bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of sheared toroidal rotation on ion temperature gradient turbulence and resistive kink stability in a large aspect ratio tokamak
Authors: Hobbs C. G. , House M. G. , Leboeuf J. N. , Dawson J. M. , Decyk V. K. , Kissick M. W. , Sydora R. D.
Published: July 2002

The effect of externally imposed sheared toroidal rotation on ion temperature gradient turbulence (ITG) and magnetohydrodynamic (MHD) stability in a large aspect ratio tokamak has been studied using nonlinear gyrokinetic particle-in-cell and linear reduced MHD computer calculations. Compared to sheared poloidal rotation, it is found that more sheared toroidal rotation is needed to reduce or suppress ITG turbulence and sheared toroidal rotation appears to always be linearly destabilizing for the paradigmatic resistive internal kink MHD mode studied.
Profile consistency of an elongated field-reversed configuration. II. Two-dimensional solutions
Authors: Barnes D. C.
Published: July 2002

An asymptotic theory of field-reversed configuration equilibrium, where the small expansion parameter is the square of the inverse elongation of the separatrix, was previously developed [D. C. Barnes, Phys. Plasmas 8, 4856 (2001)]. This theory is used to compute consistent pressure profiles which are then used to obtain two-dimensional solutions of the Grad–Shafranov equation. Solutions are obtained for a range of normalized separatrix radii, elongations, and shapes. These solutions confirm the predictions of the asymptotic theory. Elongations up to 25:1 are obtained, and the shape is shown to assume any previously specified value.
Strain-induced channel waveguiding in bulk sapphire substrates
Authors: Liu Mingjiao , Kim Hong Koo
Published: July 2002

We report on the two-dimensional confinement of light in the channel region of a bulk sapphire substrate, which was formed by utilizing the photoelastic effect in sapphire induced by a sputter-deposited SiO2 film. The experimental result, combined with the simulation results, shows that the sputter-deposited SiO2 films are compressively stressed up to 10 GPa level and that a 1.0-μm-thick film, for example, induces an index change of 5×10−3 in sapphire in the vertical direction. This amount of index change is found sufficient to support a fundamental mode at wavelengths of 1.54 μm or below.
Energy exchange in a stably stratified flow with laterally distorting duct
Authors: Iino J. , Van Atta C. W. , Keller K. H.
Published: July 2002

The long-time evolution of the grid-generated turbulence in a stably stratified air flow is investigated using a duct that has both a vertical contraction and a lateral expansion. Through this duct a Brunt–Väisälä frequency N increases, while a constant mean velocity U is maintained, so that a nondimensional buoyancy time (Nt/2π≈1.3) longer than any other previous wind tunnel experiments is obtained. Two complete cycles of the normalized vertical buoyancy flux −wθ¯/w′θ′ oscillation have been observed for the first time experimentally. The present experiments show that the period of the vertical buoyancy flux oscillation is independent of the initial conditions, Prandtl number, Froude number, and Reynolds number, showing that it is determined by the linear processes as described by rapid distortion theory. Initial anisotropy produced by the distorting duct also does not change this period. At a stratification with N⩽2.5 s−1, we found that the oscillation of the vertical buoyancy flux with the higher Reynolds number and the Froude number decays faster, which may be explained by the nonlinear effect. Combination of the strongest stratification (N=3.0 s−1) with the smallest mesh size (M=2.54 cm) gave an internal wave behavior which could be identified by the phase spectra of Phwθ≈90° and by the vertical buoyancy flux of −wθ¯≈0. The ratio of potential energy to vertical kinetic energy becomes about 0.8 at the most downstream measuring point. The effect of mean strain on the stratified turbulence is investigated by comparing the present experiment for laterally distorted flow with the previous experiments for the nondistorted or longitudinally distorted flow. Strong countergradient flux is observed in both the laterally and longitudinally distorted flows. We found that the maximum value of the ratio of potential energy to vertical kinetic energy of the distorted flow becomes three times as large as that of the nondistorted flow. The spectral analysis shows that this large ratio has a significant effect on the strong countergradient flux in the distorted flow.
Generation of full-dimensional potential energy surface of intramolecular hydrogen atom transfer in malonaldehyde and tunneling dynamics
Authors: Yagi Kiyoshi , Taketsugu Tetsuya , Hirao Kimihiko
Published: July 2002

The potential energy surface (PES) for the malonaldehyde intramolecular hydrogen atom transfer has been generated with full dimensionality by the modified Shepard interpolation method at the computational level of the second-order Møller–Plesset perturbation theory. The reference points have been set along the reaction path of H atom transfer (51 points), in a three-dimensional reaction space determined by geometrical features of the reaction path (219 points), and in the region of cis- and trans-enol isomerization reaction paths (428 points), so the resultant PES was generated in terms of ab initio data (energies, gradients, and Hessian matrices) of 698 reference points. Following trajectory simulations on the full-dimensional PES, the energy splitting of vibrational ground states due to tunneling was estimated by the semiclassical method of Makri and Miller [J. Chem. Phys. 91, 4026 (1989)]. The tunneling splitting was evaluated as 13.9 cm−1, which is in good agreement with the experimental value of 21.6 cm−1.
Is 9-acridinamine anion a dispersion-bound anion?
Authors: Skurski Piotr , Rak Janusz , Simons Jack
Published: July 2002

