bluuebunny/crossref_metadata_2025 huggingface dataset:
Rare-earth phosphor laser-induced fluorescence thermal imaging system
Authors: Bizzak D. J. , Chyu M. K.
Published: July 2002

This article examines the measurement capabilities of a novel, two-dimensional thermal imaging system based on the fluorescence properties of an europium-doped lanthanum oxysulfide (La2O2S:Eu+3) thermographic phosphor. The foundation of the technique (i.e., the fluorescence properties of La2O2S:Eu+3), as well as the design of the thermal imaging system, are also described. The technique that is employed in the design of the system utilizes the tripled output of a pulsed Nd:YAG laser to excite the thin phosphor coating applied to a test surface. The resulting fluorescent emission of the temperature sensitive 512-nm radiative transition, along with that of the relatively temperature independent 620-nm transition, is acquired using an image-intensified charge coupled device camera. The ratio of the intensities of these two emissions, integrated during their decay, is then correlated with temperature. Phosphor calibration data that is presented demonstrate the efficacy of the technique, while results of evaluations to assess the spatial resolution and measurement accuracy provide a quantitative measure of system capabilities.
Long-pulse operation of a submillimeter wave gyrotron and its application to plasma scattering measurement
Authors: Ogawa I. , Yoshisue K. , Ibe H. , Idehara T. , Kawahata K.
Published: July 2002

Electromagnetic waves of medium power (P=110 W) in the submillimeter range (f=354 GHz) are generated in long pulses (τ=0.6 s) by a submillimeter wave gyrotron. The fluctuation levels of output power are suppressed within 8% by optimizing the operating parameters. This output has been applied to plasma scattering measurements. Preliminary results of low-frequency density fluctuations in Compact Helical System plasma are presented.
Negative-ion source for implantation and surface interaction of negative-ion beams (invited)
Authors: Ishikawa Junzo
Published: July 2002

An rf-plasma-sputter type heavy negative-ion source can deliver a few mA to 12 mA of dc negative-ion currents such as boron, carbon, silicon, and copper negative-ion beams. These negative-ion currents are comparable with the positive-ion currents for conventional high current positive-ion implantation, and thus could be newly used in place of positive ions. Surface interaction of negative-ion beams is extremely distinctive when negative ions are implanted into insulated materials or insulators. The surface charge-up voltage of insulated materials by negative-ion implantation saturates at only several volts, so that no breakdown of insulators takes place. As a whole system, a negative-ion implanter without charge neutralizer would be simpler and more economical than a positive-ion implanter.
The SERSE project
Authors: Ciavola G. , Gammino S. , Briand P. , Melin G. , Seyfert P.
Published: July 2002

The project for a superconducting electron cyclotron resonance (ECR) ion source has been funded by INFN in 1992 as a joint venture between INFN and CEA/DRFMC. The source is devoted to the production of high charge state heavy ions to be injected into the K-800 superconducting cyclotron. The magnetic system consists of three solenoids and of an hexapole which will allow one to attain a strong plasma confinement by means of a B-min field configuration with a very high magnetic field (1.4 T on the plasma chamber wall). At the intermediate frequency of 14.5 GHz, it will be possible to study the scaling of ECR ion sources at different magnetic fields far beyond the existing levels. The source will eventually work at a higher frequency, in the range 28–35 GHz of gyrotron tubes. The design of the superconducting magnets and of the cryostat has been carefully carried out, taking into account this goal, and the construction is now under course. The mechanical design of the plasma chamber is also outlined.
Review of the Eleventh International Workshop on ECR ion sources (invited)
Authors: Drentje A. G.
Published: July 2002

At the Workshop, the operation of various new and existing ECR ion sources was reported, with most of the emphasis on new methods to improve the performance and extend the variety of species. Much attention was paid to theoretical aspects, in particular to the basic question of electron heating; a complete investigation is still considered to be a long term project. A number of measurements of diagnostic character were presented. The strong radial component of the field in the magnetic trap turns out to play a crucial role in the confinement of hot electrons and hence in the production of very high charge state ion beams. A donor for cold electrons in any form—like a biased probe, plasma cathode, or electron gun—contributes strongly to increased output and stability of operation of the ECR ion source.
Ferroelectric fatigue in perovskite oxides
Authors: Warren W. L. , Tuttle B. A. , Dimos D.
Published: July 2002

We find that the reduction of the switchable polarization in BaTiO3 crystals via repeated polarization reversals (fatigue) is accompanied by the trapping of electronic charge and atomic scale distortions in the perovskite oxygen octahedron. The distortions are proposed to involve oxygen vacancies.
Noise measurements on junction field effect transistors
Authors: Pallottino Giovanni Vittorio , Zirizzotti Achille Emanuele
Published: July 2002

