bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulation of the extraction from an electron cyclotron resonance ion source under the influence of space charge
Authors: Spädtke P.
Published: July 2002

The typical extracted particle density from an ion source of the electron cyclotron resonance (ECR) type has been increased during the last few years by several improvements: stronger magnetic fields, higher radio frequency, biased probes, mixing gas, afterglow mode, and other means. The extraction system remained unchanged in most cases, causing problems in beam quality because of the stronger space charge. Simulation of the extraction is helpful in understanding the physics, but a correct simulation requires a three-dimensional model. Whereas the geometry and the solenoidal component of the magnetic field is cylinder symmetric, the hexapole field determines indirectly the spatial distribution of the ions by Coulomb interaction between electrons and ions. The area where ions are started for the simulation depends therefore on the hexapole field strength. If higher energy electrons within the plasma are present, they should be included to describe the actual plasma boundary more precise. The measured charge state distribution should be used to define the real composition of the plasma. Using all these ingredients, an accel-decel extraction system has been investigated which should be able to handle higher ion currents as were available from ECR sources so far. It could be shown that the emittance of the extracted beam strongly depends on a good matching of the particle density within the plasma to the extraction field strength. Any nonlinearity of the fields causes emittance growth. Such a nonlinearity is produced by an azimuthal change in the location of the plasma boundary. Therefore, it would be highly desirable to decrease the hexapole field close to the plasma side of the extraction system. A much better beam quality would be achievable.
Contribution of the magnetic anisotropy of the stabilization layer to the thermal stability of synthetic ferrimagnetic media
Authors: Acharya B. Ramamurthy , Ajan Antony , Abarra E. Noel , Inomata Akihiro , Okamoto Iwao
Published: July 2002

A study is reported on synthetic ferrimagnetic media, which is made of an initial or stabilization magnetic layer (L1) closer to the substrate and a thicker top magnetic layer (L2) separated by a Ru spacer layer. The effects of the magnetic anisotropy (KU-L1) and the thickness (tL1) of the stabilization layer on the thermal stability of synthetic ferrimagnetic media are systematically studied. The magnetic anisotropy KU-L1 is varied by changing the Pt content of CoCrPtB alloy while a constant thickness and the same composition are retained for the L2. Media coercivity, stabilization factor KUV/kBT, and thermal stability increase as a function of tL1. For a particular tL1 value, these factors are improved for higher KU-L1, though the interlayer antiferromagnetic coupling strength is decreased due to compositional changes.
Cooling negative-ion beams
Authors: Liu Y. , Liang J. F. , Alton G. D. , Beene J. R. , Zhou Z. , Wollnik H.
Published: July 2002

Studies have been conducted to determine the feasibility of using the collisional cooling technique as a means of reducing energy spreads and emittances of sputter-generated negative-ion beams. A gas-filled rf-quadrupole ion cooler, equipped with provisions for decelerating ion beams to sufficiently low energies prior to cooling and reaccelerating them to high energies following the cooling process, has been designed and used to cool O− and F− ion beams with initial energy spreads, ΔE>10 eV to final energy spreads, ΔE∼2 eV full width half-maximum. Overall transmission efficiencies of ∼14% for F− beams have been obtained. Experimental results show that electron detachment is the major loss mechanism for negative ions.
Characteristics of an ion beam modification system with a linear ion source
Authors: Ide-Ektessabi Ari , Yasui Nobuto , Okuyama Daisuke
Published: July 2002

Characteristics of an ion beam surface modification system with a linear ion source are described in this article. The linear ion source is principally based on an anode layer thruster, which is generally referred to as “closed drift thruster.” The linear ion source has a slit type racetrack-shape extraction geometry. The spatial current distribution of the extracted ion beam has, therefore, a racetrack shape. Experiments were carried out for the discharge voltages ranging from 500 to 1500 V and ion doses ranging from 7.3×1013 to 8.2×1014 ions/cm2, using three kinds of ion species, namely, oxygen, nitrogen, and argon. Ion beam current density was uniform in the direction of the straight part of the extraction slit. Metalization of the surface modified polymers was also performed. To study the improvement of the adhesion of the metal films to the polymers, the peel-off tests were carried out on ion-irradiated polyimide-copper films. The results indicated that adhesion strength between polyimide and copper was improved as a result of the surface modification by the linear ion source.
Electron density and energy distribution function in the plume of a Hall-type thruster
Authors: Bacal M. , Pereslavtsev A. A. , Tanguy M. , Vodopyanov A. V.
Published: July 2002

The plasma of the thruster plume was studied with oriented plane probes (these probes have only one face exposed to the plasma, either to the thruster, or to the opposite direction). The electron energy distribution function (EEDF) was determined from the second derivative of the probe curent. The electron density and effective electron temperature were determined by the integration of the EEDF and radial profiles of these parameters are reported.
Simulation of the ion source extraction and low energy beam transport systems for the Spallation Neutron Source
Authors: Welton R. F. , Stockli M. P. , Boers J. E. , Rauniyar R. , Keller R. , Staples J. W. , Thomae R. W.
Published: July 2002

