bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulation of a positive column discharge with a one-dimensional radial radiation transport coupled particle-in-cell model
Authors: Lee Hae June , Verboncoeur J. P.
Published: July 2002

A one-dimensional radial slice of an Ar positive column discharge is simulated with a radiation transport coupled particle-in-cell model. The discharge is maintained by an axial current in the positive column which induces a self-consistent axial electric field. Power balance and radiation efficiency are investigated for variations of axial driving current Iz, gas pressure p, and radius R. The parameter regimes are from 0.1 to 1 cm for radius, 1 mTorr to 20 Torr for gas pressure, from 4 to 14 eV for electron temperature, from 1015 to 1017 m−3 for peak plasma density, and from 0.15 to 50 mA for axial current. The radiation efficiency is related to the product of the pressure and the radius, pR; it is restricted by the large wall loss for small pR and by the collisional quenching of the radiative state for large pR. The optimal value is about pR=1 Torr cm for this parameter regime.
Characterization of electron and negative ion densities in fluorocarbon containing inductively driven plasmas
Authors: Hebner G. A. , Abraham I. C.
Published: July 2002

Electron and negative ion densities were measured in inductively coupled discharges containing C4F8. In addition, the identity of the negative ions in C2F6, CHF3, and C4F8 containing discharges was investigated with a photodetachment experiment utilizing a microwave resonant cavity structure. To investigate the influence of surface material, the rf-biased electrode was covered with a silicon wafer or a fused silica (SiO2) wafer. Line-integrated electron density was determined using a microwave interferometer, and absolute negative ion densities in the center of the plasma were inferred using laser photodetachment spectroscopy. Voltage and current at the induction coil and rf-biased electrode were also measured for both surfaces as functions of induction coil power, pressure, and rf bias. For the range of induction powers, pressures, and bias power investigated, the electron density peaked at 6×1012 cm−2 (line integrated), or approximately 6×1011 cm−3. The negative ion density peaked at approximately 2.2×1011 cm−3. In most cases, the trends in the electron and negative ion densities were independent of the wafer material. However, a maximum in the negative ion density as a function of induction coil power was observed above a silicon wafer. The maximum is attributed to a power-dependent change in the density of one or more of the potential negative ion precursor species. A microwave resonant cavity structure was developed to identify the negative ions using laser photodetachment spectroscopy. The technique was demonstrated for inductively coupled discharges containing C4F8, C2F6, and CHF3. Scanning the laser wavelength over the range of the F− photodetachment energy indicated that while the dominant negative ion appeared to be F−, weak evidence for other molecular negative ions was observed. Unlike traditional microwave cavity techniques, this method offers the possibility of spatial resolution.
Effects of processing history on the modulus of silica xerogel films
Authors: Jain Anurag , Rogojevic Svetlana , Gill William N. , Plawsky Joel L. , Matthew Itty , Tomozawa Minoru , Simonyi Eva
Published: July 2002

Sintered xerogel films (porous SiO2) show a higher elastic modulus than other amorphous low dielectric constant (K) materials available for the same value of K. By comparing xerogels that were sintered, templated or made with ethylene glycol or ethanol as solvents, we show that process history is at least as important as the chemistry of the solid matrix or the porosity. The modulus extrapolated to zero porosity for the porous sintered and templated films is the same as those of the dense films made by chemical vapor deposition of SiO2. This suggests that the solid matrix for sintered xerogel films is close to ideal and their modulus is better because of the ordered arrangement of pores and fusion of particles making up the matrix. The modulus measured by nanoindentation on thick xerogel films (>0.8 μm) is well explained by the open cell foam model.
Magnetic study in amorphous Fe67Y33 alloy
Authors: Hassini A. , Bouhdada A. , Lassri H. , Krishnan R.
Published: July 2002

An amorphous Fe67Y33 alloy has been prepared by the melt-spinning method and its magnetic properties have been studied. The thermomagnetization curve is found to obey the Bloch law; spin wave stiffness constant D and the exchange constant A were calculated from the experimental results. From an analysis of the approach to saturation magnetization, the local random anisotropy constant KL has been extracted. A and KL are found to decrease with increasing temperature. Experimental data show that the ferromagnetic correlation Rf increases with increasing temperature.
Hyperspherical harmonics for tetraatomic systems
Authors: Wang Desheng , Kuppermann Aron
Published: July 2002

A recursion procedure for the analytical generation of hyperspherical harmonics for tetraatomic systems, in terms of row-orthonormal hyperspherical coordinates, is presented. Using this approach and an algebraic Mathematica program, these harmonics were obtained for values of the hyperangular momentum quantum number up to 30 (about 43.8 million of them). Their properties are presented and discussed. Since they are regular at the poles of the tetraatomic kinetic energy operator, are complete, and are not highly oscillatory, they constitute an excellent basis set for performing a partial wave expansion of the wave function of the corresponding Schrödinger equation in the strong interaction region of nuclear configuration space. This basis set is, in addition, numerically very efficient and should permit benchmark-quality calculations of state-to-state differential and integral cross sections for those systems.
Light-emitting nanostructures formed by intense, ultrafast electronic excitation in silicon (100)
Authors: Hamza Alex V. , Newman Micheal W. , Thielen Peter A. , Lee Howard W. H. , Schenkel Thomas , McDonald Joseph W. , Schneider Dieter H.
Published: July 2002

