bluuebunny/crossref_metadata_2025 huggingface dataset:
Specific-heat measurements in magnetic fields up to 17.5 T
Authors: Klaasse J. C. P.
Published: July 2002

Newly developed equipment is described for measuring specific heat between 0.5 and 60 K in magnetic fields up to 17.5 T, using the traditional semi-adiabatic method in combination with a mechanical heat switch. The lower limit found for the heat capacity of sample plus holder amounts to 0.04 mJ/K at 500 mK. Under these conditions, the absolute accuracy is better than 1 μJ/K. Some recent data obtained with this equipment on an UNiAl single crystal are given as an example.
Calibration of the upgraded motional Stark effect diagnostic on TFTR
Authors: Levinton F. M. , Batha S. H. , Zarnstorff M. C.
Published: July 2002

The q profile plays a key role for plasma equilibrium and theories of magnetohydrodynamic instabilities. With the development of the motional Stark effect (MSE) diagnostic, accurate q(r,t) profiles have been measured and utilized for equilibrium and stability analysis. Improvements to the MSE diagnostic on TFTR include a new method for calibrating the system and increasing the number of sightlines from 12 to 21 channels. A technique that uses the known poloidal field at the edge of the plasma is utilized to calibrate each sightline. The major radius is moved over the course of a discharge such that the plasma edge covers each sightline radius. Then with several discharges at various plasma currents each channel is independently calibrated. This method has been compared to our earlier calibration technique using neutral beam injection into a gas filled torus and some differences in the calibration have been found that have been attributed to differences in the excitation and l mixing processes in the Stark spectrum.
Determination of inductive shielding factors in double-layer structures
Authors: Rodrigues Marcello G. , Baffa Oswaldo , Zimmerman Robert L.
Published: July 2002

Our experiments show that multilayer inductive shielding performs better than a monolayer shielding of equivalent thickness. We developed an analytic expression for the shielding factor S of a two-layer inductive shielding, extendible to an arbitrary number of layers. The experimental data, obtained from a reduced scale model, fitted this expression well. We demonstrated that multilayer inductive shielding offers better performance for a better price than a traditional monolayer shielding.
Time-domain triple-probe measurement of edge plasma turbulence on the Texas Experimental Tokamak Upgrade
Authors: Meier M. A. , Hallock G. A. , Bengtson Roger D.
Published: July 2002

The time-domain triple-probe method (TDTP) switches Langmuir probe states at high speeds to gather triple-probe information thereby avoiding errors which result when implementing the triple-probe method with spatially separated single state probes in an inhomogeneous plasma. Successful implementation of the TDTP method requires a switching frequency greater than the turbulence bandwidth so that aliased power does not degrade time interpolated estimates of triple-probe states. Additionally, transients between states, largely determined by the ratio of ion saturation current to probe capacitance, must be short enough to establish a probe–plasma equilibrium. These requirements have been met in the edge plasma and parts of the scrape-off layer on the Texas Experimental Tokamak Upgrade. Temperature fluctuations have been measured at two poloidally separated probes. Cross-phase and coherence spectra consistent with those of floating potential fluctuations and ion saturation current fluctuations are measured.
Alpha diagnostics using pellet charge exchange: Results on the Tokamak Fusion Test Reactor and prospects for ITER
Authors: Fisher R. K. , Duong H. H. , McChesney J. M. , Parks P. B. , Medley S. S. , Budny R. V. , Mansfield D. K. , Roquemore A. L. , Petrov M. P. , Gorelenkov N. N.
Published: July 2002

Confinement of alpha particles is essential for fusion ignition and alpha physics studies are a major goal of the TFTR, JET, and ITER DT experiments, but alpha measurements remain one of the most challenging plasma diagnostic tasks. The pellet charge exchange (PCX) diagnostic has successfully measured the radial density profile and energy distribution of fast (0.5–3.5 MeV) confined alpha particles in TFTR. This article describes the diagnostic capabilities of PCX demonstrated on TFTR and discusses the prospects for applying this technique to ITER. Major issues on ITER include the pellet’s perturbation to the plasma and obtaining satisfactory pellet penetration into the plasma.
Calibration techniques for a fast duo spectrometer
Authors: Chapman J. T. , Den Hartog D. J.
Published: July 2002

We have completed the upgrade and calibration of the ion dynamics spectrometer (IDS), a high-speed Doppler duo spectrometer which measures ion flow and temperature in the MST reversed-field pinch. This paper describes an in situ calibration of the diagnostic’s phase and frequency response. A single clock was employed to generate both a digital test signal and a digitizer trigger thus avoiding frequency drift and providing a highly resolved measurement over the system bandwidth. Additionally, we review the measurement of the spectrometer instrument function and absolute intensity response. This calibration and subsequent performance demonstrate the IDS to be one of the fastest, highest throughput diagnostics of its kind. Typical measurements are presented.
Measurements of high intensity laser beam transmission through a large scalelength plasma
Authors: Moody J. D. , MacGowan B. J. , Kirkwood R. K. , Montgomery D. S.
Published: July 2002

We describe an instrument used to measure the light transmitted through a large scalelength plasma. Light that passes through the plasma scatters diffusely from a frosted silica scatter plate. An optical system images this scattered light onto several detectors which measure its spatial and temporal characteristics. Low and high dispersion spectral measurements of the transmitted light are made using optical fiber collectors placed behind the scatter plate.
A versatile stable scanning proximal probe microscope
Authors: Jahncke C. L. , Hallen H. D.
Published: July 2002

