bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantitative measurements with x-ray microscopes in laser-fusion experiments
Authors: Marshall Frederic J. , Su Qichang
Published: July 2002

X-ray imaging of laser-fusion target implosions has been performed on the University of Rochester’s OMEGA laser system by means of grazing-incidence optical imaging with Kirkpatrick–Baez (KB) microscopes. High spatial resolution imaging (∼5 μm) of hard x-ray emission (up to ∼7 keV) has been achieved. New grazing-incidence optics are currently being fabricated for the OMEGA Upgrade experimental laser-fusion facility. Projected performance indicates that resolution may be increased to ∼2 μm at the center of the field of view and sensitivity extended to ∼8 keV. Uses of KB microscopes on the OMEGA Upgrade will include hard x-ray imaging, grating-dispersed imaged spectroscopy, and framed imaging. A novel technique for monochromatic imaging with KB microscopes has also been demonstrated enabling images of target emission in a narrow energy band (10 to 20 eV) to be obtained.
Excitation and detection of ICR modes for control and analysis of a multicomponent plasma
Authors: Schweikhard L. , Ziegler J. , Beiersdorfer P. , Beck B. , Becker St. , Elliott S.
Published: July 2002

Methods are being developed to analyze and control the ionic composition of a confined plasma with use of ion cyclotron modes. Resolving powers much higher than possible with time-of-flight analysis are achieved. Selected heating and removal of a given species from the plasma are demonstrated. The methods have been extended from singly charged ions confined in a Penning trap to very highly charged ions such as bare Kr36+ confined in an electron beam ion trap.
Double-focusing small-angle x-ray scattering camera at an ESRF undulator
Authors: Riekel C. , Bösecke P. , Diat O. , Lorenzen M. , Sanchez del Rio M. , Snigireva I.
Published: July 2002

A double-focusing small-angle x-ray scattering camera has been installed at the European Synchrotron Radiation Facility. The camera uses a low-β undulator as insertion device. Stable operation has been demonstrated at 13 keV. A beam size at the sample position in the range of 100–200 μm and a flux in excess of 1010 Ph/s have been obtained. The camera allows to resolve the first order of collagen (67 nm).
Heterodyne radiometer at Rijnhuizen Tokamak Project for electron cyclotron emission and absorption measurements
Authors: van Gelder J. F. M. , Husmann K. C. E. , Miedema H. S. , Donné A. J. H.
Published: July 2002

The 20-channel heterodyne radiometer of the Rijnhuizen Tokamak Project (RTP) measures microwaves in the range between 86 and 146 GHz. The spatial resolution is ∼7–16 mm parallel and 25–1300 mm2 perpendicular to the viewing direction, depending on the position in the torus. A waveguide network gives the opportunity to do alternate measurements of X- and O-mode electron cyclotron emission (ECE) from the low-field side (LFS) and X-mode ECE from the high-field side (HFS). A backward wave oscillator is installed at the HFS, for the purpose of measuring the electron cyclotron absorption (ECA) of the plasma. This set-up also provides a possibility for fast relative calibration of the radiometer. To reduce the effects of multiple-pass reflections and standing waves, Macor viewing dumps are mounted at both sides. A comparison of HFS and LFS ECE measurements during electron cyclotron heating will be given as a first result. First results of ECA measurements were obtained but will be presented in the future.
A new design for a simple and effective pyrolysis nozzle in a supersonic free jet
Authors: Cameron Melanie R. , Kable Scott H.
Published: July 2002

A new design for a pyrolysis nozzle to be used in conjunction with a supersonic free jet is presented. Advantages include its simple construction and inexpensive materials. The difluorocarbene (CF2) radical was chosen as a test molecule, and its Ã(1B1)←X̃(1A1) electronic transition was examined using laser induced fluorescence spectroscopy. The radical was formed by pyrolysis of C2F4 at ∼1200 K within the nozzle. The effect of different nozzle designs on the subsequent vibrational and rotational cooling was investigated. Small changes in design and expansion conditions resulted in large changes in ultimate rotational and vibrational temperature.
Effect of local electric fields on microchannel plate detection of incident 20 keV protons
Authors: Funsten H. O. , Suszcynsky D. M. , Harper R. W. , Nordholt J. E. , Barraclough B. L.
Published: July 2002

We present data demonstrating the influence of an applied electric field E oriented normal to the input surface of a microchannel plate (MCP) detector on the critical operating parameters of the detector, including the quantum detection efficiency, the spatial resolution, and pulse height distribution. The MCP detector response is characterized using 20 keV protons as the primary radiation. An applied electric field E<−4 V/mm, where a negative value of E corresponds to a nearby object that is biased positive relative to the input surface, results in a high spatial resolution and a quantum detection efficiency that is approximately equal to the open area ratio of the MCP. An electric field −1<E<5 V/mm results in low spatial resolution, in which up to 32% of the measured signal appears as a localized noise that extends several millimeters from the point of ion impact, and a maximum quantum detection efficiency of approximately 0.87. Furthermore, a separate peak in the pulse-height distribution arises from ions striking the web of the MCP detector and has a much lower pulse magnitude than that of ions striking channels. For E≳5 V/mm, the spatial resolution increases, and the quantum detection efficiency slightly decreases from its maximum value with increasing E. The characteristics of each of these electric field configurations are analyzed in the context of the yield and transport of secondary electrons created at the web of the MCP detector, and the results can be scaled to other ions and energies according to the secondary electron yield of ions striking the web.
Volume scaling and magnetic field scaling on SC-ECRIS at MSU-NSCL
Authors: Gammino S. , Ciavola G. , Antaya T. , Harrison K.
Published: July 2002

