bluuebunny/crossref_metadata_2025 huggingface dataset:
Overview of the European neutral beam program for the next step fusion device (invited)(abstract)
Authors: Jacquot C.
Published: July 2002

Neutral beam injection systems (NBI) are capable of injecting powers greater than 20 MW, with pulse length of 5 s. These systems, based on acceleration and neutralization of positive deuterium ions, provide heating and current drive capability and are highly reliable and available. For possible application to a ‘‘next step’’ fusion device (ITER or NET), a large extrapolation of neutral deuterium energy is necessary to sustain a noninductively driven toroidal current. For good electrical efficiency of these injectors, the choice of acceleration and neutralization of deuterium negative ions beams is an attractive option. A conceptual European design for ITER/NET is proposed with a pure D− ion source (15 A) biased at a high voltage of −1 MV, a multistage electrostatic accelerator with multihole apertures, a grounded gas neutralizer and an electrostatic deflection beam dump. Special supplies are being studied in order to energize the accelerator (1 MV–15 A) with low stored energy and fast switch off time during a fault in the accelerator. By using nine similar injectors, a neutral power of 75 MW can be installed to drive the ITER current. The expected efficiency is better than 40%. A scalable model (4-A D−, 1 MV) to produce a power of 2-MW D0 can be in operation in 1995. The main areas of uncertainty (D− source, electron trapping, large power accelerator, breakdowns, and power supplies) will be studied with this scalable model. When this first phase has been achieved, the final-size injector will be built.
Radio-frequency ion sources for space propulsion (invited)
Authors: Groh K. H. , Loeb H. W.
Published: July 2002

After more than 25 years of research, development, and qualification work at Radiofrequency Ion Thrusters, so-called RIT, the RIT 10 engine, designed for north–south stationkeeping of geosynchronous satellites, is now ready for a space test onboard the European Retrievable Carrier EURECA. Since two years, the European Space Agency ESA/ESTEC is working at a new technological satellite, called ARTEMIS, at which ion propulsion shall be used operationally for north–south stationkeeping. In the scope of the RIT 10 ground qualification work, an ion beam diagnostic device has been designed and built up to determine the mechanical beam parameters. Moreover, a small test stand has been designed that allows full thruster operation in order to measure the radiated electromagnetic spectrum in an anechoic test chamber. Besides, the development and tests of a scaled-up 50 mN engine RIT 15 have been continued successfully with xenon, krypton, and also argon as propellants. The ion beam profiles have been measured and the influence of the accel-decel ratio on the beam divergence has been studied. A large ion engine with 35 cm ionizer diameter, the RIT 35, has been developed for primary propulsion aiming at a thrust level in the 250 mN range. A laboratory prototype has been subjected to extensive testing and performance mapping. This preliminary work has been finished waiting for further programmatic decisions.
Negative hydrogen ion ECR source
Authors: Dougar-Jabon V. D. , Reznikov D. V. , Santos Mayorga R.
Published: July 2002

To find optimum conditions for the generation of negatively charged hydrogen ions, an ECR source has been investigated. The source consists of a cylindrical cavity placed between Sm-Co disk-type magnetic poles, and microwave and extraction systems. The way in which the negative ions are produced is by the capture of low-energy electrons by vibrationally excited molecules as a result of which the dissociative attachment of negatively charged molecules takes place. Molecules are excited in the plasma volume. The low-energy electrons emerge due to bombardment of the first electrode of the extraction system by the ECR-heated electrons. The intensity of the extracted negative hydrogen ion beam appears to be sensitive not only to pressure, microwave power, and extraction voltage, but also depends on the shape of the ECR surface. Experiments indicate that the hyperboloid of one sheet-type resonance surface is the most effective. Measurements carried out with microwave of 600 W at 2.45 GHz, and at a pressure of 0.3 mTorr show that the negative ion yield attains 1.2 mA through a 0.3-cm-diam extractor hole.
An ECR ion source for ion implantation
Authors: Henke D. , Hentschel R.
Published: July 2002

The lifetime advantage of the filamentless discharge of high-current ECR ion sources is still often diminished through the degradation of the dielectric microwave transmitting window or the antenna. A 2.45 GHz ECR ion source that is now under construction and intended for the production of singly charged ions from reactive or contaminating gases is presented. The microwave power of up to 500 W is coupled into the entirely metallic discharge chamber through a resonant slit. The teflon vacuum sealing window is placed far from the plasma behind a high vacuum waveguide bend and is thus protected from backstreaming electrons and covering source material.
Pulsed operation of a MPDR-type ECR-plasma source for high-power applications
Authors: Papenbreer R. L. , Engemann J.
Published: July 2002

We have developed and tested a new kind of 2.45 GHz microwave plasma disk ion source based on the Asmussen and Root approach1 using only metal, ceramics, and metal–ceramic sealings for high-power operation in excess of 1.2 kW. This corresponds to power densities of more than 1 W/cm3. To reduce thermal runaway, the discharge chamber is fabricated from high-purity aluminia. Ion extraction optics with diameters up to 75 mm (3 in.) can be mounted. The source works in various single-mode resonance conditions controlled by an automatic matching unit. Pulsed magnetron power supplies with pulse frequencies up to 20 kHz and duty cycles adjustable in 10% steps have been found to be very efficient with respect to the extractable ion current density (Jextr.). Therefore this mode of operation makes possible high-power applications while simultaneously lowering the thermal load of the plasma chamber.
A high-current microwave ion source for ion implantation
Authors: Walther S. R.
Published: July 2002