We present a novel scanning proximal probe microscope design utilizing a piezoelectric driven coarse positioning mechanism in x, y, and z, while maintaining relatively small lateral dimensions. The instrument is suitable for insertion into a Dewar. The primary purpose of this work is to develop a stable yet versatile instrument in order to meet the signal averaging limitations imposed by low signal level measurements. We have implemented a near field scanning optical microscope with this system, whose key features include simultaneous detection of reflected and transmitted signals, unique “center of mass” tip oscillator for shear force feedback, and overall microscope stability.
Fiber orientation and concentration analysis by light scattering: Experimental setup and diagnosis
Authors: Girasole T. , Le Toulouzan J. N. , Mroczka J. , Wysoczanski D.
Published: July 2002

A simple and independent optical diagnosis (concentration and orientation of fibers in a polymer composite) is developed. An experimental setup has been designed to record maps of scattered light from a laser beam as it crosses a cloud of fibers. From the consideration of the ellipses which fit the recorded images, the fiber orientation and concentration inside a composite polymer sample are determined. The method of measurement is tested with glass fiber-polycarbonate matrix polymer composites.
Concatenated gas saturation vapor pressure apparatus
Authors: Bruno Thomas J. , Mayrath James E.
Published: July 2002

This article presents a gas saturation vapor pressure apparatus capable of simultaneous vapor pressure measurements on a total of up to six samples. The apparatus operates at 280–365 K and total pressures of 100–200 kPa. The apparatus features a series of alternating saturators and adsorbers allowing multiple vapor pressure measurements to be made with a single carrier gas stream. Total carrier gas flow is derived from mass measurements. The apparatus provides multiple simultaneous vapor pressure measurements for series or families of compounds allowing correlations of physical properties within the families.
Portable ocular laser Doppler red blood cell velocimeter
Authors: Logean E. , Geiser M. H. , Petrig B. L. , Riva C. E.
Published: July 2002

A new hand-held bidirectional ocular laser Doppler system for measurement of red blood cell (RBC) velocity in retinal vessels and blood flow in the optic nerve head tissue and in the choriocapillaris is described. Laser power at the cornea is below the maximum permissible level. The instrument is based on the well-established laser Doppler velocimetry/flowmetry techniques. The optical systems for the delivery of the probing laser beam to the eye fundus and bidirectional detection of the light scattered by the RBCs have been implemented in a portable Kowa Genesis fundus camera. In vitro experiments demonstrate the performance of the instrument and in vivo measurements illustrate the feasibility of retinal blood velocity and choriocapillaris blood flow measurements in awake volunteers.
Specificity, accuracy, and interpretation of measurements of ethylene oxide gas concentrations during sterilization using a microwave spectrometer
Authors: Zhu Z. , Matthews I. P. , Dickinson W.
Published: July 2002

This article reports the update in the design of a microwave spectrometer for measuring concentrations of ethylene oxide gas during sterilization. The specificity of the measurement (absorption line at 23.134 GHz) using the spectrometer has been found to be virtually 100%. A great number of calibrations have been conducted in the range of concentrations 100% to 40% of ethylene oxide gas at intervals of −10% in order to determine the accuracy of the spectrometer. It was found that the maximum standard deviation from the regression curve was 1.2% full scale (0%–100%). A mathematical model based on a diffusion equation has been developed and was used to interpret the real time measurement data during sterilization. Numerical simulation using this model has demonstrated that it is possible to predict the dynamic distributions of ethylene oxide concentration within the load being sterilized.
New approach to the cooling of fixed exit double crystal monochromator at the European Synchrotron Radiation Facility
Authors: Souvorov A. , Snigirev A.
Published: July 2002

The stability and reproducibility of positioning of the fixed exit double crystal monochromator are the crucial points at the modern synchrotron beamlines dealt with the high resolution imaging techniques and microscopy at high energies. Due to high heat load, the monochromator crystals must be cryogenically cooled. The cooling loop of the second crystal impact the performance of the monochromator. We suggest the use of the silicon-germanium (Si1−xGex) bulk crystal as the first cooled crystal of the monochromator. The second crystal in that case is held at room temperature.
A low cost microsatellite instrument for the in situ measurement of orbital atomic oxygen effects
Authors: Harris Ian L. , Chambers Alan R. , Roberts Graham T.
Published: July 2002

A small, low-cost sensor for measuring orbital atomic oxygen fluxes and their corrosive effect on spacecraft materials has been developed. Its operation is based on the reaction between hyperthermal atomic oxygen and a thin silver film. The electrical conductivity of the silver oxides formed is negligible allowing the reaction rate to be monitored through resistance measurements of the film. Atomic oxygen effects on spacecraft coatings can be investigated by placing a sample above the silver film. The construction of the sensor emphasizes simple techniques and components to improve reliability and reduce costs, while its small size and mass will allow it to be used on a wide range of spacecraft, increasing flight opportunities. An instrument comprising 12 of the sensors has been tested in orbit on the Space Technology Research Vehicle (STRV-1a) microsatellite mission. Results from this experiment agree well with those from ground-based simulation facilities. The successful outcome of this demonstration flight shows that the sensor can operate successfully and usefully in space. Several improvements to the technique are suggested for follow-on flights.
Calibration of charge coupled devices and a pinhole transmission grating to be used as elements of a soft x-ray spectrograph
Authors: Schriever G. , Lebert R. , Naweed A. , Mager S. , Neff W. , Kraft S. , Scholze F. , Ulm G.
Published: July 2002