The application of the high B mode concept has allowed an effective upgrading of the superconducting electron cyclotron resonance (ECR) ion source SC-ECRIS, which is now one of the best operating ECR ion sources in the world in terms of highly charged ion production. To increase the high charge state intensities and the total extracted current we tried to enlarge the plasma volume, but no clear evidence of volume effects was substantially achieved. We also tried to increase the magnetic field of the trap. The theory which led to these experiments is outlined in the following along with the results of tests using larger plasma volumes and tests with larger magnetic field. Even if the theoretical basis is not always well established, the beneficial effect of magnetic field enhancement on ECR source performances is confirmed. The capability of superconducting ECR ion sources to get higher results with respect to room temperature source by means of a higher and variable hexapolar field is underlined.
80 Hz repetitive centrifuge injector for hydrogen pellets
Authors: Lang P. T. , Cierpka P.
Published: July 2002

The repeating centrifuge pellet injector developed for plasma fuelling experiments at ASDEX Upgrade was improved to give higher repetition rates. The system is now capable of launching pellet series at rates of up to 80 Hz and speeds of up to 1.2 km/s. Differently sized (nominal pellet masses 1.7–4.3×1020 atoms) deuterium pellets have been injected into ASDEX Upgrade. The only limitations at present derive from the pellet feed-in by a single storage cryostat. These might be overcome by using several feed-in sources
Production of U92+ with an electron beam ion trap (invited)
Authors: Marrs R. E.
Published: July 2002

A super electron beam ion trap has been used to produce bare U92+ ions at an electron beam energy of 198 keV. Evaporative cooling with light ions was used to trap a population of 5×104 highly charged uranium ions for many seconds and reduce their temperature to less than 2q eV, suggesting that a very low emittance source of these ions is possible. Roughly 10 U92+ and 500 U91+ ions were present in the Super electron beam ion trap as determined from x-ray emission spectra of the trapped ions.
Cesium injection into a large rf-driven hydrogen negative-ion source
Authors: Takanashi T. , Takeiri Y. , Kaneko O. , Oka Y. , Tsumori K. , Kuroda T.
Published: July 2002

A large rf-driven hydrogen negative-ion source has been developed for a neutral beam injection (NBI) system in the fusion application. The rf plasma generator is a metal-walled multicusp bucket source, the dimensions of which are 30 cm×30 cm in cross section and 20 cm in depth. An induction coil antenna is fully immersed in the rf plasma generator, and is used for coupling the rf power into plasma. A strong external magnetic filter is generated in front of the plasma electrode for negative-ion production, and a filter field strength of more than 1000 G cm is required to reduce the electron temperature in the extraction region as low as 1 eV. Precisely 5.5 mA of a negative-ion current was obtained from a single aperture, corresponding to 4.1 mA/cm2 of current density. A small amount of cesium was supplied to the rf plasma generator from a cesium oven. As a result, a lowering of the operational gas pressure and improvement of the negative-ion production efficiency were observed. The optimum bias voltage was reduced by the cesium injection, which may be related to the reduction of the plasma potential.
Radio frequency, microwave, and electron cyclotron resonance ion sources for industrial applications: A review (invited)
Authors: Wartski L. , Schwebel C. , Aubert J.
Published: July 2002

We recall the different classes of electromagnetic field excited ion sources and their characteristic features in the scope of industrial applications. Emphasis is laid on various criteria and conditions: long source lifetimes, intense inert or reactive ion beams free from contaminants, low process pressures, severe environmental conditions, reliability, possibility of automatic control, simplicity in handling, and maintenance. Examples of sources particularly suited to processes involving deposition or surface modification of materials are reviewed. Specific technological solutions and designs applied to these sources for industrial applications are examined. A few examples of applications using ion-beam processes in different fields (optics, microelectronics, and mechanics) are presented and further trends, especially for inline surface treatments, are examined.
Spectral measurements of hyper-Rayleigh light scattering
Authors: Kaatz P. , Shelton D. P.
Published: July 2002

An apparatus is described for the measurement of second-order nonlinear optical properties via hyper-Rayleigh scattering with 1 cm−1 spectral resolution of the scattered light. The setup allows a complete investigation of the polarization dependence of the second-harmonic scattered light. The combination of good spectral resolution, polarization analysis, and high sensitivity allows the determination of accurate polarization ratios of the scattered light. Consequently, information on the relative magnitude of hyperpolarizability components may be inferred from the measurements. Liquid phase measurements of a number of pure organic solvents including substituted benzene compounds are reported with approximately 5% uncertainty in the relative scattered intensities. Vapor phase measurements are also possible using the same apparatus, allowing a separation of the intrinsic molecular nonlinearities from contributions to hyper-Rayleigh scattering due to intermolecular interactions.
Effusive flow delay times for gaseous species in a compact rf ion sourcea)
Authors: Welton R. F. , Piotrowski A. , Alton G. D. , Murray S. N.
Published: July 2002

