bluuebunny/crossref_metadata_2025 huggingface dataset:
Coherent grating x-ray diffraction (CGXD) and its applications (invited)
Authors: Shen Qun
Published: July 2002

We show that an x-ray interference phenomenon, coherent grating x-ray diffraction (CGXD), can be used to study lateral nanostructure arrays on crystal surfaces and interfaces. Compared to Fraunhofer grating diffraction of visible light, x-ray grating diffraction contains information not only about geometric profiles of the surface but also about the internal crystalline structures and lattice strain distributions in the grating features. The grating diffraction pattern can also be measured in a white-beam Laue method using highly collimated polychromatic synchrotron radiation, which provides a parallel data collection scheme and may be useful in in situ studies on evolution of nanostructure arrays.
Personnel Safety System for the beamlines at the Advanced Photon Source
Authors: Hawkins J. , Seaver C. , Stein J. , Stoffel J. , Friedman N.
Published: July 2002

The Personnel Safety System (PSS) at the Advanced Photon Source is a high reliability, fail-safe, redundant, engineered safety system that provides personnel access control to prevent inadvertent entry into experimental stations when hazardous radiation conditions exist and warns personnel of changes in safe operating conditions inside these stations. Single fault tolerant access control is provided by two independent interlock ‘‘chains’’ implemented via programmable logic controllers (PLCs). Reduction of common mode failures is accomplished by different hardware and software platforms for the two chains. The system design is presented.
SINBAD: A synchrotron infrared beamline at DAFNE
Authors: Ambrogini G.R. , Burattini E. , Calvani P. , Marcelli A. , Mencuccini C. , Nucara A. , Sánchez del Río M.
Published: July 2002

Different optical layouts for a beamline that extracts infrared synchrotron radiation from a bending magnet are discussed, and their performances are compared by use of ray-tracing simulations. Specific results are presented for SINBAD, the beamline to be mounted on the new Frascati collider DAΦNE.
X-ray backlit imaging measurement of in-flight pusher density for an indirect drive capsule implosion
Authors: Kalantar D. H. , Haan S. W. , Hammel B. A. , Keane C. J. , Landen O. L. , Munro D. H.
Published: July 2002

Both the efficiency of an implosion and the growth rate of hydrodynamic instability increase with the aspect ratio of an implosion. In order to study the physics of implosions with high Rayleigh–Taylor growth factors, we use doped ablators which should minimize x-ray preheat and shell decompression, and hence increase in-flight aspect ratio. We use x-ray backlighting techniques to image the indirectly driven capsules. We record backlit 4.7 keV images of the full capsule throughout the implosion phase with 55 ps and 15 μm resolution. We use these images to measure the in-flight aspect ratios for doped ablators, and we infer the radial density profile as a function of time by Abel inverting the x-ray transmission profiles.
Toward a near-field optical array
Authors: Pantano Paul , Walt David R.
Published: July 2002

The fabrication and characterization of three near-field optical array types is presented. In all cases, a coherent fiber-optic bundle was chemically etched to produce an array of nanometer-sized, optical fiber tips. The 270 μm diameter bundle comprised ∼6000 tapered optical fibers and the smallest, etched optical fiber tips had an ∼50 nm radius of curvature. This array could be metal coated, and a metal-coated array could be polished to yield an array of nanometer-sized apertures. These variable nanoarchitectures should be amenable to a large number of near-field scanning optical microscopies.
The electron cyclotron absorption diagnostic at the Rijnhuizen tokamak project
Authors: van Gelder J. F. M. , Miedema H. S. , Donné A. J. H. , Oomens A. A. M. , Schüller F. C.
Published: July 2002

A new 20-channel electron cyclotron absorption diagnostic has been developed at the Rijnhuizen tokamak project. It is the first time the electron pressure profile in a tokamak plasma can be measured directly with a time resolution of 1 ms. The diagnostic measures simultaneously the emission and absorption of the second harmonic electron cyclotron frequencies. Microwaves are injected from the high field side and detected at the low field side in the equatorial midplane. The transmitted power is measured after a single pass through the plasma column. The absorption measurements are complicated by nonresonant losses: refraction of the injected microwaves (losses up to 100%), and scattering of microwaves by density fluctuations (losses 2%–3%). A fast algorithm has been developed to obtain a quantitative measure for these nonresonant losses. This calculation method is based on a parametrization of the experimental data. Combining the electron cyclotron absorption (ECA) measurements and the parametrization provides a reliable tool for determining the optical depth, the electron temperature, and the electron pressure. A good agreement was found between pressure and temperature profiles, measured with ECA and other diagnostics.
High pressure flow gravimetric apparatus for supercritical fluid extraction studies
Authors: Jwayyed Alzubair M. , Humayun Raashina , Tomasko David L.
Published: July 2002