The development of new types of sophisticated soft x-ray sources requires the knowledge of their emission characteristics such as photon flux, spectral distribution, and size of the radiation source. Calibrated spectrographs for the soft x-ray region are needed to determine these properties. The components of a soft x-ray spectrograph consisting of a pinhole gold transmission grating and a charge coupled device (CCD) camera are calibrated at the radiometry laboratory of the Physikalisch-Technische Bundesanstalt using the synchrotron radiation facility BESSY. Two different kinds of CCD-based photon detectors (one thinned and back illuminated, one coated with a phosphorous layer) are compared with regard to their sensitivities in the spectral range between 50 eV and 1.7 keV. The results obtained for the thinned CCD are compared with theoretical calculations of the sensitivity.
Precise force curve detection system with a cantilever controlled by magnetic force feedback
Authors: Yamamoto Shin-ichi , Yamada Hirofumi , Tokumoto Hiroshi
Published: July 2002

We present the development of an atomic force microscope (AFM) with an externally controllable force using an electromagnet. The position of the AFM cantilever with magnetic material at the end of the backside is controlled directly by the external magnetic field of an electromagnet. It is possible to use an optical detection system because the electromagnet is located inside the piezo tube on which the sample is mounted. A magnetic force feedback system has been implemented in this AFM. The effective stiffness of the cantilever is increased by the open loop gain of the feedback. We are able to control the motion of a soft cantilever (0.16 N/m) with this feedback system in air. Force feedback using an electromagnet allows the elimination of “snap-in” contact which may physically damage the tip and mica sample.
Double window configuration as a low cost microwave waveguide window for plasma applications
Authors: Baskaran R.
Published: July 2002

Waveguide windows are major components of a transmission line used in microwave plasma devices. The function of the waveguide window is to provide vacuum isolation of the source side from the plasma chamber while transmitting microwaves with minimum attenuation. Commonly a single thin dielectric plate is sandwiched between a choke type flange and a flat flange and is used as a waveguide window. To arrive at a better window configuration in terms of the low power reflection coefficient, the voltage standing wave ratio calculation is carried out for different window configurations (single window and double window) and for various window thicknesses. It is found that the power reflection is the minimum in the case of double window configuration. The minimum power reflection is as low as 0.8% for a combination of alumina and a quartz plate each of 1 cm thickness in the double window configuration. Also, it is more advantageous to use radial microwave coupling than axial coupling in order to increase the life time of the microwave waveguide window.
Application of a Si-diode detector for fusion product measurements in ASDEX Upgrade
Authors: Ullrich W. , Bosch H.-S. , Hoenen F.
Published: July 2002

The efficient confinement of the energetic charged fusion products and the complete transfer of their kinetic energy to the plasma is of great importance for the realization of a fusion reactor which will depend on alpha-particle heating. In todays fusion experiments with deuterium plasmas, this aspect can be investigated using the 1 MeV tritons from the d(d,p)t reaction. The slowing down behavior of these tritons can be studied by measuring the 14 MeV neutrons from the t(d,α)n reaction (triton burnup). At ASDEX Upgrade a time-resolved diagnostic based on a silicon barrier detector has been installed to measure the time evolution of the 14 MeV neutron rate. Using the Si(n,p)Al and Si (n,α)Mg reactions the high energy neutrons, with an energy above the 6 MeV threshold, are converted to charged particles directly inside the semiconductor diode. The complete functionality of the detector system is demonstrated by the successful measurement of the complex spectrum of the charged reaction products in silicon triggered by fusion neutrons during plasma discharges. As an integral component of this diagnostic a time dependent burnup code based on classical slowing-down theory has been developed for the use at ASDEX Upgrade to analyze the complex time evolution of the 14 MeV neutron rate. First measurements are compared to the results of the code. A new application for such detectors is proposed, as in conjunction with the materials of the tokamak structure it can be operated simultaneously as an in situ activation system.
Transient responses of a piezoelectric tube scanner
Authors: Yang Shengyuan , Huang Wenhao
Published: July 2002

By treating the electric signals applied to a piezoelectric tube scanner for scanning probe microscopy as external excitations, this article gives the exact equations of motion of the scanner. The solution method and process to solve these equations are also presented. The closed form solutions of the equations give the transient responses of the scanner, and show explicitly the extension motion and deflection motion of the scanner subject to a bias. Experiments support the theoretical conclusions. The solutions presented here are useful for the design and analysis of a scanning probe microscope and other systems including piezoelectric tubes as well.
In situ generation and atomic scale imaging of slip traces with atomic force microscopy
Authors: Oele W. F. , Kerssemakers J. W. J. , De Hosson J. Th. M.
Published: July 2002

