bluuebunny/crossref_metadata_2025 huggingface dataset:
Stabilization and calibration of x-ray wavelengths for anomalous diffraction measurements using synchrotron radiation
Authors: Evans G. , Pettifer R. F.
Published: July 2002

An apparatus and technique are described for the characterization and energy stabilization of a monochromatic x-ray beam from a synchrotron radiation source that is used for diffraction experiments. The energy of the beam between 6–30 keV can be absolutely measured to an accuracy of 0.3 eV and continuous stability can be guaranteed to 0.2 eV for the duration of an experiment. The particular case of multiple wavelength anomalous diffraction is considered in detail.
A 3D position controller for a charged particle suspended in a modified electrodynamic chamber
Authors: Zhang Xuefeng , Bar-Ziv Ezra
Published: July 2002

A three-dimensional (3D) position control system for a charged particle suspended in an electrodynamic chamber (EDC) was developed. The new controller is based on two major developments: (i) modification of the EDC that allowed the adjustment of the particle position at all three dimensions, by three dc electrodes and (ii) a special hardware that enabled the reading of the correct position of an arbitrarily shaped particle at high speed from its shadow, measured by a photodiode array (PDA). Three 128-pixel linear PDAs were used to measure the trace of the particle at the three dimensions. The hardware extracted directly the digital value of the particle position at each dimension by determining the center of the particle shadow. The three coordinates of the particle position were fed into a computer that served as a proportional-integral derivative and a storage device. The hardware allowed sampling of the particle position at frequency (7.8 kHz) and was able to handle particles at a wide range of sizes and various shapes (for example, with holes). The 3D position controller can maintain a particle at the center of the EDC, with a short characteristic time, under a wide range of disturbances, acting from arbitrary directions. The controller can also maintain the particle without an ac field. The results can be summarized as follows: (i) for a step disturbance, acting on a particle from an arbitrary direction, the controller can fully follow a force value as much as 10% of particle weight with a characteristic time of 100 ms; (ii) for a gradual disturbance, acting on the particle from an arbitrary direction, the controller can correct the disturbance with a changing force rate of 1 g/s with a delay time of less than 25 ms.
Transient behavior of the terminal voltage in a recirculating electrostatic accelerator for a long-pulse free-electron laser
Authors: Cho Sung Oh , Lee Byung Cheol , Jeong Young Uk , Kim Sun Kook , Lee Jongmin , Chung Kie Hyung
Published: July 2002

For long-pulse, single-mode operation of free-electron lasers, transient behavior of the terminal voltage in a recirculating electrostatic accelerator is analyzed. It is found that the rate of terminal voltage drop depends on the position where the current loss of electron beam occurs. The rate is measured to be 507 V/A μs for the current loss in the terminal and 100 V/A μs for the current loss in the deceleration tube. By increasing the capacitances between the adjacent electrodes of a deceleration tube, the accelerator becomes more stable with low rate of terminal voltage drop and increased recovery efficiency.
Technique for the removal of electrons from an extracted, pulsed, H− ion beam
Authors: Perkins Luke T. , Herz P. R. , Leung K. N. , Pickard D. S.
Published: July 2002

A small, permanent-magnet insert structure for the removal of electrons from pulsed, extracted, negative ion beams has been developed at Lawrence Berkeley National Laboratory. The device was computer modeled and designed for an extraction field strength of 3 kV/mm. The testing was carried out with a rf driven multicusp ion source optimized for the production of H− ions and pulsed at a few Hz with pulse widths of several hundreds of μs. It is demonstrated that the insert structure together with a collar can remove over 98% of electrons from the extracted H− ion beam without any significant deterioration of the H− ion output. Application to other negative ion beams can be expected from this magnetic collar insert.
Pulsed resonance saturation spectroscopy for plasma diagnostic
Authors: Khare Alika
Published: July 2002

Possibilities are discussed for using pulsed resonance saturation spectroscopy to measure the density of hydrogen and other impurities for pulsed plasma devices. It is shown that species under consideration can be excited to some higher energy level to saturation with a pulsed high-power laser in a time short compared to the lifetime of that particular excited state. Computational results are presented for a general three level system, hydrogen and iron. Comparison of the results with and without collision processes shows that plasma parameters are not required for estimation of impurity density offering a major advantage over conventional plasma diagnostics.
Closed cycle cryogenic fiber extrusion system
Authors: Rahman H. U. , Ruden E. L. , Strohmaier K. D. , Wessel F. J. , Yur G.
Published: July 2002

A fiber extrusion system is described that produces frozen fibers of almost any condensible gas. This extruder has the advantage of employing a closed-refrigeration system. To date, this system has produced fibers of H2, D2, and Ne of a diameter ranging from 100 to 130 μm. The extrusion occurs at a specific temperature which is several degrees below the triple point of these gases. Once the fiber is extruded it can survive in vacuum for 20 min if the nozzle (extrusion) temperature is lowered to 8 K. The length of these fibers can be of the order of 1 m. D2 fibers will be used in a staged Z-pinch experiment as a fuel for thermonuclear fusion. For this application a guiding structure is needed to position the fiber between the electrodes with millimeter precision, without significantly affecting its quality.
New electrochemical cell for in situ tunneling microscopy, cyclovoltammetry, and optical measurements
Authors: Schindler W. , Kirschner J.
Published: July 2002