An experimental apparatus has been developed for real time measurements of fluid–solid adsorption (or desorption) rates and equilibria at elevated pressures. In addition to controlling pressure and flow rates simultaneously, this setup is able to operate at higher flow rates than previously possible in supercritical fluid experiments. The system consists of a high pressure microbalance, two high pressure syringe pumps, and an absorbance detector. The microbalance enables the collection of data at a greater time resolution, resulting in a more accurate measurement of rate data. Because of the dual syringe pump design, there is no pressure drop in the system, making it possible to operate at a wide range of flow rates (at experimental conditions). The buoyancy force was measured with helium experiments, while the hydrodynamic forces were measured using a clean solid sample and supercritical carbon dioxide at different flow rates. It was found that the hydrodynamic force increased with flow rate as expected. The apparatus was tested by conducting two desorption experiments of phenol from activated carbon at 141±0.07 bar, 36.0±0.02 °C, and 0.47 ml/min (at experimental conditions). The amount of phenol removed was 16.4% and 18%, respectively, in the two runs which is consistent with previously published results and indicates the difficulty of regenerating activated carbon loaded with phenol.
Deposition of high-quality TiN using tetra-isopropoxide titanium in an electron cyclotron resonance plasma process
Authors: Weber A. , Poeckelmann R. , Klages C.-P.
Published: July 2002

High-quality TiN films were deposited in an electron cyclotron resonance (ECR) plasma process at low substrate temperatures between 100 and 450 °C using tetra-isopropoxide titanium (TIPT) {Ti[OCH(CH3)2]4} as precursor. TIPT was introduced into the downstream region of an ECR nitrogen or ammonia plasma. The electrical properties of the gold colored TiN layers (100–400 μΩ cm) depend on the deposition rate and the substrate temperature. Despite the use of an oxygen containing titanium precursor the oxygen content in the TiN was found to be ≤2 at.%. The measured resistivities and the purity of the TiN films indicate a selective cleavage of the isopropoxide ligand in the ECR downstream plasma. The films were characterized by resistivity measurements and secondary ion mass spectrometry.
Beam development at the new 14 GHz electron cyclotron resonance ion source of ATOMKI
Authors: Biri S. , Vámosi J.
Published: July 2002

The first highly charged heavy ion beams in Hungary were obtained in October 1996. The new 14.5 GHz electron cyclotron resonance (ECR) ion source of ATOMKI produced remarkable intensity of multiply charged ion beams yet at the first experiments (e.g., charge states up to 12+ were detected for argon) just with “basic” ECR ion source configuration. Since then some further developments were carried out. A negatively biased electrode remarkably increased the intensity of the highly charged ions. The testing of the seven-elements electrostatic extraction system is continued successfully. Experimental study was done in order to find the optimal position of the mirror peaks. Visual studies and spectroscopic measurements of the visible light coming from the ECR plasma, were carried out.
Negative ion sources for neutral beam injection into fusion machines
Authors: Trainham R. , Jacquot C. , Riz D. , Simonin A. , Miyamoto K. , Fujiwara Y. , Okumura Y.
Published: July 2002

Plasma heating and current drive in future machines for magnetically confined thermonuclear fusion will require neutral beam injectors based upon negative ion sources. Although the technology of filament arc ion sources is considered adequately mature for large scale injectors, such as for ITER, ion source efficiency and reliability need to be improved. The power loading of the source and accelerator are especially problematic. This is particularly important for long pulse (1000 s) operation. Investigations with the Kamaboko source, a small scale model of the ITER arc source, illustrate the importance of the conditions of the plasma grid for reducing electron loading of the accelerator.
The development of an electron cyclotron resonance ion source for the heavy ion research facility in Lanzhou
Authors: Zhanwen Liu , Wen Zhang , Hongwei Zhao , Ping Yuan , Xuezhen Zhang , Xiaohong Guo , Zimin Zhang , Xixia Li , Hui Wang , Yucheng Feng , Jinyu Li , Jiyuan Gao , Baohua Ma , Hailiang Lei , Sixin Zhou , Yifang Wang , Baowen Wei
Published: July 2002

A new working condition for an electron cyclotron resonance (ECR) source for the heavy ion research facility in Lanzhou (HIRFL) is reported. This condition is based on the full use of the secondary electrons injected into the source plasma near the extraction region of source cavity, and allows ion extraction from a denser plasma. A new magnetic field configuration which could move the Bmin of the mirror field towards the extraction region is also described. Using these technologies, our 10 GHz ECR source has delivered beam current of 320 and 80 eμA for the Ar9+ and Ar11+ ion, respectively. An ion extraction construction with a biased electrode was tested recently. Some details and the preliminary results are presented as well.
Development of a Bi+ source for heavy ion fusion
Authors: Weber M. , Volk K. , Beller P. , Lakatos A. , Maaser A. , Klein H.
Published: July 2002

A volume source based on the high efficiency source is being developed for heavy ion production. Bismuth was chosen for exemplifying investigations because of its low melting point. The ion source is driven by an arc discharge ionizing bismuth atoms which are evaporated from an oven inside the source chamber. It has been optimized to produce a beam with a fraction of singly ionized bismuth above 92%. A multiaperture extraction system was built consisting of seven holes with a radius of 3 mm each. For that system, the perveance limit was achieved at a beam current of 70 mA and an extraction voltage of 27.5 kV. The corresponding emission current density amounts to 35 mA/cm2. This value was obtained for an arc power of only 280 W. Furthermore, the emittance of a beam extracted from the multiaperture extraction system has been determined with a high power emittance scanner. It amounts to 0.27π mm mrad (80%, normalized, 4 rms). In this case, the emittance of a single beam is 0.017π mm mrad. This article will give a detailed description of both the source and the experimental setup. In addition, various dependencies between the plasma parameters and the beam composition are presented.
A compact superconducting magnet for magnetic resonance microscopy
Authors: Crozier Stuart , Doddrell David M.
Published: July 2002