We have designed, constructed, and tested a three-point bending system for in situ studies of slip in ionic crystals with an atomic force microscope (AFM). The work is aimed at developing a novel instrumental attachment for an in situ study of plastic deformation. The bending system is installed inside the optical head of the AFM on top of the piezoelectric scanner. Since the bending should not obstruct scanning, a piezocrystal is used for bending as well as an external stepper motor, which is connected with a screw in the bending system via a flexible shaft. The bending system performs over a relatively wide, continuous deflection range. The operation of the three-point bending system is illustrated by experiments on an ionic material in which the effect of macroscopic bending is demonstrated at an atomic scale.
Distance measurement method using the two intermode beat frequencies of a three-longitudinal mode He–Ne laser
Authors: Eom Ick-Jae , Kim Kyung-Chan , Suh Ho-Sung
Published: July 2002

The frequency of a three-longitudinal mode He–Ne laser was stabilized by the method of detecting the secondary beat frequency between modes. The stabilized laser has been efficiently used as a laser source for a distance meter. In distance measurement, two intermode beat frequencies (875 MHz, 145 kHz) were, respectively, used as a modulation frequency instead of an optical modulator. The resolution of the distance meter was higher than 20 μm. The total uncertainty was within 20 μm by correction of errors except for the uncertainty of the refractive index of the air.
Analysis of a pressure sensor based on an array of collector-assisted field-emission triodes
Authors: Nicolaescu Dan , Filip Valeriu , Okuyama Fumio
Published: July 2002

The purpose of this paper is to analyze the operation of a pressure sensor based on an array of collector-assisted field-emission triodes (FETs). The silicon membrane (the anode of the device) put in front of the array is bent by the external pressure, and thus, the field-emission current is modified. An analytical solution has been used to calculate the deflection of the silicon diaphragm when the pressure is applied and a numerical model was developed for the single emitter FET. The array emission current is obtained adding the contributions of all the FETs in the array, no interaction between the emitters being considered. The device sensitivity and resolution have been computed as functions of both the silicon membrane and FET array parameters. Better sensor sensitivity and resolution are obtained for those situations, which assure higher field-emission currents. A simple analytical model was developed for the field-emission pressure sensor, supporting these observations. The obtained modeling results can be further used for sensor design improvement.
A combined mass gate–energy discriminator
Authors: Becker Israela , Cheshnovsky Ori
Published: July 2002

A mass gate allows transmitting a selected mass in a time-of-flight mass spectrometer and to block other masses. The conventional stopping-potential mass gate does not discriminate against spontaneous fragments, which are generated in the drift tube. We present a simple improved version of a mass gate, which discriminates against fragments by using the fact that their kinetic energy is lower than that of the parent ion.
An evaluation of multilayer mirrors for the soft x ray and extreme ultraviolet wavelength range that were irradiated with neutrons
Authors: Regan S. P. , May M. J. , Soukhanovskii V. , Finkenthal M. , Moos H. W. , Farnum E. H. , Clinard F. W. , Tarrio C. , Watts R.
Published: July 2002

The Plasma Spectroscopy Group at the Johns Hopkins University develops high photon throughput multilayer mirror (MLM) based soft x ray and extreme ultraviolet (XUV 10 Å<λ<304 Å) spectroscopic diagnostics for magnetically confined fusion plasmas. The D-T reactions in large fusion reactor type devices such as the International Thermonuclear Experimental Reactor will produce neutrons at a rate as high as 5×1019 n s−1. The MLMs, which are used as dispersive and focusing optics, will not be shielded from these neutrons. In an effort to assess the potential radiation damage, four MLMs (No. 1: Mo/Si, d=87.8 Å, Zerodur substrate with 50 cm concave spherical curvature; No. 2: W/B4C, d=22.75 Å, Si wafer substrate; No. 3: W/C, d=25.3 Å, Si wafer substrate; and No. 4: Mo/Si, d=186.6 Å, Si wafer substrate) were irradiated with fast neutrons at the Los Alamos Spallation Radiation Effects Facility (LASREF). The neutron beam at LASREF has an energy distribution that peaks at 1–2 MeV with a tail that extends out to 100 MeV. The MLMs were irradiated to a fast neutron fluence of 1.1×1019 n cm−2 at 270–300 °C. A comparison between the dispersive and reflective characteristics of the irradiated MLMs and the corresponding qualities of control samples will be given.
A photospectrometer realized in a standard integrated circuit process
Authors: Simpson Michael L. , Dress William B. , Ericson M. Nance , Jellison Gerald E. , Sitter David N. , Wintenberg Alan L. , French David F.
Published: July 2002

A photospectrometer has been realized in a standard integrated circuit (IC) process. Only the masks, materials, and fabrication steps inherent to this IC process were used (i.e., no post processing to add mechanical or optical devices for filtering). The spectrometer was composed of a set of 18 photodetectors with independent spectral responses. The responses of these devices were weighted and summed to form outputs proportional to the input optical power in discrete wavelength bands in the region from ∼400 to ∼1100 nm. With the solution space restricted to a 60 nm band, this instrument could resolve Gaussian input spectra (σ=5 nm) with a peak-to-peak spacing of less than 15 nm. This device could easily be integrated with additional analog, digital, or wireless circuits to realize a true laboratory instrument on-a-chip.
The present status of the Tokyo electron beam ion trap
Authors: Nakamura N. , Asada J. , Currell F. J. , Fukami T. , Hirayama T. , Kato D. , Motohashi K. , Nojikawa E. , Ohtani S. , Okazaki K. , Sakurai M. , Shimizu H. , Tada N. , Tsurubuchi S. , Watanabe H.
Published: July 2002