The possibility of electron binding to 9-acridinamine (9-AA) was studied at the second order Møller–Plesset perturbation theory level with the aug-cc-pVDZ basis set augmented with a diffuse 6s6p4d set that has proven appropriate in earlier studies of weakly bound anions. It was found that both the amino and imino tautomers of 9-AA bind an excess electron to form stable anions. The vertical electron attachment energies corresponding to the amino and imino form were calculated to be 20 and 41 cm−1, respectively. It was found that while the imino 9-AA tautomer forms a typical dipole-bound anion, the electron binding energy for the amino tautomer calculated at the electrostatic Koopmans’ theorem level appears to be cancelled when the correlation correction to the dipole moment of the neutral is taken into account at the MP2 level. Therefore, the stability of the latter anion may be caused only by additional electron correlation effects, which are dominated by dispersion interactions. For this reason, we suggest that this anion may be termed a dispersion-bound anion.
Spin-dependent tunnel junctions with ZrOx barriers
Authors: Wang Jianguo , Freitas P. P. , Snoeck E. , Wei P. , Soares J. C.
Published: July 2002

Spin-dependent tunnel junctions with crystalline ZrOx barriers were fabricated, with tunnel magnetoresistance (TMR) reaching 20% and a resistance×area product of 24 k Ω μm2, after annealing at 260 °C. Effective barrier height and thickness are 1.6 eV and 10.6 Å, respectively. The ZrOx barriers were fabricated by rf plasma oxidation of a 5 Å thick Zr layer. High-resolution transmission electron microscopy and Rutherford backscattering spectrometry were used to characterize the as-deposited barrier. Both ZrO and ZrO2 phases are present, together with (CoFe)Ox. Upon annealing, the interfacial oxygen moves into the barrier, resulting in an increase of TMR from 2% to 19.2%, an increase of barrier height from 0.3 to 1.6 eV, and a reduction of barrier thickness from 18.5 to 10.5 Å.
Liquid crystal dynamics in the isotropic phase
Authors: Gottke S. D. , Brace David D. , Cang Hu , Bagchi Biman , Fayer M. D.
Published: July 2002

The dynamics in the isotropic phase of the liquid crystal 1-isothiocyanato-(4-propylcyclohexyl) benzene (3-CHBT) are investigated from very short time (∼1 ps) to very long time (>100 ns) as function of temperature. The data decay exponentially only on the longest time scale (>10 ns). The temperature dependence of the long time scale exponential decays is described well by the Landau–de Gennes theory of the randomization of pseudo-nematic domains that exist in the isotropic phase of liquid crystals near the isotropic to nematic phase transition. Over the full range of times, the data are fit with a model function that contains a short time power law. The power law exponent is temperature independent over a wide range of temperatures. Integration of the function gives the empirical polarizability–polarizability (orientational) correlation function. A preliminary theoretical treatment of collective motions yields a correlation function that indicates that the data can decay as a power law at short times. The power law component of the decay reflects intradomain dynamics.
Hindered rotation of H2 adsorbed interstitially in nanotube bundles
Authors: Kostov M. K. , Cheng H. , Herman R. M. , Cole M. W. , Lewis J. C.
Published: July 2002

A theoretical study of the rotational dynamics of H2 molecules trapped in the interstitial channels of a carbon nanotube bundle is presented. The potential used in this study is modeled as a sum of atom–atom (C–H) van der Waals interactions and electrostatic interactions of the molecule with the surrounding nanotubes. The rotational energy spectra is calculated using a product wave function, where the coupling between translational and rotational modes is treated in a mean-field manner. A molecular dynamics simulation study was performed for estimating the hydrogen rotational barrier. Both theoretical calculations and simulation results reveal the existence of a large rotational barrier (∼40 meV). The consequences of this rotational barrier for the rotational energy levels are worked out in detail.
Scanning tunneling microscopy-controlled dynamic switching of single nanoparticle luminescence at room temperature
Authors: Silly Fabien , Gusev Alexander O. , Charra Fabrice , Taleb Abdelhafed , Pileni Marie-Paule
Published: July 2002

Room-temperature manipulation of a single nanoparticle with simultaneously recorded scanning-tunneling-microscope-induced light emission is presented. We show that the luminescence intensity of an individual nanoparticle can exhibit marked variations when it is moved into different sites. A nanosized bistable luminescence switch based on the tip-controlled positioning of a single nanoparticle was thus realized.
Experimental assessment of a new form of scaling law for near-wall turbulence
Authors: Jacob B. , Olivieri A. , Casciola C. M.
Published: July 2002