Magnetic resonance microscopy (MRM) depends on the use of high field, superconducting magnet systems for its operation. The magnets that are conventionally used are those that were initially designed for chemical structural analysis work. A novel, compact magnet designed specifically for MRM is presented here, and while preserving high field, high homogeneity conditions, has a length less than one-third that of conventional systems. This enables much better access to samples, an important consideration in many MRM experiments. As the homogeneity of a magnet is strongly dependent on its length, novel geometries and optimization techniques are required to meet the requirements of MRM in a compact system. An important outcome of the stochastic optimization performed in this work, is that the use used of a thin superconducting solenoid surrounded by counterwound disk windings provides a mechanism for drastic length reductions over conventional magnet designs.
Design and validation of guarded hot plate instruments for measuring heat flow between evacuated plane-parallel glass surfaces
Authors: Dey C. J. , Simko T. M. , Collins R. E. , Zhang Q.-C.
Published: July 2002

This article discusses the design and construction of guarded hot plate instruments for measuring the heat flow through an evacuated space between plane-parallel glass surfaces. In this structure, the insulating region is surrounded by two pieces of relatively highly conducting material. High resolution measurements of heat flow using these instruments therefore requires the detection of quite small temperature differences (10−4 K) between the metering piece and the guard. The instruments are calibrated, and the linearity evaluated, by measuring radiative heat transfer through the evacuated space between uncoated soda lime glass sheets; this is because this heat flow can be calculated to high accuracy from the infrared optical properties of the glass. The level of parasitic heat flow in the instruments is estimated by measuring radiative heat flow between glass surfaces coated with very low emittance layers, such as evaporated gold. These instruments operate over a range of temperatures from 0 to about 70 °C. It is shown that the heat flow between evacuated glass surfaces can be measured with these instruments to high resolution (∼10 μW) and high accuracy (∼1%) over an area of ∼1 cm2. The departures from linearity, and the level of parasitic heat flow, are within the measurement resolution. For a temperature difference across the sample of 20 K, the measurement resolution corresponds to an uncertainty in the thermal conductance of the sample of ∼0.005 W m−2 K−1.
Mechanical modulated waveguide spectroscopy
Authors: Fahrwald A. , Skupin H. , Fischer Th. M. , Kremer F.
Published: July 2002

Mechanically modulated waveguide spectroscopy is a technique for measuring simultaneously the thickness modulation and changes in orientation of surface stabilized liquid crystalline cells. The possibilities of this technique are presented for cells filled with a ferroelectric liquid crystal. Constant thickness modulation of 20 nm is achieved in the liquid crystal at 50 °C over a frequency range from 1 to 105 Hz. The technique is useful for studying the piezoelectric reorientation processes in liquid crystals.
Theoretical analysis of electron cyclotron resonance x-ray sources
Authors: Baskaran R.
Published: July 2002

In this article, the important physical parameters which affect the electron current and energy in electron cyclotron resonance x-ray source are discussed. The electron trajectory in an empty cylindrical cavity (TE111 mode), magnetized with dc magnetic field is plotted for the electrons with and without the initial velocity. Magnetic field tapering effect on the electron acceleration and the maximum attainable energy of the electron is studied. The advantages of waveguide coupling over the coaxial coupling for exciting the TE111 mode of the cavity are discussed.
Production of multicharged radioactive ion beams: New results for the 1+→n+ method with the MINIMAFIOS and SARA-CAPRICE electron cyclotron resonance ion sources
Authors: Lamy T. , Bruandet J-F. , Chauvin N. , Curdy J.-C. , Fruneau M. , Geller R. , Gimond G. , Sole P. , Vieux-Rochas J-L. , Gaubert G. , Maunoury L. , Sortais P. , Villari A. C. C.
Published: July 2002

The backward and forward injection of a 1+ ion beam in a MINIMAFIOS type electron cyclotron resonance ion source (ECRIS) have given good results for the 1+→n+ method. Due to the technological simplicity of the forward injection, additional experiments have been performed with this configuration. Different primary sources (1+) have been used for the injection (2.45 GHz ECRIS, hollow cathode source, simplified 10 GHz NANOGAN type ECRIS), an increase of the performances has already been obtained (Zn, Kr, Ar), and a measurement of the absolute efficiency with the NANOGAN type-MINIMAFIOS association is performed. Due to the high performance of the 10 GHz CAPRICE source used as a highly charged ion injector in the first cyclotron of SARA (Système Accélérateur Rhône-Alpes), it has been tested as a different n+ source for the 1+→n+ method. In this purpose, a low energy spread–low emittance thermoionization Rb ion source has been used as 1+ injector. A standard operation of the SARA-CAPRICE source has been kept with respect to the microwave coupling. The spectra of the Rbn+ ions extracted are compared when using N2 and O2 as support gases. The highest efficiency is obtained for the Rb13+.
A high-energy x-ray microscope for inertial confinement fusion
Authors: Marshall F. J. , Bennett G. R.
Published: July 2002