We report the experimental results of noise measurements performed on junction field effect transistors (2SK162) in the frequency range 1–100 kHz, where the internal correlation effects are not negligible. The experimental data have been analyzed to determine the input current noise spectrum and the spectral energy sensitivity of the device, expressed in terms of noise temperature. We obtained Vn≂0.6 nV/√Hz, and In≂4 fA/ √Hz at 1 kHz, In≂25 fA/ √Hz at 100 kHz. We also report and discuss the results of measurements performed at the temperature of 200 K, which show that the reduction of the noise is not very significant for this specific device.
Laboratory grazing-emission x-ray fluorescence spectrometer
Authors: de Bokx P. K. , Urbach H. P.
Published: July 2002

We have developed a laboratory grazing-emission x-ray fluorescence (GEXRF) spectrometer. The instrument utilizes in vacuo wavelength-dispersive detection. Due to the high resolution of a crystal monochromator at long wavelengths, the range of applicability of grazing x-ray techniques is substantially extended to the longer wavelengths as compared to techniques used presently. It is demonstrated that interference fringes in the take-off angle dependence of the fluorescent x-ray intensity of a layered sample can be resolved using a conventional x-ray tube.
Low and high temperature uniaxial stress devices for the study of ferroelastic crystals
Authors: Burkhardt E. , Ye Z.-G. , Schmid H.
Published: July 2002

Detailed techniques for the construction of low (4–300 K) and high (300–700 K) temperature uniaxial stress application devices are described, designed for studying stress-induced effects, including ferroelastic (/ferroelectric) detwinning, induced phase transitions, piezo-optical effects in ferroic crystals under in situ optical control of their domain states by means of polarized light microscopy. Examples of the successful application of these systems to YBa2Cu3O7−δ , K3Fe5F15, and Cr3B7O13Cl crystals are presented and discussed.
Marriage of the Burger–Van Cittert and Allen deconvolution methods yields a highly improved overlapping line resolver
Authors: Flores-Llamas H.
Published: July 2002

A new procedure, based on the iterative method of Burger and Van Cittert, to correct instrumental and/or intrinsic broadenings has been developed. The Burger and Van Cittert method has been improved by combining it with another simple deconvolution method. A comparison of the results for simulated and experimental spectra among Burger and Van Cittert method and Jansson’s method and the new method are presented. The new procedure proves that for very overlapped lines it outperforms Jansson’s method in the trial carried out.
Integration of D-shaped gradient coils in a Bruker TM circular cavity for X-band electron spin resonance imaging
Authors: Gualtieri G. , Placidi G. , Sotgiu A. , Del Monaco S.
Published: July 2002

A very compact design for the coil assembly of an X-band imaging apparatus is described. The design is based on D-shaped coils obtained by cutting a circular current distribution by two parallel chords. The coils make the best possible use of the space available within the particular geometry of a cylindrical Bruker TM110 cavity. Its compact design results in a maximum width of 45 mm, which is available in most electromagnets used for electron paramagnetic resonance (EPR) spectroscopy. Using nitroxide free radicals of 60 mT in linewidth and field gradients of 1.5 mT/cm, a resolution of 100 μm was obtained.
Computer vision based morphometric characterization of neural cells
Authors: Costa Luciano da F.
Published: July 2002

This article reports on the application of computer vision techniques, implemented on an IBM PC-compatible machine, as a means of obtaining morphometric characterization of neural cells. The features considered include projection polar histograms, orientation polar histograms, and the determination of the convex hull of dendritic (or axonal) arborizations. As will be discussed in this work, the Hough transformation technique has proven to be of great help for the determination of all the above-mentioned parameters. Two actual application examples respective to the analysis of retinal ganglion cells are also presented and discussed.
Selective ion heating as a means of charge state manipulation in electron cyclotron resonance ion sources
Authors: Shirkov G. , Meyer D. , Bolshukhin D. O. , Vinogradov I. P. , Wiesemann K.
Published: July 2002

A numerical simulation of the effect of selective light ion cyclotron resonance heating on the charge state distribution of an electron cyclotron resonance (ECR) source running in a gas mixture is presented which gives good agreement with experiments recently performed in this laboratory. It is shown that heating results in enhanced transport of the heated species out of the plasma. Applying this to light ions increases containment of the heavy ones. Applying this method to highly charged ions may yield improvement of the yields of the heated species in the pulsed afterglow mode of ECR ion sources. Numerical simulation shows that the respective ion pulses can be compressed, i.e., shortened and increased in amplitude. Thus higher pulse repetition frequencies seem feasible. This may be of interest in applications.
STM system for spectroscopic and topographic studies at liquid–helium temperatures
Authors: Weinstein Vladimir , Arenshtam Aleksandre , Slutzky Michael , Ben-Jacob Eshel
Published: July 2002

A cryogenic STM system for high-sensitivity topographic and spectroscopic measurements is presented. The methods of noise suppression are discussed. The efficiency of the system is demonstrated via the imaging of gold surfaces and measurements of I–V characteristics showing Coulomb effects.
High-resolution integrated germanium Compton polarimeter for the γ-ray energy range 80 keV–1 MeV
Authors: Sareen R. A. , Urban W. , Barnett A. R. , Varley B. J.
Published: July 2002