Scaling laws and intermittency in the wall region of a turbulent flow are addressed by analyzing data obtained by single component hot wire anemometry in the boundary layer of a flat plate at Reθ=2200. The article aims in particular at the experimental validation of a new form of refined similarity recently proposed for the shear dominated range of turbulence, where the classical Kolmogorov–Oboukhov inertial range theory is inappropriate. An approach inspired by the extended self-similarity allows for the extraction of the different power laws for the longitudinal structure functions at several wall normal distances. A double scaling regime is found in the logarithmic region, confirming previous experimental results. Approaching the wall, the scaling range corresponding to the classical cascade-dominated range tends to disappear and, in the buffer layer, a single power law is found to describe the available range of scales. The double scaling is shown to be associated with two different forms of refined similarity. The classical form holds below the shear scale Ls. The other, originally introduced on the basis of direct numerical simulation data for a turbulent channel, is experimentally confirmed to set up above Ls. Given the experimental difficulties in the evaluation of the instantaneous dissipation rate, some care is devoted to check that Taylor hypothesis and the one-dimensional surrogate do not bias the results. The increased intermittency as the wall is approached is experimentally found entirely consistent with the failure of the refined Kolmogorov–Oboukhov similarity and the establishment of its new form near the wall.
Bubble rising in an inclined channel
Authors: DeBisschop Kevin M. , Miksis Michael J. , Eckmann David M.
Published: July 2002

Here we investigate the dynamics of a gas bubble rising through an inclined channel in two dimensions. The fluids obey the Stokes equations and a boundary integral method is used to solve for the dynamics of the bubbles. Bubbles with and without an insoluble surfactant are considered. We study the dynamics of the bubbles as a function of the angle of inclination, the Bond number, and the other physical parameters of the problem. We find that for large enough Bond numbers a thread of liquid is formed on the bubble interface. We also find that for large enough angles of inclination, it is possible for the bubble to bounce along the top wall of the channel. Our computations are consistent with recent experimental results.
Effect of passivation and aging on the photoluminescence of silicon nanocrystals
Authors: Ledoux Gilles , Gong Jiong , Huisken Friedrich
Published: July 2002

Silicon nanocrystals were prepared by laser pyrolysis of silane in a gas flow reactor and deposited on substrates by cluster beam deposition. The evolution of the photoluminescence was measured as a function of the time the samples were exposed to air. With gradual air exposure and oxidation, the photoluminescence increases in intensity and its peak wavelength shifts to the blue. At the same time, the photoluminescence band becomes wider. To remove the oxide layer, the samples were exposed to hydrofluoric acid (HF) vapor. The HF attack has no influence on the band position but leads to a smaller width. The observations can be explained in terms of quantum confinement as the origin of the photoluminescence. Only for the smallest Si nanocrystals, an interface state seems to limit the maximum photoluminescence energy to 2.1 eV.
Film flow of a suspension of liquid drops
Authors: Li X. , Pozrikidis C.
Published: July 2002

The film flow of a two-dimensional suspension of neutrally buoyant liquid drops down an inclined plane wall is investigated by numerical simulation in the limit of vanishing Reynolds numbers. The results show that well-separated and solitary drops migrate toward an equilibrium position located between the free surface and the wall, for a broad range of the fluid physical properties and flow conditions. The precise location of the equilibrium position is determined by the ratio of the drop viscosity and the viscosity of the film fluid, and by the deformability of the drop interface and free surface expressed by the drop and free-surface capillary numbers. The motion of a periodic file of drops is found to be unstable to periodic perturbations whose amplitude exceeds a critical threshold. The instability leads to periodic accumulation of drops within bands developing in the streamwise direction. Large scale numerical simulations of dilute and concentrated random systems show that the drops spontaneously migrate toward the film interior, thereby causing the development of particle-free zones along the inclined wall and free surface. In contrast to the case of pressure-driven channel flow where peaks in the drop number density distribution are observed near both walls, in the case film flow a peak develops near the inclined plane but not near the free surface.
Experimental study of ion extraction from a 2.45 GHz electron cyclotron resonance multicharged ion source
Authors: Kato Yushi , Sugiyama Saori , Ishii Shigeyuki
Published: July 2002

Extraction and transport of multicharged ions have been experimentally investigated on a 2.45 GHz electron cyclotron resonance (ECR) source. The extractor consists of an electrode facing the ECR plasma (plasma electrode) and three cylindrical electrodes (E1–E3). The extractor is moved at several positions on the geometrical axis. The gap length between the plasma and E1 electrodes can be moved in vacuum while keeping gaps of the other electrodes constant. Characteristics of the total extraction current are investigated by a Faraday cup set just downstream at the extractor while simultaneously monitoring the currents flowing to electrodes and the drain in various experimental conditions. Several kinds of potential forms of the electrodes are investigated and the gap lengths are surveyed and optimized experimentally. The mass/charge spectrum of the extracted multicharged ion current is investigated by the Faraday cup set downstream at the sector magnet. The features of the extraction condition for the charge states are also investigated. After optimization in these procedures, the multicharged ion currents have been enhanced by 1 order of magnitude more than those in the previous experiments.
Experimental study of ion injection into an extended trap of the Brookhaven National Laboratory EBIS
Authors: Pikin A. , Alessi J. , Beebe E. , Kponou A. , Prelec K.
Published: July 2002