A new 2.45 GHz microwave ion source has been developed for high-current ion implantation. The source uses permanent magnets to generate the ECR magnetic field. This leads to a much simpler and more compact design than typical solenoidal field microwave sources. The strong magnetic field and high-microwave power density are used to achieve a 11B+ ion fraction of up to 30% in extracted boron beams. Previous work on microwave ion sources for ion implantation has ordinarily not dealt with performance or lifetime issues for boron operation, which are critical in evaluating the overall utility of an implanter ion source. This is due to the generally poor performance of microwave sources with boron, as well as the limited source lifetime. Details of the performance and lifetime characteristics of this source with BF3 are presented in this paper.
Ion species measurement of high current metal ion beams extracted from a multicusp ion source
Authors: Matsuda Yasuhiro , Inami Hiroshi , Yamashita Takatoshi , Fujiwara Shuichi , Inouchi Yutaka , Matsunaga Kouzi , Matsuda Koji
Published: July 2002

Ion charge state and impurities extracted from a multicusp ion source have been studied with the use of a magnetic momentum mass analyzer. Impurities contained in high current metal ion beams are crucible materials (such as Al2O3, BN, Y2O3, C) and high melting point materials (such as Mo, Ta, W). To reduce these impurities, the dependence of the impurity on the arc discharge voltage has been investigated experimentally. Amounts of impurities and multicharged ions are decreased with arc discharge voltage. For example, at the arc discharge voltage of 60 V, aluminum ion beam contains 1% impurities and 4% multicharged ions, and at the arc discharge voltage of 20 V, impurities and multicharged ions are less than 1% in all. High-purity single-charged metal ion beams have been obtained.
Influence of different Langmuir probe surface cleaning procedures on its I-V characteristics
Authors: Shun’ko E. V.
Published: July 2002

An influence of different procedures and conditions of cleaning the Langmuir probe surface on its current-voltage characteristic in a plasma is experimentally studied. It is shown that the electronic bombardment of the probe surface and its ohmic warm-up lead to a very effective cleaning of the surface.
High-field ion sources and applications (invited) (abstract)a)
Authors: Mühle R.
Published: July 2002

High electric fields are used for ion generation in gas field ion sources and liquid metal ion sources. With the preparation of stable microprotrusions on refractory metals stably emitting gas field ion sources for hydrogen and helium ions with angular intensities of 35 and 20 μA sr−1, respectively, they are available with a high chromatic angular intensity. Liquid metal ion sources can stably deliver a variety of ions with a source life in some cases over more than 1000 h. They are an essential element for patterning in the nanometer region and other focused ion beam applications.
Field evaporation of gold atoms onto a silicon dioxide film by using an atomic force microscope
Authors: Koyanagi Hajime , Hosaka Sumio , Imura Ryo , Shirai Masataka
Published: July 2002

To investigate whether field evaporation of gold atoms is responsible for dot formation in an atomic force microscope (AFM) gold-coated tip/vacuum/SiO2 film/p-type Si substrate configuration, we have performed elemental analysis of the dots and measured the dependence of the threshold voltage on SiO2 thickness with both polarities for the dot formation. The experiments demonstrate that it is feasible to form gold dots on SiO2 films 17–107 Å thick by adjusting the pulsed voltages applied to the gold-coated AFM tip. Energy dispersive x-ray spectroscopy (EDX) shows that the dots include gold. The threshold voltages increase almost linearly with the SiO2 thickness. Furthermore, the voltage with negative polarity is lower than that with positive polarity. These results provide evidence that the dot formation on the SiO2 film using AFM occurs by field evaporation.
Sensitive pulsed EPR spectrometer with an 8–18 GHz frequency range
Authors: Sturgeon Bradley E. , Britt R. David
Published: July 2002

The design and construction details of a kW power level pulsed EPR spectrometer with an 8–18 GHz frequency range are presented. The spectrometer is designed for high sensitivity over this wide frequency range. A synthesized sweeper is used as the microwave source. Details of the pulse electronics, pulse timings, cryogenics, and the Macintosh computer interface are described. Representative three pulse electron spin echo envelope modulation patterns of a Cu (II) tetraimidazole complex at X- and P-band frequencies are presented.
Pressure generation by a double-stage system using sintered diamond as the last stage anvil
Authors: Bilyalov Ya. R. , Kaurov A. A. , Tsvyashchenko A. V.
Published: July 2002

Two versions of a double-stage ‘‘2-2 type’’ apparatus have been made in which 5- or 10-mm-diam sintered diamond anvils with 2.5- or 4-mm-diam tips, respectively, are used in the second stage. The experiments show that these apparatuses are capable of attaining static pressures of over 20 GPa. The calibration curves based on electric resistance transitions in Bi, Pb, ZnS, GaP, and on densification of vitreous silica are shown. The characteristic features of the present type of apparatus are discussed.
Frequency stabilization of a GaAlAs semiconductor laser to an absorption line of iodine vapor
Authors: Ludvigsen Hanne , Holmlund Christer
Published: July 2002