Parameters which govern the choice of a detection system to measure the linear polarization of γ rays at low energies are discussed. An integrated polarimeter is described which is constructed from a single crystal of germanium. It is a compact planar device with the sectors defined electrically, and which gives an energy resolution in the add-back mode of 1 keV at 300 keV. Its performance is demonstrated in a series of calibration measurements using both unpolarized radiation from radioactive sources and polarized γ rays from the 168Er(α,2n)170Yb reaction at Eα=25 MeV. Polarization measurements at energies as low as 84 keV have been achieved, where the sensitivity was 0.32±0.09. The sensitivity, efficiency, and energy resolution are reported. Our results indicate that energy resolution should be included in the definition of the figure of merit and we relate the new definition to earlier work. The comparisons show the advantages of the present design in the energy range below 300 keV and its competitiveness up to 1500 keV.
Characteristics of a microwave electron cyclotron resonance plasma source
Authors: Camps Enrique , Olea Oscar , Gutiérrez-Tapia C. , Villagrán Mayo
Published: July 2002

The description and performance characteristics of a microwave electron cyclotron resonance (ECR) overdense plasma source are presented. The discharge was generated by introducing the circular TE11 mode wave at a frequency of 2.45 GHz into a cylindrical cavity, which is inmersed in an external static magnetic field from three solenoid coils. For magnetic field values corresponding to the ECR condition, and at pressures 10−4–10−2 Torr, in argon and methane the plasma initiation occurred with 10 W of incident power. The plasma density and temperature were measured using electric probes, and their dependence on the pressure and magnetic field are shown. Optical emission spectroscopy was carried out to identify chemically active species in the plasma. It was found that a high microwave power absorption level could be achieved by reducing the external magnetic field to values near half the resonant one, giving as result the production of a plasma with a density greater than the critical one (overdense plasma).
Coreless transformers with high coupling factor
Authors: Fontana Giorgio
Published: July 2002

A winding geometry for the construction of coreless transformers has been devised. The geometry can be employed for the construction of transformers with both a high turn ratio and high coupling factor. If made with superconductors, the transformers could find applications for matching the input coil of a SQUID to a high impedance source. A turn ratio of 1500 with a coupling factor k=0.91 has been obtained experimentally using commercial wire. The high power superconducting version of this transformer could also find application at advanced energy distribution sites.
Piezoelectric detection of vibrational overtones at cryogenic temperatures
Authors: Manzanares I. Carlos , Mina-Camilde Nairmen , Brock Ansgar , Peng Jingping , Blunt Victor M.
Published: July 2002

A resonant optoacoustic technique is described using continuous wave laser excitation and piezoelectric detection of overtone absorptions of liquefied gases at cryogenic temperatures. This technique uses a piezoelectric detector directly attached to a low temperature cell inside a cryostat. The liquefied sample inside the cell is vibrationally excited in the visible region with a continuous wave dye laser. The laser is modulated around 100 kHz with an acousto-optic modulator. The modulation frequency corresponds to an acoustic resonance frequency of the cylindrical cell which increases the sensitivity of the detection system. The pressure wave detected by the piezoelectric transducer is sent to a lock-in amplifier and processed with a microcomputer. This sensitive technique is used to obtain the visible spectra of pure liquid methane and ethane. Spectra of the fourth overtone of the C-H stretch vibration of methane, in solution with liquid argon at 94 K, and in solution with liquid nitrogen at 84 K, are also reported. Comparison is made with nonresonant and pulsed acoustic techniques.
Optimum event rate for a CCD detector
Authors: Hall B. D. , Reinhard D. , Monot R.
Published: July 2002

A simple event-counting technique is considered that can be implemented on detector systems with adjustable exposure times. A single measurement cycle has two steps: exposure and readout. During readout a threshold is used to discriminate against background noise, making it impossible to differentiate between single or multiple events. The actual event rate can be estimated by accumulating the results of repeated measurement cycles, and applying a correction based on the probability for multiple events to occur. By considering the uncertainty in the estimation of the event rate, and assuming a Poisson process, it is shown that optimum exposure requires an average event count per exposure of roughly 1.7. The technique is applied to a high-energy electron-counting system based on a linear CCD photodetector.
An optoelectronic prototype for the detection of road surface conditions
Authors: Ciamberlini C. , Innocenti G. , Longobardi G.
Published: July 2002

This paper describes an optoelectronic system suitable for road surface tests. Its purpose is to detect the presence of ice, water, or mud on road surfaces. The system uses backscattered and reflected light information. A considerable amount of the work was done to investigate scattered light patterns as they relate to asphalt conditions. Results from a laboratory prototype are presented for four asphalt conditions.
An integrated PC-based characterization system for optical waveguides
Authors: Singh B. K. , Hivarkar U. N. , Gharpure D. C. , Shaligram A. D.
Published: July 2002

