bluuebunny/crossref_metadata_2025 huggingface dataset:
Position monitor and readout electronics for undulator and focused bending magnet beamlines
Authors: Schildkamp Wilfried , Pradervand Claude
Published: July 2002

Hard x-ray undulator radiation and focused wiggler radiation from third generation synchrotron radiation sources need to be characterized after a series of apertures and windows. In order to measure the vertical and horizontal position of the centroid of the undulator radiation a nondestructive position monitor was designed, constructed, and used for experiments that utilize undulator radiation. The accuracy of the calibration curve was about 5 μm when the monitor was used as a null instrument, with a resolution of less than 1 μm and a bandpass of 1000 Hz.
Linear systems description of the CO2 laser-based tangential imaging systema)
Authors: Lo E. , Wright J. , Nazikian R.
Published: July 2002

It is demonstrated that the phase variation produced by the projection of the density fluctuations onto a laser beam that is aligned tangent to the magnetic field lines in a toroidal plasma is, in fact, a convolution of the density fluctuation profile in the tangency plane with a shift-invariant point spread function. Thus a spatial filter can be used to invert the corresponding transfer function to produce an undistorted image of the plasma density fluctuations at the tangency plane. Numerical simulations demonstrate that a spatial filter consisting of a simple and versatile step-function form of a Zernike phase mirror will recover a reasonably accurate image of the fluctuations [Lo et al., Buld. APS 38, 2005 (1993)].
In situsensitivity calibration of an XUV spectrometer for plasma spectroscopy: Branching ratio method and collisional-radiative model
Authors: Kawachi T. , Suemitsu H. , Sawada K. , Fujimoto T. , Maehara T. , Yoshimura S. , Maekawa T. , Terumichi Y.
Published: July 2002

We have observed spectra of lithium-like oxygen and carbon ions from the WT-3 tokamak plasma with an XUV spectrometer. On the basis of the branching ratios to visible UV spectral lines and the collisional-radiative model calculation for excited level populations, we have determined the absolute sensitivity of the spectrometer from 11.5 through 31.2 nm. From the line intensities emitted from the scrape-off layer plasma, we have estimated the charge exchange recombination rate coefficients of helium-like oxygen ions colliding with neutral hydrogen atoms or molecules.
Operation of two grating polychromators on TFTR and new observations of magnetohydrodynamic phenomena
Authors: Janos A. , McCarthy M. , Fredrickson E. , McGuire K. , Taylor G.
Published: July 2002

A second grating polychromator instrument has been installed recently on the Tokamak Fusion Test Reactor device. Both this new instrument and the original one, at a different toroidal location, measure electron cyclotron emission from which electron temperature fluctuations and profiles can be obtained. This combination of instruments is designed to provide crucial information on both the poloidal and toroidal structure of magnetohydrodynamic phenomena internal to the TFTR plasma. These instruments are designed to operate within the high neutron flux environment of deuterium-tritium operation in TFTR. Already, this combination of instruments has proven extremely valuable in identifying toroidally nonaxisymmetric phenomena. In addition to toroidal mode numbers, these instruments have yielded valuable new information on the evolution of the structure of the temperature profile during both high-density and high-beta disruptions, and the precursors to these disruptions. In the high-density case, the fast growing (m,n)=(1,1) structure of a cold bubble is verified conclusively. In the high-beta case, a ballooning type of precursor, toroidally and poloidally localized, appears to play an important role in the disruption. Also, this combination of instruments has provided positive verification of the existence of locked and stationary modes, and the temporal evolution of these modes.
A new device for injection of iron atoms into plasmas
Authors: Hsuan H. , Bitter M. , Ayers W. M. , Gorman J. , Hill K. W. , Manos D. , Schwarzmann J. D. , Smith A. , Timberlake J.
Published: July 2002

Reduction of indigenous metal impurities in tokamak plasmas and impurity requirements for the x-ray diagnosis of central plasma parameters necessitates artificial introduction of metal atoms. A new inexpensive method is described using ferrocene, Fe(C5H5)2, a substance which sublimes. A prototype device was tested at the Atomic-Beam Facility at PPPL. Ferrocene was injected into a pulsed helium plasma with an electron density of 2×1013 cm−3 and an electron temperature of 5 eV. The injected amount of ferrocene was controlled by varying the sublimation temperature in the range from 70 to 150 °C and adjusting the pulse length of a solenoid valve; the resulting iron atom concentration in the plasma was determined by monitoring the intensity of the Fe line at 5269 Å. The device and the test results are presented.
The Hard X-ray Camera on the PBX-M tokamak (invited) (abstract)a)
Authors: Goeler S. von , Jones S. , Kaita R. , Bell R. , Bernabei S. , Davis W. , Gettelfinger G. , Ignat D. , Roney Ph. , Petravich G.
Published: July 2002

