bluuebunny/crossref_metadata_2025 huggingface dataset:
A fluorescent sample platform for ultraviolet laser desorption studies
Authors: Dal Pozzo Paul , Lewis Lisa B. , Estler Ron C.
Published: July 2002

Laser desorption studies often require the visualization of an ultraviolet laser source on a metallic surface for the purpose of irradiating a specific surface site and for repositioning the laser source to other surface sites. In some laser desorption techniques, for example, matrix assisted laser desorption ionization, the highest ionization efficiency for biological samples, is obtained at or near the ablation threshold (106 W/cm2) of the ultraviolet-absorbing organic matrix. At these low laser intensities, the laser beam footprint is difficult to observe on the sample or the surrounding support surface. To aid this visualization, we have used anodization to incorporate a fluorescent dye into the surface oxide layer of aluminum. The result is a hard, chemically noncontaminating, intensely fluorescent sample support surface for laser desorption investigations.
On line and in situ quantification of gas mixtures by matrix interval algebra assisted quadrupole mass spectrometry
Authors: Kaiser R. I. , Jansen P. , Petersen K. , Roessler K.
Published: July 2002

A novel, efficient technique to identify and quantify complex gas mixtures is described. This approach can be applied on line and in situ and is extendible to samples with reactive and thermally labile species. Complex hydrocarbon mixtures are prepared in test experiments by irradiating frozen methane targets with 9 MeV α particles in an ultrahigh vacuum chamber and releasing them during successive heating of the solid samples from 10 to 293 K after each ion bombardment. A quadrupole mass spectrometer monitors time-dependent ion currents of selected m/z values, which are proportional to partial pressures in the case of a nonoverlapping fragmentation pattern. Predominantly, parent molecules and fragments of different molecular species add to a specific m/z value, i.e., C2H+4, N+2, and CO+ contribute to m/z=28. Programmed m/z ratios are chosen to result in an inhomogeneous system of linear equations including the measured ion current (right-hand vector), partial pressures (unknown quantity), and the calibration factors of fragments of individual gases determined in separate experiments. Since all quantities are provided with experimental errors, matrix interval algebra, i.e., an IBM high accuracy arithmetic subroutine defining experimental uncertainties as intervals, is incorporated in the computations to extract individual, calibrated components of complex gas mixtures. This proceeding enables the quantitative sampling of calibrated hydrocarbons, and, especially, H2 and D2 without further time-consuming preseparation devices on line and in situ, hence justifying the use of this approach in space missions to elucidate the chemical composition of, e.g., planetary atmospheres without payload wasting gas chromatographs.
Three-filter colorimetry in DIII–D to measure in situ erosion and deposition of plasma facing surfaces
Authors: Weschenfelder F. , Wienhold P. , Winter J. , Jackson G. L. , Brooks N. H. , West W. P. , Lee R. L.
Published: July 2002

Three-filter colorimetry has been introduced in the DIII–D tokamak to measure in situ the growth and the erosion of transparent wall coatings (a-C/B:H) in the divertor region. Colorimetry uses the interference of light on a transparent layer to measure the film thickness. The colorimetry setup at DIII–D consists of a light source, a black and white camera, and a filter wheel equipped with three broadband color filters. A white light source illuminates the area of interest. A picture with each filter is recorded and digitized. Thus the interference color of a semitransparent layer is measured and the film thickness is computed using the formalism of thin film optics. Since color cameras are more sensitive to neutron damage, a set of three filters was chosen which best matches the responsivity of a radiation-hardened B/W camera. In fact, one infrared filter and two visible filters are used. The three 2D camera images obtained from rotating the three filters into the line of sight of the camera are used to produce a 2D image of the change in film thickness due to the high flux of particles and power incident on the film during a diverted discharge. In a first measurement, the technique was used to measure the growth of a boron film in situ in the DIII–D tokamak.
Experimental device for measuring the influence of a uniaxial stress on specific heat: Application to the strontium titanate ferroelastic crystal
Authors: Gallardo M. C. , Jiménez J. , del Cerro J.
Published: July 2002

A conduction calorimeter where the sample is pressed between two identical heat fluxmeters, each having 50 chromel–constantan thermocouples, is described. The fluxmeters were built to obtain linear heat conduction and with enough rigidity to apply a controlled uniaxial stress on the sample. The method of measurement, together with the fact that the sensors themselves apply the stress to the sample, allow us to obtain absolute values of the specific heat. The specific heat of strontium titanate ferroelastic crystal is measured without stress and under an applied uniaxial stress on the face (110). The measurements were carried out while cooling the sample at a constant rate of 0.06 K/h. The data obtained at intervals of 0.02 K are compared with those obtained with an unannealed and an annealed sample, respectively.
Characterization of ALS undulator radiation—High K, taper, and the near field effect
Authors: Mossessian D. A. , Heimann P. A.
Published: July 2002