Recent progress of the Tokyo electron beam ion trap (Tokyo-EBIT) project is described. The Tokyo-EBIT is of an original design and construction with several features different from other EBITs in the world. The maximum energy and current of the electron beam are designed to be 340 keV and 300 mA with a magnetic field of 4.5 T. The ongoing and planned physics experiments are described and the results for the initial stage of operation of the Tokyo-EBIT are given.
Electron cyclotron resonance ion source ionic currents (both in the stable and periodic regimes) modeled in relation with the hot electron temperature via the potential dip
Authors: Pras R. , Lamoureux M. , Girard A. , Khodja H. , Melin G.
Published: July 2002

We have developed a semiempirical simulation of the ionic currents extracted from an ECRIS (electron cyclotron resonance ion source). Our main contribution was to find an empirical dependence of the negative potential dip ΔΦ created by the hot electrons on the temperature parameter T⊥ which characterizes the non-Maxwellian electrons. Our model satisfactorily reproduces the extracted ionic currents, both for weekly and highly charged ions, and for both the stable and the periodic regimes. In the latter case, the currents undergo strong fluctuations. The highly charged ion currents exhibit an elaborate time evolution reflecting the competition between their production and their extraction which are, respectively, favored and inhibited by an increase in T⊥. These results confirm that the ions are electrostatically confined in the plasma and clearly show that T⊥ is a key parameter of the ECRIS plasmas.
A simple design of sextupole magnets with optimized circular pole faces
Authors: Sarma P. R. , Bhandari R. K.
Published: July 2002

A circular pole face for a sextupole magnet makes the mechanical design simple to fabricate. We have optimized the radius of the circular face to minimize the field error. We have obtained a thumb rule that the optimized radius for a sextupole should be 0.56 times the half-aperture of the magnet.
Electrical and optical characteristics of AlAsSb/GaAsSb distributed Bragg reflectors for surface emitting lasers
Authors: Blum O. , Hafich M. J. , Klem J. F. , Lear K. L. , Chu S. N. G.
Published: July 2002

We demonstrate an undoped 20 1/2 pair AlAsSb/GaAsSb distributed Bragg reflector (DBR) grown lattice matched to an InP substrate by molecular beam epitaxy. Reflectivity measurements indicate a stop band centered at 1.78 μm with a maximum reflectivity exceeding 99%. We also measure current–voltage characteristics in a similar 10 1/2 period p-type DBR and find that a current density of 1 kA/cm2 produces a 2.5 V drop. Hole mobilities and doping concentrations in AlAsSb and GaAsSb are also reported.
New design of a variable-temperature ultrahigh vacuum scanning tunneling microscope
Authors: Mugele F. , Rettenberger A. , Boneberg J. , Leiderer P.
Published: July 2002

We present the design of a variable-temperature ultrahigh vacuum (UHV) scanning tunneling microscope which can be operated between 20 and 400 K. The microscope is mounted directly onto the heat exchanger of a He continuous flow cryostat without vibration isolation inside the UHV chamber. The coarse approach is performed with an inertial slider driven by the same piezo tube that is also used for scanning. The performance of the instrument is demonstrated by two different kinds of measurements: First we show topographic images of close packed metal surfaces with atomic resolution. Then, we present results from scanning tunneling spectroscopy measurements on WSe2 under illumination at variable temperatures.
Etched chalcogenide fibers for near-field infrared scanning microscopy
Authors: Unger M. A. , Kossakovski D. A. , Kongovi R. , Beauchamp J. L. , Baldeschwieler J. D. , Palanker D. V.
Published: July 2002

Typical infrared transmitting fibers comprise a chalcogenide core surrounded by a sulfur-selenide cladding, which is in turn coated with a polymer such as polyamide. For use in a near-field scanning infrared microscope (NSIM), such infrared-transmitting fibers must be tapered to a sharp point. Sharper points allow smaller apertures, which allow higher resolution. The light throughput of the probe depends on the length of the taper region: the longer the taper length, the further the infrared radiation must propagate through a waveguide smaller than its wavelength. Thus, shorter taper lengths should give higher light throughput. We describe a method for etching chalcogenide fibers to submicron points by simple chemical means. Methods are described for removal of the polyamide coating, stripping of the SSe cladding surrounding the core, and etching the chalcogenide fiber core to a sharp point. Removal of the polyamide coating is most easily accomplished by dissolution in 4-Chloro-1-butanol. The SSe cladding is removed by soaking the fiber in 0.1 M NaOH overnight. The chalcogenide core is tapered to a sharp point by immersion in a two-phase etching system, where the top phase is an inert organic solvent, and the bottom phase is a strong oxidant. Fibers both with and without cladding have been tapered. The resulting fibers have a taper length on the order of the core diameter, and terminate with a submicron end radius of curvature. The potential for use in a NSIM, as well as other uses, is discussed.
Transient one-dimensional heat flow technique applied to porous reactive medium
Authors: Han Jong Hun , Cho Kil Won , Lee Kun- Hong , Kim Hwayong
Published: July 2002