The modification and control of the plasma current profile by lower hybrid current drive is considered one of the most promising avenues to control MHD instabilities and improve the high beta performance of tokamaks. The Hard X-ray Camera on PBX-M records images of the bremsstrahlung emitted by suprathermal electrons that carry part of the plasma current during lower hybrid current drive. The Hard X-ray Camera is a pinhole camera that uses a 9 in. diam x-ray intensifier as detector. It provides a tangential view of the tokamak plasma and delivers 64 images with 128×128 pixels per plasma shot. The spatial resolution in the plasma is approximately 2 cm, and the time resolution 3 ms. The camera is sensitive to x rays between 30 and 200 keV. The photon energy (and the energy of the suprathermal electrons) is measured with an absorber foil method. Modeling of the x-ray emission has reproduced the experimental images with a better than 10% accuracy. In addition, two inversion techniques have been developed: one of these can be performed on line between shots. Illustrative examples of important applications of hard x-ray imaging will be given. The hard x-ray images provide information on the radial location of the absorption of the lower hybrid waves, on the velocity distribution of the suprathermal electrons, on the diffusion of superthermal electrons, and on anomalous hot electron transport induced by MHD instabilities.
Information aspects of optical images (abstract)a)
Authors: Pergament M. I.
Published: July 2002

The possible applications of information theory methods to the optical system analysis and to the constructed image investigation are discussed. Visual images are not considered here but only the images in the form of two-dimensional numerical arrays are under consideration. The extraction of information about the investigated object from the numerical arrays and suitable data processing procedures is also described. Algorithms and methods of optical image entropy calculations taking into consideration the features of the real measuring systems and the spectral and stochastic properties of signals and noises are proposed. The expressions for the optical channel capacity and the information capacity of the optical memory units are derived. The reconstruction accuracy is shown to be determined by the difference between image and noise entropies only. Thus the value of this difference can be used as a quantitative estimation of the real measuring system possibilities.
Zeeman absorption measurements of two-dimensional magnetic field structures (abstract)a)
Authors: Spanjers G. G. , Yadlowsky E. J. , Hazelton R. C. , Moschella J. J. , Settersten T. B.
Published: July 2002

A diagnostic technique is presented where polarization measurements of transmitted resonant laser light are used to determine the two-dimensional magnetic field profiles in a plasma. The diagnostic laser is propagated parallel to the magnetic field direction and resonant with circularly polarized transitions. Tuning the laser slightly off-resonance results in differing absorption coefficients for right and left circularly polarized light. Analysis of the transmitted light, combined with independent measurements of the resonant line profile, results in a measurement of the magnetic field. Spectral analysis of the Zeeman splitting has been commonly used to measure plasma magnetic fields, both in emission and absorption. The intensity comparison of the right and left circular components to measure relatively small magnetic fields has its origins in the astrophysics community. Here, the intensity comparison technique is used in conjunction with resonant absorption, and the information is stored using a high-speed framing camera. This results in a measurement of relatively small magnetic fields, with a high signal-to-noise ratio and two-dimensional spatial resolution.
Observation of Doppler shifted Tα emission from TFTR tritium neutral beams
Authors: Kamperschroer J. H. , Grisham L. R. , Lagin L. J. , O’Connor T. E. , Newman R. A. , Stevenson T. N. , von Halle A. , Wright K. E.
Published: July 2002

195 tritium ion source shots were injected into Tokamak Fusion Test Reactor (TFTR) high power plasmas during December 1993–March 1994. In addition, four highly diagnosed pulses were fired into the calorimeter. Analysis of the Doppler shifted Tα emission of the beam in the neutralizer has revealed that the extracted ion compositions for deuterium and tritium are indistinguishable: 0.72±0.04 D+; 0.22±0.02 D+2; 0.07±0.01 D+3 compared to 0.72±0.04 T+; 0.23±0.02 T+2; 0.05±0.01 T+3. The resultant tritium full-energy neutral fraction is higher than for deuterium due to the increased neutralization efficiency at lower velocity. To conserve tritium, it was used only for injection and a few calorimeter test shots, never for ion source conditioning. When used, the gas species were switched to tritium only for the shot in question. This resulted in an approximately 2% deuterium contamination of the tritium beam and vice versa for the first deuterium pulse following tritium. Data from the calorimeter shots indicate that tritium contamination of the deuterium beam cleans up in five to six beam pulses, and is reduced to immeasurable quantities prior to deuterium beam injection.
A model for edge spectral line emission and application to ion temperature measurements with charge-exchange recombination spectroscopy
Authors: Synakowski E. J. , Bell R. E. , Bush C. E.
Published: July 2002

A model for characterizing the cold edge component of spectra measured in charge-exchange recombination spectroscopy (CHERS) applications is presented. It provides a rapid means of constraining the amplitude and width of the cold component of spectra for which the characteristics of the hot charge-exchange emission are desired. The model utilizes the CHERS measurements themselves and measurements of the electron density near the radius of peak background emissivity. A comparison of model predictions with direct measurements of the background emission during neutral beam injection is presented. Influences of changes in background emission on the inferred ion temperature during a neutral beam pulse are discussed.
New instrument for measuring magnetic-field tilt profile and pellet clouds emission structure
Authors: Miroshnikov I. V.
Published: July 2002