Experiments on the Brookhaven National Laboratory EBIS electron beam test stand (EBTS) with the ion trap extending beyond the edges of the superconducting solenoid had the main goal to study ion trap operation with a trap length exceeding that of the normal EBTS trap. Preliminary results indicate that the ion trap with a length of 107 cm is stable and controllable in the same fashion as our normal 70 cm trap with a multiampere electron beam. EBTS operation with ion trap 145 cm long and with electron current up to 3 A in earlier experiments also was stable and yielded more ions than from the basic “short” trap. These results increased our confidence in operation of the proposed RHIC in a stable mode and in the correctness of linear scaling of ion intensity with the length of the ion trap.
Progress report on EBIS devices in Frankfurt
Authors: Kleinod M. , Becker R. , Mücke M. , Zipfel B.
Published: July 2002

The crossover electron beam ion source (XEBIST) without confining magnetic field has made an important step towards higher electron beam energies. By proper matching using a magnetic lens system, a high compression of the electron beam has been achieved. The importance of reducing the lens aberrations by partial neutralization of the beam space charge in the lens section has been demonstrated. The effective current density in the trap region has been further increased by self-pinching in connection with space-charge neutralization. In our first experiments at an electron energy of 22 keV, the average current density in the trap increased from 10 to 150 A/cm2 at 40 ms neutralization time. Highly charged ions like Ar17+ were produced in this way. The combined Penning ion trap and electron beam source (PITEBIS) was operated successfully by radio-frequency modulating the current of the electron beam. This new kind of modulation could be used not only for cleaning EBIS sources from unwanted ion species but also to enhance the yield of highly charged ions by ion cooling. The effect of selective rf heating is demonstrated.
Further development of low noise vacuum arc ion source
Authors: Oks Efim , Yushkov George , Litovko Irina , Anders André , Brown Ian
Published: July 2002

Based on the idea of a space-charge-limited mode of operation, the influence of a pair of electrostatic meshes on the beam parameters of the Lawrence Berkeley National Laboratory MEVVA-5 ion source was investigated. The meshes were placed in the expansion zone of the vacuum arc plasma. Apart from reducing the level of beam current fluctuations, this mode of operation provides significant control over the ion charge state distribution of the extracted beam. These effects can be understood taking not only space charge but also the high-directed ion drift velocities, which are the same for different ion charge states of a material, into account. The results of simulations of the processes involved are in good agreement with the experimental results.
The plasma–vacuum transition in rf sources for negative hydrogen ions
Authors: Peters J.
Published: July 2002

An intensive study has been made at DESY of the transition region between the plasma and vacuum, the so-called sheath, of rf sources for negative hydrogen ions. The plasma and sheath have been analyzed with Langmuir probes even at extraction at 35 kV, with different geometric arrangements utilizing specially designed collars. Langmuir probes were installed in one of the collars. The use of a long ceramic insulated Langmuir probe made a three-dimensional analysis possible. The density, temperature, and potential of the plasma have been calculated based on these data. These studies have resulted in a better understanding of the transition region of not just rf sources but also of magnetron and Penning sources. Studies with a nine-ring collar made it possible to develop a design with a new method to dump the electrons and deliver an increased negative hydrogen current.
Photoelectron spectroscopy of Si2C3− and quantum chemistry of the linear Si2C3 cluster and its isomers
Authors: Duan Xiaofeng , Burggraf Larry W. , Weeks David E. , Davico Gustavo E. , Schwartz Rebecca L. , Lineberger W. Carl
Published: July 2002

The 364 nm photoelectron spectrum of Si2C3− is reported, together with high level ab initio calculations of the linear anion, and six linear and eight nonlinear structures of the neutral Si2C3. The adiabatic electron affinity of Si2C3, corresponding to the transition from the linear anion to the lowest electronic state of the linear singlet neutral, is found to be 1.766±0.012 eV. Theoretical results were essential for interpreting the spectrum. The level of theory necessary to accurately describe the electronic structure of Si2C3 cluster isomers is presented and discussed. Several vibration frequencies for the neutral linear structure are obtained from the spectra and compared to results from different levels of theory.
Domain configuration and crystal structure of Pb(Zn1/3Nb2/3)O3–5%PbTiO3 crystals as a function of the electric-field direction
Authors: Lee Jung-Kun , Yi Jae Yun , Hong Kug-Sun , Park Seung-Eek , Millan Jorge
Published: July 2002

The domain configuration of 0.95Pb(Zn1/3Nb2/3)O3–0.05PbTiO3 single crystals was investigated as a function of the applied electric-field direction with respect to the crystallographic orientation. A normal ferroelectric domain structure, which was not observable in virgin crystals (not exposed to electric field), appeared upon the electric-field (E-field) induced transition from the relaxor state to the normal ferroelectric state. After E-field was applied along the polar 〈111〉 direction and removed, a band-shaped domain configuration appeared as a result of subsequent depolarization. The depoled 〈111〉 crystal consisted of predominantly (110) domain boundaries, which represents the minimum energy domain state in rhombohedral ferroelectrics. In contrast, crystals must transform into the phase with the symmetry lower than rhombohedral, i.e., monoclinic structure, by an E-field application along 〈001〉. Domain boundaries in 〈001〉 poled crystals were indexed to be (001), being a favorable state for monoclinic ferroelectrics. The dependence of the domain configuration upon the E-field application direction could be explained using the relationship between the mechanical compatibility with respect to the ferroelectric strain and the crystal symmetry of a domain. The residual strain on domain boundaries in 〈001〉 crystals may inhibit crystals to recover the rhombohedral structure, resulting in a monoclinic ferroelectric crystal even upon the removal of the E-field.
Effect of the second-order anistropy constant on the transverse susceptibility of uniaxial ferromagnets
Authors: Spinu L. , Stancu Al. , O’Connor C. J. , Srikanth H.
Published: July 2002