We have developed a microscope capable of imaging x-ray emission from inertial confinement fusion targets in the range of 7–9 keV. Imaging is accomplished with a Kirkpatrick-Baez type, four-image microscope coated with a WB4C multilayer having a 2d period of 140 Å. This microscope design (a standard used on the University of Rochester’s OMEGA laser system) is capable of 5 μm resolution over a region large enough to image an imploded target (∼400 μm). This design is capable of being extended to ∼40 keV if state-of-the-art, short-spacing, multilayer coatings are used (∼25 Å), and has been configured to obtain 3 μm resolution with the appropriate choice of mirror size. As such, this type of microscope could serve as a platform for multiframe, hard x-ray imaging on the National Ignition Facility. Characterization of the microscope and laboratory measurements of the energy response made with a cw x-ray source will be shown.
Visible radiation sliced image emission velocimeter interferometer fluctuation diagnostic
Authors: Marmar E. S. , Zweben S. J. , Fulghum S. , Rostler P. S.
Published: July 2002

An instrument designed to measure k-filtered plasma fluctuations has been used to look at edge fluctuations in Alcator C-Mod tokamak plasmas. The instrument utilizes a sieve technique, whereby an optical image is split and filtered through two out-of-phase, striped transmission masks, and then imaged onto photodiode detectors. The difference signal is then digitized and analyzed to give the frequency characteristics of the fluctuations at a particular value of k, as determined by the wavelength of the mask stripes. Measurements have been made looking at the edge plasma with hydrogen Balmer-alpha filtering, and k both parallel and perpendicular to the magnetic field, with |k| in the range from 5 to 15 cm−1. Broad band (ν<500 kHz) fluctuations are seen for k perpendicular to B, and characteristics in ohmic and L-mode plasmas are described.
Applying object oriented concepts to on-line data acquisition
Authors: Dulya C. M. , Crémy C. , Vega J. , Sánchez E. , Portas A.
Published: July 2002

Concepts of object oriented programming have been applied to the on-line part of the data acquisition system of the TJ-II flexible heliac. The programs were written in C++ for a VxWorks operating system which uses general purpose interface bus (GPIB) connections to control computer automated measurement and control (CAMAC) crates with various types of digitizer modules. Since the digitizers have similar functionality, the application of object oriented methods is particularly efficient. Unfortunately, the control code of the CAMAC had to be built up in layers since the CAMAC/GPIB system is not well suited for good object oriented organization.
Noise and sensitivity of x-ray framing cameras at Nike (abstract)
Authors: Pawley C. J. , Deniz A. V. , Lehecka T.
Published: July 2002

X-ray framing cameras are the most widely used tool for radiographing density distributions in laser and Z-pinch driven experiments. The x-ray framing cameras that were developed specifically for experiments on the Nike laser system are described. One of these cameras has been coupled to a CCD camera and was tested for resolution and image noise using both electrons and x rays. The largest source of noise in the images was found to be due to low quantum detection efficiency of x-ray photons.
Argon Kα measurement on DIII–D by Ross filters technique (abstract)
Authors: Snider R. T. , Bogatu I. N. , Brooks N. H. , Wade M. R.
Published: July 2002

Techniques to reduce the heat flux to the divertor plates in tokamak power plants and the consequent erosion of, and subsequent damage to the divertor target plates include the injection of impurities such as argon, that can dissipate the energy (through radiative or collisional processes) before it reaches the target plates. An important issue with this type of scheme is poisoning of the plasma core by the impurities introduced in the divertor region. Subsequently, there is a desire to measure the profiles of the injected impurities in the core. X-ray Ross filters with an effective narrow band pass centered on the argon Kα line at 3.2 keV, have been installed on two of the existing x-ray arrays on DIII–D in order to help determine the argon concentration profiles. Emissivity profiles of the Kα lines and the emissivity profiles for the argon enhanced continuum can be inferred from the inverted filtered x-ray brightness signals if Te, ne, and Ar18+ profiles are known. The MISTReference 1 code is used to couple the filtered x-ray signals to the time dependent measurements of Te and ne. Further, the Ar16+ profiles measured by charge transfer spectroscopy, are used as a constraint on the MIST code runs to calculate Ar18+ profiles and unfold the argon emissivity profiles. A discussion of the Ross filters, the DIII–D argon data, and the data analysis scheme for inferring argon emissivity profiles will be discussed. Estimates of the total argon concentration in the core determined from this technique in DIII–D argon puff experiments will be presented.
Enhancement of the spectroscopic method for mapping microwave fields in tokamak plasmas
Authors: Gavrilenko V. P. , Oks E.
Published: July 2002

A significantly enhanced spectroscopic method for mapping microwave fields in tokamak plasmas is suggested. The method employs the laser-induced fluorescence from a hydrogen or deuterium beam. The first draft of the method was published by us previously and implemented in a model experiment. In distinction to that, the method proposed here does not require a calibration at the zero microwave field and also is more accurate. It is based on our novel theoretical results on the interaction of H-like quantum systems with both a strong microwave and a laser field.
Hall effect characterization of silicon activation and segregation in planar doped GaAs–AlAs superlattices
Authors: Sellitto P. , Sicart J. , Robert J. L. , Planel R.
Published: July 2002

We have analyzed Hall data in GaAs–AlAs superlattices grown by molecular beam epitaxy. All samples had a very short period (3.7 nm) and were planar doped with silicon at a sheet density of 3.3×1010 cm−2 per plane. Silicon was introduced selectively either in the GaAs layers, in the AlAs layers, or at the interface. The silicon electrical activation did not depend on the doping plane location. Conversely, the thermal activation energy of the Hall carrier concentration was found to depend strongly on the doping plane location. From our experimental results, we estimate the silicon segregation length to be lower than 1.5 nm at a growth temperature of 550 °C.
Metalorganic chemical vapor deposition of tantalum nitride by tertbutylimidotris(diethylamido)tantalum for advanced metallization
Authors: Tsai M. H. , Sun S. C. , Chiu H. T. , Tsai C. E. , Chuang S. H.
Published: July 2002