A single mode GaAlAs semiconductor laser operating at around 830 nm has been locked in frequency to the center of an absorption line of molecular iodine vapor. A relative frequency stability of better than 10−9 was obtained for time periods longer than 1 s. This stabilization scheme increases the flexibility of wavelength selection. A method has been developed to estimate the stability when only one stabilized system is available.
An automatic field-emission tip conditioning system
Authors: Ruan Shengyang , Kapp Oscar H.
Published: July 2002

An automatic system has been completed for conditioning cold field-emission tips to obtain high flux density and low-noise emission. It was designed as a real-time control and operating system for the electron source of a new sextupole-corrected scanning transmission electron microscope and is able to condition the tip in situ. All of the control devices in this system are interfaced to a computer and communication across the electric field created by the 200-kV acceleration voltage is accomplished with light pipes. A program, written in Pascal, controls the conditioning process. This system has been utilized to experimentally determine the optimal flash level for a newly fabricated tip as well as performing corrective maintenance to the conditioned tip to extend its maximum useful lifetime.
Three-dimensional localization system for small magnetic dipoles
Authors: Incardona F. , Narici L. , Modena I. , Ernè S. N.
Published: July 2002

We developed a system for localizing orthogonal triplets of small magnetic dipoles with an array of magnetometers. These triplets can be used to measure, in quasi-real time, the position of an object. This system is particularly useful when used with superconducting biomagnetic multichannel detectors. We present here a complete numerical simulation of the system performances and the first experimental tests with a biomagnetic detector (an array of 37 superconducting magnetometers). This system can be operated at frequencies outside the range of interest for biomagnetic measurements (that is typically 10−2–103 Hz). It features an accuracy of ±0.3 cm driving the triplet at a field intensity ≊10−12 T. The speed of the algorithm allows for quasi-real-time operation (t ∼ 10−1 s).
Hot wire anemometer operating at cryogenic temperatures
Authors: Castaing B. , Chabaud B. , Hébral B.
Published: July 2002

A micronic-size hot wire anemometer operating at cryogenic temperatures (4 K) has been developed; using superconducting and resistive thin films, its electrical resistance is very sensitive to the velocity of a gaseous 4He subsonic jet. The fabrication procedure is described and the measured characteristics are compared with a simple thermal equilibrium model.
A prototype Helmholtz–Thompson nonlinear oscillator
Authors: del Río E. , Rodríguez-Lozano A. , Velarde M. G.
Published: July 2002

A prototype electronic (analog) circuit has been built to mimic a nonlinear oscillator proposed a century ago by Helmholtz in order to account for combinational tones in the drumskin, and more recently by Thompson to account for ship stability to waves in windy situations and its potential and eventual capsize. Besides a careful discussion of elements and their expected performance, several tests have been used to assess the reliability of the prototype.
Simple computer-controlled potentiostat for the characterization of electrochromic films
Authors: Kirkup L. , Bell J. M. , Green D. C. , Smith G. B. , MacDonald K. A.
Published: July 2002

We describe a simple and inexpensive potentiostat, incorporating current boosting and filtering circuitry for use in the study of coloration and bleaching in electrochromic thin films. The system is sufficiently flexible to permit utilization in other electrochemical applications.
The Advanced Photon Source at Argonne National Laboratory–Summer 1991
Authors: Moncton D. E.
Published: July 2002

The Advanced Photon Source at Argonne National Laboratory is designed as a national synchrotron radiation user facility where extremely bright 1–100 keV x-ray beams will be used for multidisciplinary research. Construction of the facility has begun. Accelerator components, insertion devices, optical elements, and optical element cooling schemes have been and continue to be the subjects of intensive research and development. Proposals to conduct research at the Advanced Photon Source have been received from industrial, university, and national laboratory scientists representing a broad range of scientific disciplines.
Tests of 250-nm pitch multilayer gratings in the XUV low-energy range on the Super-ACO Storage Ring at LURE
Authors: Troussel P. , Schirmann D. , Dalmasso J. M. , Malek C. Khan , Berrouane H. , Barchewitz R.
Published: July 2002

Two laminar amplitude multilayer gratings with 250-nm pitch were produced using UV holography and reactive ion etching. The diffraction properties of these structures were measured at 150 eV using synchrotron radiation. The experimental results, giving the position and absolute reflectivity of the various orders, are discussed within a kinematical model.
Automatic calibration of inductive voltage dividers for the NASA Zeno experiment
Authors: Avramov Svetlana , Oldham Nile M.
Published: July 2002

Two inductive voltage dividers (IVDs) used for temperature measurements in NASA’s Zeno experiment were tested. In order to obtain the required resolution of 10 parts-per-billion, a 30-bit binary inductive voltage divider developed at the National Institute of Standards and Technology was used to measure the differential linearity of the Zeno IVDs. Automatic measurements were performed on the dividers in the Zeno engineering model at frequencies of 266 and 351 Hz over a ratio range of 0.55–0.56. The measured differential linearity limits the temperature resolution to 5 μK.
Two scanning tunneling microscope devices for large samples
Authors: Picotto G. B. , Desogus S. , Barbato G.
Published: July 2002