A rf ion source is presently being developed and evaluated as a potential candidate for use in generating radioactive ion beams (RIBs) for the experimental research program at the Holifield Radioactive Ion Beam Facility (HRIBF) now under construction at the Oak Ridge National Laboratory. For this application, any time delays that are excessively long with respect to the half-life of the radioactive species of interest can result in significant losses of the RIB intensity; therefore the times for effusive flow through the ion source are of fundamental importance since they set limits on the minimum half-life of radioactive species that can be processed in the source. Complementary experimental and computational techniques have been developed which can be used to determine the characteristic delay times for gaseous species in low-pressure ion source assemblies. These techniques are used to characterize the effusive delay times for the stable counterparts of various atomic and molecular radioactive species in the ORNL-rf source: He, Ne, Ar, Kr, Xe, H2, CO, CO2, N2, N2O, and O2.
Sectional and projectional emittance measurementsa)
Authors: Sarstedt M.
Published: July 2002

For many applications of ion sources the quality of the generated ion beam plays an increasingly important role. Ion sources consist of the plasma generator and the extraction system. Both parts can, due to high ion temperature or various aberrations, contribute to a degrading of the beam quality. Though the beam quality is determined by many more factors, the transverse motion of the particles certainly is one of the important parameters. Knowledge of it can be obtained by an emittance measurement. This is best done in a four-dimensional phase space, yielding a density distribution as function of the transverse spatial and momentum coordinates. Often, however, due to practical considerations, only two dimensions of the four-dimensional ‘‘trace space’’ are being measured. This two-dimensional data can be obtained as a section or as a projection of the four-dimensional trace space, where both methods have their merits. Projectional emittance measurements can usually be performed much easier and quicker, but by the projection of the four-dimensional space onto a two-dimensional plane information is lost. And although not all the particles of the beam are represented in a section of trace space, here aberrative distortions of the emittance can be seen most clearly and allow an easier comparison to numerically obtained data. The advantages and disadvantages of both methods are discussed. Numerical and experimental examples are presented.
Secondary bremsstrahlung dose rates from glancing incidence target
Authors: Job P.K. , Haeffner D.R.
Published: July 2002

Several collaborative access teams at the Advanced Photon Source (APS) are planning to use a vertically or horizontally reflecting mirror as the first optical element in the insertion device beamlines. The scattering of the bremsstrahlung from the glancing incidence mirrors is significantly different than that from normal incidence targets. The Electron Gamma Shower program (EGS4) was used to calculate the angular distribution of the scattered secondary bremsstrahlung from copper and silicon glancing incidence mirrors. These calculations were done for an incident angle of 0.15°. Pair production, positron annihilation at rest and in flight, Moliere multiple scattering, Moller and Bhabha scattering, delta ray production, Compton scattering, the photoelectric effect, and the continuous energy loss by Bethe-Bloch formalism were the processes simulated in this calculation. The dose at one meter away from the mirror, due to the scattered secondary bremsstrahlung, was calculated from the energy deposited in the standard ICRU tissue placed at that location. Since the EGS4 result is expressed as the dose per photon, the dose rate was obtained by multiplying the dose per photon by the total number of photons produced in unit time in the insertion device vacuum chamber. The dose rate results and its implication for the design of the first optical enclosures are presented in this paper.
A circular arc bending model of piezoelectric tube scanners
Authors: Wei Cao , Zhang Honghai , Tao Lu , Li Wenju , Shi Hanmin
Published: July 2002

Based on a circular arc scanning model of piezoelectric tubes, the influence of the tip length mounted on a tube upon the transverse scanning and the relation between the vertical and the transverse displacement of the tip are reported. With this simple model one can obtain three- dimensional features of a piezoelectric tube scanner by just measuring the vertical deformation and a few geometric sizes of the tube without knowing the detailed parameters of the tube. The estimated scanning by the model may be 15% larger than the actually measured one for a certain piezoelectric tube because of the edge effects of the tube. However, the model can be simply revised on the basis of experiments.
Polarization modulated transmission spectro-ellipsometry
Authors: Fukazawa Tomoyuki , Fujita Yasuhiko
Published: July 2002

A polarization modulated transmission spectro-ellipsometer (PMTSE) features high sensitivity for retardation and high-speed data acquisition. Although optical servo control of a photoelastic modulator (PEM) has improved the accuracy of the system, the residual birefringence mainly of the PEM hinders detection of minute retardation. We have installed a compensator in order to cancel out the residual birefringence and realized base line shift that is within 0.2% of full scale. Optical anisotropies are formulated in the Mueller matrices. Accuracy for a large signal was verified from measurements of a sheet polarizer and a quartz rotator. Detectability was ascertained from the retardation spectrum, <1 nm, of a amorphous poly-olefin film and aqueous solution of a chiral metal complex, Δ−[Co(en)3]3+, whose peak signal magnitude is <1% of full scale. A time resolution of 1 ms was utilized in the dynamic response measurement of a liquid crystal, 5CB, that had a response time of 3–4 ms.
Real time monitoring of the growth of transparent thin films by spectroscopic ellipsometry
Authors: Kildemo M. , Drévillon B.
Published: July 2002