A generalized theoretical approach of the transverse susceptibility, χT, in the case of uniaxial ferromagnets is presented. This advances the classical model of transverse susceptibility where only the first-order anisotropy constant, K1, is taken into account and makes possible the study of the influence of the second-order anisotropy constant, K2 on the χT curves. It is shown that additional Barkhausen jumps driven by higher-order anisotropy constants emerge more evidently in the field dependence of χT making their detection much easier than from the hysteresis loop. Based on the obtained results, we propose a simple method to determine both, K1 and K2 independently from χT experiments.
A slit-end extraction Penning ionization gauge ion source with a permanent magnet
Authors: Zhizhong Song , JinXiang Yu , Guocai Dong , Jun Zhang , Zhongyi Wang , Weijiang Zhao
Published: July 2002

A new slit-end extraction Penning ionization gauge ion source with a SmCo permanent magnet has been developed. The cathode is a 5 mm diam×25 mm long LaB6 cylinder, the anode with a hole of 8×32 mm is made in stainless steel, and the ion emission hole size on the anticathode is in a range of 14–28×2 mm for the different limited extraction current. The preliminary experiment indicated that the discharge was easy and smooth for this source. More than 10 mA of the total beam current for the positive oxygen ion has been measured at discharge current 200 mA and extraction voltage 25 kV and the milliampere magnitude of the negative oxygen ion beam can be extracted from this source.
High intensity ECR ion source (H+, D+, H−) developments at CEA/Saclay
Authors: Gobin R. , Beauvais P.-Y. , Bogard D. , Charruau G. , Delferrière O. , Menezes D. De , France A. , Ferdinand R. , Gauthier Y. , Harrault F. , Jannin J.-L. , Lagniel J.-M. , Leroy P.-A. , Mattéi P. , Sherman J. , Sinanna A. , Ausset P. , Bousson S. , Pottin B.
Published: July 2002

Source of light ions with high intensities The (SILHI) source has been producing proton beams since 1996. The first aim is to produce up to 100 mA cw beams at 95 keV for the injector of protons for high intensity demonstrator. This prototype is developed by a CEA/DSM–CNRS/IN2P3 collaboration for applications such as accelerator driven systems for nuclear waste transmutation, production of radioactive ion beams, or secondary particles. To measure installation reliability, continuous 5 day long runs have been performed. In October 1999, a 99.96% availability was achieved with a single short beam off and a 103 H uninterrupted beam. A new extraction system leads to lower beam losses and higher LEBT transparency. SILHI now produces a 95 keV–130 mA total beam with a proton fraction higher than 80%. Up to a 157 mA (247 mA/cm2) total cw beam has been extracted. The new EPICS control system, electromagnetic interference hardened devices and automatic control procedures now allow us to do longer runs. To analyze the reliability of these upgrades, a 4 week test was planned. In the framework of the International Fusion Material Irradiation Facility project CEA participation, 135 mA–95 kV deuteron pulsed beams were produced. Extraction simulations and recent SILHI results are also presented. In addition, a new test bench has been recently developed to analyze H− beam production.
Ab initio study of pressure effect on elastic properties of crystalline Au
Authors: Tsuchiya Taku , Kawamura Katsuyuki
Published: July 2002

Pressure dependence of elastic properties of crystalline Au is calculated based on the first-principles method within the local density approximation for the first time. The calculated equation of state agrees quite well with the results of previous high-pressure experiments. From the present study we find several unique features of the elasticity of Au as follows. (1) The calculated dependence of elastic constants on pressure supports the experiments demonstrating relatively smaller pressure derivatives. (2) The small tetragonal shear constant cs=(c11−c12)/2 in Au is remarkably insensitive to pressure, but elastic instability does not appear in the calculated pressure range. This feature is inferred to result from a small covalent nature in the chemical bonding in Au. (3) The elastic anisotropy increases with pressure. The normalized elastic constants considerably deviate from the ideal values and keep almost constant in wide volume variations.
N
2
and CO2 vibrational modes in solid nitrogen under pressure
Authors: McCluskey M. D. , Zhuravlev K. K.
Published: July 2002