We deposited tantalum nitride (TaN) films by low-pressure metalorganic chemical vapor deposition (LP-MOCVD) using a new precursor tertbutylimidotris(diethylamido)tantalum (TBTDET). Strong Ta–N double bond in the precursor preserved the ‘‘TaN’’ portion during the pyrolysis process. This method has yielded low-resistivity films. It changed from 10 mΩ cm (deposited at 500 °C) to 920 μΩ cm (obtained at 650 °C). The carbon and oxygen concentrations were low in the films deposited at 600 °C, as determined by x-ray photoelectron spectroscopy. Transmission electron microscopy and x-ray diffraction analysis indicated that the as-deposited films exhibited polycrystalline structures with the lattice constants close to the bulk TaN value. The TaN barrier layer was successfully applied as a glue layer for CVD tungsten (W) metallization schemes.
Tip-sample interaction in a “shear-force” near-field scanning optical microscope
Authors: Hsu Kate , Gheber Levi A.
Published: July 2002

The interaction between the tip of a near-field scanning optical microscope (NSOM) and the sample it scans is analyzed and compared to a simple tapping model. The approach curves acquired with the NSOM are in excellent agreement with the model, and additional experiments strongly point against a noncontact interaction (such as shear force). Based on this model we are also able to explain the oscillations pattern of the feedback loop. We conclude that our straight-fiber tip, operating under “shear-force” control, intermittently contacts the surface it is scanning, in a way similar to the tapping mode in atomic force microscope.
Portable oil bath for high-accuracy resistance transfer and maintenance
Authors: Shiota Fuyuhiko
Published: July 2002

A portable oil bath containing one standard resistor for high-accuracy resistance transfer and maintenance was developed and operated for seven years in the National Research Laboratory of Metrology. The aim of the bath is to save labor and apparatus for high-accuracy resistance transfer and maintenance by consistently keeping the standard resistor in an optimum environmental condition. The details of the prototype system, including its performance, are described together with some suggestions for a more practical bath design, which adopts the same concept.
Voltage monitoring device for characterization of semiconducting and superconducting circuits
Authors: Christoforou Y. , Xenikos D. G.
Published: July 2002

The characterization of semiconducting and superconducting devices under extreme temperature or radiation conditions imposes certain restrictions on the connection of the sample to the tester, which may involve elements with electrical properties that are not well controlled. Specifically, insufficient characterization of the potential drop along long cables, contact resistances, or interconnects may render the voltage biasing of the device extremely difficult. In this article, we present a measurement setup that complements commercial equipment and solves the problem for a wide range of ohmic loads, for several types and any length of cable, and for typical cryogenic conditions down to liquid helium temperature. As examples, we test a low-noise GaAs MESFET preamplifier at frequencies of 0–100 kHz and temperatures of 4–300 K and discuss the capability of the device to characterize high Tc superconducting strips.
Uncoated hollow taper as a simple optical funnel for laser delivery
Authors: Ilev Ilko K. , Waynant Ronald W.
Published: July 2002

We propose a simple uncoated hollow taper as a novel technique for laser radiation delivery and laser-to-optical waveguide coupling over a wide spectral range. The principle of operation of the hollow taper is based on the effect of light at grazing incidence. An uncoated Pyrex-glass hollow taper is used for direct launching, without any intermediate focusing elements, of laser radiation including from powerful lasers into the taper. Because of the high reflectance coefficients close to 100% at the light grazing incidence, we obtain high laser-to-taper coupling efficiency exceeding 90% for a He–Ne laser (λ=632.8 nm) and 80% for a Er:YAG laser (λ=2.94 μm).
Ion source development for isotope separator on-line based radioactive nuclear beam facility at KEK-Tanashi
Authors: Jeong S. C. , Ishiyama H. , Ishida Y. , Kawakami H. , Kawashima H. , Miyatake H. , Mizutani S. , Oyaizu M. , Takaku S. , Tojyo E. , Yoshikawa N. , Wada M. , Katayama I. , Nomura T.
Published: July 2002

For an isotope separator on-line based radioactive nuclear beam facility at KEK-Tanashi, two different types of ion sources are currently employed: a single stage 6.4 GHz electron cyclotron resonance ion source for Ne2+18 and Ne2+19 ions and a surface ionization-type ion source for Li1+8 ions. The production target for Ne radioisotopes is LiF powder. Enclosed in a water-cooled Cu target cell, the target can sustain proton beam power of 120 W for a long term. The methods to suppress unwanted isotopes, like F19 in Ne19 and O18 in Ne18, are discussed. For the production of Li1+8 with the surface ionization-type ion source, a recoil-catcher method is adopted. The feasibility is discussed, comparing to a thick target method.
Status of the Brookhaven National Laboratory high current electron beam ion source test stand
Authors: Beebe E. , Alessi J. , Bellavia S. , Hershcovitch A. , Kponou A. , Lockey R. , Pikin A. , Prelec K. , Stein P. , Kuznetsov G. , Tiunov M.
Published: July 2002