Real time monitoring of the growth of plasma deposited transparent thin films by spectroscopic phase modulated ellipsometry is presented. Two on-line methods of determination of the refractive index n and the film thickness d are evaluated, before extension to feedback control. The first one is based on the inversion of the Fresnel equations. This method is very fast (0.2 s with a conventional PC 486 computer) but requires the simultaneous measurement of various photon energies to be extended on thick layers. A 5% relative precision is obtained on 5000–6000-Å-thick films even when deposited at a high deposition rate (32 Å s−1). On the other hand, better precision can be obtained using a slower least square fit procedure based on single photon energy measurement of the outermost layer. In particular, in the latter case, the product nd can be determined with a 1% precision, up to 5000–6000 Å.
Pyrometric temperature measurement method and apparatus for measuring particle temperatures in hot furnaces: Application to reacting black liquor
Authors: Stenberg J. , Frederick W. J. , Boström S. , Hernberg R. , Hupa M.
Published: July 2002

A specialized two-color pyrometric method has been developed for the measurement of particle surface temperatures in hot, radiating environments. In this work, the method has been applied to the measurement of surface temperatures of single reacting black liquor char particles in an electrically heated muffle furnace. Black liquor was introduced into the hot furnace as wet droplets. After drying, the resulted particles were processed in different atmospheres corresponding to combustion, pyrolysis, and gasification at furnace temperatures of 700–900 °C. The pyrometric measurement is performed using two silicon photodiode detectors and 10 nm bandpass filters centered at 650 and 1050 nm. Thermal radiation is transferred using an uncooled fiberoptic probe brought into the vicinity of the char particle. The key features of the pyrometric apparatus and analysis method are: (1) Single particle temperature is resolved temporally at high speed. (2) The thermal radiation originating from the furnace and reflected by the particle is accounted for in the measurement of the surface temperature. (3) Particle temperatures above or below the furnace temperature can be measured without the need of a cooled background assisting the measurement in the hot furnace. To accomplish this, a minimum particle size is needed that is a function of the temperature difference between the particle and furnace. Particles cooler than the furnace can be measured if their diameter is more than 0.7 mm. Surface temperatures of 300–400 °C above the furnace temperature were measured during combustion of black liquor char particles in air. In atmospheres corresponding to gasification, endothermic reactions occurred, and char temperature remained typically 40° below the furnace temperature.
Balloon-borne x-ray spectrometer for detection of x rays produced by thunderstorms
Authors: Eack Kenneth B.
Published: July 2002

A new balloon-borne instrument designed by the author detects x rays produced in thunderstorms. The instrument uses a sodium iodide (NaI) scintillation detector, and flies on a small meteorological balloon. A three bin (30 to 60, 60 to 90, and 90 to 120 keV) x-ray spectrum is acquired every 0.25 s. The deployment of these detectors with electric-field meters has resulted in several vertical profiles of x-ray intensity and electric-field strength. These data support the hypothesis that the electric field generated by the thunderstorm can produce energetic electrons, which in turn emit bremsstrahlung x rays.
Characteristics of an x-ray excited current detected with a scanning tunneling microscope tip
Authors: Tsuji Kouichi , Hirokawa Kichinosuke
Published: July 2002

We have found that a tip current is detected with a scanning tunneling microscope apparatus under the conditions of x-ray irradiation at a tip–sample distance of about 600 nm. At this distance the tunneling current was undetectable. This tip current was generated by the electrons emitted from a sample of thin metallic film by a photoelectric effect. The tip current is amplified in the presence of molecular gases such as O2 depending on their pressures. Thus, we speculate that the emitted electrons ionize the molecules, and produce many electric carriers, which are detected as a tip current. Furthermore, it was found that the tip current increased when the bias voltage and the x-ray power were amplified. A line scan of the tip current indicated that the electrons emitted from an area about 2 mm in diameter contributed to the tip current.
Corundum-filled resonator systems for high-pressure and low-temperature electron paramagnetic resonance studies
Authors: Krupski Marcin
Published: July 2002

A cylindrical corundum-filled resonator of the TE112-type in the microwave X band, coupled to a coaxial line, is used in two systems designed for the high-pressure, low-temperature electron paramagnetic resonance (EPR) studies. The first one is used up to 800 MPa and over a temperature range of 80–400 K. The second permits EPR measurements down to 4 K in the pressure range below 400 MPa. Pressure and temperature can be simultaneously varied and controlled with the high accuracy needed to study spectral anomalies in the vicinity of the phase transitions in solids.
New doser for chemical vapor deposition of low vapor-pressure solid precursors
Authors: Serghini-Monim S. , Coatsworth L. L. , Norton P. R. , Puddephatt R. J.
Published: July 2002