The intense, ultrafast electronic excitation of clean silicon (100)–(2×1) surfaces leads to the formation of silicon nanostructures embedded in silicon, which photoluminescence at ∼560 nm wavelength (∼2 eV band gap). The silicon surfaces were irradiated with slow, highly charged ions (e.g., Xe44+ and Au53+) to produce the electronic excitation. The observation of excitonic features in the luminescence is particularly unusual for silicon nanostructures. The temperature dependence and the measurement of the triplet–singlet splitting of the emission strongly support the excitonic assignment.
Generalized Weyl–Wigner map and Vey quantum mechanics
Authors: Dias Nuno Costa , Prata João Nuno
Published: July 2002

The Weyl–Wigner map yields the entire structure of Moyal quantum mechanics directly from the standard operator formulation. The covariant generalization of Moyal theory, also known as Vey quantum mechanics, was presented in the literature many years ago. However, a derivation of the formalism directly from standard operator quantum mechanics, clarifying the relation between the two formulations, is still missing. In this article we present a covariant generalization of the Weyl order prescription and of the Weyl–Wigner map and use them to derive Vey quantum mechanics directly from the standard operator formulation. The procedure displays some interesting features: it yields all the key ingredients and provides a more straightforward interpretation of the Vey theory including a direct implementation of unitary operator transformations as phase space coordinate transformations in the Vey idiom. These features are illustrated through a simple example.
High quality ZnO thin films grown by plasma enhanced chemical vapor deposition
Authors: Li B. S. , Liu Y. C. , Chu Z. S. , Shen D. Z. , Lu Y. M. , Zhang J. Y. , Fan X. W.
Published: July 2002

High quality ZnO thin films have been grown on a Si(100) substrate by plasma enhanced chemical vapor deposition using a zinc organic source [Zn(C2H5)2] and carbon dioxide (CO2) gas mixtures at the low temperature of 180 °C. The dependence of ZnO thin film quality on the gas flow rate ratio of Zn(C2H5)2 to CO2 (GFRRZC) is studied by using x-ray diffraction (XRD), optical absorption (OA) spectra, and cathodoluminescence (CL) spectra. High quality ZnO thin films with a c-axis-oriented wurtzite structure are obtained when the GFRRZC is 0.33. XRD shows that the full width at half maximum of (0002) ZnO located at 34.42° is about 0.2°. At room temperature, a pronounced free exciton absorption peak around 365 nm is clearly observed. Also, a strong free exciton emission without deep level defect emission is observed around 385 nm, and its temperature dependence is studied from the photoluminescence spectra. These observations indicate the formation of a high quality ZnO film. Additionally, nitridation of the Si surface caused by releasing NH3 plasma into the deposition chamber is an effective way to improve film quality.
New cohomology ring for supermanifolds
Authors: Varsaie S.
Published: July 2002

In this paper the concept of pesudodifferential forms on supermanifolds is extended and a new complex is introduced. At last it is shown that the corresponding cohomology ring is sensitive to “super” structure.
Room temperature ferromagnetic properties of (Ga, Mn)N
Authors: Reed M. L. , El-Masry N. A. , Stadelmaier H. H. , Ritums M. K. , Reed M. J. , Parker C. A. , Roberts J. C. , Bedair S. M.
Published: July 2002

Dilute magnetic semiconductor GaN with a Curie temperature above room temperature has been achieved by manganese doping. By varying the growth and annealing conditions of Mn-doped GaN we have identified Curie temperatures in the range of 228–370 K. These Mn-doped GaN films have ferromagnetic behavior with hysteresis curves showing a coercivity of 100–500 Oe. Structure characterization by x-ray diffraction and transmission electron microscopy indicated that the ferromagnetic properties are not a result of secondary magnetic phases.
Lorentz invariant Lagrangians
Authors: Teleman Kostake
Published: July 2002

The aim of this article is to study certain Lorentz invariant Lagrangians. The first of these Lagrangians could be related to a particle of spin 12 moving in a particular Yang–Mills gauge field. The second Lagrangian is related to the relativistic Newton–Coulomb problem. For each of these Lagrangians, we write the corresponding wave equations and determine the negative energy levels. The article concludes with the construction of a class of Lagrangians associated with pairs of particles, one of which has zero mass.
Adsorption of a fluid in an aerogel: Integral equation approach
Authors: Krakoviack V. , Kierlik E. , Rosinberg M.-L. , Tarjus G.
Published: July 2002

We present a theoretical study of the phase diagram and the structure of a fluid adsorbed in high-porosity aerogels by means of an integral-equation approach combined with the replica formalism. To simulate a realistic gel environment, we use an aerogel structure factor obtained from an off-lattice diffusion-limited cluster–cluster aggregation process. The predictions of the theory are in qualitative agreement with the experimental results, showing a substantial narrowing of the gas–liquid coexistence curve (compared to that of the bulk fluid), associated with weak changes in the critical density and temperature. The influence of the aerogel structure (nontrivial short-range correlations due to connectedness, long-range fractal behavior of the silica strands) is shown to be important at low fluid densities.
On solitons with nonminimally coupled scalar fields
Authors: Castellani O. C. , Oliveira H. P. de
Published: July 2002