This paper reports an automatic instrument developed for characterization of optical waveguides. A specially designed waveguide excitation unit offers a flexible platform for measurement of optical waveguide characteristics like number of propagating modes, mode field intensity distribution, the refractive index profiles, waveguide geometry, attenuation, and dispersion. Further, the availability of attachments like filters, polarizers, chopper, intensity profiler, and CCD camera make the instrument flexible enough for a variety of other experiments also. The instrument is PC controlled and assisted by user friendly menu-driven software. A large number of waveguides have been analyzed using the setup. These results are also presented in the paper.
A finite element analysis of room-temperature silicon crystals for the advanced photon source bending-magnet and insertion-device beamsa)
Authors: Assoufid Lahsen , Lee Wah-Keat , Mills Dennis M.
Published: July 2002

In this paper, the results of a series of thermal and distortion finite element analyses performed on room-temperature silicon for the three standard APS sources, namely, the bending magnet, wiggler A, and undulator A, are reported. The modeling was performed with the silicon cooled directly with water or liquid gallium through rectangular channels.
Distortions of the exit beam from asymmetric and inclined double-crystal synchrotron radiation monochromatorsa)
Authors: Hrdý Jaromír , Busetto Edoardo , Bernstorff Sigrid
Published: July 2002

The vertical divergence of a photon beam impinging onto a double-crystal monochromator with asymmetric crystals, and the horizontal divergence in an inclined double-crystal monochromator, cause an optical distortion of the exit beam. The consequence of this distortion is that a real point-like source is transformed into a virtual source which has a finite vertical dimension. This may manifest itself on the size of the focus when using conventional focusing optics after the monochromator. For some real sources the height of the corresponding virtual sources are estimated, and it is shown that this effect is more serious in the case of the inclined monochromator. The beam distortions are confirmed also by raytracing simulations.
Square-root valve
Authors: Houtman H.
Published: July 2002

A new type of valve is introduced, the square-root valve, in which the valve stem radius is machined to vary as the square root of the turn number N. The open area then varies in direct proportion to the turn number, and the measured flow rate Qs(N) was found to be adequate to allow this valve to be used in an automatic feedback control system. As the flow-rate function will generally depend on the source and load impedances, a systematic method to empirically obtain precise linear (or other) flow-rate functions is outlined.
All solid state switched high efficiency pulser sustainer TEA CO2 laser
Authors: Satyanarayana D. V. , Sajeev Mohan M. , Nundy U.
Published: July 2002

Operation of an UV preionized pulser sustainer TEA CO2 laser with a discharge volume of 45 cc is described. The laser could provide 522 mJ optical pulses of 6 μs duration (full width at half- maximum) with 12% efficiency for a 1:1:6 (CO2:N2:He) gas mixture at one atmospheric pressure. To the best of our knowledge, this is the maximum energy per pulse reported so far for an all solid state switched TEA CO2 laser with this efficiency.
A computer controlled flame-CFS spectrometer with photon counting detection and multipass mirror configuration
Authors: Bedenbender Heinz , Hermann Gerd M. , Lasnitschka Georg F. , Szardening Thomas W.
Published: July 2002

An automated flame coherent forward-scattering (CFS) spectrometer with a xenon high-pressure lamp has been constructed for fast sequential multielement analysis. To improve detection limits an on-axis multipass mirror system is used and, in addition, the light intensity is detected by the photon counting technique. The spectrometer is operated by a menu oriented program. Computer controlled functions, interfacing, data acquisition, and handling as well as analytical modes are described. Nonlinear analytical curves are used for evaluation and for calculating the detection limits and the analytical working range. The detection limits of the analytical system are compared with those of other CFS, AAS, and AES spectrometers. Even with a continuum light source, which allows fast sequential multielement capability, the detection limits are lower than those reported for flame CFS before. Analytical results obtained for drinking water samples are compared to measurements with flame AAS.
Technique for visualization and quantification of three dimensional intracellular ion measurements in vascular endothelial cells
Authors: Patrick Charles W. , McIntire Larry V.
Published: July 2002

A first generation digital imaging video microscopy system has been developed that is able to provide both quantitative and visual three dimensional information from individual vascular endothelial cells. More specifically, with the combination of optical sectioning, video microscopy, digital image processing and analysis, deconvolution, fluorescence ratio imaging, and scientific visualization we are able to measure the dynamic changes in spatial distributions of intracellular ions. The technique presented involves the following steps: acquiring three dimensional biological data by optical sectioning of a specimen, preprocessing the digitized volume data, experimentally determining the digital imaging system’s point spread function (PSF), deconvolving the volume data with the PSF to remove the inherent out-of-focus information, and finally postprocessing and volume rendering in order to display the volume data in a quantitative and comprehensible manner. This technique permits high resolution visualization and quantification of three dimensional spatial distributions of ions as well as traditional temporal changes in ion concentration. It has the potential to aid immensely in research since the three dimensional spatial information is often a prerequisite for understanding the molecular mechanisms involved in many complex cellular processes.
Deposition of high quality YBa2Cu3O7−x films on ultrathin (12 μm thick) sapphire substrates for infrared detector applications
Authors: Piqué A. , Harshavardhan K. S. , Moses J. , Mathur M. , Venkatesan T. , Brasunas J. C. , Lakew B.
Published: July 2002