In this article we describe a new ultrahigh vacuum compatible device to maximize the volatilization of low vapor-pressure precursors used in chemical vapor deposition processes while minimizing their dissociation. A differentially pumped system that places the precursor close to the target substrate was adopted to achieve this configuration; it also allows loading and unloading of the precursor reservoir without breaking vacuum. The device permits the volatilization of low vapor-pressure solid precursors by passing a preheated carrier gas through the precursor which is placed between two fritted disks. This device was also used without a carrier gas and proved its efficiency. The complexes (1,1,1,5,5,5-hexafluoropentanedionato)(1,5-cyclooctadiene) copper (I), [(hfac)Cu(COD)], and (1,1,1,2,2,3,3-heptafluoro-7, 7-dimethyl-4, 6-octanedionato) (trimethylphosphine) silver (I), [(fod)AgPMe3], proved the efficacy of this doser in delivering intact precursors to the substrate using reflection-absorption infrared spectroscopy and mass spectrometry techniques during the adsorption of these precursors on polished Al disks and on polyurethane thin films spun cast onto similar polished Al disks.
Simultaneous measurement of size and velocity of small particles in laminar flows
Authors: Es-Satte M. , Pellat-Finet P. , Schmied L. , Lesage A. , Richou J.
Published: July 2002

A new laser anemometer gauge is presented here. The velocity and the size of spherical particles are simultaneously measured without uniform illumination and preliminary calibration. The used method is based on Mie’s scattering light theory. The device is able to measure the velocity and size of hydrogen bubbles electrolytically produced by a platinum wire immersed in the water flow.
Reply to ‘‘Comment on ‘Comments on the use of asymmetric monochromators for x-ray diffraction on a synchrotron source’ ’’ [Rev. Sci. Instrum. 66, 2174 (1995)]
Authors: Nave Colin , Clark Graham , McSweeney Sean
Published: July 2002

The issue raised in Nave et al. [Rev. Sci. Instrum. 66, 2174 (1995)] is the description and results given by Sanchez del Rio and Cerrina [Nucl. Instrum. Methods A 301, 589 (1991)] and has no bearing on our understanding or otherwise of the SHADOW code (we do not refer to SHADOW in our article). The problem is whether Sanchez del Rio and Cerrina demonstrate that a demagnified image is obtained from asymmetric monochromators when operating in the white beam on a synchrotron source.
A piezotube scanner for atomic force microscopy in solution
Authors: Mou Jianxun , Huang Gang , Shao Zhifeng
Published: July 2002

A novel piezotube scanner used in the atomic force microscope (AFM) is described. Unlike other designs where the electrodes on the outside are subjected to high voltage, in our design all electrodes are placed on the inside of the tube scanner, and the outside electrode is simply grounded. With this design and a proper choice of piezomaterials, the scan range of a 1.75 in. tube can be as large as 15 μm when used with NanoScope III, and is not vulnerable to leaking solutions, which often cause severe damage to both the piezotube and the high-voltage driver with the other designs. Therefore, this new design will be valuable for biological AFM where imaging in solution is often required, and is simple enough to be fitted to an existing AFM.
Fabrication and characterization of 100-nm-thick GaAs cantilevers
Authors: Harris J. G. E. , Awschalom D. D. , Maranowski K. D. , Gossard A. C.
Published: July 2002

We describe a new process for making submicron, micromechanical cantilevers out of GaAs epilayers grown by molecular beam epitaxy. The extremely high aspect ratios of these cantilevers (typically 100 nm thick and 100 μm long) give spring constants as low as 10−4 N/m. We present characterizations of the cantilevers’ resonant frequencies, quality factors, and spring constants. The ability to fabricate III–V GaAs-based mechanical microstructures offers new opportunities for integration with electronics for strain-sensitive force detection.
A photoacoustic scanning method to determine thermal effusivity of solid samples
Authors: Philip J.
Published: July 2002

A technique is demonstrated to determine thermal effusivity of solids using a photoacoustic scanning method. The technique involves changing the backing medium for a highly absorbing sample layer by scanning its surface with an intensity modulated light beam. The method is free of photoacoustic cell parameters as well as experimental conditions and is demonstrated to give good results.
Lock-in amplifier with autotracking bandpass filter
Authors: Sato A. , Ohara A. , Ogawa Y. , Suzuki M.
Published: July 2002

A simple, low-cost lock-in amplifier was described. This system has an autotracking bandpass filter which synchronizes its center frequency automatically with the reference frequency
A liquid nitrogen cooled ionizer for a quadrupole mass spectrometer
Authors: Farrall Paul D. , Engel Thomas
Published: July 2002

An ultrahigh vacuum compatible cooled ionizer suitable for use with a quadruple mass spectrometer has been constructed. It allows one to monitor rapidly changing signals of condensable gases as are commonly encountered in modulated molecular beam studies of surface reaction kinetics with minimal distortions due to adsorption/desorption phenomena within the ionizer.
Design and construction of a rapid thermal processing system for in situ optical measurements
Authors: Conrad K. A. , Sampson R. K. , Massoud H. Z. , Irene E. A.
Published: July 2002

A rapid thermal processing system is described incorporating features that enable in situ optical measurements. In particular, a system incorporating an in situ spectroscopic ellipsometer is described highlighting some of the unusual features necessary for ellipsometry measurements. These features include independent optical, vacuum, and heating modules, optical and heating window design, reflector design, and sample manipulation to enable proper positioning for measurement. Although specifically designed with ellipsometry in mind, many of the same principles used in the design of this system will apply to systems for other optical measurements.
Cubic electrodynamic levitation trap with transparent electrodes
Authors: Allison E. E. , Kendall B. R. F.
Published: July 2002