The ion source for the Spallation Neutron Source is a radio-frequency (rf) multi-cusp, volume-type H− source that is coupled to a rf quadrupole accelerator through a low energy beam transport (LEBT) system consisting of five electrostatic elements. To gain a deeper understanding of the operation of this system and to continue to refine the design, we have performed ion extraction and transport simulations using the computer code PBGUNS. A comparison is presented between simulation and the measured phase space of the beam for various values of LEBT electrode potentials. Both the emittance magnitude and orientation in phase space were found to be in reasonable agreement with measurement. A design study is also presented where the angle of the source outlet electrode has been optimized with the aid of PBGUNS simulations, resulting in a substantial reduction of the emittance.
Simultaneous measurement of spatially separated forces using a dual-cantilever resonance-based touch sensor
Authors: Phan Jack V. , Hocken Robert , Smith Stuart T. , Keanini Russell G.
Published: July 2002

A simple device for simultaneously measuring two spatially separated contact forces is described. The device uses a monolithic dual-cantilever touch sensor driven by a piezoelectric PZT actuator. A phase-locking method allows measurement of resonant frequency shifts at constant phase, based on the strain response of a second attached PZT. Calibration and force measurement procedures are developed to extract applied contact forces from the dual-cantilever’s coupled, nonlinear response. Based on a preliminary calibration, the present device exhibits maximum relative measurement error on the order of 6%. Procedures for reducing this error are described.
Chemical reactivity and phase behavior of NH4Cl by molecular dynamics simulations. I. Solid–solid and solid–fluid equilibria
Authors: Guillot Bertrand , Guissani Yves
Published: July 2002

To quantify the role played by the proton transfer reaction (NH4++Cl−⇔NH3+HCl) on the phase behavior of ammonium chloride (NH4Cl) we have developed a simple interaction potential (independent atom model) to implement in a molecular dynamics simulation (MD). In using one phase and two phase MD simulations, the solid–solid and solid–fluid coexistence lines have been located. When the proton transfer reaction is found to play no role in the stability and coexistence of the solid phases (ionic), the occurrence of covalent species (NH3, HCl) in the fluid phase has an important influence on the melting process and on the solid–fluid equilibria. In particular, a solid–fluid coexistence is found between a purely ionic solid and a fluid mixture composed of ionic and covalent species in nearly equal proportions.
Further development of the E-MEVVA ion source
Authors: Batalin V. A. , Bugaev A. S. , Gushenets V. I. , Hershcovitch A. , Johnson B. M. , Kolomiets A. A. , Kuibeda R. P. , Kulevoy T. V. , Oks E. M. , Pershin V. I. , Petrenko S. V. , Seleznev D. N. , Yushkov G. Yu.
Published: July 2002

We report detailed investigations of the electron-beam metal vapor vacuum-arc (E-MEVVA) ion source, which were performed jointly among the Institute for Theoretical and Experimental Physics, Moscow, Russia, the High Current Electronics Institute, Tomsk, Russia, and Brookhaven National Laboratory, USA. The experiments were performed in Moscow and Tomsk with nearly the same design of ion sources. Recently, the first successful ion charge states enhancement for this kind of ion source was demonstrated. This article presents comparisons of electron-beam effects and examines their influence on E-MEVVA performance. Substantial enhancement of high ion charge states enhancement was observed clearly in both experimental setups with two different methods of measuring the ion charge state distributions. These results can be considered as a proof of the E-MEVVA principle.
Ion depletion effects in sheath dynamics during plasma immersion ion implantation—models and data
Authors: Kellerman Peter L. , Qin Shu , Bradley Michael P. , Saadatmand Kourosh
Published: July 2002

In plasma immersion ion implantation, the wafer is negatively pulsed while immersed in a dc ambient plasma. During this high voltage pulse, the sheath expands, and plasma ions are accelerated to the wafer. The essential character of this plasma sheath expansion can be described by a simple mathematical model, first proposed by Lieberman. In this article, we build on Lieberman’s model, extending it to describe the ion current before and after the pulse. We find that a dip in ion current is predicted immediately after the pulse, due to the depletion of ions within the sheath. This simple model is tested using Faraday cup data, and is also compared to a particle-in-cell simulation.
Use of ion sources for nonsemiconductor surface modification (plenary)
Authors: Iwaki Masaya
Published: July 2002

At RIKEN, studies have been made on surface modification of metals, ceramics, and polymers using ion implantation in order to improve surface properties of various materials. For fundamental studies of surface modification, about 60 kinds of ions have been used as implanted elements, using rf-type, Nielsen-type, and hollow cathode-type ion sources. The Nielsen-type ion source has been the most useful for obtaining various ion species by modification to the evaporation oven and by selection of the source material. High current beams of some kinds of ions were obtained using Freeman-type or microwave-type ion sources. Ion beam modification with nonmass analyzed ions was investigated for practicable use of ion implantation. In this article, these ion sources are described, and their utilization in a variety of applications is reviewed. The improvement of the lifetime of tools by nitrogen implantation is introduced as a topic in the fields of nonsemiconductor materials, and several points for expansion of the field are emphasized. As a successful example in Japan, the dynamic mixing used in industry is introduced and ion sources are shown to be one of the technologically important factors. Plasma based ion implantation is compared with traditional surface finishing. Finally, the fabrication of small vascular grafts controlling cell adhesion is introduced as the applications of ion beams to biomedical materials.
Fusion energy science research progress (abstract)(plenary)
Authors: Logan B. G.
Published: July 2002