A transient one-dimensional heat flow technique was presented to measure the effective thermal conductivity of porous reactive media. The porous reactive medium was in contact with a flat thermistor in a cell, and vacuum was applied to remove the air and the moisture. Afterwards, ammonia atmosphere was maintained in the cell under a fixed temperature and pressure. A varistor with max. 100 Ω was used to equate with the resistance of the thermistor corresponding to the fixed temperature. The temperature increase of thermistor was 2–3 °C, which was sufficient to avoid the enthalpy effect due to chemical reaction. A graphite-CaCl2⋅nNH3 complex was given as a test specimen for the porous reactive medium. Measurements showed that the thermal conductivity of graphite-CaCl2⋅8NH3 complex has distinctively higher values than the graphite-CaCl2⋅4NH3 and CaCl2⋅2NH3 complex. The accuracy of measured conductivity was estimated to be within 10%.
A compact rotating-mirror autocorrelator design for femtosecond and picosecond laser pulses
Authors: Riffe D. M. , Sabbah A. J.
Published: July 2002

An interferometric rapid-scanning autocorrelator employing two antiparallel rotating mirrors in a variable arm is optimized for maximum optical path difference as a function of the separation of the two rotating mirrors. A very compact design (mirror separation≈mirror diameter) is possible without a reduction in the maximum pulse width that can be measured.
Intrinsic doped fluorescence decay-time based measurements—strain and temperature characteristics for sensor purposes
Authors: Sun T. , Zhang Z. Y. , Grattan K. T. V. , Palmer A. W.
Published: July 2002

With current research in “smart” structures driving interest in the development of intrinsic (in-fiber) sensors for simultaneous strain and temperature monitoring, a new sensor approach is presented. In this, the fluorescence decay-time technique, which is familiar as a method of temperature monitoring with a range of materials is extended to investigate the strain sensitivity of an important temperature probe using Nd-doped fiber, in both single and multimode form. For these fibers, strain and temperature sensitivities are presented, “stress annealing” effects are investigated and the potential for compact, multiparameter intrinsic sensors using Nd-doped fiber is discussed.
High speed tangential soft x-ray camera for the study of magnetohydrodynamics instabilities
Authors: von Goeler S. , Kaita R. , Bitter M. , Fuchs G. , Poier M. , Bertschinger G. , Koslowski H. R. , Toi K. , Ohdachi S. , Donné A.
Published: July 2002

A fast camera system is being prepared for the TEXTOR tokamak for the investigation of magnetohydrodynamics (MHD) instabilities. The camera will consist of a scintillator screen for conversion of x rays into visible light, a fiberoptic cable for transport of the visible images out of the Textor magnetic field, an electrostatic image converter for amplification and demagnification of the images, and a fast charge-coupled device (CCD) camera for capturing and storing the image data. The purpose of our camera is two-dimensional imaging of magnetic islands and the structure of MHD instabilities. In order to increase the signal intensity and simultaneously reduce statistical noise, we maximize the diameter of the scintillator screen to 100 mm. For good time response, we use fast scintillators and phosphors, and plan to employ a 1 MHz framing CCD camera. MHD events having an amplitude larger than 1% can be observed with a time resolution of 100 kHz and a spatial resolution of 3 cm. In the future, the camera will be used on the Large Helical Device in Japan.
Spectroscopic measurements of hydrogen ion temperature during divertor recombination
Authors: Stotler D. P. , Skinner C. H. , Karney C. F. F.
Published: July 2002

We explore the possibility of using the neutral Hα spectral line profile to measure the ion temperature, Ti, in a recombining plasma. Since the Hα emissions due to recombination are larger than those due to other mechanisms, interference from nonrecombining regions contributing to the chord integrated data is insignificant. A Doppler and Stark broadened Hα spectrum is simulated by the DEGAS 2 neutral transport code using assumed plasma conditions. The application of a simple fitting procedure to this spectrum yields an electron density, ne, and Ti consistent with the assumed plasma parameters if the spectrum is dominated by recombination from a region of modest ne variation. General measurements of the ion temperature by Hα spectroscopy appear feasible within the context of a model for the entire divertor plasma.
Advanced one-dimensional x-ray microscope for the Omega Laser Facility
Authors: Bennett Guy R.
Published: July 2002

An analytical study of the on-axis aperture defect (spherical aberration) convolved with diffraction, for a simple spheric-based Kirkpatrick–Baez (KB) grazing incidence x-ray microscope, indicates the optimum performance is achieved by using a short object plane to mirror distances, steep grazing angles, and high x-ray energies. Other aberrations occur for off-axis field points, but if the spherical aberration can be reduced significantly the image improvement of an extended object should be dramatic. In the quest for ultrahigh x-ray spatial resolution, the Los Alamos one-dimensional (1D) KB (at the time of writing, under fabrication) fully exploits these facts in a 40 mm working distance, steep grazing angle multilayer mirror, 4.316 keV design. A rigorous analysis of Zernike surface deformations, and all other fabrication/assembly errors indicates negligible image degradation of the predicted very high resolution performance; a similar study of existing KBs closely models the 3–5 μm resolutions over the relevant field sizes. In addition, a novel analytical and ray trace optimization technique allows larger working distances at even higher resolutions. Due to instrument length constraints, however, this approach was not incorporated into the 4.316 keV 1DKB; although, in the future such designs could be easily accommodated on The National Ignition Facility.
Vacuum ultraviolet divertor impurity monitor for the International Thermonuclear Experimental Reactor
Authors: Ebisawa K. , Ando T. , Costley A. E. , Janeschitz G. , Martin E. , Sugie T.
Published: July 2002