An unconventional electrodynamic suspension system with transparent planar electrodes is described which stably levitates charged solid particles or liquid droplets without the need for feedback control. The system has been used with particles ranging from about 1 to 100 μm diam, under vacuum and within stationary and flowing gases. Operation within low conductivity liquids is possible in principle. The suspension system consists of six transparent conducting electrodes arranged as faces of a hollow cube. Four of these electrodes are driven by a variable-frequency two-phase ac source operating in the low audio frequency range. Advantages of this type of trap for aerosol studies include relatively wide-angle optical access and a geometry naturally suited to the use of three-axis dc crossfields for particle manipulation. Conditions for stable levitation are reviewed as well as methods for determining the radius, mass, charge, and density of a spherical levitated object.
Macromolecular neutron crystallography facilities at Brookhaven National Laboratory’s high flux beam reactor
Authors: Korszun Z. R. , Popeanos M. , Morano S. , Caruso E. , Bosshard H. , Lara J.
Published: July 2002

Neutron crystal diffraction experiments are complementary to x-ray diffraction studies of macromolecules because neutrons are strongly scattered by hydrogen and/or deuterium and can therefore be used to locate these atoms directly in a macromolecule. Since hydrogen atoms constitute about half of the total number of atoms in a macromolecule, and are functionally and structurally important in determining the biological properties of the system, a detailed knowledge of their location can often provide unique information about the system under study. However, because of the relatively low flux (on the order of 106 neutrons/s/cm2) of neutrons available at the highest flux steady-state reactors, high resolution diffraction experiments require large crystals and long data collection times. Typical crystal volumes exceed a cubic millimeter and data collection times approach three to four months to collect complete data to atomic resolution. Because of these limitations, relatively few high resolution neutron structures have been completed to date. To improve data collection efficiency and throughput, we have redesigned the macromolecular neutron crystallography beam line (H3A) at Brookhaven National Laboratory’s high flux beam reactor. In this report, the new facility is described.
A system for grabbing integrated video frames remotely
Authors: Halpern M. , Knotek S. , Tucker G. S.
Published: July 2002

A system for grabbing integrated video frames produced by a remote camera is described. As part of the pointed platform in a balloon-borne experiment, we use a video charge-coupled-device camera to obtain wide field star images. To obtain images with a sufficient signal-to-noise ratio, integration times of up to 1 s are required. In applications where the frame grabber and camera are physically close to each other, timing the frame grabber trigger is straightforward; however, there are several advantages to locating the frame grabber not on the balloon payload. As a result commands issued simultaneously to the frame grabber on the ground and the camera on the balloon can be delayed relative to each other, resulting in failure to acquire an image. We have developed a system where, at the end of an integration, a tone is injected into the video field preceding the transmission of the integrated frame; the tone is used on the ground by a decoder circuit to control the frame grabber acquisition of the integrated frame. The system has operated successfully in the flight of a stratospheric balloon-borne telescope.
Workshop on performance optimization of synchrotron radiation storage rings (invited)
Authors: Decker G. , Safranek J.
Published: July 2002

The purpose of this workshop was to provide a forum, with user participation, for accelerator physicists working in the synchrotron light source field to discuss current and planned state-of-the-art techniques to optimize storage ring performance. The scope of the workshop focused on two areas: lattice characterization and measurement, and fundamental limitations on low frequency beam stability.
Evaluation of Au/GaAsP and Au/GaP Schottky photodiodes as radiometric detectors in the EUV
Authors: Vest R. E. , Canfield L. R.
Published: July 2002

Many applications of synchrotron radiation require an absolute measurement of photon flux. Schottky photodiodes consisting of a thin Au film deposited on GaAsP or GaP are sensitive to radiation in the extreme ultraviolet (EUV) and may be considered for use as radiometric transfer standard detectors. A radiometric detector should exhibit high quantum efficiency, spatial uniformity, resistance to radiation-induced changes, and temporal stability. While Au/GaAsP and Au/GaP Schottky photodiodes display high sensitivity, good uniformity, and resistance to radiation damage, they suffer from temporal instability. Results presented in this paper indicate that the quantum efficiency of Au/GaAsP and Au/GaP photodiodes degrades in the region from 50 nm to 150 nm during normal storage and is unstable at wavelengths as long as 254 nm. This loss of sensitivity is not substantially affected by ambient humidity and may be affected by heating the device. While useful as detectors, Au/GaAsP and Au/GaP Schottky photodiodes are not suitable for use as transfer standards in this spectral region and may not be suitable for other applications in which detector efficiency must be stable over periods longer than a week.
Active trajectory control for a heavy ion beam probe on the compact helical system
Authors: Fujisawa A. , Iguchi H. , Lee S. , Crowley T. P. , Hamada Y. , Hidekuma S. , Kojima M.
Published: July 2002

A 200 keV heavy ion beam probe (HIBP) on the compact helical system heliotron/torsatron uses a newly proposed method in order to control complicated beam trajectories in nonaxisymmetrical devices. As a result, the HIBP has successfully measured potential profiles of the toroidal helical plasma. This article will describe the results of the potential profile measurements, together with the HIBP system and procedures to realize the method.
Argonne National Laboratory high performance network support of APS experiments
Authors: Knot Martin J. , McMahon Robert J.
Published: July 2002