Two scanning tunneling microscopes (STMs) operating in air were designed for imaging samples with dimensions up to 75 mm diam and 25 mm thickness. Both STMs allow a wide sampling range capability to be obtained by means of xy sample positioning stages spanning 25 mm with 0.1 μm resolution. The automatic tip-sample approach is achieved in the two devices by moving either the head scanning stage or the sample holder. These STMs were successfully used to image highly oriented pyrolithic graphite, gratings, and indentations made on hardened steel.
A linear magnetic field spectrometer for electron energy-loss measurements
Authors: Page S. C. , Mei L. , Palfreyman D. , Read F. H.
Published: July 2002

A new type of electron energy-loss spectrometer has been developed, in which the electrons are confined by a unidirectional magnetic field that extends over a length of 2 m. Magnetic-field-immersed Wien filters are used for energy selection and analysis. The new spectrometer is characterized by a high collection efficiency and hence it is especially suitable for the study of processes that have low cross sections, such as excitation of autoionizing and inner-shell states. Electron energy-loss spectra of inner-shell states of Xe have been obtained with the new spectrometer.
Exact two-dimensional quadrupole field and superposition of a homogeneous field
Authors: Wang Y. , Wanczek K.-P. , Jiang X. Q. , Hua Z. Y.
Published: July 2002

A method is described to generate the exact two-dimensional quadrupole field by closed boundaries with continuously variable potential, especially with linearly variable potential, in a ideal case by simple square or rectangle boundaries with linearly variable potential. For the latter square or rectangle structure, the technique to realize linearly variable potential on the boundaries is described. Within the same square or rectangle boundaries, an exact two-dimensional homogeneous electric field can be superimposed without interaction with the quadrupole field. The electrode structure can be employed in quadrupole mass spectrometers and in electron optical systems to generate focusing and/or deflection within the same interior regions. Experiments with electron beam tubes show good agreement with the theory and the practicability of the proposed structures.
Whole electronic cantilever control for atomic force microscopy
Authors: Takata Keiji
Published: July 2002

This article describes a new method of measuring the force gradient between the tip and a sample without directly detecting fine cantilever displacement in an atomic force microscope (AFM). The force sensing principle is based on the fact that the impedance of a piezoelectric vibrator varies sharply with frequency near the mechanical resonance. Therefore, when the piezoelectric vibrator is incorporated into the cantilever and the impedance is measured while vibrating, the resonant frequency shift of the cantilever caused by the force gradients changes the impedance, thus the force detection is achieved by measuring the impedance. The cantilever deflection is controlled by applying a dc voltage to the piezoelectric vibrator, so that the cantilever itself can hold the tip-to-sample spacing by the feedback signal to keep the impedance constant. This method greatly simplifies the AFM system and enables us to use a scanning tunneling microscope as an AFM merely by exchanging the tip probe.
Measurement of displacement current across single monolayers with thermal stimulation
Authors: Kubota Tohru , Iwamoto Mitsumasa
Published: July 2002

The displacement-current-measuring system equipped with a thermally stimulated system used for detecting the reorganization of monolayers on solid substrates is described. Since the displacement current flows due to the dynamic behavior of polar molecules on solid substrates with thermal stimulation, dipole moment of the consistent molecules of monolayers can be investigated without physically damaging the monolayers themselves.
Formation and measurement of tapers in optical fibers
Authors: Brophy Timothy J. , Shankar P. Mohana , Bobb Lloyd C.
Published: July 2002

A simple fabrication method is described which is capable of producing physically repeatable biconical tapers in optical fibers. A resistively heated platinum wire furnace provides the heat with standard fiber-optic positioning equipment to secure the fiber. The method does not require computer control and has the advantages of low cost, fast sample turn-around time, and the ability to concatenate multiple tapers on a single fiber. Experimental results demonstrating repeatable taper formation and the wavelength filtering property of the tapers is shown. Issues of varying the taper shape are addressed and measurement methods of the physical and optical characteristics are presented. Limited control of the taper symmetry is discussed, and recommendations for enhancement at the cost of simplicity are included.
Collocated and simultaneous measurement of surface slope and amplitude of water waves
Authors: Barter J. D. , Beach K. L. , Lee P. H. Y.
Published: July 2002

We demonstrate by experiment that, in addition to the local surface slope, local surface elevation can also be directly measured using the refracted light beam traversing an air-water interface, thus showing the feasibility of a new surface slope and wave height amplitude gauge for use in studying water waves. We have achieved surface height resolutions as small as 40 μm for the range of surface wavelengths λ∼1.2–2.4 cm used in the present experiments. This measurement principle is readily adaptable to waves of different scale. The available dynamic range defined by the ratio of maximum wave amplitude to minimum resolvable amplitude need only be limited by the useful dynamic range of the photodetector when matched to a laser of suitable frequency and sufficient power.
The gas-chromatographic analysis system in the JET active gas handling plant
Authors: Lässer R. , Grieveson B. , Hemmerich J. L. , Stagg R. , Dowhyluk T. , Torr K. , Massey R. , Chambers P.
Published: July 2002