The feasibility of installing a vacuum ultraviolet spectrometer at the divertor level on the International Thermonuclear Experimental Reactor is examined including the related engineering aspects. A narrow gap of 10 mm between divertor cassettes is used as an access for lines of sight that cover the area from the X point to the lower half of the divertor leg, and good diagnostic performance is predicted. Further work necessary to develop this configuration is identified.
Development of steady-state magnetic sensor
Authors: Hara S. , Kasai S. , Nishitani T. , Nagashima A. , Nakayama T.
Published: July 2002

A prototype of a new mechanical sensor for steady-state magnetic field has been manufactured and tested which consists of a sensing coil and a load cell. The mechanical force sensor is a new type of magnetic sensor feasible for frequencies smaller than 0.1 Hz and employs the measurement of steady-state electromagnetic force. The sensor has been examined, and the following results were obtained. (1) A signal proportionality to simulated force was obtained in the load cell tests. (2) Reproducible signal drift concerning the temperature was obtained over the range of the International Thermonuclear Experimental Reactor environment. (3) Signal proportionality to the magnetic field was obtained in the steady-state magnetic field measurement tests. (4) The significant increase of load cell linearity error was not observed after irradiation of 7.2×106 Gy. These results indicate that the mechanical sensor will provide the practical feasibility in the long time magnetic field measurement.
A cost-effective method for minimizing the sphere-of-confusion error of x-ray microdiffractometers
Authors: Noyan I. C. , Kaldor S. K. , Wang P.-C. , Jordan-Sweet J.
Published: July 2002

Microdiffractometers are used to obtain x-ray diffraction data from regions that are tens of microns or less in size. If a microdiffractometer’s rotation circles do not share the same center, or if the feature of interest on a sample does not lie at the center of all rotations, the sample feature will, upon rotation of the diffractometer circles, precess through a finite volume known as the sphere of confusion (SoC). If the size of the beam used for diffraction analysis is smaller than the SoC diameter, the beam may actually move off the region of interest. In this article, we describe a new technique, based on x-ray fluorescence imaging and coordinate transforms, which can maintain the sample position to within ±6 μm over all rotations even when a commercial diffractometer is used as the base for the microdiffractometer system. In this scheme, a grid held in place on the specimen surface is mapped using fluorescent radiation at various sample tilts. The transformation matrices, which relate the grid coordinates to the sample stage coordinates at different sample tilts, can then be used to bring the sample stage into coincidence with its original position.
First measurement of tangential Faraday rotation of CO2 laser wave in a tokamak plasma
Authors: Kawano Yasunori , Chiba Shin-ichi , Shirai Hiroshi , Inoue Akira , Nagashima Akira
Published: July 2002

The first measurement of the Faraday rotation of CO2 laser wave propagating in toroidally tangential direction in a tokamak plasma has been demonstrated in JT-60U tokamak. An infrared polarimeter using a couple of photoelastic modulators has reliably detected the polarization angle of a CO2 laser wave even when incident laser intensity is varied. So far, the accuracy of the measured polarization angle is ∼0.1°. Simultaneous measurements of polarimetry and interferometry has been achieved stably. The verification of principles of the tangential Faraday rotation for electron density measurement in large tokamaks has been presented.
Ion beam synthesis of ternary phase CoFe-silicide in (111) silicon
Authors: Tavares J. , Bender H. , Wu M. F. , Vantomme A. , Langouche G. , Lin C.
Published: July 2002

A transmission electron microscopy (TEM) investigation is presented of ion beam synthesized buried CoFe-silicide prepared by sequential equal-dose implantations of both metals. The TEM analysis shows strong evidence for the formation of a metastable ternary Co0.5Fe0.5Si2 phase during the implantation. Annealing of these structures at 1000 °C results in the formation of a continuous buried layer, but phase separation occurs into B-oriented CoxFe1−xSi2 and twinned α-FexCo1−xSi2 (both with x close to 1).
Special modulator for high frequency, low-voltage plasma immersion ion implantation
Authors: Tian Xiubo , Wang Xiaofeng , Tang Baoyin , Chu Paul K. , Ko Ping K. , Cheng Yiu-Chung
Published: July 2002

Plasma immersion ion implantation is a burgeoning surface modification technique and not limited by the line-of-sight restriction plaguing conventional beam-line ion implantation. It is therefore an excellent technique to treat interior surfaces as well as components of a complex shape. To enhance the implant uniformity and increase the thickness of the modified layer, we are using a high frequency, low-voltage process to achieve high temperature and dose rate to increase the thickness of the modified layer. The low voltage conditions also lead to a thinner sheath more favorable to conformal implantation. In this article, we will describe our special modulator consisting of a single ended forward converter with a step-up transformer. The modulator is designed to operate from 5 to 35 kHz and the output voltage is adjustable to an upper ceiling of 5000 V that is deliberately chosen to be our voltage limit for the present experiments. We will also present experimental data on SS304 stainless steel materials elucidating the advantages of our modulator and high frequency, low-voltage experimental protocols.
Novel thin membrane probe and a new twisting modulation force detection method of an atomic force microscope
Authors: Nakano Katsushi , Suzuki Yoshihiko
Published: July 2002