We present a new electrochemical cell design, which enables in situ tunneling microscopy (STM), cyclic voltammetry, and optical measurements in a single setup and at the same surface area of the substrate. The design is compatible with the Nanoscope III system and allows the deposition and investigation of metal films down to the submonolayer range. We show in situ STM of the Cu(001) surface, cyclic voltammetry of the deposition of ultrathin Co films on Cu(001) from an aqueous Na2SO4/CoSO4 solution and in situ magnetization measurements by magneto-optical Kerr effect on these Co films in the monolayer range.
Encoding technique for high data compaction in data bases of fusion devices
Authors: Vega J. , Crémy C. , Sánchez E. , Portas A. , Dormido S.
Published: July 2002

At present, data requirements of hundreds of Mbytes/discharge are typical in devices such as JET, TFTR, DIII-D, etc., and these requirements continue to increase. With these rates, the amount of storage required to maintain discharge information is enormous. Compaction techniques are now essential to reduce storage. However, general compression techniques may distort signals, but this is undesirable for fusion diagnostics. We have developed a general technique for data compression which is described here. The technique, which is based on delta compression, does not require an examination of the data as in delayed methods. Delta values are compacted according to general encoding forms which satisfy a prefix code property and which are defined prior to data capture. Several prefix codes, which are bit oriented and which have variable code lengths, have been developed. These encoding methods are independent of the signal analog characteristics and enable one to store undistorted signals. The technique has been applied to databases of the TJ-I tokamak and the TJ-IU torsatron. Compaction rates of over 80% with negligible computational effort were achieved. Computer programs were written in ANSI C, thus ensuring portability and easy maintenance. We also present an interpretation, based on information theory, of the high compression rates achieved without signal distortion.
A simple and inexpensive circuit for emission and capture deep level transient spectroscopy
Authors: Reddy C. V. , Fung S. , Beling C. D.
Published: July 2002

A simple and inexpensive circuit for deep level transient spectroscopy is described, which allows rapid characterization of emission as well as capture activation energies of deep levels. This flexibility of making capture activation studies affords more information on defect morphology than the more standard emission activation studies. This is demonstrated by making a representative capture activation energy measurement on the EL6 level in undoped n-type GaAs of 0.484±0.005 eV. Also the spectrometer has shown better performance than earlier reported systems by its ability to resolve the side peaks of the EL6 level, for which emission activation energies of 0.29 and 0.4 eV are assigned. Constructed around a commercially available capacitance meter and pulse generator, the control circuitry is designed and developed using inexpensive and off-the-shelf integrated circuits.
Double pulse Thomson scattering system at RTP
Authors: Beurskens M. N. A. , Barth C. J. , Chu C. C. , Donné A. J. H. , Herranz J. A. , Lopes Cardozo N. J. , van der Meiden H. J. , Pijper F. J.
Published: July 2002

In this article a double pulse multiposition Thomson scattering diagnostic, under construction at RTP, is discussed. Light from a double pulsed ruby laser (pulse separation: 10–800 μs, max. 2×12.5 J) is scattered by the free electrons of the tokamak plasma and relayed to a Littrow polychromator for spectral analysis. The spectrally resolved light is recorded by two ICCD detectors. Simulations show that the system sensitivity will be such that electron temperatures in the range of 100 eV–7 keV can be determined with an accuracy as good as 2%–3% for electron densities of 1020 m−3, with a spatial resolution down to 2.6 mm. With this diagnostic the dynamics of small scale structures in the electron temperature profile will be studied.
Maximum-likelihood fitting of data dominated by Poisson statistical uncertainties
Authors: Stoneking M. R. , Den Hartog D. J.
Published: July 2002

The fitting of data by χ2 minimization is valid only when the uncertainties in the data are normally distributed. When analyzing spectroscopic or particle counting data at very low signal level (e.g., a Thomson scattering diagnostic), the uncertainties are distributed with a Poisson distribution. We have developed a maximum-likelihood method for fitting data that correctly treats the Poisson statistical character of the uncertainties. This method maximizes the total probability that the observed data are drawn from the assumed fit function using the Poisson probability function to determine the probability for each data point. The algorithm also returns uncertainty estimates for the fit parameters. We compare this method with a χ2-minimization routine applied to both simulated and real Thomson scattering data. Differences in the returned fits are greater at low signal level (less than ∼10 counts per measurement). The maximum-likelihood method is found to be more accurate and robust, returning a narrower distribution of values for the fit parameters with fewer outliers.
Multilayer mirror based line emission tomography for spherical Tokamaks
Authors: Stutman D. , Hwang Y. S. , Menard J. , Choe W. , Ono M. , Finkenthal M. , May M. J. , Regan S. P. , Soukhanovskii V. , Moos H. W.
Published: July 2002