A gas chromatographic system for the analysis of gas species to be collected from the JET torus and to be processed in the JET active gas handling plant during the active operation phase with deuterium and tritium plasmas was designed and built by CFFTP under contract with JET. The gas-chromatograph consists of a compression/injection stage and of two parallel, analytical stages, one for the detection of helium, hydrogen, oxygen, nitrogen, methane, carbon monoxide, and the six hydrogen molecules by means of a thermal conductivity detector (TCD) and one for the detection of carbon monoxide, methane, carbon dioxide, and higher hydrocarbons by means of a flame ionization detector (FID). A flow proportional counting detector (FPCD) is placed in series to TCD and FID for the specific analysis of tritiated gas compounds. A detailed description of the system and of its performance will be given which was evaluated using several calibrated gas mixtures including test runs with tritiated species at JET. The gas species mentioned above can be detected in the concentration range from ppm levels to 100%. The estimated error is about 20% at very low concentrations and 1% at high concentrations. The required minimum detection limit for the TCD can be achieved by the injection of large samples and the use of large filament currents. In addition, neon or helium can be chosen as carrier gas. The use of Ne increases the sensitivity for hydrogen and allows the detection of He, whereas He carrier gas gives superior TCD results for all other gases. Due to the high sensitivity of the FPCDs ppb levels of tritiated gas species can be detected.
Femtosecond transient absorption microspectrophotometer combined with optical trapping technique
Authors: Tamai N. , Asahi T. , Masuhara H.
Published: July 2002

A transient absorption microspectroscopic system with 200-fs temporal and micrometer (<2.5 μm) spatial resolutions was developed by using a microscope and a laser trapping technique. A pump beam, a white-light continuum generated by focusing an intense femtosecond laser pulse into water, and a trapping laser beam were coaxially introduced into a microscope and focused onto a sample by a reflecting objective lens. Advantages of a reflecting objective lens are discussed for the measurements of transient absorption spectra. This method was applied to a dye-doped single liquid droplet in water and α- and β-perylene single microcrystals.
New vaporizing assembly for Q-plasma sources
Authors: Paris P. J. , Fasoli A. , Rynn N.
Published: July 2002

The design and operation of a new vaporizing assembly used for Q-plasma sources are described in this article. The vaporizing system, consisting of two ovens and an effuser, is used to vaporize and direct atoms onto a hot ionizer plate. The hot plate, which may be of tantalum, tungsten, or rhenium, singly ionizes the atoms on contact. The main advantages of this new assembly, compared to previous designs, are the production of higher plasma densities and the control of the radial plasma profile. The heaters of the two atomic beam ovens are independently controlled and monitored so that the gradients of the radial plasma profile can be modified. Plasma production with two ion species can also be performed.
Single photon avalanche diode for single molecule detection
Authors: Li Li-Qiang , Davis Lloyd M.
Published: July 2002

A commercially available single photon avalanche photodiode in a passively quenched circuit is used with time-correlated single photon counting modules to achieve subnanosecond time response together with high quantum efficiency and low dark noise. These characteristics are required for experiments in single molecule detection and spectroscopy in which time-gated detection schemes are used. By tightly focusing the input light onto the active area, a quantum efficiency of over 50% and a single photon timing jitter of 168 ps full width at half-maximum are achieved. In addition, the full width at one-hundredth maximum, which is of greater importance for time gating, is 790 ps, comparable to that from a microchannel plate photomultiplier. Measurements of the detector dead time, and the quantum efficiency, dark counts, time response, and pulse height distribution for different operating conditions are also reported.
Experimental study of the velocity field around a falling needle viscometer
Authors: Kim Insik , Irvine T. F. , Park N. A.
Published: July 2002

Fully developed velocity profiles around the side of a needle falling at terminal velocity in a falling needle viscometer and the flow disturbance region near the ends of the needle were experimentally investigated. A flow visualization technique was used to obtain the main features of the flow field around the falling needle. Comparisons made between the experimental and predicted fully developed velocity profile showed good agreement. The regions where the flow field is disturbed by the needle ends were analyzed from photographs and found to be about 6% of the total needle length.
A high resolution laboratory-based high pressure x-ray diffraction system
Authors: Atou Toshiyuki , Badding John V.
Published: July 2002

An improved x-ray powder diffraction system for use with a diamond anvil cell is described. To obtain a small, strong, nearly monochromatic, low divergence incident beam for x-ray powder diffraction, a focusing technique based on the Johansson–Guinier principal is employed. The system consists of a rotating anode x-ray generator, a quartz curved monochromator, a horizontal collimator, motor-driven x, y, and z stages, and a Debye–Scherrer-type film cassette together with a lever-arm-type Mao–Bell diamond anvil cell. The system is designed to function in an analogous manner to synchrotron-based diffraction systems. Its performance is superior to conventional laboratory-based diffraction systems. Many experiments that formerly required a synchrotron source can now be performed in the laboratory.
Fe2+ and Fe3+ ions distinguishable by x-ray anomalous scattering: Method and its application to magnetite
Authors: Sasaki Satoshi
Published: July 2002