A nonsingular static and spherically symmetric space–time endowed with nonminimally coupled scalar field described by the action S=∫d4 x (−g/2)(R−gαβφ,α φ,β−ξ R φ2) is presented for the case in which the coupling parameter ξ>1/6. This solitonlike space–time is obtained using the technique of conformal transformation that associates solutions produced by ordinary scalar fields in general relativity with those with nonminimally coupled scalar fields. The dynamical stability of the solution is examined through the Galerkin method.
The global finite structure of generic envelope loci for Hamilton–Jacobi equations
Authors: Cardin Franco
Published: July 2002

We discuss in some detail the existence of global generating functions describing Lagrangian submanifolds connected with evolution problems for Hamilton–Jacobi (H–J) equations. First, we produce a physical application of a result by Viterbo: for generic (in a suitable sense) Hamiltonian functions and initial data, the envelopes, i.e., the wave front sets, related to Hamilton–Jacobi problems are globally finitely generated. Furthermore, we show how to compute global space–time generating functions with finite parameters for geometric solutions of a H–J equation of the evolution kind.
Collision-induced absorption in the ν2 fundamental band of CH4. II. Dependence on the perturber gas
Authors: Hartmann J. M. , Brodbeck C. , Flaud P.-M. , Tipping R. H. , Brown Alex , Ma Q. , Liévin J.
Published: July 2002

The integrated intensities of the collision-induced enhancement spectra of the ν2 band of CH4 perturbed by rare gases and linear molecules (N2, H2, and CO2) are calculated theoretically using the quadrupole transition moment obtained from an analysis of CH4–Ar spectra. In addition to the isotropic quadrupole mechanism responsible for the enhancement in CH4-rare gases, there is additional absorption arising from the anisotropic quadrupole mechanism in the case of molecular perturbers. This latter effect involves the matrix element of the anisotropic polarizability for the ν2 transition in CH4 that is available from the analysis of the depolarized Raman intensity measurements. Overall, the theoretical values for the slope of the enhancement spectra with respect to the perturber density are in reasonably good agreement with the experimental results, thus confirming that the collision-induced absorption arises primarily through the quadrupolar induction mechanism.
Subharmonic projections for a quantum Markov semigroup
Authors: Fagnola Franco , Rebolledo Rolando
Published: July 2002

This article introduces a concept of subharmonic projections for a quantum Markov semigroup, in view of characterizing the support projection of a stationary state in terms of the semigroup generator. These results, together with those of our previous article [J. Math. Phys. 42, 1296 (2001)], lead to a method for proving the existence of faithful stationary states. This is often crucial in the analysis of ergodic properties of quantum Markov semigroups. The method is illustrated by applications to physical models.
Spectroscopic properties of Yb-doped silica glass
Authors: Lu K. , Dutta N. K.
Published: July 2002

We have carried out a systematic study of optical emission in Yb-doped fiber glass materials which can be used for fiber laser applications. The stimulated emission crosssections of these materials have been calculated. The wavelength dependence of emission of these materials has been studied. The peak emission cross section in Yb-doped silica glass is 2.6 pm2 and the peak wavelength is at 974 nm. The codopants do not significantly alter the emission cross section or the peak wavelength of this cross section.
Phase-separation dynamics of a ternary mixture coupled with reversible chemical reaction
Authors: Tong Chaohui , Yang Yuliang
Published: July 2002

The phase-separation dynamics of a ternary mixture (A, B and C) coupled with a reversible chemical reaction between the two constituents A and B is presented. It is demonstrated that the free-energy functional form of time-dependent-Ginzburg-Landau equation describing the phase-separation dynamics of the ternary mixture coupled with a reversible chemical reaction is similar to that of the mixture composed of a block copolymer and a homopolymer. Our simulation study reveals that for the case of equal forward and backward reaction rates, the lamellar thickness scales with the reaction rate constant as a single power law λL∼Γ−0.22, regardless of high or low reaction rate regimes. This study sheds insight to the unique features of the involvement of chemical reaction in the phase separation of the ternary mixture. If chemical reaction and phase separation take place simultaneously, the different pattern evolutions at high and low reaction rate constants are originated from the balance between the domain coarsening due to phase separation and the breakup of the continuous phase due to the chemical conversion. The different pattern evolution at high and low reaction rate constants when chemical reaction lags behind phase separation can be interpreted in terms of the discrepancy between the domain sizes at the time step immediately before the turning on of the chemical reaction and the inherent lamellar thickness. It is also pointed out that the crossover of the ternary mixture from one phase region to another, due to the concentration change between A and B, might generate interesting steady-state domain patterns.
Effect of plasma chamber surface for production of highly charged ions from ECRIS
Authors: Kidera M. , Nakagawa T. , Higurashi Y. , Kase M. , Yano Y.
Published: July 2002

The effect of the surface of Al2O3 on the beam intensity of highly charged Ar ions is described. To investigate this effect clearly, we directly plated the surface with 20 μm Al2O3 of the Al cylinder (Al2O3 plating method). This cylinder was inserted into the plasma chamber and it covered its inner wall of. We then measured the beam intensity of highly charged Ar ions carefully. By comparing the beam intensity using the Al2O3 plating method and the Al cylinder, it is confirmed that the Al2O3 surface is very effective in increasing the beam intensity of highly charged heavy ions. The best result of 290 eμA of Ar11+ was obtained by using this method.
Tubular electron beam ion source
Authors: Donets E. D. , Donets E. E. , Donets D. E.
Published: July 2002

