and D. C. Barnes, Fusion Technol. 38, 28 (1998); D. C. Barnes and R. A. Nebel, Phys. Plasmas 5, 2498 (1998)] have suggested that a tiny oscillating ion cloud may undergo a self-similar collapse in a harmonic oscillator potential formed by a uniform electron background. By tuning the external radio-frequency electric fields to this naturally occurring mode, it is then possible to heat the ions to obtain very high densities and temperatures simultaneously during the collapse phase of the oscillation through adiabatic compression. However, a major uncertainty in this oscillating plasma scheme is the dynamics and stability of the background electrons in the virtual cathode. Recent work based on the electron fluid equations have demonstrated that the required electron cloud is susceptible to an instability that is analogous to the Rayleigh–Taylor mode present in fluid mechanics [R. A. Nebel and J. M. Finn, Phys. Plasmas 8, 1505 (2001)]. This paper describes an inertial electrostatic confinement device at Los Alamos National Laboratory that is being used to test the electron dynamics in a virtual cathode and will subsequently be used to verify this heating and compression scheme. Results from the device operation will be presented including the formation of deep potential wells and bifurcations in the potential equilibria. A simple model is used to explain this bifurcation.
Exact solutions of cylindrical and spherical dust ion acoustic waves
Authors: Sahu Biswajit , Roychoudhury Rajkumar
Published: September 2003

Cylindrical and spherical modified Korteweg–de Vries (KdV) equations are derived for dust ion acoustic waves. It is shown that a suitable coordinate transformation reduces the cylindrical KdV equation into the ordinary KdV equation which can be solved analytically. A completely different analytical solution is obtained using the group analysis method. However, for cylindrical and spherical modified KdV equations group analysis method yields trivial analytical solutions. Numerically, solutions to these modified KdV equations are obtained assuming initial profiles similar to those in one-dimensional soliton solutions.
Renormalization for the Harper equation for quadratic irrationals
Authors: Dalton J. , Mestel B. D.
Published: September 2003

In this paper, we use renormalization methods to study self-similarity in the fluctuations ηi of the Harper equation in the strong-coupling limit for quadratic irrationals of the form (a2+4−a)/2 for a∈N. Using the decimation method, we obtain a second-order functional recurrence which we prove rigorously has an entire fixed point. This fixed point governs the scaling of the fluctuations ηi in the strong-coupling limit.
Algebro–geometric constructions of the discrete Ablowitz–Ladik flows and applications
Authors: Geng Xianguo , Dai H. H. , Cao Cewen
Published: September 2003

Resorting to the finite-order expansion of the Lax matrix, the elliptic coordinates are introduced, from which the discrete Ablowitz–Ladik equations and the (2+1)-dimensional Toda lattice are decomposed into solvable ordinary differential equations. The straightening out of the continuous flow and the discrete flow is exactly given through the Abel–Jacobi coordinates. As an application, explicit quasiperiodic solutions for the (2+1)-dimensional Toda lattice are obtained.
General soliton matrices in the Riemann–Hilbert problem for integrable nonlinear equations
Authors: Shchesnovich Valery S. , Yang Jianke
Published: September 2003

We derive the soliton matrices corresponding to an arbitrary number of higher-order normal zeros for the matrix Riemann–Hilbert problem of arbitrary matrix dimension, thus giving the complete solution to the problem of higher-order solitons. Our soliton matrices explicitly give all higher-order multisoliton solutions to the nonlinear partial differential equations integrable through the matrix Riemann–Hilbert problem. We have applied these general results to the three-wave interaction system, and derived new classes of higher-order soliton and two-soliton solutions, in complement to those from our previous publication [Stud. Appl. Math. 110, 297 (2003)], where only the elementary higher-order zeros were considered. The higher-order solitons corresponding to nonelementary zeros generically describe the simultaneous breakup of a pumping wave (u3) into the other two components (u1 and u2) and merger of u1 and u2 waves into the pumping u3 wave. The two-soliton solutions corresponding to two simple zeros generically describe the breakup of the pumping u3 wave into the u1 and u2 components, and the reverse process. In the nongeneric cases, these two-soliton solutions could describe the elastic interaction of the u1 and u2 waves, thus reproducing previous results obtained by Zakharov and Manakov [Zh. Éksp. Teor. Fiz. 69, 1654 (1975)] and Kaup [Stud. Appl. Math. 55, 9 (1976)].
Ball lightning as a magnetostatic spherical force-free field plasmoid
Authors: Tsui K. H.
Published: September 2003