Due to their highly shaped plasma and possible poloidal asymmetry in impurity concentration, spherical Tokamaks will require tomographic reconstruction of local emissivities to assess impurity content and transport. To collect in an effective manner the data required for such reconstruction, we develop arrays of high throughput “mini-monochromators” using extreme ultraviolet multilayer mirrors as dispersive elements and filtered surface barrier diodes as detectors. We discuss monochromator optimization and show that by working at near normal incidence throughput and spectral resolution are simultaneously maximized. A system proposed for tomographic reconstruction of C V and C VI resonance emission at 33.7 and 40.5 Å respectively, achieves 0.9 Å spectral resolution, 2 cm spatial resolution, and 0.2 ms temporal resolution, together with good sensitivity and background rejection. Preliminary results obtained from CDX-U low aspect ratio tokamak are also presented.
Magnetic resonance force detection and spectroscopy of electron spins in phosphorus-doped silicon
Authors: Wago K. , Züger O. , Wegener J. , Kendrick R. , Yannoni C. S. , Rugar D.
Published: July 2002

Electron spin resonance (ESR) of phosphorus-doped silicon was detected using a low temperature magnetic resonance force microscope (MRFM). Force-detected ESR spectra were obtained using an amplitude or frequency modulated microwave field to cyclically saturate the spin magnetization. For a sample containing 4×1018 phosphorus atoms/cm3, a single strong ESR line was observed. For a sample containing 8×1016 phosphorus atoms/cm3, a pair of lines split by the 42 G P31 hyperfine interaction was observed. This result demonstrates the possibility of using MRFM techniques for spectroscopic purposes.
An improved electron transmission method for measuring electron trapping cross sections at the surface of dielectric films
Authors: Nagesha K. , Gamache J. , Bass A. D. , Sanche L.
Published: July 2002

We investigate several problems inherent in the low energy electron transmission (LEET) technique for measuring cross sections σCT for charge trapping, by submonolayer (ML) quantities of a target molecule deposited onto the surface of a dielectric film. In particular we see that the energy of the incident electron beam while charging the film was poorly defined in the original method. Furthermore, we demonstrate that interactions between trapped charges and the metallic substrate set a limit of about 100 mV for the maximum surface potential that should be allowed in absolute measurements of CT cross sections. To surmount these problems, we show how the surface potential ΔV generated by electrons of specific incident energy can be obtained rapidly, by monitoring the relative transmitted current Ir at a single reference energy EREF, rather than by recording multiple LEET spectra (or injection curves). The approach allows several measurements at different incident electron energies to be made on a single film and increases markedly the rate of data acquisition. The overall uncertainty in these measurements has an upper limit of ∼50%.
Design concept and performance considerations for fast high power semiconductor switching for high repetition rate and high power excimer laser
Authors: Goto Tatsumi , Kakizaki Kouji , Takagi Shigeyuki , Satoh Saburoh , Shinohe Takashi , Ohashi Hiromichi , Endo Fumihiko , Okamura Katsuya , Ishii Akira , Teranishi Tsuneharu , Yasuoka Koichi
Published: July 2002

A semiconductor switching power supply has been developed, in which a novel structure semiconductor device, metal-oxide-semiconductor assisted gate-triggered thyristor (MAGT) was incorporated with a single stage magnetic pulse compression circuit (MPC). The MAGT was specially designed to directly replace thyratrons in a power supply for a high repetition rate laser. Compared with conventional high power semiconductor switching devices, it was designed to enable a fast switching, retaining a high blocking voltage and to extremely reduce the transient turn-on power losses, enduring a higher peak current. A maximum peak current density of 32 kA/cm2 and a current density risetime rate di/dt of 142 kA/(cm2×μs) were obtained at the chip area with an applied anode voltage of 1.5 kV. A MAGT switching unit connecting 32 MAGTs in series was capable of switching on more than 25 kV–300 A at a repetition rate of 5 kHz, which, coupled with the MPC, was equivalent to the capability of a high power thyratron. A high repetition rate and high power XeCl excimer laser was excited by the power supply. The results confirmed the stable laser operation of a repetition rate of up to 5 kHz, the world record to our knowledge. An average output power of 0.56 kW was obtained at 5 kHz where the shortage of the total discharge current was subjoined by a conventional power supply with seven parallel switching thyratrons, simultaneously working, for the MAGT power supply could not switch a greater current than that switched by one thyratron. It was confirmed by those excitations that the MAGT unit with the MPC could replace a high power commercial thyratron directly for excimer lasers. The switching stability was significantly superior to that of the thyratron in a high repetition rate region, judging from the discharge current wave forms. It should be possible for the MAGT unit, in the future, to directly switch the discharge current within a rise time of 0.1 μs with a magnetic assist.
Use of a charge coupled device-camera system for optical diagnostics of intense ion beams
Authors: Sarstedt M. , Dölling R. , Wicke L. , Klein H.
Published: July 2002