Electron beam ion sources (EBISs) provide the highest charge states of ion produced, high pulse ion currents, and a good emittance of an ion beam but an average ion current usually less than that for other sources of highly charged ions, for example, electron cyclotron resonance. The reason for that is an unusually small volume of electron–ion interaction, which is limited by the acceptable length of the source and by the electron beam perveance. To overcome the last limit while conserving all the advantages of the EBIS mentioned, the general idea of a tubular electron beam ion source (TEBIS) with an off-axis ion extraction is proposed. Construction of a TEBIS and its use in the normal or in the reflex mode of operation could increase an EBIS ion output 100–1000 times. The configuration of TEBIS and the current status of its development is described.
Magnetic-field configuration fitted to the microwave ion-source plasma
Authors: Sakudo Noriyuki , Ito Hiroyuki , Matsunaga Yasuhiko , Hayashi Keiji , Miyamoto Atsushi , Tazaki Yoshiaki
Published: July 2002

Microwave ion sources for implantation have many advantages, such as the long life of source operation and the cleanliness of extracted beam, over the traditional dc-arc-discharge-type ion sources. We reported that optimizing the plasma-chamber structure made the microwave source exceed most of traditional dc-arc-discharge sources in extracted-ion currents of most species that are used for fabricating modern ultralarge scale integrations. After studying the source magnetic field in detail by computer simulation, the relationship between the magnetic-field profile and the plasma-chamber structure is found to be essential. Two-dimensional analysis is carried out since the plasma is generated between parallel plate electrodes. The optimum chamber structure with which the maximum current was obtained in the last beam-extraction experiments is shown to contain the major magnetic field that is focused by the iron pole pieces. Most of the magnetic-field lines that are crossing the region where ions are first generated do not disappear into the sidewalls of the chamber. Since the lifetimes of ions become longer, the plasma density increases.
Development of an H− ion source for the high intensity proton linac
Authors: Oguri H. , Okumura Y. , Hasegawa K. , Namekawa Y. , Shimooka T.
Published: July 2002

A volume production type negative ion source is under development for a high intensity proton linear accelerator. The source plasma is produced by an arc discharge using tungsten filaments. The cesium vapor was introduced into the plasma chamber by using an oven. The beam extractor consists of three electrodes with a single aperture of 8 mm in diameter. Negative ion current of 72 mA was achieved at the arc discharged power of 56 kW. The emittance measurement indicated that normalized emittances were 0.13 (horizontal plane) and 0.15 (vertical plane) π mm mrad at 70 keV and 60 mA.
A robust miniature acoustical liquid level gauge with micrometer resolution
Authors: Donlagić Denis
Published: July 2002

This paper presents concept and design of a miniature liquid level gauge. An experimental level gauge with the measurement range of 5 cm, relative accuracy better than 0.5% and resolution better than 0.1%, has been demonstrated in practice. The proposed gauge proves to be robust in terms of jams, foams, deposits, residues, etc. In addition, the system uses relatively simple and potentially low cost design. Therefore, the proposed measurement system can be used independently or as a part of scientific, chemical, biomedical, industrial, or similar instrumentation.
Patterned growth of single-walled carbon nanotubes on full 4-inch wafers
Authors: Franklin Nathan R. , Li Yiming , Chen Robert J. , Javey Ali , Dai Hongjie
Published: July 2002

Patterned growth of single-walled carbon nanotubes (SWNTs) is achieved on full 4-in. SiO2/Si wafers. Catalytic islands with high uniformity over the entire wafer are obtained by a deep ultraviolet photolithography technique. Growth by chemical vapor deposition of methane is found to be very sensitive to the amount of H2 co-flow. Understanding of the chemistry enables the growth of high quality SWNTs from massive arrays (107–108) of well-defined surface sites. The scale up in patterned nanotube growth shall pave the way to large-scale molecular wire devices.
rf gas plasma source development for heavy ion fusion
Authors: Ahle L. , Hall R. P. , Molvik A. W. , Kwan J. W. , Leung K. N.
Published: July 2002

Presently the Heavy Ion Fusion Virtual National Laboratory is researching ion sources and injector concepts to understand how to optimize beam brightness over a range of currents (50–2000 mA argon equivalent). One concept initially accelerates millimeter size, milliamp beamlets to 1 MeV before merging them into centimeter size, ampere beams. Computer simulations have shown the final brightness of the merged beams is dominated by the emittance growth of the merging process, as long as the beamlets’ ion temperature is below a few electron volts. Thus, a radio frequency multicusp source capable of high current density can produce beams with better brightness compared to ones extracted from a colder source with a large aperture and lower current density. Initial experiments with such a source have successfully demonstrated simultaneously high current density, ∼100 mA/cm2, and fast turn on, ∼1 μs. Results from these experiments are presented as well as progress and plans for the next set of experiments for these sources.
Low cost upgrade of 6.4 GHz ECRIS and recent results with 14 GHz ECRIS at JYFL
Authors: Koivisto H. , Heikkinen P. , Liukkonen E. , Ärje J. , Vondrasek R.
Published: July 2002