A chemical shift of about 5 eV was observed between ferrous and ferric ions in the XANES absorption spectra of FeO and Fe2O3 where the Fe ions coordinate in regular octahedra. Experimental f′e was estimated based on the cross-section data in the 108 eV region at the Fe K edge using the Cromer and Liberman’s equation. The result shows that the maximum difference in f′e between Fe2+ and Fe3+ is about 2.5 at the longer wavelength side of the Fe2+K edge. The XANES spectrum of Fe3O4 (magnetite) lies between those of FeO and Fe2O3. Synchrotron x-ray-diffraction data of a magnetite crystal were measured on a vertical-type four-circle diffractometer and used for evaluation at seven wavelengths of 1.7415, 1.7420, 1.7425, 1.7431, 1.7452, 1.7499, and 1.7567 Å. The difference-Fourier technique promises the possibility of mapping valence differences for atoms of the same atomic species in a mixed-valence crystal.
High-performance low-cost Hall probe measuring head
Authors: Testa L. , Sotgiu A. , Masciovecchio C. , Villani M. , Chiricozzi E.
Published: July 2002

An electronic circuit is described that allows the use of an inexpensive Hall probe as a high-performance magnetic-field sensor. The circuit contains a high-precision voltage reference, a proportional control thermostat, a 16 bit serial analog-to-digital converter, and a digital control subsystem integrated into a single programmable logic device. The precision of the probe is of about 4 μT.
Comparison of external and internal planar radio frequency antennae for inductively coupled plasma
Authors: Eng K. , Strohmaier K. , Palmer R. , Stoner B. , Washburn S.
Published: July 2002

Radio frequency (rf) antennae, coated with glass, were inductively coupled to an Ar plasma inside the processing chamber. Coupling efficiency η and electron density Ne were measured for moderate pressures (0.1–200 T) and rf power (10–2000 W). Decreasing the dielectric thickness between the antenna and the Ar led to an increase in η and a decrease in Ne. Instabilities and hysteresis were observed for the internal antennae.
Micronic-size cryogenic thermometer for turbulence measurements
Authors: Chanal O. , Baguenard B. , Béthoux O. , Chabaud B.
Published: July 2002

Micronic-size thermometers (1.5×1.5×0.5 μm3) designed for local measurements in turbulent gaseous helium in the range of 4–80 K, have been developed and tested. Their very short time response (⩽1 μs) and micronic spatial resolution allow to perform measurements down to the Kolmogorov dissipative length scale, for high Reynolds or Rayleigh numbers flows. These thermometers, designed to be nonperturbative in the flow, are based on Au–Ge thin films deposited by sputtering process on drawn glass fibers. Their relative sensitivities σ=|(T/R)(dR/dT)| are ranging from 0.15 to 0.9, and are nearly constant on the whole temperature range.
Production of multicharged radioactive ion beams: The 1+ to n+ charge state transformation for the Production, Ionisation, Accélération de Faisceaux Exotiques project
Authors: Tamburella C. , Belmont J. L. , Bizouard G. , Bruandet J. F. , Geller R. , Gimond G. , Vignon B.
Published: July 2002

Two types of 1+→n+ ion conversion devices have been developed for the Production, Ionisation, Accélération de Faisceaux Exotiques project. Both can be utilized for short lived radioactive ions beams. They are based on collisions inside an electron cyclotron resonance ion source (ECRIS). They transform a 1+ ion beam into a n+ ion beam in less than 0.1 s. In the first device, ions are introduced into the ECR plasma through the extraction hole (backward injection), in the second device they are introduced as usual (forward injection). The particle conversion efficiencies can reach for noble gases ∼6.5% for Kr9+/Kr1+ and for alkali elements ∼2.8% for Rb9+/Rb1+.
Optical deflection setup for stress measurements in thin films
Authors: Bicker M. , von Hülsen U. , Laudahn U. , Pundt A. , Geyer U.
Published: July 2002

We demonstrate an optical two-beam deflection setup for in situ stress measurements in thin films. By using improved position sensitive photodetectors we reach a resolution of better than 10−4 m−1 for substrate curvature measurement at a bandwidth of 1 kHz, with a relatively short optical path of 0.53 m and without employing a lock-in technique.
High pressure fiber optic light scattering spectrometer
Authors: Zhou Shuiqin , Chu Benjamin , Dhadwal H. S.
Published: July 2002

A high-pressure fiber-optic light-scattering spectrometer has been constructed for in situ observation of molecular dissolution/association as well as the polymerization process in supercritical fluids. Single (or multiple) fiber-optic probes, each comprised of a single optical fiber (or multiple optical fibers) and a graded index microlens, are used to transmit the incident laser beam and to receive the scattered light as well as the transmitted light from the high pressure cell. The direct immersion in the scattering medium of the fiber-optic probes makes the spectrometer more compact and more flexible with an easier alignment process. With the miniaturization and flexibility, our high-pressure light-scattering cell can be transported and adapted in combination with other physical techniques, such as synchrotron small angle x-ray scattering which requires a different set of windows (e.g., made of diamond) suitable for x-ray transmissions. This spectrometer has been successfully used for the in situ study of the molecular association behavior of a diblock copolymer of 1,1-dihydroperfluorooctylacrylate and vinyl acetate in supercritical carbon dioxide under pressures up to 552 bar.
Disk plasma generation using a holey-plate surface-wave structure on a coaxial waveguide
Authors: Yoshida Yoshikazu
Published: July 2002