Following the withdrawal of the U.S. from the International Thermonuclear Experimental Reactor project, the U.S. Fusion Energy Science program has put increased emphasis on plasma science addressing the fundamental scientific issues facing the realization of fusion energy, with decreased emphasis on long-term fusion technology development, except for that which is needed to support near-term experiments. At the same time, the U.S. fusion program has broadened research from the nearly exclusive development of the Tokamak previously, to include now a variety of smaller-scale alternative fusion approaches, including more work on inertial fusion energy (primarily heavy-ion induction accelerators), Spheromaks, Spherical Tori, Stellerators, reversed field pinches, and field-reversed configurations. The largest U.S. Tokamak, the TFTR at PPPL, has been shut down after achieving over 10 MW of DT fusion power, and is now being decommissioned. The powerful TFTR neutral beams, including the ones that injected 120 keV tritium beams, have been decontaminated and stored for possible future use. One of the TFTR beamlines is being used to power the 1 MA National Spherical Torus Experiment (NSTX) located in what was the nearby TFTR hot-cell room. For heavy-ion fusion, the advent of 100 s, 100 TW table-top lasers has increased interest in using field ionization to achieve controlled levels of high-charge-state heavy ions.
Fast neutron radiography and trace element analysis: New application of electron cyclotron resonance ion sources (abstract)
Authors: Nakagawa T. , Kidera M. , Higurashi Y. , Kase M. , Yano Y.
Published: July 2002

We have started a new project, in which we have utilized an electron cyclotron resonance ion source (ECRIS) and a heavy ion linac for trace element analysis. This combination is expected to identify many kinds of trace elements simultaneously with very low background [very low detection limits (sub-pg/g) were attained by this method] without the pretreatment of a sample. This system is also applicable to fast neutron radiography, because it is possible to produce intense fast neutron beams. When we produce 100 μA of a Li beam from the ECRIS and use the nuclear reaction of H(Li,n)B at ∼2 MeV/u for production of neutrons, we can easily produce an intense focused fast neutron beam (∼2 MeV, 1010 particles/s). It has great advantages for neutron radiography. (1) We can minimize the background of the neutrons and gamma rays produced by the neutron-induced reaction, because the neutrons are emitted just at a forward angle. (2) Intense fast neutron beams can be easily produced. This kind of beam is very useful for fast neutron radiography. In this article, we present the experimental results of trace element analysis of several ceramic rods. We also present the basic idea of fast neutron radiography using this system and the planned experiment in detail.
The liquid–glass transition of silica
Authors: Coluzzi Barbara , Verrocchio Paolo
Published: July 2002

We studied the liquid–glass transition of SiO2 by means of replica theory, utilizing an effective pair potential which was proved to reproduce a few experimental features of silica. We found a finite critical temperature T0, where the system undergoes a phase transition related to replica symmetry breaking, in a region where experiments do not show any transition. The possible sources of this discrepancy are discussed.
Nonlinear stability analysis of viscoelastic Taylor–Couette flow in the presence of viscous heating
Authors: Al-Mubaiyedh U. A. , Sureshkumar R. , Khomami B.
Published: July 2002

Recently, based on a linear stability analysis we demonstrated the existence of a new thermoelastic mode of instability in the viscoelastic Taylor–Couette flow [Al-Mubaiyedh et al., Phys. Fluids 11, 3217 (1999); J. Rheol. 44, 1121 (2000)]. In this work, we use direct time-dependent simulations to examine the nonlinear evolution of finite amplitude disturbances arising as a result of this new mode of instability in the postcritical regime of purely elastic (i.e., Re=0), nonisothermal Taylor–Couette flow. Based on these simulations, it is shown that over a wide range of parameter space that includes the experimental conditions of White and Muller [Phys. Rev. Lett. 84, 5130 (2000)], the primary bifurcation is supercritical and leads to a stationary and axisymmetric toroidal flow pattern. Moreover, the onset time associated with the evolution of finite amplitude disturbances to the final state is comparable to the thermal diffusion time. These simulations are consistent with the experimental findings.
Crossed beam investigations of the reaction dynamics of O(3P) with allyl radical, C3H5
Authors: Kwon Han-Cheol , Park Jong-Ho , Lee Hohjai , Kim Hee-Kyung , Choi Young-Sang , Choi Jong-Ho
Published: July 2002

The reaction of ground-state atomic oxygen (O(3P)) with allyl radical (C3H5) was investigated in the crossed beam configuration. O(3P) and C3H5 were generated by the photodissociation of NO2 and the supersonic flash pyrolysis of allyl iodide, respectively. The nascent internal distributions of the OH(X2Π : v″=0,1) reaction product from the newly observed channel of O(3P)+C3H5→C3H4+OH were probed by laser induced fluorescence (LIF) spectroscopy. The distributions showed significant excitations with an unusual bimodal feature: the low and high rotational components without spin-orbit and Λ-doublet propensities in the ground and first excited vibrational states. On the basis of population analysis and comparison with the ab initio and statistical calculations, the experimental distributions are estimated to be totally non-statistical and suggest that the dynamics of the reaction might be described by two competing mechanisms: a major direct abstraction process and an indirect short-lived addition-complex forming process.
Coupled granular/continuous perpendicular recording media with soft magnetic underlayer
Authors: Sonobe Y. , Muraoka H. , Miura K. , Nakamura Y. , Takano K. , Do H. , Moser A. , Yen B. K. , Ikeda Y. , Supper N.
Published: July 2002