The results of the measurements of spectral and angular distribution of the U5.0 (5 cm period) and U8.0 (8 cm period) Advanced Light Source (ALS) undulators are described. The spectra of on-axis undulator radiation were measured for various values of the deflection parameter K. In particular, the high K case was studied, representing the region between the undulator and wiggler limits. Good agreement in harmonic peak flux and width is found between the measurements and the computations that include the real magnetic field, the electron beam energy spread, and the electron beam emittance. The effect of the undulator taper on the spectral characteristics of the radiation was analyzed. At small taper (∼0.5% gap variation) significant reduction in peak brightness and flux of the fifth harmonic was observed with small effect on the fundamental. The near field effect in the undulator radiation was studied by measuring the off-axis spectral and angular distributions of the radiation. The broadening and the fine structure in the distributions at large off-axis angles were observed, resulting from the near field effect.
Depth profiling using the glancing-incidence and glancing-takeoff x-ray fluorescence method
Authors: Tsuji K. , Sato S. , Hirokawa K.
Published: July 2002

We have developed a new analytical method, which we call the glancing-incidence and glancing-takeoff x-ray fluorescence (GIT-XRF) method. In this method, a fluorescent x ray is measured at various combinations of incident and takeoff angles. A nondestructive depth profiling is possible by using this GIT-XRF method, because the effective observation depth is changed by both the incident and takeoff angles. Here, we introduce the idea of depth profiling using the GIT-XRF method, and then we apply this method to an Au–Si interface reaction.
Measurements of internal MHD fluctuations in PBX-M by an ECE heterodyne radiometer (invited) (abstract)a)
Authors: Zolfaghari A. M.
Published: July 2002

Localized measurements of internal MHD activity in PBX-M have been made using a heterodyne radiometer. The radiometer measures third harmonic optically gray ECE from the center to the outer edge of the plasma on 8 radially localized frequency channels from 112–127 GHz. The radiometer uses a focusing gaussian optics system which provides a vertical resolution of approximately 6 cm throughout the plasma. The radial resolution of the diagnostics is limited by the relativistic broadening to approximately 2–3 cm. Long wavelength (k<0.5 cm−1) temperature and density fluctuations can therefore be detected using this diagnostic. Correlation techniques have been used on the data to provide fluctuation sensitivity as low as 0.4%. An analytical theory has been developed which relates the measured amplitude of the coherent ECE fluctuations caused by a MHD mode to its mode characteristics. Using the analysis, the MHD mode displacement amplitude ξ(r) has for the first time been calculated for observed MHD activity in a tokamak plasma. ξ(r) and δP/P have been calculated for high n-number MHD modes in high-βp PBX-M plasmas. The results of these measurements will be presented.
Antenna decoupling requirements in a gyrotron collective Thomson scattering diagnostic (CTS) (abstract)a)
Authors: Orsitto F. , Tartari U.
Published: July 2002

The required rejection ratio of the stray light in a CTS, respect to the launching power is investigated, for obtaining useful signal-to-noise ratio. This problem is faced considering the central gyrotron frequency f0, as well as the in-band stray light raising from the spurious mode of the gyrotron and amplified cyclotron emission (the so-called gyrotron noise), falling into the scattered light spectrum. The statistical nature of the gyrotron noise in the scattering band is important because the required decoupling is obtained using the S/N formula where the fluctuation of the plasma radiation and the gyrotron noise fluctuation appears. It turns out that the total decoupling required at f0 is of the order of or greater than 80 dB, while in the scattering band could be less than 40 dB.
Phaedrus-T probe techniques
Authors: Diebold D. A. , Hershkowitz N. , Pew J. , Sorensen J. , Tanaka T. , Walsh R. , Wang E. Y. , Wang X. , Winz G.
Published: July 2002

Probe techniques employed in ohmic, rf, and H-mode Phaedrus-T tokamak plasmas are discussed. The floating potentials of nonemitting probes are found to be insensitive to plasma potential fluctuations at the rf frequency. Both Langmuir and emissive probes have been swept. The Langmuir probes were swept into electron saturation where a low-frequency oscillation was sometimes observed. Large probes (biased electrodes) have been used to perturb the plasma into an H mode. The biased electrode I-V characteristics differ from those of nonperturbing Langmuir probes and can be used to help identify the H mode. Probe behavior during the H mode is discussed. Two novel reciprocating probe designs have been developed. The faster of the two achieves average speeds of 5 m/s, which to our knowledge makes it the world’s fastest.
Development of heavy ion beam probe diagnostics (abstract)
Authors: Melnikov A. V.
Published: July 2002

The results of the activity of Kharkov and Moscow joint HIBP group during recent years are presented in this report. The mathematical aspects of the diagnostics are discussed more specifically. The HIBP diagnostics need the preliminary trajectory calculations to find the probing pattern, which is possible to realize the plasma facility, and to determine the compatibility between the device and diagnostics. The idea is to receive as much information as possible (that means to cover the maximal plasma cross section by the detector grid) leads to the formulation of the HIBP optimization problem. The properties of this multidimensional optimization problem are discussed and the examples of its solution (HIBP projects for a large number of facilities) are presented. The processing of the experimental data is discussed mainly from the point of view of the formulation of the mathematical problems, the sensitivity and the clearance of the integral operational relations between the plasma parameters to be found, and the measured beam properties. The computational aspects and the results of numerical tests and treatment of the experimental data are discussed for the problems of the electric field, plasma density, and current distribution determination. The common feature of the integral operators containing the specific parts for describing the secondary ionization point in the plasma is emphasized and their regularizing properties are discussed. The probing apparatus used for measurements of the plasma electric potential, density, and current are described. Some results of recent measurements are discussed and the newest data obtained on T-10 tokamak are presented.
In situ neutral pressure measurements in a compact high-field tokamak, Alcator C-Mod
Authors: Niemczewski A. , Lipschultz B. , LaBombard B. , McCracken G. M.
Published: July 2002