Plasma created and sustained by a surface wave from a partial-coaxial cavity resonator have been studied. In this work, two types of plasma source geometries are compared, (1) a dielectric disk on ground plane structure (DPSW), and (2) a dielectric disk between a parallel plate structure with a holey top plate (HPSW). In both cases, an evanescent electric field is produced from the cavity resonator to a plasma production chamber of 40 mm diameter. Thus, high-density plasma is generated by the interaction of the evanescent field with particles. This work shows that the plasma density and uniformity of the holey-plate structure is higher than that of the dielectric disk structure. For the holey-plate structure, the plasma density is 7.5×1011 cm−3 with an electron temperature of 3 eV at an argon gas pressure of 13 Pa.
A spectroscopic system for time- and space-resolved studies of impurities on the EXTRAP-T2 reversed field pinch
Authors: Sallander J.
Published: July 2002

The radial distribution of impurity line emission in the EXTRAP-T2 reversed field pinch (RFP) is studied with a five viewing chord, absolutely calibrated, spectrometer system. The light is analyzed with a single 0.5 m grating spectrometer. Different parts of the entrance slit are used for different channels. This arrangement makes it possible to use the system over a wide wavelength range, from 2500 to 6500 Å, without having to recalibrate the relative sensitivity for the different channels. The rather short plasma pulses of 10–15 ms require a high time resolution. The use of photomultiplier tubes provides a time resolution of 10 μs which is limited by the transient recorders used. The result is a robust, low-cost system that produces reliable measurements of the radial dependence of emission from a wide range of impurity ions.
An inertial tribometer for measuring microslip dissipation at a solid–solid multicontact interface
Authors: Baumberger Tristan , Bureau Lionel , Busson Michel , Falcon Eric , Perrin Bernard
Published: July 2002

An apparatus has been built to measure the shear response of a multicontact interface between flat-ended solid bodies, rough at the micron scale. The device makes use of inertia to apply a steady sinusoidal shear force to a slider without direct mechanical drive. Both elastic compliance and damping losses are deduced from the in-phase and out-of-phase components of the submicronic shear displacement. Operating frequencies range between 15 Hz and 1 kHz, while below 100 Hz quasistatic motion of the slider is achieved. Acceleration amplitudes range typically between 0.1 and 7 m s−2, where gross sliding occurs. The resolution of the microslip detection is 1 nm. Apparatus design and operation are described, and the application and limitation of the method to a weakly nonlinear response are discussed and illustrated by experimental results with a polymer glass.
Optical access to the large volume, high pressure environment
Authors: Secco R. A. , Balog P. S.
Published: July 2002

A new technique of gaining optical access to the large volume, high pressure environment using optical fibers is reported. High pressure experiments of light transmission through optical fibers brought out through the gasket region in optically opaque, solid medium cubic anvil pressure cells have been performed in a large volume cubic apparatus. Photographic records of the transmitted light signal, taken at constant pressure settings, demonstrate optical continuity up to pressures of 12 kbar on metal tube-encased fibers. Progressive degradation in light intensity is observed with increasing pressure. Time exposure photographs taken during loading track the movement of the fiber in the gasket during extrusion. At pressures above 14 kbar, the maximum pressure of optical continuity through a fiber in this study, microbending of the fiber in the gasket region causes fracture and termination of the optical path.
Digital signal processing technique for white light based sensing systems
Authors: Jorge P. A. S. , Ferreira L. A. , Santos J. L.
Published: July 2002

A digital signal processing technique for interferometric peak localization in white light sensing systems is presented. The procedure is based on computational processing of the acquired interferometric signal using Fourier mathematical operations for fringe visibility improvement. Tests are made by computer simulations.
Reference reconvolution analysis by phase plane method
Authors: Novikov Eugene G.
Published: July 2002

The phase plane method for deconvoluting fluorescence decay curves is generalized to the case of reference reconvolution. Particular cases of the reconvolution are considered: reconvolution via single exponential reference, analysis of two double exponential decays, and simultaneous analysis of parallel and perpendicular components of fluorescence with respect to each other. Results of simulation experiments, demonstrating possibilities of the proposed approach, are presented.
Instrumentation for time-resolved electron diffraction spanning the time domain from microseconds to picoseconds
Authors: Lobastov Vladimir A. , Ewbank John D. , Schäfer Lothar , Ischenko Anatoli A.
Published: July 2002

Recent instrumental improvements which successfully extend the time resolution of pulsed beam electron diffraction to the picosecond regime are described. Based on modifications of an existing nanosecond apparatus, a new sample inlet system, electron pulse generation laser, and amplified detector have been incorporated into the design such that significant improvements in both the signal level and ultimate time resolution are achieved; an upper estimate of the electron pulse width is ∼20 ps. Enhancements are such that, for operation in the nanosecond time domain, an entire diffraction pattern over a useful range of scattering angles may be collected from a gas-phase sample in a single electron pulse.
A compact fluorescence and polarization near-field scanning optical microscope
Authors: Merritt G. , Monson E. , Betzig E. , Kopelman R.
Published: July 2002