Fabrication, magnetic properties, and read/write characteristics of coupled granular/continuous (CGC) perpendicular media are described. The media consist of continuous Co/Pt multilayers, which have a strong in-plane exchange coupling, and a granular CoCrPt layer on top of a soft magnetic underlayer. These continuous and granular layers are magnetically coupled, thus the switching field distribution becomes effectively narrower. Recording measurements using a single-pole writer and a giant magnetoresistive reader show substantial improvement in the head output and resolution of the CGC medium, compared to the plain granular medium. Transition jitter and medium noise are reduced in the CGC media. As a result, the CGC media have 3–5 dB higher signal-to-noise ratio (SNR) and better thermal stability than the plain granular medium. The concept of CGC perpendicular media is a viable way to achieve both the thermal stability and medium SNR requirements for high-density recording.
Interface-related decrease of the permittivity in PbZrxTi1−xO3 thin films
Authors: Grossmann M. , Lohse O. , Bolten D. , Boettger U. , Schneller T. , Waser R.
Published: July 2002

In ferroelectric thin films, a decrease of the permittivity is observed obeying a logarithmic time dependence. In the literature, a similar effect has been reported for ferroelectric single crystals and ceramics, which is referred to as ferroelectric aging, and different models have been proposed to explain this phenomenon. In this letter, ferroelectric aging of PbZrxTi1−xO3 thin films is studied as a function of dopant types and concentrations as well as the temperature. The results clearly show that the traditional models for the aging mechanism of ferroelectric single crystals and ceramics are not applicable. Based on these results, a mechanism is proposed which explains the decrease of the dielectric constant in ferroelectric thin films by the growth of a thin surface layer with suppressed ferroelectric properties in the course of aging.
High-resolution neutron imaging of laser fusion targets using bubble detectors
Authors: Fisher R. K. , Stephens R. B. , Disdier L. , Bourgade J. L. , Rouyer A. , Jaanimagi P. A. , Sangster T. C. , Lerche R. A. , Izumi N.
Published: July 2002

The results of proof-of-principle neutron imaging experiments using bubble detectors are reported. Bubble detectors, which detect neutrons with a spatial resolution as small as 5 μ, were used to image the neutrons from laser-driven compressed deuterium–tritium target plasmas in OMEGA [Boehly et al., Opt. Commun. 133, 495 (1997)]. The results demonstrate that bubble detectors should revolutionize the design of coded aperture neutron imaging systems. Prospects for imaging target plasmas in the National Ignition Facility [Kilkenny et al., Rev. Sci. Instrum. 66, 288 (1995)] with 5 μ spatial resolution in the target plane appear excellent.
Dissociative electron attachment to molecules in the gas phase and in rare gas solids
Authors: Burrow P. D. , Aflatooni K.
Published: July 2002

Measurements of dissociative electron attachment (DEA) cross sections in chloroalkanes and chlorofluoromethanes have shown strong correlations between the peak DEA cross sections and the vertical attachment energies (VAEs) of these compounds. We explore the extent to which these gas phase data can be used to predict such cross sections for molecules embedded within or on the surface of a Kr solid. Effective VAEs are computed that include polarization of the solid by the anion and effects due to electron motion in the lattice. Comparisons are made with recent surface and bulk measurements and show good agreement for CF3Cl both within and on the surface. Satisfactory agreement is found for CH3Cl in the bulk but not on the surface.
Zero electron kinetic energy photoelectron spectroscopy and density functional calculations of Al–P(CH3)3 and Al–As(CH3)3
Authors: Li Shenggang , Rothschopf Gretchen K. , Yang Dong-Sheng
Published: July 2002

Aluminum-trimethylphosphine and trimethylarsine have been prepared by pulsed laser vaporization. Their electronic spectra have been obtained for the first time, using pulsed field ionization zero electron kinetic energy (ZEKE) photoelectron spectroscopy. The ZEKE spectra reveal the information about adiabatic ionization energies, intermolecular and ligand vibrations, and charge effects on molecular geometries. In coordination with the experimental measurements, density functional theory has been used to calculate equilibrium geometries, vibrational frequencies, and bond dissociation energies for the neutral and ionic complexes. The calculations predict that ionization causes the most significant geometry changes in the Al–P–C or Al–As–C angles, in agreement with the experimental observations. The aluminum ion and atom bind phosphorus more strongly than arsenic in these species.
Absolute reflectance measurements by a modified cavity phase-shift method
Authors: Mogg S. , Chitica N. , Plaine G. , Hammar M.
Published: July 2002