The Alcator C-Mod advanced divertor program requires fast in situ, absolutely calibrated neutral pressure measurements. The concept of a linear-geometry ionization gauge, first implemented at Princeton and Garching, was further developed at the MIT Plasma Fusion Center, to meet Alcator C-Mod requirements (high field, compact design). In order to correctly interpret experimental data, the gauge was subjected to a series of in situ calibration tests. It has been found that the gauge sensitivity increases with increasing parallel (to gauge axis) magnetic field. In the high-pressure, high-field limit the basic assumption of the operation of ionization gauges, Ii/Ie≪1, no longer holds. Consequently a modified expression for the gauge sensitivity, which is a strong function of the primary electron current, is necessary to linearize gauge response over a broad pressure range. Representative pressure measurements from the Alcator C-Mod divertor are included.
Method for neutral spectra analysis taking ripple-trapped particle losses into account
Authors: Dnestrovskij A. Yu. , Bengtson Roger D. , Karzhavin Yuri , Ouroua A.
Published: July 2002

An analysis technique of charge exchange neutral spectra is proposed and tested to obtain ion temperatures of a tokamak plasma. The technique models the deviation of the ion distribution from Maxwellian because of ripple trapped particles and introduces a hot ion effective temperature as a fitting parameter. The analysis code has been used to analyze active charge exchange data from TEXT discharges in which a significant up-down asymmetry in the neutral spectra was noted. An analysis considering ripple trapped particles removed some of the asymmetry and indicated the need for another mechanism for distorting charge exchange spectra.
The 3ω technique for measuring dynamic specific heat and thermal conductivity of a liquid or solid
Authors: Moon I. K. , Jeong Y. H. , Kwun S. I.
Published: July 2002

We show how to measure dynamic specific heat and thermal conductivity of a solid or liquid sample using the 3ω technique, which is an ac-modulation method where we use a heater simultaneously as the sensor. By varying the width of the heater relative to the thermal decay length, one can choose the proper regime to measure thermal conductivity or specific heat. The technique is applied to window glass and the results confirm the validity of the method. Experimental results for potassium dihydrogen phosphate crystal demonstrate the first-order transition at the Curie point, and the dynamic specific heat of supercooled liquid potassium–calcium nitrate is shown.
Examining deep holes by rocking the beam in the scanning electron microscope
Authors: Wells Oliver C.
Published: July 2002

The beam-rocking method in the scanning electron microscope can show either the inner surface of a deep hole or the outer surface of a parallel-sided pillar in ways that are not possible when scanning in the usual way. This has been demonstrated using test samples of both kinds. It is believed that this method can be successfully applied to examine deep holes and narrow pillars of micrometer dimensions by applying computer control and data analysis techniques of the kind that are used in automated semiconductor fabrication and/or metrology systems.
A long-pulse 300 keV electron gun with a plasma cathode for high-pressure gas lasers
Authors: Gielkens S. W. A. , Peters P. J. M. , Witteman W. J. , Borovikov P. V. , Stepanov A. V. , Tskhai V. N. , Zavjalov M. A. , Gushenets V. I. , Koval N. N.
Published: July 2002

The design and main features of a plasma cathode electron gun for high-pressure gas lasers are discussed. The mesh plasma cathode in combination with a low-pressure gas discharge was used for the formation of a large cross-section (55×4 cm2) electron beam with emission current densities up to 1.7 A/cm2, accelerating voltages up to 300 kV, and a pulse length of 20 μs (full width at half maximum).
Deposition of smooth tetrahedral amorphous carbon thin films using a cathodic arc without a macroparticle filter
Authors: Chhowalla M. , Weiler M. , Davis C. A. , Kleinsorge B. , Amaratunga G. A. J.
Published: July 2002

It is shown that for a cathode consisting of compressed graphite powder, the cathodic arc discharge is confined within deep erosion holes and the macroparticle emission is greatly reduced. Electron energy loss spectroscopy and scanning electron microscopy show that smooth tetrahedral amorphous carbon films with up to 85±10% sp3 bonding can be deposited without the use of magnetic filters. The new carbon arc discharge process holds potential for deposition of smooth tetrahedral amorphous carbon films on large area substrates due to the elimination of the magnetic filtering stage.
Analysis of standard reference materials following digestion using a modified appliance grade microwave oven
Authors: Schaumloffel John C. , Siems William F.
Published: July 2002

Microwave digestion provides a rapid means of sample preparation in the analytical laboratory. The major disadvantage of this method is the high cost of commercial microwave digestion systems. Modifications to the magnetron timing circuits of an appliance grade oven to make it suitable for sealed vessel microwave digestion are reported. The oven was modified without alteration to the irradiation cavity, and all initial safety features remain intact. Following digestion with the modified oven, NIST Standard Reference Materials (SRMs) were analyzed by inductively coupled plasma emission spectroscopy. The analytical data are similar to the certified concentrations in the SRMs, indicating that the modified oven provides a durable, rapid, cost-effective means of sample preparation.
Surface modifications with a scanning force microscope
Authors: Tegen S. , Kracke B. , Damaschke B.
Published: July 2002