As part of a new, compact heavy ion injector for the AGS/RHIC complex at Brookhaven National Laboratory we are developing an electron beam ion source (EBIS) that would satisfy present and future requirements. Such a source should be capable of producing intensities of, e.g., Au35+ ions of about 3×109 particles/pulse or U45+ of about 2×109 particles/pulse. To achieve this, the required e-beam intensity is 10 A, at a pulse length of 100 ms. An EBIS test stand has been constructed, designed for the full electron beam power and having close to 1/2 of the trap length of an EBIS for RHIC. Initial electron beam tests have resulted in a 50 μs, 13 A electron beam. Ion production and extraction has been shown with a 3.1 A, 50 ms electron beam, achieving an ion yield of 19 nC/pulse (neutralization degree of 61%); fast extraction trials have yielded extracted ion pulses of 1 mA peak current and 18 μs at FWHM. Details of the test stand construction, results of the electron beam studies, and properties of the extracted ion pulse are presented.
A study of electron strings and their use for efficient production of highly charged ions
Authors: Donets E. D. , Donets D. E. , Donets E. E. , Salnikov V. V. , Shutov V. B. , Syresin E. M. , Bjorkhage M. , Carle P. , Liljeby L. , Rensfelt K.-G. , Becker R. , Kleinod M. , Kultashev O. K.
Published: July 2002

An electron string is a state of a one component electron plasma, which can arise when multiply reflected electrons are accumulated in a strong solenoidal magnetic field. Based on the electron beam ion source (EBIS) in the reflex mode of operation the processes of the string formation and its decay were observed and the characteristic times of the processes have been measured. Information about the electron energy distribution in electron strings has been obtained using four independent methods. It was shown, the distribution is broad and, moreover, there is some amount of electrons, having energies higher than the energy of the electrons used for feeding the string. An instability was observed as a starting point of electron string formation. The instability is strongly suppressed and the string is formed when the injecting electron current reaches a threshold value, which depends on a quality of electron focusing. Most likely the instability observed is responsible for the string electron energy spread. The results of the string formation using various constructions of electron gun and electron repeller, situated in magnetic fields of various induction, are presented. Similar to electron beams in EBIS, electron strings were successfully used for production of highly charged ions. The first attempts of a theoretical description of the electron string phenomenon are briefly discussed.
Electron cyclotron resonance ion source for high currents of mono- and multicharged ion and general purpose unlimited lifetime application on implantation devices
Authors: Bieth C. , Bouly J. L. , Curdy J. C. , Kantas S. , Sortais P. , Sole P. , Vieux-Rochaz J. L.
Published: July 2002

The electron cyclotron resonance (ECR) ion sources were originally developed for high energy physic applications. They are used as injectors on linear accelerators and cyclotrons to further increase the particle energy via high charge state ions. This ECR technology is well suited for sources placed on a high voltage platform where ac power available is limited by insulated transformers. The PANTECHNIK family of ion source with its wide range of ion beam (various charge states with various beam currents) offers new possibilities and perspectives in the field of ion implantation. In addition to all these possibilities, the PANTECHNIK ion sources have many other advantages like: a very long lifetime without maintenance expense, good stability, efficiency of ionization close to 100% (this improves the lifetime of the pumping system and other equipment), the possibility of producing ion beams with different energies, and a very good reproducibility. The main characteristics of sources like Nanogan or SuperNanogan will be recalled. We will especially present the results obtained with the new Microgan 10 GHz source that can be optimized for the production of high currents of monocharged ion, including reactive gas like BF3 (2 mA e of B+) or medium currents of low charge state like 0.5 mA e of Ar4+. The latest results obtained with Microgan 10 GHz show that it is possible to drive the source up to 30 mA e of total current, with an emittance of 150 π mm mrad at 40 kV and also to maintain the production of multicharged ions like Ar8+.
Development of a H− ion source for the high intensity proton linac at Japan Atomic Energy Research Institute
Authors: Oguri H. , Tomisawa T. , Kinsho M. , Okumura Y. , Mizumoto M.
Published: July 2002

A volume production type negative ion source has been designed and tested for the high intensity proton linear accelerator at Japan Atomic Energy Research Institute. The dimensions of the plasma chamber are 150 mm in diameter and 200 mm in length. The beam extractor consists of four electrodes with a single aperture of 8 mm in diameter. Negative ion current (density) of 40 mA (80 mA/cm2) was achieved with a duty factor of 5%.
Compact microwave ion source for extremely low energy ion irradiation system
Authors: Gotoh Y. , Kubo H. , Tsuji H. , Ishikawa J.
Published: July 2002

The performance of a compact microwave ion source developed for extremely low energy ion extraction was measured. The ion source was modified to be fitted for the ion extraction at the voltage lower than 100 V. The current–voltage characteristics, mass spectrum, absolute ion energy, and energy spread of argon ion beam were estimated with a sector magnet. The results showed that the mass spectrum showed a clear separation of singly charged ions and doubly charged ions even at the extraction voltage of 4 V. Mass separated Ar+ current of 0.5 nA at 4 V extraction was obtained. An excess ion energy due to presence of plasma potential was 14 eV at the pressure of 5×10−3 Pa, and 66 eV at 9×10−4 Pa. Energy spread was narrower than 12 eV, from rough estimate of the mass spectrum. These results summarize that the present ion source can be used for extremely low energy ion irradiation system.
Hydrogen negative ion beam acceleration in a multiaperture five-stage electrostatic accelerator
Authors: Watanabe K. , Fujiwara Y. , Hanada M. , Kashiwagi M. , Kitagawa T. , Miyamoto K. , Morishita T. , Okumura Y. , Takayanagi T. , Taniguchi M.
Published: July 2002