This article reports on a modified cavity phase-shift (CAPS) method for accurate and reliable characterization of high reflectance mirrors. Our approach relies on using a directly modulated Fabry–Pérot laser to circumvent the difficulties encountered in previous attempts with the CAPS method. The Fabry–Pérot laser diode ensures a constant coupling between the probe laser and test cavity modes. This results in a stable beam intensity transmitted through the test cavity allowing for accurate measurements of the phase shift from which the absolute reflectance can be determined. The experimental arrangement presented in this article is versatile and easy to use. The method is nondestructive and especially suited for the characterization of distributed Bragg reflectors (DBRs) employed in vertical-cavity optoelectronic devices. A premium feature of this method is its capability to probe a relatively small area of less than 1 mm which can be positioned anywhere across the surface of the wafer. We demonstrate the use of the method by measuring the absolute reflectance of metalorganic vapor-phase epitaxy grown AlAs/GaAs DBRs for 1.3 μm vertical-cavity lasers.
Detection of systematic errors in a measurement process using fuzzy set theory
Authors: Gao Y. , Xia X. , Wang Z. , Tao Z.
Published: July 2002

Detection of systematic errors is an important issue in the treatment of measurement data. Existing methods such as the t-detection method and the residual error method are based on the statistics theory that requires large sample sizes and known distributions. For small sample sizes and unknown distributions, these methods could become ineffective. To solve this problem, a new method is proposed to detect the systematic errors in a measurement process, based on fuzzy set theory. In the proposed method, the distribution of measured data may be unknown and the sampling size small. Mathematical models for systematic error detection are presented together with criteria for the detection. Results of the case studies show that the proposed method is effective and the proposed criteria are consistent in identifying monotonic and periodic systematic errors.
Grand canonical ensemble simulation studies of polydisperse fluids
Authors: Wilding Nigel B. , Sollich Peter
Published: July 2002

We describe a Monte Carlo scheme for simulating polydisperse fluids within the grand canonical ensemble. Given some polydisperse attribute σ, the state of the system is described by a density distribution ρ(σ) whose form is controlled by the imposed chemical potential distribution μ(σ). We detail how histogram extrapolation techniques can be employed to tune μ(σ) such as to traverse some particular desired path in the space of ρ(σ). The method is applied in simulations of size-disperse hard spheres with densities distributed according to Schulz and log-normal forms. In each case, the equation of state is obtained along the dilution line, i.e., the path along which the scale of ρ(σ) changes but not its shape. The results are compared with the moment-based expressions of Monsoori et al. [J. Chem. Phys. 54, 1523 (1971)] and Salacuse and Stell [J. Chem. Phys. 77, 3714 (1982)]. It is found that for high degrees of polydispersity, both expressions fail to give a quantitatively accurate description of the equation of state when the overall volume fraction is large.
Two-dimensional Rayleigh model for bubble evolution in soft tissue
Authors: Friedman Menahem , Strauss Moshe , Amendt Peter , London Richard A. , Glinsky Michael E.
Published: July 2002

The understanding of vapor bubble generation in a soft tissue near a fiber-optic tip has in the past required two-dimensional (2D) hydrodynamic simulations. For 1D spherical bubble expansions a simplified and useful Rayleigh-type model can be applied. For 2D bubble evolution, such a model has not been developed. In this work we develop a Rayleigh-type model for 2D bubble expansion that is much faster and simpler than 2D hydrodynamic simulations and can be applied toward the design and understanding of fiber-based medical therapies. The model is based on a flow potential representation of the hydrodynamic motion and is described by a Laplace equation with a moving boundary condition at the bubble surface. In order for the Rayleigh-type 2D model to approximate bubble evolution in soft tissue, we include viscosity and surface tension in the fluid description. We show that the 1D Rayleigh equation is a special case of our model. The Laplace equation is solved for each time step by a finite-element solver using a fast triangular unstructured mesh generator. Our simulations include features of bubble evolution as seen in experiments and are in good agreement with 2D hydrodynamic simulations.
Millimeter-wave two-dimensional imaging optical system for interferometer of the GAMMA 10 tandem mirror
Authors: Watabe K. , Oyama N. , Mase A. , Mizuno K.
Published: July 2002

A millimeter-wave optical system for plasma diagnostics for measuring the two-dimensional distribution of electron density in the Tsukuba GAMMA 10 tandem mirror has been developed. Two-dimensional images of plasma density of a cross-sectional area of 83 mm×67 mm in the machine axis direction were successfully measured with the optical system. The position at which the present imaging system is installed corresponds to the plug region, and the plasma radius is relatively narrow (less than 100 mm). Information about the density in the area is valuable in the study of confining-potential formation. This optical system was developed for a millimeter-wave phase-imaging interferometer and was designed with the ray tracing method to reduce aberration. It was evaluated experimentally by measuring images of point sources and phase images of dielectric targets. The receiving optical system from the plasma to detector array was designed with a spatial resolution of 28.7 mm and a magnification of 0.30. Ray tracing indicated that the transverse spherical aberration was 78% of the sampling interval of 5.0 mm on an image plane and that even for the worst image point the distortion was 10% of the sampling interval. In the design of the optical system for plasma diagnostics, the off-focus effect due to plasma size (plasma diameter: 200 mm) with electron density profile is proposed and considered.
Vacuum-compatible vibration isolation stack for an interferometric gravitational wave detector TAMA300
Authors: Takahashi R. , Kuwahara F. , Majorana E. , Barton Mark A. , Uchiyama T. , Kuroda K. , Araya A. , Arai K. , Takamori A. , Ando M. , Tsubono K. , Fukushima M. , Saito Y.
Published: July 2002