Nitrogen has a complex phase diagram that has presented a formidable challenge to theoretical models. In this study, infrared (IR) spectroscopy has been performed on solid nitrogen at low temperatures and pressures up to 6 GPa. In the ε phase, two IR absorption peaks were observed that correspond to N–N stretch modes. The presence of two IR-active N2 vibrons is consistent with a tetragonal structure (P43212) and is inconsistent with an earlier proposed rhombohedral (R3̄C) structure. The matrix isolation of CO2 molecules in solid N2 led to the observation of transverse (ν2) vibrational modes, which showed a splitting consistent with the structures of the different N2 phases. The ν3 mode of CO212 and CO213 molecules was measured as a function of pressure, as well as combination modes. All the vibrational-mode frequencies shifted discontinuously at the critical pressures for N2 phase transitions. For CO2 concentrations of 0.1%, phase separation is present at low pressures, but is suppressed for pressures greater than 1 GPa. In summary, these studies have contributed to the knowledge of the N2 phase diagram and the nature of guest-host interactions in molecular systems.
Low-energy electron collisions with tetrafluoroethene, C2F4
Authors: Winstead C. , McKoy V.
Published: July 2002

We report calculated cross sections for elastic and inelastic collisions of low-energy electrons with tetrafluoroethene, C2F4. The elastic cross section shows a number of resonance features, which we classify according to symmetry and analyze in relation to available experimental data. Electron-impact excitation cross sections are obtained for the 1 3B1u (T) and 1 1B1u (V) states arising from the π→π* transition, as well as for eight other low-lying excited states arising from excitations out of the highest occupied molecular orbital. As expected, the T and V states make the largest individual contributions to electron-impact excitation at low energies; however, the other states are shown to contribute significantly to the total excitation cross section at impact energies from 10 to 25 eV.
A photon echo study of two-level systems in polyisobutylene under high pressure
Authors: Yamaguchi Masashi , McIntire Michael J. , Chronister Eric. L.
Published: July 2002

We report pressure (0–28 kbar) and temperature (1.1–4.3 K) dependent photon echo results for tetra-tert-butyl-terrylene (TBT) in a polyisobutylene (PIB) host. Increased pressure is found to increase the homogeneous dephasing rate over the temperature range of this study, in contrast to pressure dependent hole burning results reported for other polymer systems at somewhat higher temperatures (⩾4.2 K). A relatively small pressure increase (0 to 9 kbar) resulted in a change in the temperature dependence of the dephasing characterized by a lowering of the temperature power law exponent from ∼1.3 to ∼0.9. Further pressure increase above 9 kbar was characterized by an additional increase in the homogeneous dephasing rate without further change in the temperature exponent. The results are compared to high pressure photon echo studies of other polymer systems, and discussed in terms of the TLS (two-level-systems) model.
Extraction of highly charged Au ions from a multiampere electron beam EBIS at BNL
Authors: Beebe E. N. , Alessi J. G. , Gould O. , Graham D. , Kponou A. , Pikin A. , Prelec K. , Ritter J.
Published: July 2002

Excellent progress has been made in the operation of the Brookhaven National Laboratory electron beam ion source (EBIS), which is a prototype for an EBIS that could meet requirements for a RHIC preinjector. We have achieved very stable operation of the electron beam at 10 A through the EBIS trap. Ion injection of low charge gold ions from a low energy vacuum ion source [Brown et al., Rev. Sci. Instrum. 65, 1260 (1994)] and subsequent extraction of these ions with most probable charge state Au34+ has been demonstrated with electron beams up to 8 A. The total ion charge for gold measured on current transformer at the EBIS exit was 55 nC after a 30 ms confinement period. This corresponds to ∼85% of the theoretical ion trap capacity and exceeds our goal of 50% neutralization. The collected ion charge is proportional to the electron current and the gold charge state scales with the electron current density. Details of the EBIS configuration, total charge measurements, and time-of-flight spectra are given.
Development and operation of laser source of highly charged ions for ITEP terraWatt accumulator facility
Authors: Balabaev A. , Balanutsa V. , Kondrashev S. , Konukov K. , Lozhkin A. , Marchenko A. , Mescheryakov N. , Nikolaev V. , Savin S. , Sharkov B. , Shumshurov A. , Sydykov R. , Zahodnov E.
Published: July 2002

Laser ion source (LIS) is the most intense source of highly charged ions to fill the synchrotron rings in a single turn injection mode. For this reason LIS is used for ITEP TerraWatt Accumulator (TWAC) facility aiming at the production of TerraWatt power level (100 kJ/100 ns) of intense ion beams. Total current density, charge state distribution, and emittance of carbon ion beam generated by the 5 J/0.5 Hz rep-rate CO2 laser were measured at the exit of the source. A low energy beam transport line (LEBT) consisting of Einzel lenses and a buncher were used to match the source to 2 MV/2.5 MHz injector I-3. The C+4 ion beam with current up to 5 mA was accelerated by injector I–3 and about half of this amount have been injected into booster synchrotron. LIS was operated with rep-rate of 0.25 Hz during more than one year with few short breaks. Prolongation of intervention free period of LIS operation up to 3 months was achieved by using of CO2 laser gas mixture regeneration circuit.
A decaborane ion source for high current implantation
Authors: Perel Alex S. , Loizides William K. , Reynolds William E.
Published: July 2002