Among the various possibilities for investigating the properties of ion beams, two of the most important principles for determining the beam quality are profile measurements using wires or slit apertures, and different kinds of emittance measurement devices. However, most of the commonly used systems have the disadvantage of being either destructive to the beam, or at least to have a considerable influence on the further beam propagation downstream of the point of measurement. Also, for the investigation of intense ion beams, thermal problems on the scanners themselves might arise. Observation of particles emitted from the ion beam in radial direction allow an indirect but nondestructive observation of the beam. Of the different optical methods that exist to accomplish this, we recently conducted an investigation on the possibilities to employ a charge coupled device-camera system for such nondestructive beam diagnostics in our space-charge compensation test stand. First, experimental results on optical profile measurements are presented and compared to results obtained by a slit scanner and a wire scanner. Additionally, to gain a better understanding of the measured data, optically obtained sectional profiles behind a slit and a circular aperture were analyzed. Possibilities for gaining information on the two-dimensional beam profile and the beam emittance are explored.
Tracer-encapsulated cryogenic pellet production for particle transport diagnostics
Authors: Sudo S. , Itoh H. , Khlopenkov K.
Published: July 2002

A device for producing a tracer-encapsulated cryogenic pellet is constructed for an accurate transport diagnostic system to measure particle transport both parallel and perpendicular to the magnetic-field lines in magnetic confinement devices. As for the typical configuration of the tracer-encapsulated pellet, it is proposed that a 50–250 μm diam tracer made of a light atom such as lithium, carbon, etc., is encapsulated in the center of a 1–3 mm diam cylindrical pellet of hydrogen. For demonstration of the device operation, a 240 μm diam carbon sphere is encapsulated in the center of a 3 mm diam cylindrical pellet of hydrogen, and accelerated by a light gas gun to velocities of 400–800 m/s in a test chamber. The pellet has been photographed simultaneously from two directions and the two two-dimensional images are reconstructed to a three-dimensional image. Thus, the proof of principle of the device operation has been demonstrated.
Atomic absorption spectroscopy system for flux monitoring and atomic-layer control of molecular beam epitaxial growth of BiSrCaCuO
Authors: Kasai Yuji , Sakai Shigeki
Published: July 2002

Atomic absorption spectroscopy (AAS) system for accurate and in situ atomic-flux-monitoring during molecular beam epitaxial growth is reported in detail. Hollow cathode lamps are used as light sources. They emit the light with inherent spectral lines of the elements to be measured. A turret system with multiple hollow cathode lamps and line pass filters is equipped, which is suited in particular for atomic layer-by-layer growth. The intensities of the transmitted light on both conditions in the presence and absence of atomic beam flux are measured. An analytic expression for in situ calculating the beam flux rate using these measured quantities is discussed. A method for determining an unknown constant included in this expression is described. This uses the inductively coupled plasma spectroscopy technique to estimate the amount of atoms impinging on the substrate. Within the range of BiSrCaCuO growth conditions, the AAS measurements are not influenced by changing either the substrate temperature or the condition of ozone that is oxidizing agent. The resolution of the flux measurement is better than 1011 cm−2 s−1 for Sr and Ca, 1012 cm−2 s−1 for Cu, 1014 cm−2 s−1 for Bi. This AAS system is applied to a real-time flux control of an atomic layer-by-layer growth of BiSrCaCuO.
New method for measuring low NO concentrations using laser induced two photon ionization
Authors: Lee Shan-Hu , Hirokawa Jun , Kajii Yoshizumi , Akimoto Hajime
Published: July 2002

A new method based on laser induced two photon ionization was developed for detection of low levels of NO concentration in the troposphere. A frequency-doubled pulsed dye laser operating at near 226 nm was used to photoionize NO by a (1+1) resonance enhanced two photon ionization via its A 2Σ←X 2Π(0,0) band. NO ions are detected by an electron multiplier. Air gas samples are injected through a pulsed nozzle into a vacuum chamber. Cooling of rovibrational levels during the expansion process allows better selectivity for NO detection from other nitrocompounds. Measurement conditions were optimized as a function of X/D for the nozzle (X is the distance from the nozzle orifice to the ionization area, and D is the diameter of the nozzle orifice), laser power, and electron multiplier voltage. For the first time, selectivities for NO measurement, which were obtained from ion intensity ratios of NO and other nitrocompounds such as NO2 at the same concentrations, are discussed. A selectivity of 45 for NO vs NO2 was obtained using a 44 μJ pulse energy and an X/D of 120 for the nozzle. The current detection limit determined for NO was 16 pptv with an integration time of 1 min and a pulse energy of 44 μJ.
White light continuum as a tunable radiation source for second-harmonic generation experiments
Authors: Willard Dale M. , Kung Kyle Y. , Luther Bradley M. , Levinger Nancy E.
Published: July 2002

We have used a white light continuum generated with ultrashort laser pulses from a Ti:sapphire laser system as the radiation source for second-harmonic generation measurements. The white light continuum provides easily tuned radiation for experiments requiring a range of wavelengths. Despite the small coherence length of the radiation, parametric processes, such as second-harmonic generation, are possible with this source. In particular, surface second-harmonic generation using the white light continuum is reasonable because the extent of the interface is much smaller than the coherence length of the radiation. We demonstrate second-harmonic generation from a gold surface and show that surface second-harmonic generation using the white light continuum can be used to measure absorption spectroscopy of molecules adsorbed to surfaces via resonance enhancement of the surface second-harmonic signals.
Consideration of fluctuation in secondary beam intensity of heavy ion beam probe measurements
Authors: Fujisawa A. , Iguchi H. , Lee S. , Hamada Y.
Published: July 2002