Interferometric gravitational wave detectors require a large degree of vibration isolation. For this purpose, a multilayer stack constructed of rubber and metal blocks is suitable, because it provides isolation in all degrees of freedom at once. In TAMA300, a 300 m interferometer in Japan, long-term dimensional stability and compatibility with an ultrahigh vacuum environment of about 10−6 Pa are also required. To keep the interferometer at its operating point despite ground strain and thermal drift of the isolation system, a thermal actuator was introduced. To prevent the high outgassing rate of the rubber from spoiling the vacuum, the rubber blocks were enclosed by gas-tight bellows. Using these techniques, we have successfully developed a three-layer stack which has a vibration isolation ratio of more than 103 at 300 Hz with control of drift and enough vacuum compatibility.
A note on the energy laws in gyrotropic plasmas
Authors: Hau L.-N.
Published: July 2002

Pressure or temperature anisotropy is an intrinsic characteristic of space plasmas, as is often indicated by satellite observation. A set of double-polytropic laws, d(p⊥n−1B1−γ⊥)/dt=0, d(p∥n−γ∥Bγ∥−1)/dt=0, has been proposed and shown to provide a viable closure to the earth’s magnetosheath plasmas. These equations in the limit of γ⊥=2, γ∥=3 and γ⊥=1, γ∥=1 describe the double-adiabatic and double-isothermal states, respectively. This paper gives an overview of the energy equations in gyrotropic plasmas and shows that the double-polytropic laws may be put into conservative forms conveniently implemented for numerical simulation and shock study. In addition, for ultrarelativistic gyrotropic plasmas, the energy equations may also be expressed in terms of the double-polytropic laws. In particular, a relationship of γu=(f+1)/f between the ratio of specific heats, γ, of ultrarelativistic plasmas and the degree of freedom of particles, f, may be established. As a result, for monatomic gas, γu,⊥=1.5 and γu,∥=2, in contrast to γ⊥=2, γ∥=3 for nonrelativistic case, for perpendicular and parallel motions with respect to the magnetic field.
Production of dry powder clots using a piezoelectric drop generator
Authors: Yashchuk Valeriy V. , Sushkov Alexander O. , Budker Dmitry , Lee Eric R. , Lee Irwin T. , Perl Martin L.
Published: July 2002

We have demonstrated that piezoelectrically driven, squeeze mode, tubular reservoir liquid drop generation, originally developed as a “drop-on-demand” method for ejection of microdrops of liquids or suspensions, can successfully operate with dry powder. Spherical silver powder with maximum particle diameter of 20 μm was loaded into and ejected from a 100 μm orifice glass dropper with a flat piezoelectric disk driver. Time of flight experiments were performed to optimize the dropper operation and to determine the size and velocity of the ejected particles. It was found that at certain values of the amplitude, duration, and repetition rate of the voltage pulses applied to the piezoelectric disk, one can eject powder clots of a stable size, comparable with the dropper orifice diameter. In contrast to the operation with a liquid, a clot is not ejected at each pulse, but quasiperiodically with an interval corresponding to thousands of pulses. The application for injection of atoms into helium buffer gas at cryogenic temperatures is discussed.
Molecules in high spin states: The millimeter and submillimeter spectrum of the MnS radical (X 6Σ+)
Authors: Thompsen J. M. , Brewster M. A. , Ziurys L. M.
Published: July 2002

The pure rotational spectrum of MnS (v=0) in its X 6Σ+ ground state has been recorded using millimeter and submillimeter direct absorption techniques in the range 160–502 GHz. MnS was synthesized in the gas phase by the reaction of manganese vapor and CS2 in a high-temperature Broida-type oven. Fourteen rotational transitions for this radical were measured, each consisting of six fine-structure components. In the lower rotational lines, hyperfine structure, arising from the Mn55 nuclear spin of 5/2, was also resolved in each spin component. These data were analyzed using a case (b) Hamiltonian, and rotational, fine structure, and hyperfine parameters determined for MnS. In the analysis, the third-order correction to the spin-rotation interaction, γS, and the fourth-order spin–spin coupling term, θ, were found necessary for an acceptable fit. The hyperfine constants determined suggest that MnS is more covalent than MnO, but more ionic than MnH. There additionally appears to be considerable sdσ hybridization in molecular orbital formation for this molecule. Bond lengths of the 3d transition-metal sulfides were compared as well, and those of MnS, CuS, and TiS do not follow the trend of their oxide analogs. This result indicates that there are significant bonding differences between transition-metal sulfides and transition-metal oxides.
Resonance fluorescence detection of mercury vapor in a supersonic jet
Authors: Tong Xiaomei , Barat Robert B. , Poulos Arthur T.
Published: July 2002