To develop a high power negative ion source/accelerator for 1 MeV class neutral beam injector, hydrogen negative ion beam acceleration has been studied using a five-stage, multiaperture electrostatic accelerator. After conditioning each accelerator stage, the negative ions are accelerated to 1 MeV successfully with a drain current of 25 mA for 1 s. Cs was introduced into the ion source to produce higher current density. The highenst acceleration current density of 15 mA/cm2 was successfully accelerated up to an energy of 700 keV for 1 s, keeping the optimum perveance. The total acceleration current of 200 mA was extracted from nine central apertures 14 mm diameter each. A preliminary measurement of the heat load in the accelerator showed that the direct interception of the beam for the first grid and the third grid was negligibly small. The highest heat load was 4.5% of the input power at the second grid.
Development of a high-current plasma lens for focusing broad beams of heavy metal ions
Authors: Goncharov A. , Protsenko I. , Yushkov G. , Brown I. G.
Published: July 2002

We describe the results of investigations of the manipulation of moderate energy, large area beams of heavy metal ions by a high-current electrostatic plasma lens. Electrostatic plasma lenses are essential for the focusing of high-current heavy ion beams with moderate energies of 10–100 keV. In our experiments, beams of carbon, copper, zinc, and tantalum (separately) were formed by a repetitively pulsed vacuum arc ion source with energy in the range 10–50 keV, beam current up to 0.5 A, and initial diameter 10 cm. The characteristics of the focusing of the ion beam passing through the lens were measured by a radially movable, magnetically suppressed Faraday cup. The plasma lens focusing properties were determined for a number of different distributions of the lens ring-electrode potentials. We have shown that by changing the lens electrode potential distribution we can control the lens focusing, in both the convergent and divergent regimes. Some features of heavy metal ion beam focusing under these conditions are discussed. The experiments demonstrate the versatile possibilities of the plasma lens for use with moderate-energy, high-current, heavy ion beams.
Highly charged metal ions produced from volatile organometallic compounds in a room temperature electron beam ion trap
Authors: Werner T. , Zschornack G. , Großmann F. , Ovsyannikov V. P. , Ullmann F.
Published: July 2002

A MIVOC system as it has been applied to several electron cyclotron resonance ion sources has been used to load a room temperature electron beam ion trap with a selection of different metals. X-ray measurements have demonstrated the ability of this method to produce highly charged ions for a large number of elements in a simple way and at low costs, which is favored by the low consumption rate of the used substances and operation of the ion trap at room temperature. The analysis of x-ray spectra measured with a Si(Li) semiconductor detector which is based on atomic structure calculations indicate the production of Mn23+, Fe25+, Ge30+, and Sn44+ ions.
Miniature photoconducting capacitor array as a source for tunable THz radiation
Authors: Hashimshony D. , Zigler A. , Papadopoulos K.
Published: July 2002

The prospects of a miniature photoconducting capacitor array as a source for THz radiation are discussed. The device consists of an alternately biased capacitor array built on a semiconductor substrate and illuminated by a short laser pulse. The laser pulse creates a propagating plasma front inside the crystal volume by side illumination, and triggers the discharging of the capacitor by shorting out the photoconducting material between each capacitor plate. The sequential discharge of the capacitor array inside the expending plasma region can be considered as an interaction between a static wave and a superluminous ionizing front. In the present article we have demonstrated production of two cycle pulses with a center frequency of up to 1.5 THz. The device combines elements from the well-known “frozen-wave” generator and from the photoconducting switches array. The underlying physics of this radiation mechanism is very similar to the dc-to-ac conversion mechanism inside a gas-filled capacitor array which generates coherent microwave radiation.
Growth of GaN films by hot wall epitaxy
Authors: Ishida A. , Yamamoto E. , Ishino K. , Ito K. , Fujiyasu H. , Nakanishi Y.
Published: July 2002

GaN films were prepared by hot wall epitaxy on sapphire (0001) substrates from Ga and NH3 sources. Growth characteristics of the GaN films were investigated from reflection high energy electron diffraction (RHEED) and x-ray diffraction measurements, and effects of initial layers on the film growth are discussed. High quality films with streak RHEED patterns were obtained when the films were grown on a GaN initial layer prepared by Ga predeposition and its nitridation on surface nitrided sapphire substrates.
Structural phase behavior in II–VI semiconductor nanoparticles
Authors: Bandaranayake R. J. , Wen G. W. , Lin J. Y. , Jiang H. X. , Sorensen C. M.
Published: July 2002

Cubic structured CdS, CdSe, and CdTe, II–VI semiconductor nanoparticles have been synthesized using aqueous solution precipitation at room temperature. The ‘‘as-prepared’’ particles have a size of about 30 Å. Thermal annealing causes (a) an increase in particle size; (b) a structural transition from the cubic to the bulk, hexagonal structure for CdS and CdSe; and (c) no structural transition for CdTe. The unexpected cubic phase for small particles of CdS and CdSe may be due to either metastability or an equilibrium surface effect. The latter would imply a strong correlation between structure and the size and surface properties, and that there is a minimum size for hexagonal phase stability.
InAs self-assembled quantum dots on InP by molecular beam epitaxy
Authors: Fafard S. , Wasilewski Z. , McCaffrey J. , Raymond S. , Charbonneau S.
Published: July 2002