Measurements of 2D images of pellet ablatant clouds are very important for development of plasma-pellet interaction models and diagnostic applications. It is known that clouds stretch along the magnetic-field direction with elongation ratios up to 5 for hydrogen pellets, up to 12 for carbon, and up to several tens for lithium. These circumstances open a possibility to measure a magnetic-field pitch angle profile with a precision of ±10 mrad or better. For both goals mentioned, the space-time cloud’s evolution measurements, with high enough time and spatial resolutions, are needed. Fast multiframe photography technique, as used in the T-10 experiments, satisfy these requirements. However, photography suffers from shortcomings because of the necessity of chemical developing and processing of the film. A novel technique, constructed for Asdex Upgrade pellet experiments, is reported. This system uses a cooled 2D CCD matrix detector and provides measurements up to 50 frames of the cloud images with a survey rate of about 2–50 μs per frame. For a carbon pellet injected along a major radius in the plasma midplane with typical speed of 500 m/s and observing the pellet along the flight direction from behind, this time resolution corresponds to 0.1–1 cm spatial resolution. In each frame it will be possible to measure up to 20 poloidal distributions of cloud emissivity with 1024 pixels in each of them. These distributions will be spaced on a distance of ∼9 mm for Asdex Upgrade conditions. The camera is planned to be installed during this year.
Analytic results in the theory of reflectometry in multidimensional plasma (abstract)a)
Authors: Afeyan Bedros B. , Cohen Bruce I. , Crotinger James A. , Williams Edward A.
Published: July 2002

Whereas earlier efforts to model reflectometry have concentrated on 1D models of plasmas, their success in matching experimental signatures has been limited.a) Recent careful measurements of reflectometry signals from controlled plasmas reveal the extent of these discrepancies quite clearly.b) In an attempt to assess the role played by multidimensional effects on these measurements, we have developed analytical models that allow the density fluctuations as well as the microwave field to have 2- and 3D structure. In addition, the background plasma is allowed to have inhomogeneity in more than one dimension. Green’s function techniques are used to evaluate the reflected field due to density fluctuations in first Born approximation. Attempts will also be made to compare these theoretical results to UCLA/UCD experiments and numerical simulations of the full wave equations.
Wave launching as a diagnostic tool to investigate plasma turbulence (abstract)
Authors: Tsui H. Y. W. , Bengtson R. D. , Li G. X. , Richards B. , Uckan T. , Uglum J. , Wootton A. J.
Published: July 2002

An experimental scheme to extend the investigation of plasma turbulence has been implemented. It involves driving waves into the plasma to modify the statistical properties of the fluctuations; the dynamical balance of the turbulence is perturbed via the injection of waves at selected spectral regions. New analysis techniques based on conditional sampling and high order correlation are developed for studying the wave launching and the wave-wave coupling processes. Experimental results from TEXT-U tokamak show that the launched waves interact with the intrinsic fluctuations both linearly and nonlinearly. The attainment of driven nonlinearity is necessary for this diagnostic scheme to work. It is also the key to an active modification and control of edge turbulence in tokamaks.
A multichord spectrometer using an 8×8 anode photomultiplier (abstract)a)
Authors: Carolan P. G. , O’Connell R.
Published: July 2002

A multianode photomultiplier (8×8 anodes of 2.5×2.5 mm2) is used to detect a collection of spectra in a high dispersion echelle spectrometer. A cylindrical lens is placed at the output slit to increase the dispersion at the photomultiplier. The cross talk between adjacent spectra is non-negligible (although <5%), resulting in some interspectral distortion. This is removed by solving a system of simultaneous equations, one for each channel, obtained from the measured cross-talk coefficients. The spectrometer has been used on the COMPASS-D tokamak to measure ion temperatures and fluid velocities.
In situ absolute calibration of a channel electron multiplier for detection of positive ions
Authors: Savin D. W. , Gardner L. D. , Reisenfeld D. B. , Young A. R. , Kohl J. L.
Published: July 2002

A technique has been developed to determine the absolute single particle counting efficiency of a channel electron multiplier (CEM) for positively charged ions at keV energies. The calibration technique is applicable to positive ion detectors in general. Ion beam currents of C2+ were created by charge transfer of C3+ on H2 in the thin target regime. By adjusting the H2 pressure in the beam scattering chamber from 10−10 to 10−6 Torr, C2+ currents could be created either low enough to be detected by the CEM in the particle counting mode or high enough to be measured as a current using the CEM as a Faraday cup. The CEM counting efficiency was determined by comparing the C2+ count rate to the C2+ current, scaling by the change in H2 pressure, and also scaling by the incident C3+ current for each C2+ measurement. This method, which effectively uses the charge transfer cross section as a ‘‘transfer standard,’’ allows the CEM counting efficiency to be determined in situ and to be monitored accurately over extended periods of time. The calibration requires that only the relative, not the absolute, pressure change be known. The technique does not require the value of the charge transfer cross section to be known. The accuracy of the calibration technique for the present results was 10% at a confidence level considered to be equivalent to a statistical 90% confidence level. For the present work, the peak counting efficiency of a Galileo 4039 CEM for 32.5 keV C2+ ions was determined to be 96%.
A novel technique for temperature stabilization very near a phase transition: Results for He-II
Authors: Davidowitz Hananel
Published: July 2002