High quality epitaxial YBa2Cu3O7−x (YBCO) thin films have been deposited on 12 μm thick (11̄02) oriented sapphire substrates using a CeO2 buffer layer. Both layers were deposited by pulsed laser deposition (PLD) using a blackbody-type heater. The YBCO films showed superconductive transition temperatures of 88–89.5 K and transition widths ≤0.5 K. Structural evaluation of the films indicate that the YBCO films are c-axis oriented, with the YBCO (005) peak showing a rocking angle full width half-maximum (FWHM) of about 0.7°. The φ-scans of the (103) YBCO peak indicate a high degree of in-plane epitaxy with no signs of high angle grain boundaries. The high quality of these films combined with the low heat capacity of the substrates, make these structures ideal for infrared detector applications.
A new apparatus for in situ photoluminescence spectroscopy in a transmission electron microscope
Authors: Ohno Y. , Takeda S.
Published: July 2002

We have developed an in situ TEM/PL apparatus, which enables us to excite PL emissions from a microscopic area of a specimen inside a TEM. The microscopical area of 20 μm can be examined by TEM, PL, and CL methods under the same experimental conditions. The apparatus may be applied to a transmission electron microscope of side-entry type with a minor modification. The apparatus is extremely useful for microscopic characterization of structural and electronic properties in an inhomogeneous material. Utilizing the apparatus, we have examined the spatial distribution of extended defects and point-defect complexes in CVD diamond. The apparatus will be utilized to study the structural and optical properties of materials under electron irradiation.
Conceptual design for a scintillating-fiber neutron detector for fusion reactor plasma diagnostics
Authors: Sailor W. C. , Barnes Cris W. , Chrien R. E. , Wurden G. A.
Published: July 2002

A conceptual design for a ‘‘pointing’’ neutron detector that is capable of delivering 104–105 Hz countrate of T(D,n) events from triton burnup at a deuterium-burning tokamak is described. The detector consists of collimated bundles of scintillating fibers that are separated by metal or polyethylene. These bundles in turn are set into a larger collimator that has some of the bundles set in ‘‘unplugged’’ holes and others in ‘‘plugged’’ holes whose countrate difference gives the net countrate. It is computed that the use of a 6 MeVee (electron equivalent) discriminator will allow 14 MeV neutron countrates of 2×104 Hz in a DD machine or 3 MHz in a DT machine, while effectively rejecting the gamma background. The efficiency-area product for 14 MeV neutrons will be ∼0.014 cm2. The angular resolution is computed to be 4.5° HWHM for a 35-cm-long collimator.
Effects of turbulent fluctuations on density measurements with microwave reflectometry in tokamaks (abstract)a)
Authors: Mazzucato E. , Nazikian R.
Published: July 2002

The short-scale turbulence of tokamak plasmas has deleterious effects on the measurement of plasma density with microwave reflectometry. Density fluctuations may lead to large amplitude and phase modulations of the reflected wave which can impair the measurement of the wave group delay, and hence the determination of the plasma density. The role played by different types of turbulent fluctuations and the limitations imposed on microwave reflectometry are discussed.
Phase contrast imaging system for TEXT-U
Authors: Chatterjee R. , Hallock G. A. , Gartman M. L.
Published: July 2002

A diagnostic to study plasma density fluctuations, phase contrast imaging has been developed for the Texas Experimental Tokamak-Upgrade. The diagnostic has a sensitivity of about 10−4 ne0 and is capable of detecting a wide range of wave numbers (0.5–12 cm−1) with a bandwidth of 500 kHz. The design of the diagnostic, some results of acoustic calibration tests, and preliminary results of simulation of expected spectra are presented.
Distributed temperature sensor using holmium-doped optical fiber and spread-spectrum techniques
Authors: Yataghene Arezki , Himbert Marc , Tardy André
Published: July 2002

This paper describes the feasibility analysis of using Holmium-doped single-mode fiber and spread-spectrum techniques to monitor a temperature distribution in the cryogenic range. An optimized holmium-doped fiber was realized and thermally characterized. For probing the sensitive fiber we realized an optical time domain reflectometer using pseudorandom sequences to improve the dynamic range at the operating wavelength and to obtain both rapid response time and high spatial resolution. The system, tested over a fiber length of 240 m, provides temperature dependent fiber attenuation measurements in good agreement with the transmission results. With a 10 MHz pseudorandom binary sequence the system detects changes of 24 °C with a spatial resolution of 30 m.
Simple technique for the evaluation of the finish of an edge using interference phenomena in a shadow region
Authors: Kanai Norikane , Ito Hiroshi
Published: July 2002

This paper proposes the simple technique for evaluating a straight edge using the interference phenomena in the shadow region of various sample edges. Evaluation is easier and more effective in the shadow region than in the bright region because of the higher sensitivity of an edge to a shadow’s diffraction pattern.
New etching procedure for silver scanning tunneling microscopy tips
Authors: Dickmann K. , Demming F. , Jersch J.
Published: July 2002