The possibilities for the use of a scanning force microscope as a machining tool for the modification of gold surfaces were investigated. For this purpose, a scanning force microscope for the creation of structures with constant load and with a force modulation technique was constructed. With this instrument, we are able to create and characterize structures like lines and circles in thin gold films on mica. Especially the force modulation technique is suitable for producing structures with well defined geometry. Further investigations of the shape and the stability of the structures were made.
Elliptical flexure hinges
Authors: Smith Stuart T. , Badami Vivek G. , Dale Jami S. , Xu Ying
Published: July 2002

This paper presents closed form equations based on a modification of those originally derived by Paros and Weisbord in 1965, for the mechanical compliance of a simple monolithic flexure hinge of elliptic cross section, the geometry of which is determined by the ratio ε of the major and minor axes. It is shown that these equations converge at ε=1 to the Paros and Weisbord equations for a hinge of circular section and at ε ⇒∞ to the equations predicted from simple beam bending theory for the compliance of a cantilever beam. These equations are then assessed by comparison with results from finite element analysis over a range of geometries typical of many hinge designs. Based on the finite element analysis, stress concentration factors for the elliptical hinge are also presented. As a further verification of these equations, a number of elliptical hinges were manufactured on a CNC milling machine. Experimental data were produced by applying a bending moment using dead weight loading and measuring subsequent angular deflections with a laser interferometer. In general, it was found that predictions for the compliance of elliptical hinges are likely to be within 12% for a range of geometries with the ratio βx (=t/2ax) between 0.06 and 0.2 and for values of ε between 1 and 10.
Formation and electrical properties of heteroepitaxial SrTiO3/SrVO3−x/Si(100) structures
Authors: Moon B. K. , Ishiwara H.
Published: July 2002

Heteroepitaxial growth of dielectric SrTiO3(STO)/conductive SrVO3−x(SVO)/Si(100) structures was realized using a focused electron beam evaporation method. It was found from x-ray diffraction analysis and pole figure measurement that the epitaxial relationships were (100)STO ∥(100)SVO∥(100)Si and 〈011〉STO∥〈011〉SVO∥〈001〉Si. It was also observed from depth profiling by secondary ion mass spectrometry that the interdiffusion of constituent elements among the films and Si substrate was not significant. Electrical properties of the STO film were characterized through I–V (current–voltage) and C–V (capacitance–voltage) measurements, after depositing Al electrodes on the STO/SVO/Si structure. The best values of breakdown field, resistivity, and dielectric constant were 345 kV/cm, 6.4×1012 Ω cm, and 243, respectively.
Binder extraction from green multilayer ceramics using a weight loss rate-controlled thermogravimetric analyzer
Authors: Witt Jason , Speyer Robert F. , Murali Lakshman
Published: July 2002

A weight loss rate-controlled organic extraction furnace was built and demonstrated using a multilayer green ceramic. Multirate weight loss schedules as well as automated atmosphere control and detection were demonstrated. The low thermal mass furnace showed good tracking with 300 °C heating and cooling rates. This furnace, coupled with appropriate PID control constants, facilitated feedback control which could extract organics rapidly without self-ignition to uncontrolled combustion. Controlled organic burnout was demonstrated at weight loss rates up to 0.5%/min in air. Damage-free multilayers were observed using a burnout rate requiring 150 min for extraction, rather than the days commonly associated with this task when using conventional furnaces.
A miniature single element effusion cell for the vacuum deposition of transition-metal and rare-earth elements
Authors: Harris V. G. , Koon N. C.
Published: July 2002

A miniature single element effusion cell has been fabricated and tested that allows for the high-vacuum deposition of a variety of transition-metal and rare-earth elements. The cell is designed to operate under high-vacuum conditions, ≈10−9 Torr, with low power demands, <200 W. The virtues of this evaporator are the simplicity of design and ease of fabrication, assembly, maintenance, and operation.
A design study for a holey-plate structure surface-wave ion source
Authors: Yoshida Yoshikazu
Published: July 2002

A low-pressure and high-density microwave ion source, created and sustained by a surface wave, using a partial-coaxial cavity resonator has been newly developed for the production of stable beams from gaseous feed materials. This source is called a holey-plate surface-wave ion source. A microwave of 2.45 GHz is supplied from a holey plate which is made from a 0.5 mm thick stainless steel sheet with 4 mm diameter and 5 mm pitch holes to a plasma production chamber of 40 mm diameter and 11 mm in length. An 18-mm-diameter argon ion beam is extracted and accelerated from the ion source. The ion current densities are in excess of 6 mA/cm2 at an extraction voltage of 1 kV and at microwave powers of less than 100 W.
A 3.9 MeV photoinjector and delay system for Wakefield measurements
Authors: Power J. G. , Conde M. E.
Published: July 2002

We report on the characterization of the 3.9 MeV electron beam from a rf photoinjector at the Argonne Wakefield Accelerator. This beam is used to diagnose wakefields produced by the 15 MeV beam from a second rf photoinjector. We measured the emittance with the usual quadrupole scan method but used a fitting algorithm that includes space-charge forces. This photocathode gun has produced a beam charge per pulse ranging from 10 pC to 4 nC, but is normally operated at 100 pC with a measured normalized emittance of 3.4 π mm mrad and bunch length of 8 ps full width at half maximum.
A simple spherical grating by-pass monochromator dedicated to soft x-ray emission spectroscopy
Authors: Ghiringhelli G. , Tagliaferri A. , Braicovich L. , Brookes N. B.
Published: July 2002