Ball lightning is regarded as a magnetostatic spherical force-free field plasmoid. The current carried by the conducting plasma is everywhere parallel to the magnetic field with the magnetic force being zero everywhere in the plasmoid. The plasma pressure is balanced by the surrounding atmospheric pressure. Although the magnetic field does not take part in pressure balance to determine the plasma equilibrium, it is responsible for confining the plasma by guiding the charged particles along the field lines. Such a configuration is the minimum energy state under the constraint of magnetic helicity conservation. Under the magnetic helicity constraint, the force-free magnetic field in a resistive glow plasmoid has to decay to a likewise force-free configuration. This inhibits the total magnetic field to be dissipated exponentially in one time constant, and restricts the overall magnetic decay to a path with a sequence of adiabatic small step force-free decays where one state differs very slightly to the neighboring state. Each small step magnetic decay is governed by a time constant which could add up to a total lifetime of many seconds.
Tuning the electron temperature of a nitrogen plasma by adding helium and argon
Authors: Ma Jie , Pu Yi-Kang
Published: September 2003

Using the global model and its concomitant profile shape factor and recent experimental ionization cross section, calculation of the electron temperature, Te, is carried out as a function of the mixing ratio in two-species N2/Ar and N2/He plasmas. The result is compared with measured values determined by the line-ratio technique in an inductively coupled plasma. The overall trend of the variation of the measured electron temperature is well described by the model: they agree in the N2/He plasma and the calculated Te becomes increasingly lower at higher argon partial pressure, up to ∼20% for a pure argon plasma. A second method uses an empirically determined profile shape factor for a pure nitrogen plasma and calculates the change of electron temperature due to the addition of inert gas. Except for the pure helium case, the difference between the measured and calculated value is <10% in the entire range of mixing ratio.
Electromagnetic transport components and sheared flows in drift-Alfvén turbulence
Authors: Naulin Volker
Published: September 2003

Results from three-dimensional numerical simulations of drift-Alfvén turbulence in a toroidal geometry with sheared magnetic field are presented. The simulations show a relation between self-generated poloidal shear flows and magnetic field perturbations. For large values of the plasma β we observe an increase of the transport if the viscous damping of the self-generated shear flows is absent. This behavior is in contrast to the standard argument that sheared flows suppress turbulence and transport via a decorrelation mechanism. An explanation of this behavior in terms of the transport related to magnetic flutter is proposed. The characteristics of the E×B flux are investigated using probability density distribution functions (PDFs). Although they are not Gaussian, no signs of algebraic tails in the PDFs are observed. The PDFs of the pointwise transport are found to agree well with a folded Gaussian, while the PDFs of the spatially averaged transport are in good agreement with an extreme value distribution.
High efficiency magneto-optical trap for unstable isotopes
Authors: Aubin S. , Gomez E. , Orozco L. A. , Sprouse G. D.
Published: September 2003

We have trapped over 250 000 Fr210 in a new on-line high efficiency magneto-optical trap (MOT). We describe the new apparatus and present an overview of high-efficiency MOTs for trapping rare isotopes. These traps depend on three critical components: a dry-film coating, a neutralizer, and the optical trap. We have developed a series of independent tests of the effectiveness of these components, and have used the results to construct our trap.
Probing microplatform for the study of biological adhesion forces
Authors: Whisman N. , York D. , Manning L. , Brant J. , Dyer R. , Childress A. , Marchand E. A. , Adams J. D.
Published: September 2003