Due to its physical and chemical features silver is a promising material for scanning tunneling microscopy (STM) tips in the field of nanostructuring by a laser/STM combination. This nanostructuring is archived by field enhancement of optical radiation by a factor of up to 103 in the near field between a STM tip and a substrate. The magnitude of the field enchantment depends on the geometry and material of the utilized tip. State of the art procedures of processing silver tips cannot be applied to this application due to insufficient quality and reproducibility, respectively. We have developed a new simple single-step etching procedure for silver tips with a high reproducibility and a tip radius of less than 100 nm. This was realized by electrochemical etching in an ammonia solution and subsequent electronic controlled movement of the tip out of the electrolyte.
High ion charge states in a high-current, short-pulse, vacuum arc ion source
Authors: Anders André , Brown Ian , MacGill Robert , Dickinson Michael
Published: July 2002

Ions of the cathode material are formed at vacuum arc cathode spots and extracted by a grid system. The ion charge states (typically 1–4) depend on the cathode material and only a little on the discharge current as long as the current is low. Here we report on experiments with short pulses (several μs) and high currents (several kA); this regime of operation is thus approaching a more vacuum sparklike regime. Mean ion charge states of up to 6.2 for tungsten and 3.7 for titanium have been measured, with the corresponding maximum charge states of up to 8+ and 6+, respectively. The results are discussed in terms of Saha calculations and freezing of the charge state distribution.
Determination of recombination parameters in silicon wafers by transient microwave absorption
Authors: Gaubas E. , Kaniava A.
Published: July 2002

Principles of measurement of photoconductance transients by time-resolved microwave absorption and reflection mode are presented. The microwave transmission (absorption) mode is a new implementation of the time-resolved microwave conductivity method. This instrument is more sensitive with respect to microwave response signal and less critical to instabilities induced by phase modulation of the response. An adjustment of the measurement system into a local resonance for each particular sample under investigation and the whole set of experimental conditions is crucial to ensure the highest sensitivity and reliability of the instruments. The waveguide slot resonance antenna provides mapping of recombination parameters in silicon wafers of thickness d≥50 μm and resistivity ρ≥1 Ω cm with a spatial resolution of 1–2 mm. Theoretical models and validity of the approximations for carrier decay analysis and determination of the recombination parameters are discussed. The nonlinearities of the recombination processes (Shockley–Read–Hall, Auger type, or carrier trapping) arising at the moderate and high level of excitation are analyzed. Determination of the recombination parameters in this case is based on correlated measurements and numerical simulations taking into account the dominant recombination mechanisms. The activation energies of carrier traps Etb=0.16±0.02 eV and Ets=0.20±0.02 eV in neutron transmutation doped n-Si material have been derived from temperature dependent carrier lifetime measurements.
Digital image processing of images obtained with a Pu–Be (∼107) neutron source
Authors: Panchal C. G. , Sinha A. , Bhawe B. D. , Shyam A. , Srinivasan M. , Joshi V. M.
Published: July 2002

A Nuclear particle scintillation imaging system, developed earlier by the authors, has been upgraded and tested for its radiographic performance using a low intensity Pu–Be (∼107 n/s) source. The main objective of this work was to check the feasibility of a neutron radiography facility using a low intensity Pu–Be isotopic source and evaluate its performance. To accumulate the neutron exposure, an on-line frame integration method was used for imaging static objects. Because integrated images from the system were mottled and poor in contrast, a video image processing system was employed to enhance the quality of the integrated images. Significant improvements in image quality are seen, when image processing techniques such as smoothing, contrast stretching, edge enhancement, and histogram equalization are employed. This article provides an overview of the improvement in the image quality consequent to implementation of image processing techniques.
A multiple white light interferometer
Authors: Raz Eli
Published: July 2002

A multiple interferometer using the short coherence length of white light has been constructed and its operation demonstrated. With this apparatus, it is possible to count the number of light reflections between two parallel mirrors. The shift in fringe position resulting from differences in the optical thickness is proportional to the number of reflections between the two mirrors, enabling the resolution and measurement of a step difference of the order of 20 Å. This technique inherently has higher resolution than Michelson interferometers. As compared with Fabry–Perot interferometers, it offers an independent determination of the density of fringes, and has lower sensitivity to errors in minor parallelism. Further, the method does not require the extreme closeness in mirror spacing as compared to the Tolansky interferometer.
Fluorometer to spectrophotometer converter
Authors: Garner H. R.
Published: July 2002

A simple accessory has been constructed that will convert a standard laboratory spectrofluorometer into a spectrophotometer. This attachment fits within the sample compartment of a spectrofluorometer and consists of a cuvette holder, two mirrors, and two collimators. Light is redirected from the excitation lamp through the cuvette and then into the emission detector to measure absorbance instead of fluorescence. One to the collimators is a pinhole that greatly restricts the amount of emission light to prevent saturating the detector that is much more sensitive than is needed for spectrophotometry. This accessory is inexpensive, simple, and can preclude the need to buy both types of instruments saving money and laboratory bench space.
Microprocessor based interface unit for coupling a picosecond laser oscillator with external laser amplifiers
Authors: Navathe C. P. , Ansari M. S. , Upadhyaya J. , Sreedhar N. , Chandra R. , Kumbhare S. R. , Chakera J. A. , Gupta P. D.
Published: July 2002