The old JYFL 6.4 GHz electron cyclotron resonance ion source (ECRIS) at the University of Jyväskylä, Department of Physics (JYFL), is in the process of being upgraded. The calculations have shown that the magnetic field configuration of the SC–ECRIS at the NSCL/MSU can be closely achieved using present coils, power supplies, plasma chamber, and permanent magnets. The hexapole magnetic field will be upgraded later using an iron cylinder around the plasma chamber. Calculations have shown that the improvement of around 30% can be obtained to the strength of the hexapole field. A new AECR–U-type ion source was completed in spring 2000 for the program of the nuclear physics in the laboratory. The MIVOC method and the internal oven for the production of several metal ion beams with the new source have been tested.
Development of an ECR ion source for carbon therapy
Authors: Muramatsu M. , Kitagawa A. , Sato Y. , Yamada S. , Hattori T. , Hanagasaki M. , Fukushima T. , Ogawa H.
Published: July 2002

A compact electron cyclotron resonance ion source has been developed for heavy-ion medical facilities. The beam intensity and stability were considerably improved by recent modifications on three points (length of sextupole, cooling system for the extraction electrode, and position of the Einzel lens). Initial results of C4+ beam tests show that an intensity of 180 eμA can be routinely obtained with simple tuning. The best record was 220 eμA for C4+, which meets the medical requirements. Throughout these tests, CH4 gas was used with 0.1 cc/min and the extraction voltage was fixed at 25 kV. Results on beam emittance and long-term stability are also briefly discussed.
Simulation of laser ion loading into ECR ion source
Authors: Shirkov G.
Published: July 2002

Different regimes on pulsed neutral injection into an ECR source are studied and analyzed in a series of numerical simulations. The Frankfurt University experiments and these simulations have shown some evident advantages of the combination of ECR and laser sources. The presented simulations of laser-pulsed loading into a 18 GHz type ECR source have shown that an ion pulse of Au35+ about 0.5 mA and of 0.5 ms duration could be produced in the afterglow operation mode.
Synthetic paths to the heavy elements (plenary)
Authors: Loveland W.
Published: July 2002

Recent work on the synthesis of new heavy nuclei is reviewed. Special attention is given to future experiments and the possible demands for more intense beams.
Intense beam production from RIKEN 18 GHz ECRIS and liquid He free SC-ECRISs
Authors: Nakagawa T. , Kurita T. , Kidera M. , Imanaka M. , Higurashi Y. , Tsukada M. , Lee S. M. , Kase M. , Yano Y.
Published: July 2002

Intense beams of heavy ions with medium charge states (1.3 mA of Ar8+, 200 μA of Xe20+) have been produced from a RIKEN 18 GHz electron cyclotron resonance ion source (ECRIS) using various kinds of techniques, e.g., utilization of an aluminum cylinder and a biased disk, and optimization of the plasma electrode position. Furthermore, we have recently constructed two superconducting ECRISs (operational frequencies of 14 and 18 Hz) which have unique characteristics, i.e., they do not need liquid He to obtain the superconductivity of solenoid coils and utilize the G–M refrigerator instead. These sources are suitable to generate intense beams of heavy ions with very high charge states. We obtained 10 μA of Xe30+, 5 μA of Xe33+, and 1.5 μA of Xe36+ at a radio frequency power of 700 W (14 GHz microwave) without using the gas mixing method. Through various experiments, we confirmed that not only the magnetic field strength and microwave power but also the characteristics of the plasma chamber surface play the essential role for the production of highly charged heavy ions.
Rotational-state selective nuclear magnetic resonance spectra of hydrogen in a molecular trap
Authors: Tomaselli M. , Meier B. H.
Published: July 2002

A nuclear magnetic resonance (NMR) study of the molecular quantum dynamics of hydrogen trapped in solid C60 is presented. Rotational-state selective NMR spectra are shown. The analysis of the spectra provides a direct map of the molecular orientational probability distribution and of the rotational wave functions. Perturbations of the free rotor behavior due to rotor-phonon interactions and due to the S6 symmetry of the confining cage potential are discussed.
Three-dimensional simulation of an ECR plasma in a minimum-B trap
Authors: Dougar-Jabon V. D. , Umnov A. M. , Diaz D. Suescun
Published: July 2002

The results of the three-dimensional (3D) self-consistent simulations of a 14 GHz minimum-B electron cyclotron resonance ion source plasma obtained upon 1.8×104 microwave periods by the particle-in-cell code are reported. The initial density of plasma contained in a chamber of 24 cm length and 6.3 cm in diameter is 0.6×1012 cm−3. We have used the explicit Boris-leap-frog scheme on the three-dimensional computer grid of 32×32×64 size. The results of the relativistic simulations show that the confined plasma has a complex spatial structure with a zone of periodic bounce oscillations as well as areas where banana trajectories are observed. The obtained electron energy distribution function makes it evident that in the electron cyclotron resonance minimum-B plasma there coexist three separable electron groups: a group of cold electrons with the energy up to 80 eV, a group of hot electrons whose energy extends to 80 keV, and a group of superhot electrons accelerated up to hundreds of kilo-electron volts. The space distributions of plasma ions have been found.
A very large Paul trap ion gun for delivering bunched low energy ion beams
Authors: Ghalambor-Dezfuli A. M. , Moore R. B. , Schwartz Stefan
Published: July 2002