PoLIFEMo (Polarized Light Improved Flux Efficiency Monochromator) is the name of a spherical grating monochromator designed with the purpose of maximizing the photon intensity on a sample. The device is mainly conceived to improve performances of an x-ray emission spectrometer, whose limiting factor is often the counting rate. By keeping the exit slit fixed, it is possible to get a small spot size (∼35 μm vertically) on a sample placed just near the exit slit, without the need of postgrating refocusing optics. No entrance slit is used because of the low beam divergence, allowing the use of a virtual source in a converging beam geometry. The tuning of the output energy is done by translating and pitching the spherical grating. The resolving power is higher than 1000 over the whole energy range (500–1500 eV). A detailed analysis of the optical performances is given, mostly in comparison with the Dragon-type monochromator. The actual realization of the device is described, together with the specific motivations and the experimental performances. PoLIFEMo has been installed on beam line ID12B at the European Synchrotron Radiation Facility since July 1996.
Apparatus and experimental method for measurements of the potential distributions in dc glow discharges
Authors: Bindemann T. , Tichý M. , Behnke J. F. , Deutsch H. , Becker K.
Published: July 2002

We present an apparatus and experimental method for the measurement of the potential distributions in dc glow discharges. The apparatus employs a combination of internal and external electrodes. The internal electrodes are cylindrical or planar Langmuir probes whose collector is aligned with the inner wall of the discharge tube. The external electrodes consist of a thin Al foil wrapped around the outside of the discharge tube. The discharge is periodically switched on and off (pulsed) with a typical frequency of 10 Hz using an electronic valve controlled by optically isolated couplers. The apparatus allows measurements of the time and temperature dependence of the potentials on the electrodes. The potentials on the electrodes are sensed by two voltage followers with extremely high input impedance (5×1011 Ω input resistance, ∼1 pF input capacitance), so that direct measurements of the potential differences between two electrodes are possible. The data acquisition and control of the experiment is accomplished using an input/output data acquisition/control board (AT-MIO from National Instruments) connected to a personal computer (PC). The maximum time resolution of the system is 10 μs, the maximum measurable voltage difference is about 2 kV. In addition to direct floating and wall potential measurements, the apparatus also allows measurements of the characteristics of a Langmuir probe by using a floating probe circuit coupled to a computer-controlled external data acquisition system using isolation amplifiers. The data acquisition/control system enables time-resolved probe characteristic and floating/wall potential measurements as a function of temperature. We present a series of measurements which demonstrate the capabilities of the new apparatus and experimental method.
A novel ion beam monitor using Kapton foils
Authors: Guharay S. K. , Hamabe M. , Kuroda T.
Published: July 2002

Kapton foils can be used as a simple ion beam monitor. These foils act as a self-developing medium and quantitative information about the distribution of the striking beam can be obtained easily. The “burn” pattern on the film due to irradiation by the ion beam is analyzed to determine the beam distribution, here the beam power density distribution. Given the beam voltage this information can be translated to the ion current density distribution. The linearity of response of the Kapton foil with beam current density is shown. The threshold for response of the Kapton foil seems quite good; a clear response is observed with a foil of thickness=50 μm for H− beam current density of about 35 μA/cm2 at 88 kV.
Hydrogen and nitrogen bonding in silicon nitride layers deposited by laser reactive ablation: Infrared and x-ray photoelectron study
Authors: Fejfar A. , Zemek J. , Trchová M.
Published: July 2002

Silicon nitride layers deposited by an excimer laser reactive ablation of silicon target in ammonia on Si(100) wafers kept at 300 or 600 °C have been studied by infrared absorption and angular resolved x-ray photoelectron spectroscopy. Presence of hydrogen in the deposits unexpected at the high substrate temperatures is documented. The observed deposit thicknesses, stoichiometry, and the hydrogen content as a function of ammonia pressure suggest a picture of the deposition process with Si3N4 synthesis taking place on the growing deposit surface, contrary to the liquid phase reaction model suggested for analogous TiN deposition.
High resolution optical shaft encoder for motor speed control based on an optical disk pick-up
Authors: Yeh Wei-Hung , Bletscher Warren , Mansuripur M.
Published: July 2002

Using a three-beam optical pick-up from a compact disk player and a flexible, shaft-mounted diffraction grating, we obtain information about the rotation speed and angular position of the motor’s spindle. This information may be used for feedback to the motor for smooth operation. Due to the small size of the focused spot and the built-in auto-focus mechanism of the optical head, the proposed encoder can achieve submicrometer resolution. With high resolution, reliable operation, and low-cost elements, the proposed method is suitable for rotary and linear motion control where accurate positioning of an object is required.
Blast wave diagnostic for the Petawatt laser system
Authors: Budil K. S. , Gold D. M. , Estabrook K. G. , Remington B. A. , Kane J. , Bell P. M. , Pennington D. , Brown C. , Hatchett S. , Koch J. A. , Key M. H. , Perry M. D.
Published: July 2002