Heavy ion beam probes have the capability to detect the local fluctuation of density in the interior of plasmas through the fluctuation of the intensity of the detected beam. However, this intensity fluctuation may suffer from a certain degree of distortion from fluctuations of electron density and temperature along the beam trajectory; as a result, the fluctuation signal may be quite different from the local density fluctuation. This article presents the conditions where the intensity fluctuation can be regarded as being local fluctuation of electron density, where it cannot, and discusses the contamination of the fluctuations by fluctuations along the trajectory, particularly in the case of magnetohydrodynamics fluctuations.
Vacuum near-field scanning optical microscope for variable cryogenic temperatures
Authors: Behme G. , Richter A. , Süptitz M. , Lienau Ch.
Published: July 2002

We describe the design of a novel near-field scanning optical microscope for cryogenic temperatures and operation in vacuum. A helium flow cryostat is used for active temperature control of the sample in the range between 8 and 330 K, while all components of the near-field microscope are kept at room temperature. This design greatly simplifies near-field microscopy at variable sample temperatures and permits large piezoelectric scan ranges of up to 100×100×10 μm 3, the implementation of hardware-linearized piezoelectric scan stages, as well as flexible coarse positioning. First experiments with single GaAs quantum wires demonstrate the excellent performance of this new instrument.
Rapid and precise method to convert a two dimensional image from Cartesian to polar coordinate system
Authors: Wu Weimin , Kato Yoshihiro , Yamazaki K. , Yoshino M. , Danjo A. , Kobayashi N.
Published: July 2002

A method is described to convert a two-dimensional image, which is the pattern of the scattered electrons from on target gas measured by a torodial type analyzer with a detector consists of a pair of multichannel plates and a position sensitive detector from detector’s recording system, a Cartesian coordinate system, to a polar coordinate system in which physical quantities (the energy and angle of a scattered electron) are expressed. By this method, the converting coefficients are calculated with high precision and the kernel (nonzero) coefficients are stored for data conversion on disk. Since there is symmetry in the coefficients, only part of the coefficients need to be calculated and stored. A simple method for compressing the storage space of the coefficients also is described.
Frequency stable superconducting resonator with buffer layers
Authors: Abbas Farhat
Published: July 2002

The resonant frequency of a superconducting planar resonator is dependent on the material properties and thicknesses of the superconductors, the dielectric (substrate), and the buffer layers. In this article, we compute the first and second derivatives with respect to temperature of a wave velocity ratio (with respect to free space) for various combinations of material properties. The dependence of resonant frequency on the dielectric constant and thicknesses of the substrate and buffer layers is discussed. An example of YBCO thin films on rutile with sapphire buffer layers was computed. From this example, it may be concluded that, if a turning point can be realized at T=60 K and the temperature controlled to better than 0.1 mK, then frequency standards with stabilities of parts in 1015 should be attainable.
Self-illumination calibration technique for luminescent paint measurements
Authors: Ruyten W. M.
Published: July 2002

In a recent article [W. M. Ruyten, Appl. Opt. 36, 3079 (1997)] a theoretical model is presented which accounts for the effects of self-illumination and spectral leakage of a diffusely reflecting test article in luminescent paint measurements. It is shown in the present work how measurements on two, square, painted samples at a range of included angles can be used to check the applicability of the above model for a particular paint, and to determine the spatially averaged reflection coefficient of the paint, Rred, at the emission wavelength. The technique is demonstrated for the pressure-sensitive paint FIB7, yielding Rred=0.79±0.15, where the uncertainty indicates the degree to which the reflection characteristics of the paint deviate from those of a diffuse reflector. The proposed technique constitutes a complete calibration for the correction algorithm developed in the above-referenced article in the case that spectral leakage can be neglected.
Current source with matched common mode output impedances
Authors: Sutton John F.
Published: July 2002

A differential current source with matched common mode output impedances is described. Matching impedances reduces common mode-to-differential mode signal conversion, important in the low noise, high resolution measurement of cryogenic temperatures as low as 50 mK.
A test station facility for research and development on fuel cell components and materials
Authors: Paganin V. A. , Freire T. J. P. , Ticianelli E. A. , Gonzalez E. R.
Published: July 2002

This work describes the characteristics of a bench station designed for both the control of the operational parameters of a unitary, low temperature fuel cell and the data acquisition for performance evaluation. The controlled parameters are the current through the cell, the pressure and the flow of the reactants, and the temperature of the cell and of the gaseous reactants. The system measures the potential drop across the cell and the potential of each electrode with respect to a reference, as a function of the current, which is varied on a predetermined interval. The program plots the results and fits the experimental curve to a theoretical expression, which allows the determination of the cell resistance and the Tafel kinetic parameters of the cell reactions. The test station provides a rapid route to the work with single/half cells in the evaluation of materials and fuel cell performance. The computer controlled procedures, data acquisition, and analyses proposed here substitute with advantages time consuming manual procedures.
A high power radio frequency transformer for plasma production in a toroidal plasma source
Authors: Zhang B. C. , Cross R. C.
Published: July 2002