A tool for the study of biological adhesion forces with the atomic force microscope (AFM) is introduced. The tool, a “microplatform,” can be functionalized with variety of specimens such as bacterial cells and used to study adhesion between the specimen and a surface. This tool is easily created using commercially available silicon AFM tips and an AFM, and can be customized in size to fit specific applications. Two custom fabricated microplatforms, ∼1 and ∼2.5 μm were tested. The method of microplatform fabrication, as well as adhesion force data between E. coli bacteria and a nanofiltration membrane is presented.
Laser induced fluorescence in Ar and He plasmas with a tunable diode laser
Authors: Boivin R. F. , Scime E. E.
Published: September 2003

A diode laser based laser induced fluorescence (LIF) diagnostic that uses an inexpensive diode laser system is described. This LIF diagnostic has been developed on the hot helicon experiment (HELIX) plasma device. The same diode laser is used to alternatively pump Ar II and He I transitions to obtain argon ion and atomic helium temperatures, respectively. The 1.5 MHz bandwidth diode laser has a Littrow external cavity with a mode-hop free tuning range up to 14 GHz (≈0.021 nm) and a total power output of about 12 mW. Wavelength scanning is achieved by varying the voltage on a piezoelectric controlled grating located within the laser cavity. The fluorescence radiation is monitored with a photomultiplier detector. A narrow band interference filter is used to eliminate all but the plasma radiation in the immediate vicinity of the fluorescence wavelength. Lock-in amplification is used to isolate the fluorescence signal from noise and electron-impact induced radiation. For the Ar ion, the laser tuned at 668.43 nm is used to pump the 3d 4F7/2 Ar II metastable level to the 4p 4D5/2 level. The 442.60 nm fluorescence radiation between the 4p 4D5/2 and the 4s 4P3/2 levels is captured by the photomultiplier tube. For atomic He, the laser is tuned at 667.82 nm to pump a fraction of the electron population from the 21P state to the 31D upper level. Although the 21P level is not a metastable, the close proximity of 21S metastable makes this new He I LIF scheme possible. In this scheme, a fraction of the laser-excited electrons undergo collisional excitation transfer from the 31D to the 31P level. In turn, the 31P state decays to the metastable 21S by emitting 501.57 nm fluorescence photons.
A simple submillimeter wave reflecting setup for open dielectric resonators excitation
Authors: Annino G. , Cassettari M. , Martinelli M. , van Bentum P. J. M.
Published: September 2003

A reflection configuration scheme is proposed and experimentally realized for the excitation of open dielectric resonators. Such configuration is based on the integration of a quasisingle mode dielectric waveguide with a nonradiative mirror. Insertion loss of about 1 dB and negligible stationary waves has been demonstrated around 190 GHz.
A magnetic diagnostic on Tore Supra
Authors: Moreau Ph. , Defrasne P. , Joffrin E. , Laurent F. Saint , Martin G.
Published: September 2003

A magnetic diagnostic has been installed in Tore Supra during the year 2000. It has been designed to be compatible with the configuration Composants Internes Et Limiteur (CIEL) requirements. It consists of a set of 424 dedicated magnetic sensors, pickup coils, and flux loops. The entire system is placed in the tokamak vacuum vessel at low pressure, high temperature, and is exposed to plasma radiation. The magnetic field is determined by attaching an analog integrator to each sensor. These electronic cards were developed for long pulse operation up to 1000 s. Finally the data are acquired by a system using the VME standard. The diagnostic has been successfully operated since the restart of Tore Supra with the CIEL configuration in September 2001. It has demonstrated the capability to control the plasma during discharges of several hundreds seconds and it participates to the physics program of the CIEL Project. The technology employed for the diagnostic achievement is robust, safe, and it can be extrapolated to other tokamaks.
A device for precision neutralization of electric charge of small drops using ionized air
Authors: Fan Sewan , Kim Peter C. , Lee Eric R. , Lee Irwin T. , Perl Martin L. , Rogers Howard , Loomba Dinesh
Published: September 2003