We report on a diagnostic to measure the trajectory of a blast wave propagating through a plastic target 400 μm thick. This blast wave is generated by the irradiation of the front surface of the target with ∼400 J of 1 μm laser radiation in a 20 ps pulse focused to a ∼50 μm diameter spot, which produces an intensity in excess of 1018 W/cm2. These conditions approximate a point explosion and a blast wave is predicted to be generated with an initial pressure nearing 1 Gbar which decays as it travels approximately radially outward from the interaction region. We have utilized streaked optical pyrometry of the blast front to determine its time of arrival at the rear surface of the target. Applications of a self-similar Taylor–Sedov blast wave solution allows the amount of energy deposited to be estimated. The experiment, LASNEX design simulations and initial results are discussed.
Observation of multiple-peaked structure in the time-of-flight spectrum of the Sinp-tokamak discharge
Authors: Ray N. R.
Published: July 2002

In the present article a multiple-peaked structure in the time-of-flight (TOF) spectrum obtained in a TOF analyzer system installed in the Sinp-tokamak has been reported. An explanation of the nature of the measured TOF spectrum has been given on the basis of a proposed model describing acceleration, in the radial direction, of radially diffusing ions in the ambipolar electric field. It is concluded that the particle diffusion across the magnetic field as a result of acceleration by the dynamic ambipolar electric field and charge-exchange collisions can be studied by a TOF analyzer system coupled with a research tokamak.
Laser-induced fluorescence diagnostic for measuring magnetic fields (abstract)
Authors: Jones T. G. , Noonan W. A. , Neri J. M. , Ottinger P. F.
Published: July 2002

A novel, spatially resolved diagnostic is being developed to measure magnetic fields associated with intense ion beam propagation through a low-pressure gas, as is envisioned for ion-driven inertial confinement fusion. The diagnostic technique uses laser-induced fluorescence spectroscopy, and can be varied to measure either small or large fields. Small fields, as expected in ballistic beam transport, produce Zeeman shifts, ΔλZ, much smaller than the transition linewidth Δλ. High sensitivity to measure these sub-Doppler shifts is achieved by a variation on the Babcock technique.Reference 1 Large fields, as expected in self-pinched beam transport, produce ΔλZ larger than Δλ. These ΔλZ will be resolved using a Fabry–Pérot interferometer, in a novel technique similar to that for small fields. Results from benchtop experiments using calibrated B fields for the small-field technique will be presented. Available results from a proof-of-principle experiment for the large-field technique will also be presented.
Pellet charge exchange measurements of confined alphas in deuterium–tritium plasmas (invited) (abstract)
Authors: Fisher R. K.
Published: July 2002

Alpha particle confinement is essential to achieving ignition in deuterium–tritium plasmas, and measuring the energy and spatial distributions of fusion alphas is one of the most challenging tasks in plasma diagnostics research. Confined trapped-alpha energy spectra and radial density profiles in the Tokamak Fusion Test Reactor (TFTR) have been obtained using the pellet charge exchange (PCX) diagnostic, which measures high energy (Eα=0.5–3.5 MeV), trapped alphas (|v∥/v|=0.048) at a single time slice (Δt∼1 ms) with a spatial resolution of Δr∼5 cm. PCX measures the energy spectrum of energetic helium neutrals resulting from charge exchange interactions of alphas incident on the ablation cloud surrounding small boron and lithium pellets injected radially into TFTR. The success of PCX has led to a number of important results on the behavior of alphas in TFTR. The measured alpha energy spectrum in the plasma core of sawtooth-free discharges is consistent with the alphas being well confined and slowing down classically. Outside the plasma core, the trapped alphas show the effects of stochastic diffusion due to the toroidal magnetic field ripple, with the PCX measured profiles consistent with the functional dependence of the stochastic ripple diffusion on the alpha energy and the q profile. Large sawtooth instabilities result in radial redistribution of the trapped alphas to well outside the q=1 radius and beyond the stochastic ripple loss boundary. Broadening of the radial profiles of trapped alphas is also observed in reversed and reduced shear discharges on TFTR, with potential implications for reactor designs based on optimized shear configurations. Finally, radial redistribution of trapped alpha particles in the presence of core localized Toroidal Alfv́en Eigenmode activity is also observed. Application of PCX measurements to future experiments, including the International Thermonuclear Experimental Reactor will also be discussed.
A two-color interferometer using a frequency doubled diode pumped laser for electron density measurements
Authors: Irby J. , Murray R. , Acedo P. , Lamela H.
Published: July 2002

A new tangentially viewing interferometer has been operated on the Alcator C-Mod tokamak. This system uses both the near infrared and visible beams from a continuous wave, diode pumped, frequency doubled Nd:YAG laser to produce the two wavelengths needed for vibration subtraction. A single Bragg cell driven at two harmonically related frequencies provides the basis for a novel heterodyne detection technique. Comparison of the data from the tangentially viewing interferometer and a vertically viewing CO2 interferometer will be discussed.
Determination of neutral beam injection accelerator grid deformation using beam emission measurements
Authors: Nightingale M. P. S. , Kugel H. , Gee S. J. , Price M. N.
Published: July 2002