A novel method for achieving high temperature stability at very small reduced temperatures near a phase transition is described. In this technique, fluctuations in a temperature dependent property of the system were used to regulate the system’s temperature. This technique has been implemented in liquid helium just below the superfluid phase transition. In this case, the technique is based on second sound phase locking and uses the fact that the second sound velocity is strongly temperature dependent near the lambda transition. Phase fluctuations of a continuous second sound signal are detected and used to regulate the temperature of the system. The long term temperature stability as inferred from the stability of the second sound velocity is better than 3×10−7 K, at a reduced temperature of less than 10−5, making the technique particularly useful near the superfluid phase transition.
Laser hearth melt processing of ceramic materials
Authors: Richard Weber J. K. , Felten J. J. , Nordine Paul C.
Published: July 2002

A new technique for synthesizing small batches of oxide-based ceramic and glass materials from high purity powders is described. The method uses continuous wave CO2 laser beam heating of material held on a water-cooled copper hearth. Contamination which would normally result during crucible melting is eliminated. Details of the technique are presented, and its operation and use are illustrated by results obtained in melting experiments with a-aluminum oxide, Y–Ba–Cu–O superconductor material, and the mixtures, Al2O3–SiO2, Bi2O3–B2O3, Bi2O3–CuO. Specimen masses were 0.05–1.5 g.
High performance superconducting quantum interference device feedback electronics
Authors: Koch R. H. , Rozen J. R. , Wöltgens P. , Picunko T. , Goss W. J. , Gambrel D. , Lathrop D. , Wiegert R. , Overway D.
Published: July 2002

A dc superconducting quantum interference device (SQUID) modulation and feedback circuit operating at a modulation frequency of 16 MHz has been constructed. Using a novel wide band superconducting thin film transformer to impedance match the SQUID to a rf amplifier allows the system to operate at the SQUID noise level for most types of low-TC SQUIDs. This system has a closed loop bandwidth exceeding 2.5 MHz and a slew rate greater than 1×106Φ0/s at frequencies up to 1 MHz. This greatly improved performance compared to existing modulation methods can be obtained without enhancing the transfer function of the SQUID. The system allows low- and high-TC SQUID magnetometers and gradiometers to be operated totally unshielded without unlocking in the dc, 60 Hz, and radio frequency electromagnetic fields present in most SQUID applications.
Vacuum arc trigger systems based on E×B discharges
Authors: Nikolaev A. G. , Yushkov G. Yu. , Oks E. M. , MacGill R. A. , Dickinson M. R. , Brown I. G.
Published: July 2002

Triggering systems for vacuum arc plasma sources and ion sources have been developed that make use of a gaseous trigger discharge in a strong magnetic field. Two kinds of trigger discharge configurations have been explored, a Penning discharge and a magnetron discharge. The approach works reliably for low gas pressure in the vacuum arc environment and for long periods of operation between required maintenance: pressures in the mid-10−6 Torr range and for ≳106 pulses.
Optimization of multilayer reflectivity and bandpass for soft to hard x-ray applications [0.1–200 keV]
Authors: Vestli K. , Ziegler E.
Published: July 2002

In the last decades, the major motivation for manufacturing multilayer mirrors has been in soft x-ray applications, particularly for astronomy, microlithography, and polarimetry. The advent of high energy synchrotron storage rings has provided a new significant impetus emphasizing high energy applications and especially when flux, rather than resolution, is desired. In this paper we present the reflection properties of the most promising multilayer material combinations for the energy range from 0.1 keV up to 200 keV. Previous calculations by Rosenbluth were limited to a maximum of 2 keV and to multilayers composed of pure elements and operating under normal incidence. As alloys might be essential for a smooth growth and/or for stability under high heat load, our screening consisted of a list of up to 300 solids having a melting point above 100°C and that could be deposited in a sputtering process. A full computer search calculates 45000 multilayer combinations for each angle (or multilayer d-spacing) and energy of operation, the only necessary input variables. Other manufacture-related parameters can be specified to give a more realistic picture of the performance. As the number of layers is often limited, a nonperiodic design could minimize absorption effects.
Analytical thermal lens instrumentation
Authors: Franko Mladen , Tran Chieu D.
Published: July 2002

This review describes recent instrumentation developments of the thermal lens techniques. It will begin with a brief discussion of the theory of the techniques. Its main focus is, however, on the detail description of various instruments. Specifically, the discussion will begin with the description of single beam instruments which were initially developed following by dual beam instruments. Elaboration will be focused on some of the most sophisticated instruments which were developed recently. These include differential thermal lens instruments, multiwavelength and spectral tunable instruments, circular dichroism spectropolarimeters, rotoreflecting instruments, and miniaturized thermal lens instruments. Selection of lasers, focusing, modulation, sample position, sample cells, data acquisition, noise reduction, and applications of acousto-optic tunable filters will also be discussed. The future of the techniques in terms of instrumentation will be finally forecasted.
Be diffusion mechanisms in InGaAs during post-growth annealing
Authors: Koumetz S. , Marcon J. , Ketata K. , Ketata M. , Dubon-Chevallier C. , Launay P. , Benchimol J. L.
Published: July 2002