A high power rf transformer has been developed and implemented for the purpose of plasma production in a toroidal plasma source, PLADEPUS (plasma deposition at the University of Sydney), which is designed for plasma processing experiments. The plasma can be generated, either in a pulsed or a continuous mode, at electron densities up to about 1013 cm−3. The results show that rf power can be efficiently transferred to the plasma through the magnetic coupling of the transformer ferrite core.
Real-time determination of total radiated power by bolometric cameras with statistical methods
Authors: Maraschek M. , Fuchs J. C. , Mast K. F. , Mertens V. , Zohm H.
Published: July 2002

A simpler and faster method for determining the total radiated power emitted from a tokamak plasma in real-time has been developed. This quantity is normally calculated after the discharge by a deconvolution of line integrals from a bolometer camera. This time-consuming algorithm assumes constant emissivity on closed flux surfaces and therefore needs the exact magnetic equilibrium information. Thus, it is highly desirable to have a different, simpler way to determine the total radiated power in real-time without additional magnetic equilibrium information. The real-time calculation of the total radiated power is done by a summation over ten or 18 lines of sight selected out of a bolometer camera with 40 channels. The number of channels is restricted by the summation hardware. A new selection scheme, which uses a singular value decomposition, has been developed to select the required subset of line integrals from the camera. With this subset, a linear regression analysis was done against the radiated power calculated by the conventional algorithm. The selected channels are finally used with the regression coefficients as weighting factors to determine an estimation of the radiated power for subsequent discharges. This selection and the corresponding weighting factors can only be applied to discharges with a similar plasma shape, e.g., in our case the typical ASDEX upgrade elliptical divertor plasma.
A method of heat capacity measurement without thermometer calibration
Authors: Fominaya Fernando , Chaussy Jacques , Gandit Philippe
Published: July 2002

A new method for measuring heat capacities that makes the calibration of thermometers obsolete is presented. The particularity of the principle, based on the ac steady-state method, is the insertion of a reference mass with a heater between the ensemble substrate+sample+thermometer+heater, and the bath. The method could find a broad application in calorimetric devices where the thermometer must often be recalibrated due to, e.g., a drift of the thermometer’s characteristics with thermal cycles or magnetic field.
A Petri cell modified for atomic force microscopy suitable to investigate biological samples in liquid
Authors: Cricenti Antonio , Generosi Renato
Published: July 2002

A cell for biological samples that allows atomic force microscopy (AFM) observations in a controlled environment (air or gas or any liquid) is described. The cell is made of a modified Petri container and it is possible, through two inlet and outlet feedthroughs, to introduce an aqueous liquid during AFM observation thus directly visualizing the modifications induced on the biological specimen. Uncoated neurons and Escherichia Coli bacteria have been imaged in air and after introducing an aqueous liquid by contact-mode AFM: the microimages are similar and show a comparable resolution even though the force applied to the biological material is different.
Determination of parameters of deep level defects from numerical fit of deep level transient spectroscopy spectra: Analysis of accuracy and sensitivity to noise
Authors: Istratov A. A. , Hieslmair H. , Flink C. , Weber E. R.
Published: July 2002

The numerical fit of deep level transient spectroscopy (DLTS) spectra, used primarily to analyze complex DLTS spectra, is evaluated in terms of the accuracy of measuring deep levels and the sensitivity to noise. It is shown that by using numerical fit of DLTS spectra, the uncertainties in the emission activation energy and the capture cross section of deep level defects can be improved by three to four times over the standard Arrhenius plot method. Two modifications of the fitting procedure are tested: a fit of a DLTS spectrum using one rate window, and a simultaneous fit using five different rate windows. It is shown that simultaneous fit of spectra using different rate windows is significantly more accurate, has noticeably larger convergence radius for the initial values of parameters, and is less sensitive to noise. The advantages of the fitting routine are demonstrated on experimentally obtained noisy DLTS spectra.
Nonconventional short-time dc magnetometer for superconducting films
Authors: Valenzuela S. O. , Ferrari H. , Bekeris V. , Marconi M. C. , Guimpel J. , de la Cruz F.
Published: July 2002

A nonconventional technique for the measurement of magnetic relaxation in superconducting films at short times (∼10−5 s) is described. This technique combines the application of a pulsed magnetic field and a synchronized high-energy pulsed laser. Remanent magnetic relaxation in (Y;Gd)Ba2Cu3O7−δ thin films is reported over five decades time at reduced temperatures above 0.8.
A far-infrared laser magnetic resonance spectrometer with permanent magnets
Authors: Hübers H.-W. , Töben L. , Röser H.-P.
Published: July 2002

A laser magnetic resonance spectrometer for the far-infrared region is described. It is based on an optically pumped far-infrared laser. Zeeman tuning of the energy levels of the investigated molecule is achieved by using permanent magnets. With this setup it is possible to reach a magnetic flux density as high as 0.5 T. The design of the spectrometer is very compact compared to conventional laser magnetic resonance spectrometers based on superconducting or watercooled electromagnets. This makes it a promising tool for analytic purposes either in the laboratory or for field studies.
Design and construction of a triple-axis ultrahigh vacuum goniometer
Authors: Yao J. , Kim C. , Rabalais J. W.
Published: July 2002