Ions extracted from mass separators normally have energies in the range of tens of kilovolts and poor emittances, and are thereby not suited for soft landing, especially in ion deposition applications. In this article a system is described that has been developed for in-flight capture of continuous 60 keV ion beams and delivering them as low energy beam pulses of less than 1 μs duration and energies of less than 5 keV. They are also cooled so that their emittances and energy spreads are considerably reduced from those of the original beam. The basis of the system is a very large Paul trap as a collection system, together with a pulse-down cavity for modifying the energy of the delivered beam. The performance of the system has been analyzed using time-of-flight of the extracted ions. Experimental results are presented, together with numerical simulations of the results that lead to an understanding of the spatial and momentum properties of the ion collection in the trap. The results show how such collection systems can be designed for specific purposes, such as high-current implantation or precise implantation of smaller collections. Such a system can also be used where the ultimate destination is storage in an electromagnetic trap at ground potential.
Stopping efficiency of an ECR charge breeder for axially injected ions
Authors: Jeong S. C. , Oyaizu M. , Tojyo E. , Kawakami H. , Ishiyama H. , Miyatake H. , Enomoto K. , Katayama I. , Nomura T.
Published: July 2002

We have simulated the trajectories of ions injected into an ECR plasma, by taking into account explicitly the cumulative small angle scattering of charged ions as well as the confinement magnetic field of the ECR source. Assuming homogeneous and uniform plasma in a given volume, the stopping efficiency, defined as a probability that the injected ions are alive in the plasma volume until their initial directional motions become at random, has been extracted and discussed.
High current density production of multicharged ions with ECR plasma heated by gyrotron transmitter
Authors: Bouly J. L. , Curdy J. C. , Geller R. , Golubev S. V. , Lacoste A. , Lamy T. , Sole P. , Sortais P. , Razin S. V. , Vieux-Rochaz J. L. , Thuillier T. , Vodopyanov A. V. , Zorin V. G.
Published: July 2002

In order to study the possibilities to produce high currents of pulsed heavy ion beams dedicated to synchrotron injection, two new approaches of ECR devices are now underway. The basic principle consists in maintaining a functioning point of the source with the highest density as possible and a minimum confinement time for the production of a given charge state. It means that for a constant neτi product we try to maximize ne and minimize τi. For this purpose two experiments are in progress at ISN/Grenoblea and IAP/Nizhny Novgorod.b The first one consists of using a minimum |B| magnetic structure with a 1.8 mirror ratio characteristic value with a 28 GHz frequency injection. In this case we explore different functioning points up to 10 kW of UHF power. The second one consists of a simple mirror magnetic system (simple mirror ion source, SMIS) working at 37.5 GHz with a mirror ratio up to 3 (2.5 T) where we study discharges with a peak power up to 100 kW. We will show that, in spite of a very short rising time of the current, we can maintain the production of multicharged ions and that we can observe very high current densities. In the future, the challenge will be the design of an extraction geometry matching theses current levels.
Observation of 3d metal ion charge state distributions in the Dresden EBIT
Authors: Kentsch U. , Zschornack G. , Grossmann F. , Ovsyannikov V. P. , Ullmann F.
Published: July 2002

Ion charge states of 3d metal ions in the electron beam of the Dresden electron beam ion trap (EBIT), a room-temperature EBIT, are determined by x-ray spectroscopy. It is shown that ions of highest charge states as bare nuclei and hydrogen- and helium-like ions can be produced with ion densities of about 105 cm−3 up to 108 cm−3 in the trap. The Dresden EBIT operates at a typical working gas pressure region of 10−8 mbar down to 10−10 mbar. Thus the influence of the realized working gas pressure on the derived ion charge state distribution is investigated by model calculations.
Techniques for the measurement of ionization times in ECR ion sources using a fast sputter sample and fast gas valve
Authors: Vondrasek R. C. , Scott R. H. , Pardo R. C. , Edgell D.
Published: July 2002

Two techniques for the discrete injection of material into an Electron Cyclotron Resonance ion source (ECRIS) have been developed for the purpose of measuring the ionization and confinement times of ion species. Previously only solid materials in conjunction with a pulsed laser were used in these studies due to the discrete material introduction produced by this configuration. The first method replaces the pulsed laser with a fast high voltage pulse applied to a sputter sample. The high voltage pulse has a rise time of 100 ns, fall time of 80.0 μs, and variable pulse duration. The second method utilizes a fast-pulsed gas valve capable of producing a gas pulse 160 μs in width. These pulse widths are well below the ionization times of the lower charge states and thus allows for time measurements to be made of all charge states. Both of these techniques can be employed to study the effects of rf power, coil configuration, biased disk, and gas mixing on ionization and confinement times. Rise times for neon, argon, and gold will be presented.
Enhanced highly charged ion production using a metal-dielectric liner in the KVI 14 GHz ECR ion source
Authors: Schachter L. , Dobrescu S. , Rodrigues G. , Drentje A. G.
Published: July 2002