A microprocessor based interface unit for coupling a commercial picosecond Nd:YLF laser oscillator amplifier to external high power Nd:phosphate glass laser amplifier stages is described. The system generates charging and firing signals required for the picosecond oscillator, and also carries out the charging and firing sequence of external amplifiers for a single shot or a repetitive mode of operation. The electronics developed is simple and modular, with sufficient scope for expansion of the system, and resistant to electromagnetic interference.
An optical heterodyne mixer based on a patterned YBa2Cu3O7−δ thin film
Authors: Tanaka Ken’ichi , Danerud Martin , Sekine Matsuo , Ohtsu Motoichi
Published: July 2002

An optical heterodyne mixing technique was developed to study the photoresponse in patterned YBa2Cu3O7−δ (YBCO) thin film. Our mixing system is composed of two identical 1.54 μm wavelength laser diodes and the laser light is introduced without optical fibers onto the YBCO thin film. We succeeded in detecting the optical signals in a YBCO thin film up to 10 GHz, which could not be achieved by the conventional direct amplitude modulated method. The YBCO photodetector has a sensitivity of D*=5.0×108 cm W−1 Hz−1/2 at 77 K. This experiment enables the observation of the fast photoresponse in the resistive state. The response can be attributed to the electron heating model.
Improvements to atomic force microscopy cantilevers for increased stability
Authors: Wenzler L. A. , Moyes G. L. , Beebe T. P.
Published: July 2002

A modification of commercially manufactured atomic force microscopy cantilevers which reduces the bending of the V-shaped legs due to changes in temperature is described. Gold-coated silicon nitride cantilevers are a bimorph system in which the different thermal expansion coefficients of the materials comprising the system can produce a temperature-dependent change in curvature. Other stress-related effects might also be responsible for the observed bending. By removing the gold film and redepositing gold only at the end of the V-shaped legs, a reduction in the bending of the cantilever is accomplished while the required optical reflectivity for the laser deflection system is retained. Imaging x-ray photoelectron spectroscopy, scanning electron microscopy, and changes in the detector photodiode signal related to bending of the cantilever are shown for modified and unmodified tips.
Optical mixing based confined alpha particle diagnostic
Authors: Umstattd R. J. , Domier C. W. , Luhmann, Jr. N. C. , Cohen B. I.
Published: July 2002

A method for probing the confined alpha particle velocity distribution function in a fusion plasma by exciting and scattering from a lower hybrid wave is described. Two microwave sources propagating perpendicular to the magnetic field optically mix inside the plasma, and the frequency of one of the sources is swept such that their difference frequency passes through a lower hybrid resonance. A third microwave source propagating antiparallel to one of the mixing sources scatters from this excited beat wave with the scattered radiation propagating antiparallel to the other mixing source. Thus, the scattered signal power can be easily recovered and used to reconstruct the alpha particle distribution function since the width of the detected resonance is proportional to the slope of the alpha distribution function.
A system to measure suprathermal electron distribution functions in toroidal plasmas by electron cyclotron wave absorption
Authors: Boyd D. A. , Skiff F. , Gulick S.
Published: July 2002

A two-chord, four-beam suprathermal electron diagnostic has been installed on TdeV (B>1.5 T, R=0.86 m, a=0.25 m). Resonant absorption of extraordinary mode electron cyclotron waves is measured to deduce the chordal averaged suprathermal electron distribution function amplitude at the resonant momentum. Simultaneously counterpropagating beams permit good refractive loss cancellation. A nonlinear frequency sweep leads to a concentration of appropriately propagating power in a narrow range of time of flight, thus increasing the signal-to-noise ratio and facilitating the rejection of spurious reflections. Numerous measurements of electron distribution functions have been obtained during lower-hybrid current-drive experiments.
Variable-frequency complex demodulation technique for extracting amplitude and phase information
Authors: Gasquet H. , Wootton A. J.
Published: July 2002

We present a variable-frequency variant of the complex demodulation technique. Complex demodulation is the digital equivalent of heterodyne detection, in which the input signal is multiplied by a carrier oscillation {exp(−iωmt)} of modulation frequency ωm and then low-pass filtered. The time-dependent amplitude and relative phase can then be computed from the filtered demodulate. This technique fails when the frequency of oscillation differs from the modulation frequency by more than the cutoff frequency of the low-pass filter. We modified the standard technique by computing iteratively a time-dependent modulation frequency {ωm(t)} that tracks the signal frequency to within ±0.1% of the Nyquist frequency. This small difference frequency allows the use of very narrow filter bandwidths for the study of narrow-band oscillations with improved signal-to-noise ratio. We apply this analysis tool to Mirnov oscillations measured by a magnetic probe and show the time variation of the amplitude of the fundamental and harmonic frequencies during a plasma current ramp down. Future work will involve the application of this technique to ECE measurements.
The ultra-soft x-ray multilayer mirror-based duochromator for the reverse field experiment reversed field pinch experiment
Authors: Carraro L. , Puiatti M. E. , Scarin P. , Valisa M. , Chkhalo N. , Kruglyakov E. P.
Published: July 2002