Be diffusion during post-growth annealing has been studied in InGaAs epitaxial layers, grown between two undoped InGaAs layers. To explain the observed concentration profiles and related diffusion mechanisms, a general substitutional–interstitial model is proposed. On the one hand, a simultaneous diffusion by dissociative and kick-out models is suggested and, on the other hand, the Fermi-level effect is used to explain the functional dependence change of the effective diffusion coefficient of beryllium species with its concentration. The concentration dependent diffusivity has also been covered to perform an improved data fitting of Be diffusion profiles.
Wide range standard for scanning probe microscopy height calibration
Authors: Brodowsky Hanna M. , Boehnke Undine-C. , Kremer Friedrich
Published: July 2002

A new method for height calibration of scanning probe microscopes (SPMs), applicable for any height from 0.3 nm to beyond 100 nm, is presented. A previously calibrated piezo is set in a SPM instead of a sample. A definite time-periodic elongation at a corresponding voltage can serve as height standard. The method is easy to use, tuneable in a wide range and exact to the limits of the SPM itself.
Technique for measuring the two-port scattering matrix of a plasma current drive antenna during high power operation
Authors: Probert P. H. , Majeski R. P.
Published: July 2002

We describe a technique to routinely measure the scattering matrix of a radio frequency (rf) current drive antenna in a magnetic fusion experiment during high power operation. This technique can be used under any conditions of phase or amplitude of excitation. It involves modulation of the phase of the rf voltage applied to each of the antenna ports by a few degrees, measurement of the complex forward and reflected voltages, detection of the phase modulation, and solution of a 2×2 matrix problem to yield the scattering matrix. Further calculation then yields the antenna’s impedance matrix. Because it involves only a small modulation, this method can be used to routinely monitor matching, decoupling, or plasma loading and to provide input to tuning calculations so that the matching and phasing conditions can be maintained. We show results for the case of 400 kW Alfvèn wave current drive experiments on the Phaedrus-T tokamak. We also show how the results can be used to tune the antenna.
Neural network evaluation of tokamak current profiles for real time control
Authors: Wróblewski Dariusz
Published: July 2002

Active feedback control of the current profile, requiring real-time determination of the current profile parameters, is envisioned for tokamaks operating in enhanced confinement regimes. The distribution of toroidal current in a tokamak is now routinely evaluated based on external (magnetic probes, flux loops) and internal (motional Stark effect) measurements of the poloidal magnetic field. However, the analysis involves reconstruction of magnetohydrodynamic equilibrium and is too intensive computationally to be performed in real time. In the present study, a neural network is used to provide a mapping from the magnetic measurements (internal and external) to selected parameters of the safety factor profile. The single-pass, feedforward calculation of output of a trained neural network is very fast, making this approach particularly suitable for real-time applications. The network was trained on a large set of simulated equilibrium data for the DIII-D tokamak. The database encompasses a large variety of current profiles including the hollow current profiles important for reversed central shear operation. The parameters of safety factor profile (a quantity related to the current profile through the magnetic field tilt angle) estimated by the neural network include central safety factor, q0, minimum value of q, qmin, and the location of qmin. Very good performance of the trained neural network both for simulated test data and for experimental datais demonstrated.
An improved control technique for the electrochemical fabrication of scanning tunneling microscopy microtips
Authors: Anwei Liu , Xiaotang Hu , Wenhui Liu , Guijun Ji
Published: July 2002

The electrochemical etching technique has been widely used in the fabrication of microtips. In this article, an improved feedback control technique for the dc electrochemical fabrication of scanning tunneling microscopy microtips is presented. Distinguished from the conventional control techniques, this newly developed method directly uses the etching current as the only control signal instead of comparing it with the reference current. Therefore, the control process is more accurate. The tungsten tips with radius of curvature down to 20 nm can be produced reproducibly. By varying the cutoff time of the control circuit, tips with different radii of curvature can be fabricated.
A heatable large volume high pressure cell for neutron powder diffraction: The Kiel-Berlin Cell I
Authors: Knorr K. , Fütterer K. , Annighöfer B. , Depmeier W.
Published: July 2002

A heatable high pressure cell for angle dispersive neutron powder diffraction has been developed. This cell, called Kiel-Berlin Cell I, is of the piston–cylinder-type and based on a design first introduced by McWhan. High temperature conditions under high pressure are achieved by a graphite resistance heater surrounding the sample container. The cell operates up to temperatures of 700 K and pressures of 1.5 GPa, simultaneously. We report the design of the cell along with calibration data. We also give a brief and representative account of pressure-temperature-dependent studies in which the present cell was used.
ac-mode atomic force microscope imaging in air and solutions with a thermally driven bimetallic cantilever probe
Authors: Hillier Andrew C. , Bard Allen J.
Published: July 2002