Forming on an aluminum surface a dielectric layer of alumina (aluminum oxide) in order to create a metal-dielectric (MD) structure increases the secondary-electron emission properties. The idea of using this material as a MD (Al–Al2O3) cylindrical liner inside an ECR ion source was previously tested in the 14 GHz ECRIS of IKF (Frankfurt/Main, Germany). The purpose of the present experiment was to observe the effect of such a MD liner on the high charge state operation of the KVI 14 GHz ECRIS, in particular in comparison to the technique of gas mixing. Measurements were made both with and without the MD liner, with pure argon and with an argon plus oxygen mixture. In the case of pure argon, the source with the MD liner is running remarkably stable. The high charge state ion beam currents are by far higher than those obtained in the situation where the source was operated with pure argon but without the MD liner. With MD liner, some low intensity oxygen peaks were clearly present in the spectra, implying that oxygen escaping or sputtered from the MD structure could give rise to an effect of “gas mixing.” Therefore, the effect of mixing small amounts of oxygen into an argon plasma without the liner was studied in the same conditions of rf power and O3+ peak intensity. The conclusion was that the high charge state beam increase is not due to the oxygen gas mixing effect. The reason for the good performances of the source in the presence of the MD liner can be the increased density of cold electrons, but other effects could occur as well. This is subject of further studies.
Production of intense beams of fission fragments at MAFF
Authors: Bongers H. , Gross M. , Habs D. , Maier H. J. , Sieber T. , Thirolf P. G. , Kester O. , Köster U. , Faestermann T. , von Egidy T.
Published: July 2002

At the new Munich high flux reactor FRM-II, the Munich Accelerator for Fission Fragments (MAFF) is under development. The main objective will be the production and study of new very heavy elements (Z>100). To obtain this goal, intense beams of neutron rich isotopes (70<A<160) are required. Thermal neutron induced fission is considered the most suitable method to produce these isotopes due to the large fission cross section and high thermal neutron flux (>1014 n/s*cm2) available at the new reactor. The target ion source design is based on the ANUBIS source at OSIRIS in Studvik, optimized for very high neutron fluxes. Using 1 g of U235 diluted in a graphite target, intensities of several 1011 ions/s for Kr91, Sn132, or Cs144, e.g., are expected after mass separation. These singly charged ions will be charge bred in an electron cyclotron resonance ion source and then injected into the MAFF-LINAC to reach the energies at the Coulomb barrier. The production of intense ion beams of neutron rich isotopes by thermal neutron induced fission, the development of the target ion source, and the development of the fission target will be presented.
Plasma ignition schemes for the Spallation Neutron Source radio-frequency driven H− source
Authors: Schenkel T. , Staples J. W. , Thomae R. W. , Reijonen J. , Gough R. A. , Leung K. N. , Keller R. , Welton R. , Stockli M.
Published: July 2002

The H− ion source for the Spallation Neutron Source (SNS) is a cesiated, radio-frequency driven multicusp volume source which operates at a duty cycle of 6%. In pulsed rf driven plasma sources, ignition of the plasma affects the stability of source operation and the antenna lifetime. We report on ignition schemes, based on secondary electron generation by UV light, a hot filament, a low power rf plasma (cw, 13.56 MHz), as well as source operation solely with the high power 2 MHz rf. We find that the dual frequency, single antenna scheme is most attractive for the operating conditions of the SNS H− source.
Beam emittance measurements at the high current injector at GSI
Authors: Hollinger R. , Heymach F. , Spädtke P.
Published: July 2002

The high current injector (HSI) was set into operation in 1999. The maximum ratio of mass to charge state of this new injector has been increased from 25 to 65 with a lower injection velocity of 2.2 keV/u (11.7 keV/u before). The space charge limit of the RFQ (0.25*A/ζ[mA]) was reached for argon and lighter ions but not for U4+ or rare isotopes. For that reason further modifications of the high current ion injector, e.g., geometry of the acceleration gap, solenoid for focusing, were necessary. Here we present beam emittance measurements after the acceleration system for different ion species with beam energies up to 150 keV and beam currents up to 100 mA. For the measurements a multicusp ion source with a multiaperture accel–decel extraction system has been used to produce high ion beam currents in low charge states. The commissioning has been made using an Ar+ beam. This ion beam is easy to produce in nearly one charge state with emission current densities up to 150 mA/cm2. The emittance measurements will be presented in view of the two main dependencies: the focussing strength of the acceleration gap and the space charge forces in the acceleration gap.
First beam from the TRASCO intense proton source (TRIPS) at INFN-LNS
Authors: Ciavola G. , Celona L. , Gammino S. , Chines F. , Campisano C.
Published: July 2002

The TRASCO intense proton source (TRIPS) was installed at INFN-LNS in May 2000 and the commissioning is in progress. This article describes the design of the source along with the first results and the next developments. The source has been able to deliver more than 20 mA of protons with high reliability from a 4.5 mm extraction aperture at 65 kV, largely above the minimum requested current density. The goals in terms of beam energy (80 keV) and current (60 mA from 8 mm extraction aperture) have been achieved. Further optimization of the source is under way, with special care given to the reliability needed for the accelerator driving system purpose.
SINGAP: The European concept for negative ion acceleration in the ITER neutral injectors
Authors: de Esch H. P. L. , Hemsworth R. S. , Massmann P.
Published: July 2002