We present a transmission, fluorescence, and polarization near-field scanning optical microscope with shear-force feedback control that is small in size and simple to operate. This microscope features an ultrafine mechanical tip/sample approach with continuous manual submicron control over a range of several millimeters. The piezo-driven 12 μm x-y scan range is complimented by a 4 mm coarse mechanical translation range in each direction. The construction materials used in the mechanical feedback loop have been carefully chosen for thermal compatibility in order to reduce differential expansion and contraction between the tip and sample. A unique pressure-fit sample mount allows for quick and reliable sample exchange. Shear-force feedback light is delivered to the scan head via an optical fiber so that a remote laser of any type may be used as a source. This dither light is collimated and refocused onto the tip, delivering a consistently small spot which is collected by a high numerical aperture objective. This new scan head incorporates an optical system which will permit the linearization of scan piezo response similar to a scheme used successfully with atomic force microscopy. This is designed to both overcome the piezo’s inherent hysteresis and to eliminate drift during long duration spatial scans or spectroscopic measurements at a single location. The scan head design offers added flexibility due to the use of optical fibers to deliver the dither and scan linearization light, and functions in any orientation for use in conjunction with upright or inverted optical microscopes.
An instrument for in situ growth rate characterization of mechanically strained crystals
Authors: Zikic A. M. , Ristic R. I. , Sherwood J. N.
Published: July 2002

The crystal growth and dissolution characteristics of a certain material can be considerably influenced by the strain present in a growing (dissolving) crystal. Strain can be induced in various ways. One of the most common and always present in industrial processes, where attrition processes are always accompanied by generation of mechanical strain in a newly formed small crystal fragments, is mechanical stressing, in situ, during preparation and handling. To gain deeper insights into some aspects of this phenomenon, a sophisticated equipment is needed for in situ controlled stressing of extremely brittle and fragile crystals. For this purpose, we have developed an apparatus which comprises a specially designed straining cell coupled with a laser Michelson interferometer for growth rate measurements. The straining cell is designed to accommodate crystals that undergo fracture below 200 microstrains. The stress imposed on a crystal is computer controlled with a precision of approximately 5%. Details of the instrument are given together with two examples of straining in situ brittle paracetamol and plastic sodium nitrate crystals. The measured changes in growth rate of a paracetamol crystal, in the quasi linear region 0–70 kPa are estimated to be (−9.4±0.1)×10−11 m/s/kPa.
Efficient and robust anion source, based on a microchannel plate electron source
Authors: Schiedt J. , Weinkauf R.
Published: July 2002

In this work, an efficient, cheap, and robust anion source is described, which is based on a high-pressure supersonic expansion crossed with a pulsed high-energy electron beam. The special property of this anion source is “soft” electron attachment and efficient stabilization and cooling, which results predominantly in molecular and cluster anions of intact molecules. As electron source, a stack of microchannel plates is used, which is seeded by photoelectrons generated by a weak ultraviolet light pulse. By this special electron source 109–1010 electrons of 1 keV energy are provided at a pulse width of 150 ns. These operational conditions can be maintained up to a repetition rate of 4 kHz. Further advantages of this device are its long lifetime even at relatively high vacuum pressures and its stability against reactive samples, such as oxygen and organic molecules.
The effect of microwave frequency and grad B on the energy of electrons in an electron cyclotron resonance ion source
Authors: Koivisto H.
Published: July 2002

In an electron cyclotron resonance ion source the energy of the electrons is increased by the electric field of the microwaves. The gyrofrequency of the electrons has to be in resonance with this field. The production of highly charged ions requires very energetic electrons. As a consequence, the acceleration of electrons by the microwaves has to be efficient. In this article the energy gain of the electrons due to the microwaves has been studied. The gradient of the magnetic field and the frequency of the microwaves were the main variables. The simulations show that more efficient heating is achieved with higher microwave frequency and with smaller gradient of the magnetic field.
Control system for ALID-7 linear accelerator used in radiation processing
Authors: Martin D. I. , Jianu A. , Bestea V. , Toma M. , Oproiu C. , Marghitu S.
Published: July 2002

The data acquisition and control system for the electron linear accelerator ALID-7 of 5.5 MeV and 0.7 kW, built in Romania, used on pilot-scale radiation processing, is discussed. The system provides: personnel and sensitive device protection against dangerous events; programmed interlocking and warning signals during accelerator operation; single electron pulses or electron pulse trains with small variations in pulse dose; control of electron pulse length and repetition rate, electron beam intensity, magnetron frequency, high voltage level on magnetron and electron-gun modulators, sweeping amplitude and frequency, conveyor velocity, irradiation time, and electron pulses number; simultaneous electron beam and microwave treatment. An important feature of the installation is an original control technique for obtaining programmed beam single shots and pulse trains with programmed pulse number, pulse repetition frequency, and pulse duration, from a diode gun linear accelerator, by discrete pulse temporal position modulation of the gun electron pulses and the magnetron microwave pulses. It is particularly useful for automatic control of absorbed dose rate level, irradiation process control as well as in pulse radiolysis studies, single pulse dose measurement or for research experiments where pulse-to-pulse reproducibility is required.