As resonance fluorescence at atmospheric pressure can be limited by collisional quenching and elastic scattering, supersonic jet spectroscopy is applied in this study to improve sensitivity for the detection of atomic mercury (Hg) vapor. The supersonic jet was produced by flowing argon test gas saturated with Hg vapor through a nozzle into a vacuum. The experiment used laser radiation at 253.7 nm to interrogate the jet. A photomultiplier tube and a boxcar gated integrator were used to detect and quantify the Hg resonance fluorescence. Time gating facilitated the extraction of the fluorescence signal from the elastic scattering background. From time dependent fluorescence signal data, the natural fluorescence lifetime of Hg (3P1→1S0) has been estimated at 112±8 ns. Fluorescence linearities with laser power and sample concentration were observed. Enhanced detection sensitivity was achieved due to the reduced collisional quenching of the fluorescence in the expanding jet. A detection limit of 3 parts per billion (by volume) for a 3 s data integration was established for Hg in argon. This study has shown that resonance fluorescence in a supersonic jet is a viable analytical tool for detection of low levels of Hg vapor.
Three-dimensional fluid simulation of a plasma display panel cell
Authors: Kim H. C. , Hur M. S. , Yang S. S. , Shin S. W. , Lee J. K.
Published: July 2002

In order to understand the discharge characteristics in an alternating current plasma display panel (ac PDP) and optimize it further, a three-dimensional fluid code (FL3P) has been developed. Using this simulator, various three-dimensional features of discharges are investigated in the sustain mode of PDP. First, the striations of wall charge are observed at both the anode and cathode side. Second, the local efficiency is obtained as a function of position. It is mainly divided into the anode region and the cathode region and highest near the anode center. Finally, the effects of various three-dimensional parameters are studied. As one of the examples showing the effect of electrode shaping, the discharge characteristics of a T-shaped electrode cell are compared with those of a conventional cell. The phosphor on barrier ribs contributes to over 44% of the total luminance, but barrier ribs themselves do not play an important role in the overall discharge efficiency. Address electrode width is not always proportional to the size of the discharge because of the wall loss of the particles to barrier ribs.
Parallel inhomogeneous flows in a thermally anisotropic plasma: The electrostatic ion-acoustic branch
Authors: Spangler Robert S. , Scime Earl E. , Ganguli Gurudas I.
Published: July 2002

The linearized dispersion relation describing waves in a plasma having a uniform magnetic field, uniform density, and inhomogeneous parallel (to the magnetic field) flow is generalized to include thermal anisotropy (Ti⊥/Ti∥), a key feature existing in many space and laboratory plasmas. The growth rate and the real frequency at which the maximum growth rate occurs for the ion acoustic mode increases with increasing Ti⊥/Ti∥. The propagation angle, with respect to the background magnetic field, for ion acoustic waves is shown to depend on Ti⊥/Ti∥. Also presented is a generalized calculation of experimentally relevant perturbed distribution functions to include shear in the field-aligned flow.
High pressure ultraviolet-visible-near infrared study of colored solid hydrogen sulfide
Authors: Kume T. , Fukaya Y. , Sasaki S. , Shimizu H.
Published: July 2002

Optical absorption measurements at high pressure were extended up to 5.5 eV in the ultraviolet region by constructing an ultraviolet-visible-near infrared absorption spectrometer adapted for diamond anvil cells and by using impurity free synthetic diamonds. Using the improved spectrometer, absorption spectra of solid hydrogen sulfide (H2S) were measured under various pressures from 0.3 to 29 GPa at room temperature. The band gap estimated from the absorption edge was 4.8 eV at 0.3 GPa and decreased to 2.7 eV at 29 GPa almost linearly except for a small jump at about 11 GPa corresponding to the phase transition to phase IV. At the same pressure, an Urbach tail responsible for the coloring of the solid H2S suddenly appeared. Raman signals excited with a green Ar ion laser (2.41 eV) were found to increase in intensity with pressure, which was explained by preresonance Raman effects induced by the decreasing of the gap energy near to the Raman excitation energy.
Conditions for ohmic electron injection at the Mg/Alq3 interface
Authors: Kiy M. , Biaggio I. , Koehler M. , Günter P.
Published: July 2002

We show that the contacts formed by magnesium on tris (8-hydroxyquinoline) aluminum (Alq3) are intrinsically ohmic when they are fabricated and operated in ultrahigh vacuum. Under the same conditions, the injected current shows a steep increase approximately proportional to the seventh power of the applied voltage that we assign to trap filling. Only a subsequent contact with oxygen leads to an injection-limited behavior, where the observed steep current increase is caused by potential barriers at the contacts. In addition, we observe that electron injection in oxidized structures can be very well described by Fowler–Nordheim tunneling in the case when electrons are injected from the magnesium (Mg) contact evaporated onto Alq3.
Chaotic capture of vortices by a moving body. I. The single point vortex case
Authors: Kadtke James B. , Novikov Evgeny A.
Published: July 2002

The study of the dynamical properties of vortex systems is an important and topical research area, and is becoming of ever increasing usefulness to a variety of physical applications. In this paper, we present a study of a model of a rotational singularity which obeys a logarithmic potential interacting with a bluff body in a uniform inviscid laminar flow, e.g., a line vortex interacting with a cylinder in three dimensions or a point vortex with a circular boundary in two dimensions. We show that this system is Hamiltonian and simple enough to be solved analytically for the stagnation points and separatrices of the flow, and a bifurcation diagram for the relevant parameters and classification of the various types of motion is given. We also show that, by introducing a periodic perturbation to the body, chaotic motion of the vortex can be readily generated, and we present analytic criteria for the generation of chaos using the Poincaré–Melnikov–Arnold method. This leads to an important dynamical effect for the model, i.e., that the possibility exists for the vortex to be chaotically captured around the body for periods of time which are extremely sensitive to initial conditions. The basic mechanism for this capture is due to the chaotic dynamics and is similar to that of other chaotic scattering phenomena. We show numerically that cases exist where the vortex can be captured around an elliptic point external to (and possibly far from) the body, and the existence of other very complicated motions are also demonstrated. Finally, generalizations of the problem of the vortex–body interaction are indicated, and some possible applications are postulated such as the interaction of line vortices with aircraft wings.
On stability and instability criteria for magnetohydrodynamics
Authors: Friedlander Susan , Vishik Misha M.
Published: July 2002