Argonne National Laboratory is currently positioned to provide access to high performance regional and national networks. Much of the impetus for this effort is the anticipated needs of the upcoming experimental program at the APS. Some APS collaborative access teams (CATs) are already pressing for network speed improvements and security enhancements. Requirements range from the need for high data rate, secure transmission of experimental data, to the desire to establish a ‘‘virtual experimental environment’’ at their home institution. In the near future, 155 megabit/sec (Mb/s) national and regional asynchronous transfer mode (ATM) networks will be operational and available to APS users. Full-video teleconferencing, virtual presence operation of experiments, and high speed, secure transmission of data are being tested and, in some cases, will be operational. We expect these efforts to enable a substantial improvement in the speed of processing experimental results as well as an increase in convenience to the APS experimentalist.
Optical emission spectroscopy studies of the effects of nitrogen addition on diamond synthesis in a CH4–CO2 gas mixture
Authors: Hong Tsao-Ming , Chen Sheng-Hsiung , Chiou Yih-Song , Chen Chia-Fu
Published: July 2002

The influence of nitrogen on the growth of diamond using the gas mixtures of CH4–CO2 by microwave plasma chemical vapor deposition was investigated. A clear improvement in the surface morphology and quality of the diamond films indicates the beneficial effect of adding nitrogen to CH4–CO gas mixtures. Analysis using Auger electron spectroscopy and secondary ion mass spectroscopy shows very low and uniform levels of nitrogen in the diamond films. Atomic nitrogen plays a dominant role in C/H/O/N plasma chemical vapor deposition processes because of the amount of oxygen atoms increased via the titration reaction of nitrogen atoms (a high-rate reaction): N+NO→N2+O. This produces a significant influence on diamond synthesis in a CH4–CO2–N2 gas mixture.
Study of a laser-heated electron gun
Authors: Roy P. K. , Moon A. , Mima K. , Nakai S. , Fujita M. , Imasaki K. , Yamanaka C. , Yasuda E. , Watanabe T. , Ohigashi N. , Okuda Y. , Tsunawaki Y.
Published: July 2002

A method of cathode heating using a laser was studied for an electron gun. In order to observe the practicality of the heating system, the characteristics of the laser-heated gun with a dispenser and LaB6 thermionic cathodes have been experimentally investigated. The direct laser irradiation is so efficient that the gun is equipped without heat shielding, a cooling system, or an electrical circuit in the gun chamber for cathode heating. Modeling, based on the experimental data, indicates that the cathode temperature is proportional to one-fourth power of the laser power and that laser power loss and conduction loss of heat in the gun assembly are negligible. An electron beam current density 0.48 A/cm2 was measured with 26 W laser power for a dispenser cathode of 0.06 cm2 emission area. Current density 0.16 A/cm2 with 25 W was recorded for a LaB6 cathode of area 0.12 cm2. Electron beam emittance has been measured by using the typical pepper-pot technique. It was observed that the growth of electron beam emittance was very small in the laser heating.
Time and space resolved measurements of visible-light and soft x-ray emission from foam z-pinch plasmas and implosions
Authors: Lazier S. E. , Barber T. L. , Derzon M. S. , Kellogg J. W.
Published: July 2002

We have developed a time-resolved imaging capability to make measurements of the emission profile or spot size for low density foam z-pinch targets on the Saturn accelerator. By lens-coupling visible emission from the z-pinch target to an array of fiber optics, we obtained an emission profile as a function of time with radial resolution of 200 μm. To measure the emission at temperatures greater than ≈40 eV, x rays from the source were slit-imaged or pinhole-imaged onto a scintillator. The emission was filtered to select 50–80, 200–280, and 400–450 eV x rays. Nonuniformities were observed in both visible and x-ray emissions for solid foam targets. For wire array on foam targets, on-axis x-ray emission-spot implosion velocities calculated for the three spectral regions differed from the mass-implosion velocity. We describe the diagnostics, the image-unfold process, and results from the instrument for both visible and x-ray measurements.
Feasibility study of a method to measure the ECRH field in the plasma interior (abstract)
Authors: Castejón F. , Zurro B. , Cappa A.
Published: July 2002

The precise measurement of the power absorption in some ECRH plasma experiments can be plagued with many practical problems, which makes the direct validation of any theoretical model difficult. In the present work, the feasibility of a method to directly measure the electric field at the predicted resonant position is carried out. From the electric field it is possible to compute the local density power carried by the microwave beam and, hence, deduce the power deposition profile. The method based on measuring the ratio of near and far satellite intensities of He I lines, already used in cold plasma discharges,1 presents challenging problems when applied to a hotter plasma. The electric field is estimated using ray tracing calculations in the TJ-IU torsatron. The field is locally obtained in the plasma from the dispersion relation and the estimations for the injected power (200 kW) show that the effect of the microwave field can be non-negligible on the He I lines. An experimental setup to explore this idea in the TJ-IU torsatron will be described. The low densities of this device and the use of a signal-to-noise subtraction technique make this method feasible according to our preliminary estimation. The difficulties encountered and the results obtained will be reported.
Distinction between DD and DT neutrons in the TFTR neutron collimator (abstract)
Authors: Bitter M. , Johnson L. C. , Ku Long-Poe , Roquemore A. L. , Goeler S. von
Published: July 2002