A triple-axis goniometer was designed and constructed for positioning objects within an ultrahigh vacuum chamber. The goniometer is applied to move a large position-sensitive microchannel plate (MCP) detector which is used for scattering and recoiling imaging spectrometry (SARIS). The goniometer allows the MCP to be independently rotated in horizontal (φ) and vertical (θ) planes as well as translated with respect to a fixed sample position. The angle φ can be varied from 0° to 160° in order to change the scattering angle for SARIS. The angle θ can be varied from 0° to 80°, allowing the MCP to be moved out of the scattering plane. Translation allows the MCP to be moved relative to the sample position over a range of 10–60 cm. All of the movements are driven by computer-controlled stepping motors.
In situ density measurement for a thermal lithium beam employing diode lasers
Authors: Dinklage A. , Lokajczyk T. , Kunze H. J. , Schweer B. , Olivares I. E.
Published: July 2002

We introduce a method for a spatially and temporally resolved density measurement of atomic beams. A semiconductor diode laser was employed for measuring both the absorption and the laser induced fluorescence emerging from the beam. Absorption measurements give an absolute value for the line integrated density, whereas laser induced fluorescence yields the relative density distribution. Thus, we were able to determine nondestructively absolute density distributions of thermal particle beams.
Selection of the residual gas pressure suitable for operating a positive ion source of thermal ionization type
Authors: Kawano Hiroyuki , Ogasawara Keiko , Kobayashi Hajime , Tanaka Akihide , Takahashi Tomoko , Tagashira Yasuhide
Published: July 2002

To find the residual gas pressure (P) suitable for operating a thermal positive ion source, a beam of molecule (MX) such as LiH, NaCl, or TlI was directed with a constant flux (N≈1013 molecules cm−2 s−1) onto a surface of Re or W heated to a constant temperature (T≈1000–2100 K), and the ion current (∼10−10–10−8 A, corresponding to ∼10−7–10−5 A cm−2) of M+ was measured as a function of P(∼1×10−7–5×10−5 Torr), which was increased by the introduction of air. These data thus obtained were analyzed to determine the ionization efficiency (β+) of MX and the work function (φ+) of each surface. Analysis of the relation among P, T, β+, and φ+ indicates that to produce a strong ion beam from MX, selection of P≈1×10−6 Torr is recommended for keeping β+ as large as possible in a wide range of T≈1100–1400 K where φ+>6.3 eV is maintained by adsorption of O2, and hence where β+≈1 even for TlX is attained, but to detect rapidly a neutral beam of MX in kinetic studies of very rapid reactions, P≈1×10−5 should be selected together with ∼1600 K, thereby keeping φ+≈5.8 eV, and hence, yielding β+⩾0.9 for MX so long as the ionization energy of M is less than ∼5.2 eV.
Blind reconstruction of x-ray penumbral images
Authors: Chen Y.-W. , Otsuki K. , Nakao Z. , Kodama R.
Published: July 2002

We proposed a method to estimate the point-spread function from the power cepstrum of the penumbral image in this paper. It is used as a preprocessing step before deconvolution. Both computer simulations and experimental results for real x-ray imaging demonstrated the potential of the method for practical applications.
One and two dimensional space scannings of x-ray beams by diffraction on surface acoustic waves: Application to x-ray imaging
Authors: Tucoulou R. , Brunel M. , Roshchupkin D. V. , Schelokov I. A.
Published: July 2002

X-ray diffraction on surface acoustic waves with tunable wavelength provides a way to perform beam scannings. 1D and 2D space scannings of x-ray beams by this method are presented. The feasibility of a purely optical method to perform scanning x-ray imaging without any mechanical movement is discussed.
In situ calibration of a flat-field grazing incidence spectrograph with an x-ray charge-coupled device camera using a transmission grating and a laser-produced plasma for x-ray laser research
Authors: Fujikawa C. , Yamaguchi N. , Hara T. , Kawachi T. , Oyama H. , Ando K. , Aoyagi Y.
Published: July 2002

An in situ calibration experiment of a soft x-ray spectrograph for x-ray laser research has been performed. The calibrated spectrograph was a flat-field grazing incidence spectrometer with an x-ray charge-coupled device camera. The absolute sensitivity of the spectrograph was obtained for the wavelength range from 2.6 to 4.0 nm using a transmission grating spectrograph as a reference spectrograph set along the axial direction of a line-focused laser-produced plasma. The absolute sensitivity determined in this work shows nearly the same value as that deduced from the calibration experiment using synchrotron radiation.
A peristaltic injection nozzle for collinear laser and molecular beams
Authors: Dharmasena Kushlani , Jefferies Jennifer , Mu Guangwei , Young Joel , Bergeron Barry , Littell Robert , Shafer-Ray Neil
Published: July 2002

A novel gas nozzle design that allows for collinear laser and molecular beams is described. Unlike conventional nozzles that open and close to limit the gas flow into a vacuum chamber, this nozzle opens to release a small volume of gas into the chamber. Gas pulses of 300 μs duration and 65±5 μs opening times have been obtained. When room-temperature H2 is used as the source gas, the rotational temperature was found to be 175±12 K, whereas when room-temperature D2 was used, the rotational temperature was found to be 104±7 K. The collinear optical and molecular beam path provided in this design may be useful in photodissociation experiments, the study of atomic and molecular collisions, Rydberg state lifetime measurements, and vacuum ultraviolet generation by nonlinear mixing in gases.
The dynamic properties of the preset count digital rate meter algorithms
Authors: Arandjelović V. Dj. , Koturović A. M. , Vukanović R. B.
Published: July 2002