Theoretical modeling of 1–2 MW positive hydrogen ion neutral injectors developed at Oak Ridge National Laboratory (ORNL) has suggested that the plasma grid temperature could rise by up to 180 °C at pulse lengths above 0.5 s, leading to a grid deformation on the order of 5 mm, with a consequent change in focal length (from 4 to 2 m) and beamlet focusing. One of these injectors (on loan from ORNL) was used to achieve record β values on the Small Tight Aspect Ratio Tokamak at Culham, and two more are to be used on the Mega-Ampere Spherical Tokamak (MAST) at pulse lengths of up to 5 s. Since the grid modeling has never been tested experimentally, a method for diagnosing changes in beam transport as a function of pulse length using light emitted by the beam is now under development at Culham to see if grid modifications are required for MAST. Initial experimental results, carried out using a 50 A 30 keV hydrogen beam, are presented (including comparison with thermocouple data using an EK98 graphite beam stop). These confirm that emission measurement should allow the accelerator focal length and beamlet divergence to be determined to accuracies of better than ±0.45 m and ±0.2°, respectively (compared to nominal values of 4 m and 1.2°).
A vacuum ultraviolet study of rare-earth phosphor screens with application as diagnostics for hot plasmas (abstract)
Authors: Baciero A. , Placentino L. , McCarthy K. J. , Barquero L. R. , Ibarra A. , Zurro B.
Published: July 2002

In a previous work [Zurro et al., Rev. Sci. Instrum. 68, 680 (1997)], we outlined designs for several detector systems, based on rare-earth phosphor powders, with application as broadband VUV plasma radiation monitors in the TJ-II flexible heliac device. In addition to their immunity to microwave power, to ground loops, and to any kind of EMI, the phosphor powders considered as suitable candidates can withstand the high temperatures of the TJ-II vacuum chamber (150 °C), while possessing good sensitivity across the x-ray to UV range and fast response times. Among those selected was Y3Al5O15:Ce (P-46), which emits at 530 nm and when examined, it was found to be particularly suitable for our application due to its very fast response time (∼0.1 μs). We report on absolute efficiency measurements performed between 40 and 200 nm using a calibrated VUV source, and made on thin P-46 phosphor screens, having thicknesses between 1 and 20 mg/cm2. We combine these results with measurements made at visible wavelengths and in the x ray [A. Baciero et al., in Diagnostics for Experimental Thermonuclear Fusion Reactors 2, edited by P. E. Stott et al. (Plenum, New York, 1998)] to obtain fitting parameters for models used to predict phosphor response efficiencies in transmission and reflection modes. These models can be used to tailor the phosphor screen thickness to the radiation range of interest while reducing background noise. Such screens are currently used on the TJ-II.
An instrument for automatic measurements of critical current of superconductors in pulse mode
Authors: Gadkari S. C. , Gupta S. K.
Published: July 2002

An instrument has been developed for direct measurement of critical current and plotting of current–voltage (I–V) characteristics of superconductors in pulse mode. For these measurements, current pulses of increasing height are applied to sample and the voltage developed across the sample is monitored using a low noise voltage measuring circuit. Different sources of error responsible for limiting accuracy of pulse measurements techniques are discussed. A compensation network has been developed to reduce inductively induced voltages generated during pulse measurements, to negligible values. The instrument enables automatic critical current measurement with 1–10 μV/cm criteria in pulse mode without a computer and has voltage sensitivity of 10 nV. Critical current as a function of temperature/magnetic field and I–V characteristics of Bi-2212 single crystal and Y-123 thin films have been plotted using the circuit and the results have been compared with those obtained using direct current measurements.
Electromagnetorheological suspensions and inducted changes of their magnetic permeability and dielectric constant
Authors: Bednarek Stanisław
Published: July 2002

Two groups of well-known suspensions are described in the early part of this article. Their viscosity and other properties can be changed by means of the electric and magnetic field. The main goal of this article is to present new types of suspensions with properties which can be changed by means of both the above mentioned fields. These suspensions consist of sodium chloride and magnetite particles or nickel-zinc ferrite dispersed in transformer oil. The method of producing these suspensions is described. Also given are the results from an analysis of their magnetic permeability and their dielectric constant induced changes. A comparison and discussion of the results obtained are presented in the final part of the article.
X-ray spectral power measurements utilizing the diffraction pattern of a slit
Authors: Baker K. L. , Porter J. L. , Ruggles L. E. , Chrien R. E. , Idzorek G. C.
Published: July 2002

An instrument is described which can obtain x-ray spectral power measurements utilizing the diffraction pattern produced when x rays pass through a slit. Traditionally, these types of measurements yielding low to moderate spectral resolution have been made with filtered x-ray diodes or with a transmission grating. The instrument described below has several advantages over filtered x-ray diodes in determining the spectral power profile such as an insensitivity to surface contamination. In addition, this instrument does not require the use of filters which can be destroyed during a shot making absolute measurements difficult and very time consuming. The advantages over a transmission grating system include cost, mechanical robustness, and fewer components which require spectral calibration.
A 32-channel preamplifier chip for the multiplicity vertex detector at PHENIX
Authors: Britton C. L. , Clonts L. G. , Ericson M. N. , Frank S. S. , Moore J. A. , Simpson M. L. , Young G. R. , Smith R. S. , Boissevain J. , Hahn S. , Kapustinsky J. S. , Simon-Gillo J. , Sullivan J. P. , van Hecke H.
Published: July 2002