It is shown that for most, but not all, three-dimensional magnetohydrodynamic (MHD) equilibria the second variation of the energy is indefinite. Thus the class of such equilibria whose stability might be determined by the so-called Arnold criterion is very restricted. The converse question, namely conditions under which MHD equilibria will be unstable is considered in this paper. The following sufficient condition for linear instability in the Eulerian representation is presented: The maximal real part of the spectrum of the MHD equations linearized about an equilibrium state is bounded from below by the growth rate of an operator defined by a system of local partial differential equations (PDE). This instability criterion is applied to the case of axisymmetric toroidal equilibria. Sufficient conditions for instability, stronger than those previously known, are obtained for rotating MHD.
Stochastic resonance in thermally activated reactions: Application to biological ion channels
Authors: Bezrukov Sergey M. , Vodyanoy Igor
Published: July 2002

At the molecular level many thermally activated reactions can be viewed as Poisson trains of events whose instantaneous rates are defined by the reaction activation barrier height and an effective collision frequency. When the barrier height depends on an external parameter, variation in this parameter induces variation in the event rate. Extending our previous work, we offer a detailed theoretical analysis of signal transduction properties of these reactions considering the external parameter as an input signal and the train of resulting events as an output signal. The addition of noise to the system input facilitates signal transduction in two ways. First, for a linear relationship between the barrier height and the external parameter the output signal power grows exponentially with the mean square fluctuation of the noise. Second, for noise of a sufficiently high bandwidth, its addition increases output signal quality measured as the signal-to-noise ratio (SNR). The output SNR reaches a maximum at optimal noise intensity defined by the reaction sensitivity to the external parameter, reaction initial rate, and the noise bandwidth. We apply this theory to ion channels of excitable biological membranes. Based on classical results of Hodgkin and Huxley we show that open/closed transitions of voltage-gated ion channels can be treated as thermally activated reactions whose activation barriers change linearly with applied transmembrane voltage. As an experimental example we discuss our recent results obtained with polypeptide alamethicin incorporated into planar lipid bilayers.
Spectral softening through Compton scattering
Authors: Pereira N. R.
Published: July 2002

Flash bremsstrahlung with peak energy below 0.5 MeV can be obtained from multi-MeV electron beams by Compton backscatter from a material with low photoelectric absorption. The efficiency is low but interesting, about 30 krad per megajoule electron beam energy, irrespective of electron voltage from 3 to 10 MeV.
Influence of ionizing radiation on predamaged, amorphous SiO2
Authors: Devine R. A. B. , Fiori C.
Published: July 2002

The influence of low-energy (E∼5 eV per proton) ionizing radiation on predamaged, amorphous SiO2 has been studied through the electron spin resonance of oxygen vacancy centers (E′1). It is demonstrated that the observed line shapes can be explained in terms of dipolar broadening. By independent methods, line-shape fitting, and numerical integration, we extract the defect density as a function of low-energy irradiation dose and observe significant annealing for doses in excess of 10 J/cm2 accumulated. For medium-energy proton irradiations, contradictory results of line fitting and integration suggest the overall number of defects increases during proton irradiation but the mean defect density decreases (i.e., the defect-defect spacing increases). The fractional increase in defect numbers is much smaller than that found by others using 1-MeV electron irradiation.
Effect of alloy clustering on the high-temperature electron mobility in In1−xGaxAsyP1−y
Authors: Bhattacharya Pallab K. , Ku Joseph W.
Published: July 2002

Hall measurements on liquid phase epitaxial In1−xGaxAsyP1−y lattice matched to InP have been performed in the temperature range 300≤T(K)≤600 °C. The crystals were grown at 640 °C. Anomalous lowering of the mobility and carrier concentration has been observed at these temperatures for certain alloy compositions. It is believed that clustering due to miscibility gaps existing in these solid compositions is responsible for the observed data. Interpretations of the data based on this assumption have been made.
Raman microprobe study on temperature distribution during cw laser heating of silicon on sapphire
Authors: Yamada Masayoshi , Nambu Katsumi , Itoh Yutaka , Yamamoto Keiichi
Published: July 2002

For the first time Raman microprobe experiments have been made to measure the space-resolved temperature distribution induced in silicon-on-sapphire by a stationary elliptical Gaussian laser beam. The algorithm [J. Appl. Phys. 57, 965 (1985)] for solving the nonlinear heat equation in a two-layer structure has been also extended to include the temperature dependence of laser power absorbed besides the temperature dependencies of thermal conductivity and diffusivity. The problems involved in applying the numerical calculations to the experimental situation are discussed. The numerical calculations of temperature distributions based on the present algorithm are found to give a good agreement with the present Raman microprobe results.