An ac imaging mode for atomic force microscopy (AFM) has been developed that employs a thermally driven bimetallic cantilever to sense surface topography. Oscillations are induced in a composite cantilever, comprising a Si3N4 layer and Au overcoat, by local heating with a resistive wire heater placed in close proximity to the cantilever. Cantilever bending occurs upon heating due to the difference in thermal expansion coefficients of the Si3N4 and Au layers. The magnitude of this bending is a function of the heat input, the cantilever geometry, the frequency of the excitation, and the thermal properties of the surrounding medium. A commercially available contact mode AFM has been modified to perform ac mode imaging by driving the cantilever with a peak-to-peak amplitude of 5–15 nm using resistive heating. The heating frequency was typically fixed near the cantilever’s resonance frequency, which was in the range of 15–50 kHz in the air and 2–15 kHz in solution for the cantilevers used here. Simultaneous cantilever deflection and amplitude measurements during sample approach indicate that the cantilever free amplitude is damped upon surface contact. While imaging, a fixed damping of the cantilever oscillation is used as a feedback signal to maintain a constant tip-sample separation. Images with this ac imaging mode were obtained in both air and liquid environments. Results show an improvement in image quality in the ac mode over the corresponding contact images, which is the result of a decrease in lateral forces with an oscillating tip. This provides a simple and robust method for ac-mode AFM imaging in air and solutions that can be achieved with only slight modification to a commercially available contact-mode microscope.
Transversely magnetized microwave plasma in a rectangular waveguide under cutoff conditions
Authors: Bhattacharjee Sudeep , Amemiya Hiroshi
Published: July 2002

A plasma has been produced in 0.1–0.3 mTorr Ar inside a rectangular TE10 mode waveguide with a cross-sectional area (6.3 cm width × 4.2 cm height) much smaller than standard waveguides (12.4 cm width ×5.6 cm height), using microwaves of 2.45 GHz and 100–260 W of power. The characteristics of the plasma and the wave propagation have been studied for the perpendicularly launched waves (k⊥B) in the ordinary like (E∥B) and extraordinary like (E⊥B) modes, where a magnetic field of about 1200 G is generated inside the waveguide by rectangular blocks of permanent SmCo magnets. The maximum electron density, as measured by a plane probe, in the E∥B and E⊥B cases are 2×1010 and 3×1011 cm−3, respectively, while the electron temperatures ranged between 3 and 11 eV. Experimental results obtained in the two cases are discussed and the particle trajectories are studied from a single particle theory.
Device for the simultaneous application of uniaxial stress and hydrostatic pressure: Application to semiconductor lasers
Authors: Widulle F. , Held J. Th. , Huber M. , Hochheimer H. D. , Kotitschke R. T. , Adams A. R.
Published: July 2002

The design of a device for the simultaneous application of uniaxial stress and hydrostatic pressure is presented. Shown in detail is the design of the part that applies the uniaxial force to the sample and first results of the simultaneous application of uniaxial stress and hydrostatic pressure to a semiconductor laser.
X-ray absolute intensity measurement at HASYLAB ultrasmall angle x-ray scattering beamline BW4
Authors: Endres A. , Lode U. , v. Krosigk G. , Bark M. , Cunis S. , Gehrke R. , Wilke W.
Published: July 2002

In order to obtain small angle scattering intensities in absolute units, measurements of the incident beam intensity and the intensity transmitted through the sample are required. For this purpose the scattering intensity of a calibrated polyethylene (LUPOLEN) standard is used. For the determination of the absolute photon flux and the correction of the scattering patterns obtained with a two dimensional position sensitive detector we use the detector response function. A set of data measured subsequently at the standard and at a given sample can be evaluated in a program that calculates a pattern in absolute units corrected by means of the detector response. This program also calculates the absolute photon flux, determines automatically the center coordinates of the incident beam, and calculates the scattering vectors that belong to the different positions on the detector.
A laser induced fluorescence instrument for measuring tropospheric NO2
Authors: Fong C. , Brune W. H.
Published: July 2002

Nitrogen dioxide (NO2), an essential gas in atmospheric chemistry, is almost always measured indirectly with just one technique: photolysis of NO2 to NO, followed by detection of resulting NO. However, the photolysis introduces artifact signals that complicate the extraction of the NO2 signal at low NO2 volume mixing ratios. A new prototype instrument uses laser induced fluorescence to measure tropospheric NO2 directly. The atmospheric fluorescence spectra measured with this instrument match the fluorescence spectra of NO2 in a reference cell over the wavelength range 565.1–565.2 nm. This match indicates that fluorescence from other chemical species is not interfering with the measurements. The prototype’s current detection limit is 280 parts per trillion (pptv) in 2.5 min with an absolute uncertainty of ±15% (2σ confidence). This detection limit, which can be improved with better optical filtering and more laser power, is currently adequate for urban air conditions.
Production of microbunched beams of very highly charged ions with an electron beam ion source
Authors: Stöckli Martin P.
Published: July 2002