The TGV32, a 32-channel preamplifier–multiplicity discriminator chip for the multiplicity vertex detector (MVD) at PHENIX, is a unique silicon preamplifier in that it provides both an analog output for storage in an analog memory and a weighted summed-current output for conversion to a channel multiplicity count. The architecture and test results of the chip are presented. Details about the design of the preamplifier, discriminator, and programmable digital–analog converters performance as well as the process variations are presented. The chip is fabricated in a 1.2 μm, n-well, complementary metal–oxide–semiconductor process.
Effect of an input coil microwave resonance on dynamics and noise properties of a dc superconducting quantum interference device operating close to the hysteretic mode
Authors: Polushkin V. , Glowacka D. , Hart R. , Lumley John
Published: July 2002

The dynamics and noise of a dc superconducting quantum interference device (SQUID) with the McCumber parameter βc=2πR2IcC/Φ0 close to the unity (where Ic, R, C are the critical current, the shunt resistance, and the capacitance of the Josephson junctions comprising the SQUID, respectively, and Φ0=2.07×10−15 Wb is the magnetic flux quantum) integrated with a planar spiral input coil have been experimentally studied. The length of the spiral input coil was chosen to match its λ/4 microwave resonance frequency to the plasma resonance frequency of the SQUID. The input coil resonance enhances the overall quality factor Q of the Josephson oscillations in the SQUID and, as a result, increases the dynamic resistance Rd and the gradient of the flux-to-voltage characteristics ∂V/∂Φ without hysteresis. This relaxes the tolerance for the βc parameter, simplifies the technological process, and improves the yield of devices. A dc SQUID with loop inductance L=31.4 pH, βc=0.72, and a six turn input coil has demonstrated a nondistorted quasisinusoidal flux-to-voltage transfer function with an exceptionally large modulation depth of approximately 140 μV peak-to-peak. A spectral density of the intrinsic magnetic flux noise as low as 3.5×10−7 Φ0/Hz1/2 has been measured in the double stage configuration at a temperature of 4.2 K using direct read-out electronics. This corresponds to the intrinsic energy resolution of ε=12.5h. In combination with an intermediary transformer, the current resolution of the SQUID is as low as 1.25 pA/Hz1/2 with an input coil inductance of 58 nH. The coupled energy resolution is εc=45h in the white noise region.
A novel probe head for high-field, high-frequency electron paramagnetic resonance
Authors: Annino G. , Cassettari M. , Longo I. , Martinelli M. , Van Bentum P. J. M. , Van der Horst E.
Published: July 2002

A probe head especially useful for electron paramagnetic resonance (EPR) spectrometers working at high field—high frequency is presented. The probe head is based on the whispering gallery mode dielectric resonators that proved very effective in the ultrahigh frequency range. The excitation network uses a properly shaped dielectric waveguide sharing its external field pattern with the field of the resonators. Very simple resonators made with polyethylene in both single and doubly stacked disk configurations are used. The experimental characterization by a submillimeter network analyzer shows for the resonances studied in a wide range of frequencies up to ≈400 GHz high loaded merit factor QL values and good coupling factors. Resonators also maintain their general characteristics when large quantities of low loss samples for EPR measurements are properly inserted. Preliminary EPR spectra of diphenylpicrylhyldrazyl at 7 and 10 T obtained with the novel apparatus are finally presented.
Characterization of cooled large-area silicon avalanche photodiodes
Authors: Fox Jeffrey J. , Woodard Nathan , Lafyatis Gregory P.
Published: July 2002

We characterize the operation of large-area high-gain silicon avalanche photodiodes (APDs) at near liquid-nitrogen temperatures. The APDs that we studied have active areas of 64 mm2 and have gains of up to 20 000 at 85 K. We characterized the devices for both the usual, analog mode of operation and for doing single-photon pulse counting. The experimental results were found to be reasonably well described by the McIntyre theory. We independently measured k, the hole/electron ionization ratio—a key parameter in the McIntyre theory—and found it to be ∼6×10−4. Cooled, large-area, high-gain APDs compare favorably to photomultiplier tubes in applications that require high sensitivity at near-infrared wavelengths.
Limits on laser wakefield accelerators
Authors: Yedierler B. , Bilikmen S.
Published: July 2002

The longitudinal and radial wakefields produced by a single laser pulse in a plasma are calculated. The limits on the laser wakefield acceleration because of diffraction, optical guiding, and energy loss due to radiation are examined. In particular for a bi-Gaussian laser beam, the energy gain about 4.6 GeV/cm s is estimated. A general constraint on the plasma density is presented. All the limits are compared and a localized density channel of width 4.6×10−5 cm is proposed.
Millimeter wave polarimeter for characterizing high-power plasma heating systems
Authors: Ikezi H. , Moeller C. P. , Doane J. L. , DiMartino M. , Lohr J. , Ponce D. , Callis R. W.
Published: July 2002

We have built a millimeter wave polarimeter which measures wave polarization parameters: the polarization angle, and the ellipticity including field spin direction in an evacuated high-power system. The polarimeter was applied to diagnose the 1 MW level electron-cyclotron plasma heating system at 110 GHz for the DIII-D tokamak. We have observed the time-dependent behavior of the gyrotrons and have characterized and calibrated the high-power transmission system which consists of grooved mirror polarizers, miter bends, switches, and corrugated wave guides. This article describes the principle of operation and the design method of the polarimeter and the examples of measurements.