Progressive semiconductor device scaling in each technology node requires the formation of shallower junctions, and thus lower energy implants. The difficulties associated with extraction and transport of low energy beams often result in a loss in wafer throughput. Implantation of boron using the molecular compound decaborane has been found to allow for the shallow implantation of boron without a significant design change in the implanter. The decaborane molecule has 10 boron atoms and 14 hydrogen atoms. The implanted dose is ten times the electrical dose and the implanted depth is equivalent to the depth of a boron beam at 1/11th of the extraction energy. This advantage can only be exploited with an ion source that does not destroy the fragile molecule. We report on the design of an ion source capable of ionizing decaborane without significant fragmentation of the molecule. After it was shown that the decaborane molecule fragments above 350 °C an ion source was designed to prevent thermal dissociation of the molecule. Competitive boron dose rates were achieved using this source in a commercial high current implanter. In addition, evidence is shown that a decaborane dimer is formed in the ion source and can be implanted.
X-ray diffuse scattering of p-type porous silicon
Authors: Buttard D. , Bellet D. , Dolino G. , Baumbach T.
Published: July 2002

An x-ray diffuse scattering investigation of p-type porous silicon (PS) is reported. Synchrotron radiation and laboratory measurements of the x-ray diffuse scattering at small and large scattering wave-vector q values are presented. At small q values and for p−-type material, small isotropic crystallites of a few nanometers diameter are shown, whereas for p+-type material the main cylindrical crystallites are larger. At large q values the fine p+ PS structure is investigated and reveals the presence of small spherical crystallites around the main cylindrical crystallites. The elastic relaxation of silicon crystallites in the porous structure is also presented for oxidized and for as-formed samples, using reciprocal space maps. PS superlattice diffuse scattering is then observed. Finally, these results are discussed in relation to previous x-ray studies and other methods of structural observation.
Recent results from the low inductance Z-discharge metal vapor ion source
Authors: Debolt N. , Hershcovitch A. , Johnson B. M. , Rostoker N. , VanDrie A. , Wessel F.
Published: July 2002

The low inductance Z-discharge metal vapor (LIZ-MeV) ion source, which uses a magnetized Z-pinch, is a pseudo-spark device capable of producing intense currents (several kA) of highly charged gold or other ions. Typical operations produce an extracted charge-state distribution with a range in gold ion charge state from 4 to 19. Time-of-flight (TOF) spectra (excluding contributions from impurities) indicate that charge states at least as high as Au+12 were generated. Various TOF spectra are presented here to support this conclusion. Although the results are preliminary, LIZ-MeV shows great potential. Existing heavy-ion sources can produce either high beam currents, but low charge states (e.g., the metal-vapor vacuum arc) or high charge states, but low beam currents (e.g., the electron beam ion source). For ion beam injection our goal has been to develop an ion source that produces both high charge states and high beam currents. The existing LIZ-MeV has sufficiently large electron impact energies and electron current densities, but performance is limited by charge exchange with ambient gas and short confinement times. Plans are underway to add another Z-pinch stage to both lengthen confinement times and to minimize charge-state reducing processes. Such an enhanced LIZ-MeV should eventually produce even larger currents of more highly ionized heavy metal ions for accelerator applications.
rf ion source development for neutron generation and for material modification
Authors: Reijonen J. , Leung K. N. , Jones G.
Published: July 2002

rf driven multicusp ion sources have been successfully used in various different applications. Lately the Plasma and Ion Source Technology Group at Lawrence Berkeley National Laboratory has been developing a rf ion source for neutron production and a high current density cw-operated ion source for SIMOX (Separation by Implantation of Oxygen)-application. The group has developed a small ion source, which consists of a quartz plasma chamber, an external rf-antenna, an extraction electrode, and a target assembly, all in a tube that is approximately 25 cm in length and 5 cm in diameter. Another neutron generator currently under development is a multiaperture, high power generator. The neutron generator currently operates at 1% duty cycle, 80 kV, and 150 mA of deuterium beam. The neutron yield measured from the generator is 1.6×107 n/s. For oxygen implantation, the group has been developing a source which could provide a high percentage of O+ at high current density using cw operation. A dual-antenna has been developed for the source to ensure reliable long life operation. The development of these sources will be discussed in this article.
A high intensity dc H− source for low energy injection
Authors: Kuo T. , Baartman R. , Dutto G. , Hahto S. , Ärje J. , Liukkonen E.
Published: July 2002

While a 20 mA dc H− source system at 25–30 keV beam energy has been developed at TRIUMF several years ago, another recent demand on the system is to provide a 4 to 5 mA H− at the 4–6 keV energy range. We found that at this low energy range, the existing source/extraction system can only give ∼1 mA with poor emittance due to strong space-charge effect. Fortunately, a very special source/extraction mechanism together with the use of neutralization was discovered and developed to overcome this difficulty. Up to 4 mA with a normalized rms emittance of 0.15 π mm mr has been achieved at 6 keV. This performance finds its usefulness for injection systems where lower beam energy and higher beam intensity are required. A copy of the TRIUMF system was constructed and successfully tested in the summer of 2000 for the “H− Acceleration Project” for the K130 cyclotron at Jyväskylä University, Finland.
Alternative detection for angle-resolved photoemission spectrometer in ultraviolet range
Authors: Thomas J. , Pollini I.
Published: July 2002