Electron beam ion sources produce very highly charged ions most efficiently in a batch mode as the confinement time can be directly optimized for the production of the desired charge state. If, after confinement, the voltage of the ion-confining downstream dam is lowered rapidly, all ions escape and form an ion beam pulse with a length of a few tens of μs. Raising the main trap voltage while maintaining a constant dam voltage in a “spill-over expulsion” reduces the energy spread of the expelled ions. The longer time periods of “slow-,” “leaky batch mode-,” and “direct current (dc) batch mode-” expulsions allow for increasing the ion beam duty cycle. Combining the rapid expulsion with one of the latter methods allows for the expulsion of the ions of a single batch in many small microbunches with variable intervals, maintaining the low energy spread and the increased duty cycle of slow expulsions. Combining the “microbunching” with “dc batch mode production” and a multitrap operation will eventually allow for the production of equally intense ion bunches over a wide range of frequencies without any deadtime, and with minimal compromise on the most efficient production parameters.
Development of vacuum arc ion sources for heavy ion accelerator injectors and ion implantation technology (invited)
Authors: Oks Efim M.
Published: July 2002

The status of experimental research and ongoing development and upgrade of MEVVA-type ion sources over the last two years since the previous ICIS-95 is reviewed. There are two main application fields for this ion source: heavy ion accelerators and material surface implantation technology. For particle accelerator ion injection to accelerators it is important to enhance the fractions of multiply charged ions in the ion beam as well as controlling the charge state distribution, and to improve of beam current stability (i.e., to minimize the beam noise) and pulse-to-pulse reproducibility. For ion implantation application we need to increase both the implantation dose rate and the source lifetime (between required maintenance downtime) as well as making this kind of source more reliable and of yet low cost. Most of experimental results reported on here have been obtained in a collaborative program between research groups LBNL (Berkeley, USA), GSI (Darmstadt, Germany), HCEI (Tomsk, Russia), and other important contributions have been made by the groups at (BNU, Beijing, China), EDU (Izmir, Turkey), and elsewhere.
Experiments on a 14.5 GHz electron cyclotron resonance source
Authors: Hill C. E. , Langbein K.
Published: July 2002

The 14.5 GHz ECR4 source supplied to CERN in the framework of the heavy ion facility collaboration provided Pb27+ operational beams to a new heavy ion linac in 1994. This source, which operates in the pulsed “afterglow” mode, has surpassed its design specification of 80 eμA and now provides currents >120 eμA on an operational basis for this charge state. Early tests showed the existence of extremely stable modes of operation which are fully exploited, and in 1996 the source was operational on a 24 h basis for more than 2400 h. Future operational requirements will benefit from the 10 Hz repetition rate of the source, but will require beam pulse length modulation. In the search for higher intensities a number of experiments were performed on gas composition, rf power matching, extraction, plasma chamber liner, and a biased dynode. The results of these tests will be presented.
A high temperature oven for the production of vapors from solid materials at the Laboratorio Nazionale del Sud Superconducting Electron cyclotron Resonance SourcE
Authors: di Bartolo G. , Chines F. , Ciavola G. , Gammino S. , Marchetta C. , Marletta S. , Messina E. , Passarello S. , Wang Z.
Published: July 2002

An oven for the feed of vapors from solid materials in the Superconducting Electron cyclotron Resonance ion SourcE (SERSE) has been designed, built and tested at the Laboratorio Nazionale del Sud. It is based on an electrically heated tungsten filament. In order to have a correct temperature distribution in the whole system and to lower the heating power, a finite elements code has been used for the design of busses and thermal shielding. A crucible temperature of 2000 °C has been measured by a pyrometer and a W/Re thermocouple. The tungsten filament as well as the other components have shown no significant damage, confirming the robustness and reliability of the system. Satisfactory Ni evaporation rates have been measured.
Design aspects and status of construction of the mVINIS ion source
Authors: Efremov A. , Kutner V. , Bogomolov S. , Lebedev A. , Loginov V. , Yazvitsky N. , Dobrosavljević A. , Draganić I. , Dekić S. , Stalevski T.
Published: July 2002

The mVINIS ion source is a multiply charged heavy ion source based on the electron cyclotron resonance effect. This machine is a part of the Tesla Accelerator Installation, an ion accelerator facility whose construction has been going on at the VINČA Institute of Nuclear Sciences in Belgrade, Yugoslavia. mVINIS is an advanced version of the Dubna electron cyclotron resonance ion source 14-2, constructed at the Joint Institute for Nuclear Research (JINR) in Dubna, Russia. It is a complete injector, consisting of an ECR ion source, focusing and steering elements, an analyzing magnet, a vacuum system, and an ion beam diagnostic system. The main parts of mVINIS have been designed and manufactured at JINR, while the vacuum equipment, power supplies, ion beam diagnostics, and control system were purchased elsewhere. The preliminary testing (magnetic field measurements, vacuum testing, testing of the ECR ion source) has been performed at JINR, and the final assembly of the mVINIS and measurement of the ion beam parameters have been going on at the VINČA Institute.
Effect of cesium seeding on hydrogen negative ion volume production
Authors: Bacal M. , El Balghiti-Sube F. , Elizarov L. I. , Tontegode A. Y.
Published: July 2002