For inspection of high aspect ratio structures like narrow semiconductor trenches, a thin membrane probe and a new force detection method have been proposed. Instead of conventional conical and pyramidal tips, a thin silicon nitride cantilever was set up vertically, and its edge was used as a tip. The membrane probe named as twist-probe (TP) was oscillated in the twisting resonance to detect a force from both vertical and lateral directions. About 100 μm long, 0.7 μm thick TP was fabricated as a trial. Amplitude versus distance curve measurements showed that the TP has a high spacing change sensitivity between the tip and a sample in both vertical and lateral directions. A trench cross-section imaging was demonstrated successfully with a TP and the twist resonant force detection method.
Noncontact measurement of étalon spacing using a retroreflection technique
Authors: Thomas Paul J. , Mani R. , Khalil N.
Published: July 2002

A novel technique is described for the noncontact determination of the spacings of solid and air-gap étalons of low reflectivity by the retroreflection of a He–Ne laser beam. Gaps as small as 50 μm were measured with a precision of better than ±1 μm. Typical measurement accuracy is better than 2%.
A fast, parallel acquisition, electron energy analyzer: The hyperbolic field analyzer
Authors: Jacka M. , Kirk M. , El Gomati M. M. , Prutton M.
Published: July 2002

This article describes a new kind of electrostatic charged particle analyzer capable of the parallel detection of a large kinetic energy range. The main purpose envisaged is for the simultaneous detection of electrons scattered from surfaces and having energies between a few tens of eV to greater than 2000 eV. A prototype has been constructed that approximates a hyperbolic deflection field for the electrons entering an entrance slit. It exhibits an energy resolution of a few eV and a collection efficiency of 0.05% of 2π sr. Useful Auger spectra can be acquired in a time of less than 2 s. The significant improvement in spectrum acquisition time that this represents offers many possibilities to further Auger and photoelectron spectroscopy.
System analysis of the force-feedback method for force curve measurements
Authors: Kato Nobuhiro , Kikuta Hisao , Nakano Takashi , Matsumoto Toshiro , Iwata Koichi
Published: July 2002

The force-feedback method is a promising technique to measure accurate force curves in atomic force spectroscopy. In this article, we describe criteria of the stability for the force-feedback system containing a proportional amplifier with first-order lag. We derive the criteria from an equation of the cantilever movement with higher-order vibration modes under force interaction. The criteria predict that a proportional amplifier with a certain gain and a “very high” cutoff frequency is required to stabilize the feedback system when the critical force gradient exceeds the cantilever stiffness. To measure a force curve, including the steep part (−17 N/m) with a soft (0.2 N/m) and poor-damping (2×10−7 kg/s) cantilever, the amplifier for the force-feedback controller must have a frequency response wider than 16 MHz and gain larger than 16.8. Moreover, the feedback controller with only an integrator, which is popular in scanning tunneling microscopy and atomic force microscopy, does not contribute to reducing the discontinuity of the force curve.
Mass spectrometric estimation of gas permeation coefficients for thin polymer membranes
Authors: Nörenberg Holger , Miyamoto T. , Tsukahara Y. , Smith G. D. W. , Briggs G. A. D.
Published: July 2002

We have developed a new method to estimate the permeation coefficient of gases through polymer membranes. A fixed volume of gas is put in a gas cell and introduced into ultrahigh vacuum. After positioning the gas cell to face a quadrupole mass spectrometer, the partial pressure of the gases are measured as function of time. In a simple model, the partial pressure as function of time obeys an exponential law. A formula is derived to calculate the permeation coefficient with the time constant of the partial pressure decay and geometric parameters of the gas cell as input. Using these parameters the method gives absolute permeation values without calibration. If the time constant is difficult to establish (this may happen for membranes with a low permeation coefficient), the permeation coefficient can be estimated by extrapolating the partial pressure to t=0. The method can be used to study the permeation behavior of individual components of gas mixtures. The sample size can be about two orders of magnitude smaller than usually used in conventional permeation measurements. The method is illustrated with oriented polypropylene and polyethylene terephtalate membranes of different thickness. The estimated permeation coefficients are in reasonable agreement with values obtained from a control experiment using a gas chromatograph and with values from the literature.
A liquid helium cryostat for the study of pressure effects on hole burned spectra of hyperquenched glassy films
Authors: Hayes J. M. , Reinot T. , Shields P. , Small G. J.
Published: July 2002

A liquid helium cryostat that allows for thermospray deposition of samples in vacuum and subsequent pressure dependent studies up to 150 atm is described. Performance of the cryostat is illustrated by study of the pressure-induced shifts and broadening of holes burned in the lowest energy absorption band of aluminum phthalocyanine tetrasulfonate in hyperquenched glassy water. The hole widths exhibit an unusual dependence upon the pressure at which they are burned and also a linear frequency shift which depends upon the sign of the pressure change.
Liquid reaction apparatus for surface analysis
Authors: Chusuei C. C. , Murrell T. S. , Corneille J. S. , Nooney M. G. , Vesecky S. M. , Hossner L. R. , Goodman D. W.
Published: July 2002

A design for a liquid reaction apparatus is described which allows surfaces prepared in ultrahigh vacuum (UHV) to be reacted with solutions of a wide pH range under dry nitrogen atmosphere and subsequently returned to UHV for surface analysis.