The exact analytical expressions for the response times of the preset count moving average and exponential digital rate meter algorithms to sudden changes of count rate have been obtained. Generalized concepts of the response time equivalence and steady-state statistical fluctuations equivalence allowed a detailed comparison of the two classes of digital rate meter algorithms. The conditions for complete equivalence, i.e., equal both response times and steady-state statistical fluctuations for the two classes of algorithms have been identified. The similarities and differences between the preset time and preset count digital rate meter algorithms are indicated.
Description of an x-ray microscope with 30 nm resolution
Authors: Medenwaldt Robin , Uggerho/j Erik
Published: July 2002

The Aarhus x-ray microscope has been in operation for some years and has evolved into a scientific user facility, the activities of which include a wide range of applications. A technical description of the microscope is given with emphasis on problems that have general character for high precision instrumentation and soft x-ray equipment.
Sources of phase noise in homodyne and heterodyne phase modulation devices used for tissue oximetry studies
Authors: Ramanujam N. , Du C. , Ma H. Y. , Chance B.
Published: July 2002

The objective of this study was to characterize sources of phase noise in homodyne and heterodyne phase modulation devices (PMDs) used for tissue oximetry measurements. Each PMD incorporates a laser diode modulated at a radio frequency in the 50–200 MHz range, an optical detector and a homodyne/heterodyne phase sensitive detector. The intensity modulated light which propagates through tissue is attenuated and undergoes a phase shift, which reflects the mean time of flight of the photons through the tissue. The measured amplitude and phase can be used to determine hemoglobin saturation in tissues using equations based on diffusion theory. Four studies were performed to characterize the sources of phase noise. First, the signal to noise ratio was characterized to determine if the PMDs are operating at the shot noise or detector noise limit. Second, the accuracy of the three PMDs for measuring phase shifts in tissue were compared by using them to measure the phase shift as a function of path length change in air, at a constant amplitude, and at signal to noise ratios comparable to that measured from tissue. The third source of noise measured was the phase shift that results from optical attenuation of the signal (phase-amplitude cross talk) at a constant path length, to characterize intensity dependent phase shifts in the PMDs. Finally, the interchannel interference of a dual wavelength PMD which uses radio frequency multiplexing to perform phase measurements at two wavelengths simultaneously was compared to that of a dual wavelength PMD which uses time multiplexing to perform phase measurements at two wavelengths serially to determine the effect of each on phase error.
Temperature-induced reflectivity changes and activation of hydrogen sensitive optically thin palladium films on silicon oxide
Authors: Kalli Kyriacos , Othonos Andreas , Christofides Constantinos , Lloyd Spetz Anita , Lundström Ingemar
Published: July 2002

The optical properties of several thin metal film palladium-silicon oxide structures are examined at room temperature before and after annealing to 200 °C and also at 90 °C—in all cases in the presence of hydrogen gas. Multicycling sample activation is shown to occur in the presence of hydrogen at room temperature with an increase in reflectivity on exposure to hydrogen, in contrast to thicker 80 Å films. The reflectivity change increases with increasing film thickness (1–10 Å). The surface activation at room temperature, before and after annealing to 200 °C, is compared with the performance at 90 °C, where it is shown that heat treatment strongly influences the behavior of the metal film.
A 360°-tilt specimen holder for electron tomography in an ultrahigh-voltage electron microscope
Authors: Zhang Haibo , Takaoka Akio , Miyauchi Kyoichi
Published: July 2002

A 360°-tilt specimen holder was designed for electron tomography in an ultrahigh-voltage electron microscope. The new holder is of simple noneucentric and single-axis tilting type, with a minimum tilt step of 0.01°. It is applicable to different types of specimens with clamping arrangement. Experiments show that images can be observed around the maximum tilt range of ±85°. The direction of the tilt axis is determined from the 0°- and 180°-tilt images. The possibility of correcting image alteration due to different specimen height is also discussed.
Four-stage Marx generator using thyristors
Authors: Gregory Keith , Stevenson Paul , Burke Robert
Published: July 2002

A small-scale capacitor discharge pulse generator using thyristors in a Marx configuration is described. The four-stage generator is actively triggered in a sequential manner. The application considered is in the firing circuit of a larger switch where the generator is shown to be capable of producing pulses rising to 230 A in less than 1.5 μs from an equivalent open-circuit voltage of 2.3 kV.
Development of an electrostatic ion guide in chemical ionization mass spectrometry
Authors: Zhang Renyi , Molina Luisa T. , Molina Mario J.
Published: July 2002

An electrostatic ion guide has been developed to transmit externally formed ions in chemical ionization mass spectrometry. Transport of ions over a distance of ten or more cm is accomplished with a high efficiency. Our design of the ion guide allows efficient separation of ion from neutral molecules, which provides a relatively simple means to significantly increase the detection sensitivity in chemical ionization mass spectrometry.