For use in our Millikan type liquid drop searches for fractional charge elementary particles we have developed a simple ionized air device for neutralizing a narrow stream of small drops. The neutralizer has been used for drops ranging in diameter from 10 to 25 μm. The width of the produced charge distribution is given by the Boltzmann equilibrium charge distribution and the mean of the distribution is set by a bias voltage. Using the bias voltage, the mean can be set with a precision of better than e, the electron charge. The use of the neutralizer is illustrated in an application to mineral oil drops produced with charges of the order of 1000e. We also show the interesting case of silicone oil drops that are produced in our drop generator with a charge distribution narrower than the Boltzmann equilibrium charge distribution, the charge distribution being broadened by the neutralizer.
A new type of fiber-optic-based interferometric ellipsometer for in situ and real-time measurements
Authors: Topcu S. , Chassagne L. , Alayli Y.
Published: September 2003

It is shown that it is possible to improve interferometric ellipsometers by using a Pockels cell or a Bragg cell hence avoiding the use of any moving components. Furthermore, these methods allow one to increase the beat frequency signal permitting a better insensitiveness to mechanical disturbances. It is also shown how to incorporate an optical fiber between the neutral beam splitter and the sample without losing any information concerning the ellipsometric angles of the sample. Several configurations are described and theoretically analyzed. The last ones do not contain any active component around the sample. They offer a new measurement technique for real-time and in situ measurements.
Pulsed corona generation using a diode-based pulsed power generator
Authors: Pemen A. J. M. , Grekhov I. V. , van Heesch E. J. M. , Yan K. , Nair S. A. , Korotkov S. V.
Published: September 2003

Pulsed plasma techniques serve a wide range of unconventional processes, such as gas and water processing, hydrogen production, and nanotechnology. Extending research on promising applications, such as pulsed corona processing, depends to a great extent on the availability of reliable, efficient and repetitive high-voltage pulsed power technology. Heavy-duty opening switches are the most critical components in high-voltage pulsed power systems with inductive energy storage. At the Ioffe Institute, an unconventional switching mechanism has been found, based on the fast recovery process in a diode. This article discusses the application of such a “drift-step-recovery-diode” for pulsed corona plasma generation. The principle of the diode-based nanosecond high-voltage generator will be discussed. The generator will be coupled to a corona reactor via a transmission-line transformer. The advantages of this concept, such as easy voltage transformation, load matching, switch protection and easy coupling with a dc bias voltage, will be discussed. The developed circuit is tested at both a resistive load and various corona reactors. Methods to optimize the energy transfer to a corona reactor have been evaluated. The impedance matching between the pulse generator and corona reactor can be significantly improved by using a dc bias voltage. At good matching, the corona energy increases and less energy reflects back to the generator. Matching can also be slightly improved by increasing the temperature in the corona reactor. More effective is to reduce the reactor pressure.
Blob stability and transport in the scrape-off-layer
Authors: D’Ippolito D. A. , Myra J. R.
Published: September 2003

High-density plasma filaments extended along the magnetic field, which look like “blobs” in the plane perpendicular to B, have been observed in the scrape-off-layer (SOL) of many plasma devices. These objects become polarized and subsequently E×B drift to the wall carrying a significant flux of particles. This mechanism may account for the observed nondiffusive, intermittent transport in the far SOL of tokamaks. Previous work has examined simple models of blob propagation and shown that the radial convective velocity ux has the scaling ux∝yb−2, where yb is the poloidal blob dimension. Thus, the radial particle flux is sensitive to the details of the blob size and shape distributions; these in turn are affected by various secondary instabilities which cause blob fragmentation. A simple model of blob instability (driven by curvature in the presence of sheath boundary conditions) is studied by 1D calculations and 2D simulations to provide insight on the stability and dynamics of blobs. It is shown that a competition between the time scales for instability and transport determines the range of allowed blob sizes and shapes and constrains the overall radial velocity.
Lyapunov function of relaxed states in two-fluid plasmas: Stability of double-Beltrami flows
Authors: Ohsaki Shuichi , Yoshida Zensho
Published: September 2003