A difficult part of the analysis of the neutron collimator data is the distinction between contributions from DD and DT neutrons. This is important for the majority of TFTR discharges, which use neutral deuterium heating beams and relatively small amounts of tritium. At present, the DT-neutron contribution is determined from a comparison of the chord-integrated neutron collimator data with measurements of the DT-neutron source strength from general wide-angle detectors, using an iterative computational method. A more satisfactory solution should be obtained with detectors that measure the contributions from DD and DT neutrons, and gamma radiation, directly. Pulse-shaping techniques are insufficient, since the detectors in the neutron collimator are operated in current mode. The presently used data analysis is described and the concept of a new multilayered plastic detector that makes use of the differences in the attenuation of the various radiation components is presented. The dimensions of the detector are based on calculations of the attenuation for the expected neutron energy spectrum.
Review of possibilities for a collective Thomson scattering system on ITER
Authors: Orsitto F. , Giruzzi G.
Published: July 2002

Different scenarios for measuring the alpha particle distribution in ITER by means of a collective Thomson scattering experiment are reviewed. As a result of this analysis, two possible methods are selected, respectively using a 10.6 μm laser (tangential geometry) and a 65–70 GHz gyrotron (backscattering).
Use of thin wall imaging in the diagnosis of laser heated hohlraums
Authors: Suter L. J. , Thiessen A. R. , Ze F. , Kauffman R. , Price R. H. , Rupert V. C. , Slivinsky V. W. , Wang C.
Published: July 2002

High-Z, laser heated hohlraums can be made thick enough to contain thermal radiation, yet thin enough to let out x rays >∼6 keV produced by hot, relatively dense blow-off plasma. We use such “thin wall hohlraums” to observe the physical location of hot, dense, laser produced hohlraum plasmas. This technique has allowed us to come to some understanding of laser transport/deposition, plasma stagnation, and bulk plasma filling.
Measurement of H/D ratio and ion temperature on a HT-6M Tokamak
Authors: Wei Lehan , Lin Xiaodong
Published: July 2002

By combining optical fibers with piezoelectric scanning Fabry–Perot interferometer, the profiles of Hα and Dα have been determined simultaneously in a single Tokamak discharge. Consequently, the ratio of hydrogen to deuterium and ion temperature are obtained. Not only is the uncertainty of shot-to-shot avoided, the results of the experiment indicate that this instrumentation has the advantage of rapid wavelength scanning, large dispersion, high resolution, and good adaptability of working in adverse circumstances such as at a Tokamak site.
Internal toroidal field measurements on the helicity injected tokamak using the transient internal probe
Authors: Galambos J. P. , Bohnet M. A. , Jarboe T. R. , Mattick A. T.
Published: July 2002

Measurements of the local toroidal magnetic field have been achieved on the helicity injected tokamak (HIT) using the transient internal probe (TIP). HIT is a low aspect (a=1.5, R=0.35 m) ratio tokamak designed to study steady state current drive. The TIP diagnostic involves accelerating a small diamond clad magneto-optic probe through the plasma at high velocities (∼2 km/s) using a light gas gun. The local field is obtained by illuminating the probe with a laser and measuring the amount of Faraday rotation in the reflected beam. Measurements were conducted using unclad magneto-optic probes directed along a chord tangent to the toroidal field. Plasma conditions were typically ne∼7×1019 m−3 and Te∼40–80 eV. Measurement uncertainty is less than 2%. No changes in plasma parameters were observed during the first 200 ms (∼40 cm) of probe travel in the plasma. A temporary dip in plasma current, probably due to ablation of the retroreflecting material on the probe, is observed as the probe exits the plasma. Density is unaffected by the presence of the probe in the plasma. No long term deleterious effects to tokamak performance were observed as the TIP diagnostic was found to be quite compatible with the tokamak.
Recombination in GaAs at the AlAs oxide-GaAs interface
Authors: Kash J. A. , Pezeshki B. , Agahi F. , Bojarczuk N. A.
Published: July 2002

Interface recombination in GaAs at the GaAs/AlAs interface has been investigated before and after selective ‘‘wet oxidation’’ of the AlAs layer. Time-resolved photoluminescence of the band-edge GaAs emission has been used to characterize the interface recombination. Prior to oxidation, the interface recombination is low. After oxidation, the interface recombination has greatly increased, and is comparable to a free GaAs surface in air. However, isolating the GaAs layer from the oxide by a 30 nm layer of Al0.3Ga0.7As allows the interface recombination to remain low after the oxidation. These results help explain the low threshold currents which have been observed in vertical cavity lasers which use wet oxidation of AlAs for current confinement.
Development of surface-wave ion source using coaxial-type cavity
Authors: Yoshida Yoshikazu , Miyazawa Toshikazu , Kazama Atsushi
Published: July 2002

A compact 2.45 GHz surface-wave ion source has been developed for the production of stable beams from gaseous feed materials. The source has been operated with two different geometries of surface wave generation, that is, a dielectric disk on ground plane structure and a dielectric disk between the parallel plate structure with a holey top plate. The designer can control the intensity of the emitted microwave simply by varying the thickness of the dielectric plate. The sources have been operated with three different thicknesses of the dielectric plate: td=10, 15, and 20 mm. td=10 mm is the optimum coupling condition. Moreover, the ion beam current of the holey-plate structure is 1.5 times as high as that of the dielectric disk structure.