In contrast to the multiaperture–multigrid concept of the International Thermonuclear Experimental Reactor (ITER) injector reference design in which D− acceleration to 40 A, 1 MeV is achieved through seven grids containing 1280 apertures each, the European SINGAP (single gap–single aperture) concept proposes acceleration of 1280 preaccelerated (20–50 keV) beamlets to 1 MeV in a single step. During acceleration the beamlets are merged into 16 groups of 80 beamlets. These 16 so-called hyperbeamlets then emerge from an exit grid containing only 16 very large apertures. This concept is expected to reduce cost and increase the tolerance to mechanical errors and stray magnetic fields. The SINGAP physics is described here. The SINGAP beam optics is calculated to provide good beam transmission (86%) to the ITER.
Optimization of negative ion extractor in a JAERI 400 keV H− ion source
Authors: Takayanagi T. , Ikehata T. , Okumura Y. , Watanabe K. , Hanada M. , Amemiya T. , Kashiwagi M.
Published: July 2002

The influence of a dipole magnetic field in the extractor on the beamlet deflection has been investigated using a JAERI 400 keV H− ion source. The beam deflection angle decreased from 10.2 to 7.0 mrad when the integrated value of the magnetic field was changed from 2530 to 910 G cm. The measured deflection angle was larger than the estimated value from the ion trajectory considering the magnetic field. To understand the dominant factor that enhances the beam deflection angle, three-dimensional trajectory simulation was performed. It was confirmed that the axis of the beamlet deflected by the magnetic field in the extractor is displaced from the center of the aperture at the grounded grid (GRG). This displacement enhances the beam deflection angle due to the effect of the electrostatic lens at the GRG. This phenomenon is similar to the beam deflection by aperture displacement of the GRG.
Quantitative three-dimensional reconstruction of geometrically complex structures with nanoscale resolution
Authors: Dunn D. N. , Shiflet G. J. , Hull R.
Published: July 2002

A technique to reconstruct high resolution three-dimensional structural images and chemical maps of geometrically complex features is presented. A focused ion beam microscope is used to collect secondary electron images and secondary ion mass spectroscopy elemental maps as a function of depth in the sample. These images and elemental maps are then used to reconstruct volume images and chemical maps using shape-based interpolative methods with 25 nm lateral resolution and approximately 10 nm depth resolution. From these reconstructions, fundamental parameters such as connectivity, the volume fraction, and surface areas of features of interest can be calculated directly. These techniques open broad new opportunities for understanding three-dimensional structural and chemical relationships in materials research.
In situ UV/Vis/near-IR diffuse reflection measurement of catalysts at temperatures up to 673 K
Authors: Thiede M. , Melsheimer J.
Published: July 2002

In situ UV/VIS/near-IR diffuse reflectance spectroscopy can be carried out on catalysts with a suitable microreactor at temperatures up to 673 K. The experimental difficulties in the application of such a reactor at higher temperatures could be solved as follows. Integrating sphere and reactor are connected by a ceramic part of high reflectivity and low thermal conductivity, i.e., the integrating sphere is enlarged. The signal/noise ratio increases by a factor of 2. The standard IR detector was replaced by a temperature-stabilized version. In addition watercooling jackets were mounted at the integrating sphere. The signal/noise ratio in the near-IR region was thus improved by a factor of 2–3 with a very good reproducibility of measurements. To overcome an alteration of catalyst spectra by thermal radiation, a series of reference spectra of quartz powder (SiO2) were recorded at several temperatures. These spectra are used to correct the catalyst spectra by dividing catalyst and SiO2 spectra.
Production of multiply charged Si and Fe ions from solid materials by sputtering and evaporating methods in a 2.45 GHz ECR source
Authors: Sugiyama Saori , Kato Yushi , Ishii Shigeyuki
Published: July 2002

Multicharged Si and Fe ions are produced from solid materials in a 2.45 GHz electron cyclotron resonance (ECR) ion source. The ECR plasma is confined in a magnetic mirror field superimposed on an octupole magnetic field. Ar gas is normally chosen for working gas at pressures of 10−4 to 10−3 Pa. Si and Fe ions are produced by sputtering and evaporating solid materials, which are safe and easy to handle. The Fe (or Si) target is mounted at the tip of an insulated holder and inserted into the plasma. The negative dc bias voltages are applied to the target and multicharged Fe (or Si) ions are produced. Fe filament is evaporated in the ECR plasma by direct ohmic heating, and multicharged Fe ions are produced. Multicharged ions up to Fe6+ are produced by using both methods of sputtering and evaporating and Si4+ by using the sputtering method. The maximum ratio of the Fe and Si ion currents to total Ar ion current are about 15% and 13% obtained by the sputtering method, respectively. The maximum current densities of Fe+ and Fe4+ are 1.1×10−1 and 4.1×10−4 mA/cm2 obtained by the sputtering method, respectively.
Particle-in-cell code library for numerical simulation of the ECR source plasma
Authors: Shirkov G. , Alexandrov V. , Preisendorf V. , Shevtsov V. , Filippov A. , Komissarov R. , Mironov V. , Shirkova E. , Strekalovsky O. , Tokareva N. , Tuzikov A. , Vatulin V. , Vasina E. , Fomin V. , Anisimov A. , Veselov R. , Golubev A. , Grushin S. , Povyshev V. , Sadovoi A. , Donskoi E. , Shevelko V. , Nakagawa T. , Yano Y.
Published: July 2002

The code library is aimed for the three-dimensional simulation of the electron cyclotron resonance (ECR) plasma and ion production in an ECR ion source. The particle-in-cell method allows studying the detailed characteristics of plasma, taking into account distribution functions of particles real self and external fields, particle–particle interactions, and others.