A shear flow in a plasma brings about the non-Hermitian property, thereby invalidating the standard normal-mode analysis or energy principle for the study of stability. The Arnold method is an effective way to analyze the stability of a shear flow system. This method can give a Lyapunov stability condition to a relaxed state of two-dimensional flow or one-fluid magnetohydrodynamics (MHD). However, the Arnold method is not valid if the functional, whose first variation characterizes the relaxed (self-organized) state, is not a coercive (convex) form. Since the functional of the two-fluid MHD is not a coercive form, the stability analysis of such a flow requires a certain stronger (more coercive) constant, which corresponds to an enstrophy order constant. However, the enstrophy is not generally a constant. For a special class of two-fluid MHD flows, an enstrophy order constant can be found and a Lyapunov function that bounds the norm of all possible perturbations can be constructed.
Imaginary Killing spinors in Lorentzian geometry
Authors: Leitner Felipe
Published: September 2003

We study the geometric structure of Lorentzian spin manifolds, which admit imaginary Killing spinors. The discussion is based on the cone construction and a normal form classification of skew-adjoint operators in signature (2,n−2). Derived geometries include Brinkmann spaces, Lorentzian Einstein–Sasaki spaces and certain warped product structures. Exceptional cases with decomposable holonomy of the cone are possible.
A direct derivation of polynomial invariants from perturbative Chern–Simons gauge theory
Authors: Ochiai Tomoshiro
Published: September 2003

There have been several methods to show that the expectation values of Wilson loop operators in the SU(N) Chern–Simons gauge theory satisfy the HOMFLY skein relation. We shall give another method from the perturbative method of the SU(N) Chern–Simons gauge theory in the light-cone gauge, which is more direct than already known methods.
Supersymmetric extensions of the Harry Dym hierarchy
Authors: Brunelli J. C. , Das Ashok , Popowicz Ziemowit
Published: September 2003

We study the supersymmetric extensions of the Harry Dym hierarchy of equations. We obtain the susy-B extension, the doubly susy-B extension as well as the N=1 and the N=2 supersymmetric extensions for this system. The N=2 supersymmetric extension is particularly interesting, since it leads to new classical integrable systems in the bosonic limit. We prove the integrability of these systems through the bi-Hamiltonian formulation of integrable models and through the Lax description. We also discuss the supersymmetric extension of the Hunter–Zheng equation which belongs to the Harry Dym hierarchy of equations.
Baffled probe for real-time measurement of space potential in magnetized plasma
Authors: Demidov V. I. , Finnegan S. M. , Koepke M. E. , Reynolds E. W.
Published: September 2003

A probe for measurements of space potential in magnetized plasma is tested in a fully ionized, barium, Q-machine plasma. The probe consists of a tungsten wire tip, situated perpendicular to the magnetic field, that is partially shielded by ceramic baffles (masks). The probe works under the condition that the electron Larmor radius is much smaller than the probe radius, and that the ion Larmor radius is comparable to or larger than the probe radius. By rotating the baffle configuration around the probe tip, the ratio between the electron and ion probe current can be adjusted. The probe uses the same principles as Katsumata and plug probes [V. I. Demidov et al., Rev. Sci. Instrum. 73, 3409 (2002)], but has the advantage of convenient control of the ratio between the electron and ion current, and is not sensitive to uncertainties in the orientation of the probe tip relative to the direction of the magnetic field. Measurements of potential are made while the probe floats electrostatically. When saturated electron and ion currents have comparable magnitudes, accurate, real-time measurements of space potential can be acquired.