The effect of cesium vapor partial pressure on the plasma parameters has been studied in a dc hydrogen negative ion source. The cesium vapor pressure was varied up to 10−5 Torr and was determined by a surface ionization gauge in the absence of the discharge. Due to cesium seeding the negative ion relative density in the center of the plasma extraction region increases by a factor of 4, while the electron density decreases. The negative ion density increase is highest (a factor of 2) at the lowest hydrogen pressure. The velocity of the directed negative ion flow to the plasma electrode is also increased by the cesium seeding. Due to these factors the negative ion current is enhanced. A dramatic reduction of the electron component, which is consistent with the reduced electron density and temperature, is also observed. An enhancement of the volume production seems to occur in this type of plasma. Possible mechanisms for this type of volume process will be discussed.
Interactions between neighboring beams in a heavy ion fusion reactor chamber
Authors: Callahan Debra A.
Published: July 2002

Multiple beams in a heavy ion fusion reactor chamber can increase the beam spot size at the target. Each beam experiences the field from nearby beams and this field varies along the bunch length. These field variations cause different parts of the beam to be focused at different locations and results in a larger spot size at the target. Calculations show that this is not a large effect for a beam generated by an induction linear accelerator in which the current is nearly constant over much of the pulse. These calculations show 90%–99% of the charge reaches the target for a radiation converter radius that is 10%–20% larger than the beam radius.
An apparatus for adsorption dynamics studies using infrared measurement of the adsorbent temperature
Authors: Bourdin V. , Gray P. G. , Grenier Ph. , Terrier M. F.
Published: July 2002

An apparatus has been built for kinetics measurement in adsorption processes. It consists of a variable volume chamber where the adsorbent sample is placed. During the adsorption process the pressure and the sample temperature are measured. The temperature is measured by infrared detection achieving fast, sensitive, and nonintrusive measurements. Two methods are used for adsorption kinetics measurement: the volume step and the thermal frequency response. In the volume step method the volume is suddenly reduced and the adsorption process occurs at constant volume. Due to the sorption heat released during adsorption, the adsorbed mass is closely related to the sample temperature. This method permits one to determine the relevant thermodynamic parameters of the system and the kinetics up to 20 ms. The different mass transfer modes may then be separated. The thermal frequency response (TFR) method consists of achieving a periodic volume of the chamber. The amplitude and phase lag of the temperature, taking the pressure function as a reference, may be used to measure with great accuracy very fast kinetics (up to 1 ms). Moreover, it permits the easy discrimination of surface barrier from Fickian diffusion. Finally it allows one to measure microporous and macroporous mass transfer in the same experiment. It is shown that substantial improvements are obtained with the TFR method compared with the pressure frequency response method which was, until now, the best macroscopic method. Moreover, the TFR method has produced results in good accordance with the microscopic pulsed field gradient-nuclear magnetic resonance method. Volume step and TFR methods are limited to low pressure (less than ∼4 kPa) in consequence of nonisothermal gas compression. Experimental results are given to illustrate the possibilities of both methods.
Double-crystal diffractive modulator of synchrotron radiation
Authors: Polikarpov I. , de Oliveira R. T. , Cusatis C.
Published: July 2002

The efficiency of time-modulation of synchrotron radiation by a double-crystal monochromator periodically curved by pulsed surface acoustic waves has been studied both experimentally and theoretically. It has been shown that the efficiency of such a system is significantly higher as compared to x-ray modulation by surface acoustic waves applied to x-ray mirrors—that is under the conditions of total external reflection. Possible modifications and improvement of a synchrotron radiation double-crystal diffractive modulator are discussed. The experiments were done at the diffraction beamline at the Brazilian National Synchrotron Light Laboratory (LNLS).
A new high-sensitivity 10-ns time-resolution spectrophotometric technique adapted toin vivoanalysis of the photosynthetic apparatus
Authors: Béal Daniel , Rappaport Fabrice , Joliot Pierre
Published: July 2002

A new spectrophotometric technique has been developed in which the absorption is sampled by short flashes produced by an optical parametric oscillator (OPO) pumped by the third harmonic of a Nd:YAG laser. Continuously tunable monochromatic flashes (6 ns duration, 1 nm bandwidth) are obtained in a domain ranging from 415 to 680 nm and 730 to 2000 nm. Light-induced absorption changes can be analyzed in a time window ranging from 10 ns to 100 s, with a 10−5 noise level. This new technique opens areas of research which are not accessible to previously existing spectrophotometers. Indeed, the high energy of the detecting flashes allows the analysis of samples of large optical density such as leaves, in the blue region of the spectrum. A few examples of application of this method to the analysis of electron transfer reactions in different types of photosynthetic apparatus (leaves, unicellular algae, and bacteria) are presented. This technique is also well suited to analyze the photodissociation of ligands associated with hemoproteins, in solution or in living cells.
A pulse voltage multiplier
Authors: Soto Leopoldo , Altamirano Luis
Published: July 2002

A pulse voltage multiplier is presented. The device consists of a set of transmission lines connected in parallel at the entry and connected in series at the end. The multiplication factor can become equal to twice the number of transmission lines, depending on the conditions at the entry of the device.