We present results of room temperature photoluminescence (PL) emission from a 0-dimensional system in the ∼1.4 to ∼1.7 μm spectral region. Molecular beam epitaxy was used to grow InAs self-assembled quantum dots in AlInAs on an InP substrate. Preliminary characterizations have been performed using PL and transmission electron microscopy. The low temperatures PL spectra also display excited state emission and state filling as the excitation intensity is increased.
Multiphonon-relaxation processes in self-organized InAs/GaAs quantum dots
Authors: Heitz R. , Grundmann M. , Ledentsov N. N. , Eckey L. , Veit M. , Bimberg D. , Ustinov V. M. , Egorov A. Yu. , Zhukov A. E. , Kop’ev P. S. , Alferov Zh. I.
Published: July 2002

We report on optical studies of relaxation processes in self-organized InAs/GaAs quantum dots (QDs). Near resonant photoluminescence excitation spectra reveal a series of sharp lines. Their energy with respect to the detection energy does not depend on QD size and their energy separations are close to the InAs LO phonon energy of 32.1 meV estimated for strained pyramidal InAs QDs. The shape of the PLE spectra is explained by multiphonon relaxation processes involving LO phonons of the QD as well as of the wetting layer, an interface mode, and low frequency acoustical phonons.
Defect structures in metallic photonic crystals
Authors: Özbay E. , Temelkuran B. , Sigalas M. , Tuttle G. , Soukoulis C. M. , Ho K. M.
Published: July 2002

We have investigated metallic photonic crystals built around a layer-by-layer geometry. Two different crystal structures (face-centered-tetragonal and tetragonal) were built and their properties were compared. We obtained rejection rates of 7–8 dB per layer from both metallic crystals. Defect modes created by removing rods resulted in high peak transmission (80%), and high quality factors (1740). Our measurements were in good agreement with theoretical simulations.
Control of Co flux through ternary compound for the formation of epitaxial CoSi2 using Co/Ti/Si system
Authors: Kim Gi Bum , Baik Hong Koo , Lee Sung Man
Published: July 2002

A ternary compound of Co3Ti2Si is suggested as reaction barrier for the formation of epitaxial CoSi2 in the Co/Ti/Si system. It has a role to control Co diffusion to the Si substrate, followed by formation of CoSi2. After Co3Ti2Si was formed, CoO and Ti oxide were formed at surface, depending on Ti thickness. In the case of Ti oxide being at surface, the outdiffusion of Ti in ternary compound was accelerated. Then, the decomposition of Co3Ti2Si occurred by reaction with Ti oxide, resulting in uniform epitaxial CoSi2. However, in the case of CoO being at surface, the Ti outdiffusion was suppressed, followed by thermally decomposition of Co3Ti2Si. This caused nonuniform Co supply to form nonuniform CoSi2.
Electrical characteristics of metal/AlN/n-type 6H–SiC(0001) heterostructures
Authors: Aboelfotoh M. O. , Kern R. S. , Tanaka S. , Davis R. F. , Harris C. I.
Published: July 2002

Metal/AlN/n-type 6H–SiC(0001) heterostructures have been prepared by growing wurtzite AlN layers on vicinal 6H–SiC(0001) using gas-source molecular beam epitaxy. High-resolution transmission electron microscopy results show that the interface between the AlN layer and the Si-terminated 6H–SiC substrate is microstructurally abrupt, but contains defects originating at step sites on the 6H–SiC surface. The interface is found to have a low density of trapped charges of 1×1011 cm−2 at room temperature without any postgrowth treatment. This value is comparable to those reported for thermally grown and deposited oxides on n-type 6H–SiC(0001), and indicates the formation of a high quality interface.
Production of intense atomic nitrogen beam used for doping and synthesis of nitride film
Authors: Xu Ning , Du Yuan-Cheng , Ying Zhi-Feng , Li Fu-Ming
Published: July 2002

An arc-heated source for producing an intense nitrogen atom beam with intensity of 1019 atoms/sr s and kinetic energies of 0.5–4 eV is presented. The arc discharge has been carried out in pure nitrogen gas and maintained stable in an arc operating pressure of 30–300 Torr. The beam kinetic energy changes with the arc pressure, and is insensitive to the arc current. Auger electron spectroscopy analysis showed that a TiNO layer with a thickness of about 100 Å was formed on the smooth Ti wafer at room temperature with interaction of the atomic nitrogen beam.
Evidence of a new magnetic flux pining center in Nd1Ba2Cu3Oy single crystals
Authors: Ting Wu , Egi T. , Kuroda K. , Koshizuka N. , Tanaka S
Published: July 2002

Highly flat, clean, and stable surfaces of as-prepared Nd1Ba2Cu3Oy (Nd123) single crystals have been studied using an ultrahigh vacuum scanning tunneling microscope/spectroscopy (UHV-STM/STS) system. The results of large area STM scans together with the results of STS measurements, magnetization loops measured at several temperatures below Tc, and critical current density measurements reveal the presence of a new magnetic flux pinning center in Nd123 single crystals prepared in a reduced oxygen partial pressure. This pinning center is more conductive on the surface than the matrix and has a size ranging from several to several tens of nanometers as seen by STM. Similar pinning center may be introduced to other high temperature superconductors to increase their critical current densities in an applied magnetic field.