An angle-resolved photoemission spectrometer for use in the vacuum ultraviolet range has been developed for spectra analysis. The apparatus incorporates a light source, a monochromator equipped with a toroidal grating, a focusing mirror, and hemispherical electron analyzer. We also present a novel method of electron detection which is based on a photon beam modulation mode, followed by analogical or numerical treatment of photoemission signal.
A design of an ECR ion source for radioactive ion beams for ISAC on-line facility at TRIUMF
Authors: Jayamanna K. , Yuan D. , Dombsky M. , Bricault P. , McDonald M. , Olivo M. , Schmor P. , Stanford G. , Vincent J. , Zyuzin A.
Published: July 2002

A 2.45 GHz ECR ion source for the ISAC on-line operation is being tested at the TRIUMF ion source test stand prior to its installation in the radioactive ion beam production target module. Steps were taken at the design stage to ensure short transient time and high ionization efficiency for single charged ions. Further considerations were given to radiation hardness, reliability, and remote handling capabilities. Transient time was measured using an ultrafast piezoelectric valve. Efficiencies were measured using calibrated gas leaks of stable and radioactive isotopes such as Xe127. This article describes the overall characteristics of the source.
Pulsed plasma accelerators of different gas ions for surface modification
Authors: Tereshin V. I. , Bandura A. N. , Bovda A. M. , Brown I. G. , Byrka O. V. , Chebotarev V. V. , Garkusha I. E. , Tortika A. S.
Published: July 2002

The pulsed coaxial plasma accelerator (PPA) was utilized in experiments discussed in this article. Plasma streams with ion energy up to 2 keV, plasma density (2–3)×1014 cm−3 and plasma energy density (5–40) J/cm−2 were generated. Such plasma was used for surface modification of different steels. Experimental results of improvement of metal surfaces physical properties under their irradiation by pulsed plasma streams are presented here. It was shown that microhardness of steel samples, both nonquenched and previously quenched, was increased several times under plasma treatment. Most attention was paid to improvement of wear and corrosion characteristics of the treated materials.
Ion source antenna development for the Spallation Neutron Source
Authors: Welton R. F. , Stockli M. P. , Kang Y. , Janney M. , Keller R. , Thomae R. W. , Schenkel T. , Shukla S.
Published: July 2002

The operational lifetime of a radio-frequency (rf) ion source is generally governed by the length of time the insulating structure protecting the antenna survives during exposure to the plasma. Coating the antenna with a thin layer of insulating material is a common means of extending the life of such antennas. When low-power/low-duty factor rf excitation is employed, antenna lifetimes of several hundred hours are typical. When high-power, >30 kW, and high-duty cycles, ∼6%, are employed, as is the case of the Spallation Neutron Source (SNS) ion source, antenna lifetime becomes unacceptably short. This work addresses this problem by first showing the results of microanalysis of failed antennas from the SNS ion source, developing a model of the damage mechanism based on plasma-insulator interaction, using the model to determine the dimensional and material properties of an ideal coating, and describing several approaches currently under way to develop a long-lived antenna for the SNS accelerator. These approaches include thermal spray coatings, optimized porcelain enamel coatings, refractory enamel coatings, and novel antenna geometries designed to operate with low rf electric fields.
The microhole and strip plate gas detector: Initial results
Authors: Veloso J. F. C. A. , Maia J. M. , Morgado R. E. , dos Santos J. M. F. , Conde C. A. N
Published: July 2002

We report the initial performance of an argon gas proportional counter consisting of a microstructure: the microhole and strip plate (MHSP). The MHSP combines desirable features of both a gas electron multiplier (GEM) and a microstrip plate (MSP) into a single integrated microstructure. Like the GEM, the MHSP is fabricated with flexible printed-circuit technology. As implemented, the MHSP provides two charge-amplification stages: slotted holes that function as a GEM, and microstrip anodes that also function as the charge-collection electrode. With two stages of amplification the microstrip can be operated with bias voltages well below the breakdown threshold. Results for the operation of the MHSP in argon are presented. A charge amplification factor of seven was achieved in the microholes with a maximum electron transmission approaching 100%. The measured energy resolution for 5.9 keV x rays was 30%. Future plans include the incorporation of a photocathode into the MHSP for applications as an ultraviolet photosensor.
A method for evaluating aberration in the crossover image in mask irradiation optics of electron beam
Authors: Sohda Yasunari , Ohta Hiroya , Saitou Norio
Published: July 2002

A method for evaluating aberration in the crossover image in a cell projection lithography system has been developed. In an electron-beam lithography system of projection-type such as a cell projection lithography system, the aberration in the crossover image causes the electron beam to pass off-axis in the electron optics. Optical simulation has quantitatively shown that the aberration in the crossover image causes an electron-beam blur and a positioning error on a writing sample. The evaluating method consists of four square apertures and a mark-detection function in a cell projection system. By measuring each position of the images of the four square apertures on the writing sample at difference focuses, the aberration can be calculated. The field curvature and the astigmatism in a cell projection system were evaluated by using this method. The field curvature agrees with the simulation. In addition, the measurement of the effect of beam alignment is also demonstrated. It is thus concluded that the method can effectively evaluate the aberration in the crossover image. This method is also useful for other projection-type lithographies of charged particles—like ion and electron beams.