The ultra-soft x-ray duochromator based on two multilayer mirrors installed on the reversed field pinch experiment (RFX) reversed field pinch is described. Built at the Budker Institute of Nuclear Physics of Novosibirsk, it has been designed to monitor the time behavior of the hydrogen and helium-like resonant transitions of carbon and oxygen, the main impurities in the RFX emission spectrum, with the possibility of scanning the wavelengths between 16 and 45 Å. The wavelengths can be independently selected for both the mirrors (made of Ni/C and Cr/C layers, respectively) via a Θ–2Θ mechanism, without breaking the vacuum. The detector is based on a scintillator layer deposited on the head of a photomultiplier. Vacuum ultraviolet and visible radiation is cut by means of thin metal films (Fe, Al, Cr) deposited on a mylar substrate and on the scintillator. The wavelength resolution (λ/Δλ) of 40 to 50 in the region of interest is provided by a Soller collimator and a precollimator stage placed in front of the mirror. The relatively large etendue allows one to perform observation in a wide range of experimental conditions. Sample results of the chordal observations are compared in absolute units with the predictions of a collisional–radiative one-dimensional impurity transport code.
Bandwidth and detection limit of a crossing–sampling spectrum analyzer
Authors: Daria Vincent Ricardo , Saloma Caesar
Published: July 2002

We report the performance of a spectrum analyzer that determines the Fourier spectrum of an analog input sa(t) using only as data the time locations {ti} where sa(t) intersects with a reference sinusoid r(t)=A cos(2πWt). If A⩽|sa(t)| within the sampling period T, then one crossing exists within each interval Δ=1/2W. The spectrum is computed directly from {ti}, which consists of 2M=T/Δ crossing locations. The theoretical bandwidth and frequency resolution of the analyzer is given by 2W and 1/T, respectively. However, electronic circuits have a finite temporal response and the crossings can only be located with finite accuracy. A trade off, therefore, is expected between the measurement bandwidth and the detection limit in a real crossing-based analyzer. In our design, the accuracy can be varied to increase the bandwidth, through the use of a versatile field programable gate array. The relation between the detection limit, dynamic range, and bandwidth of our device is experimentally studied and analyzed.
Determination of field line location and safety factor in TEXT-U
Authors: Winslow D. L. , Bengtson Roger D. , Richards B. , Craven W. A.
Published: July 2002

Biasing a Langmuir probe to collect electrons creates a magnetic perturbation by drawing current along a field line. This perturbation propagates along the magnetic field as a shear-Alfvén mode and marks the affected field lines with a potential perturbation at the probe sweep frequency. This technique has been used in TEXT-U edge plasmas to locate a connection between two sensor probes separated by either 12 or 28 m along a field line, and this connection has been verified using magnetic field line tracing codes. The driver probe creates a shadow which spreads in the poloidal direction with increasing distance parallel to the magnetic field due to both the change of safety factor with minor radius and collisional effects. Determination of the radial and poloidal structure of the perturbation down the magnetic field therefore provides a measurement of the safety factor q as a function of minor radius in the edge. In addition, the technique for locating field lines has been used to establish a purely parallel connection between two floating probes and therefore provides a measurement of parallel wave number k∥⩽0.1 m−1 and parallel correlation length l∥⩾12 m.
Liquid cooled high-voltage feedthrough for the K1200 cyclotron
Authors: Pudvay D. J. , Grimm T. L. , Poe D. R.
Published: July 2002

A liquid cooled high-voltage feedthrough for the electrostatic deflectors of the K1200 superconducting cyclotron is presented. The feedthrough can deliver voltages up to 100 kV and approximately 10 W cooling down a long narrow vacuum port. The fluorinated hydrocarbon fluid used has a high dielectric strength and is vacuum compatible. Methods of increasing the cooling are discussed.
Formation of amorphous silicide nanoclusters in chromium- and titanium-implanted silica
Authors: Cattaruzza E. , Mattei G. , Mazzoldi P. , Bertoncello R. , Battaglin G. , Mirenghi L.
Published: July 2002

Amorphous nanoclusters of chromium and titanium silicides have been synthesized by implanting 35 keV chromium and 30 keV titanium ions, at a fluence of 1×1017 cm−2 in amorphous silica. The cluster stoichiometries were [Cr]/[Si]=1.6±0.3 and [Ti]/[Si]=1.1±0.3, respectively, as obtained by energy dispersive spectroscopic x-ray microanalysis and confirmed by x-ray photoelectron spectroscopy analysis. Titanium-implanted ions are more reactive than chromium ones in terms of the formation of chemical bonds with silicon of the host silica matrix.
Flexible ion conduit for use under rarefied atmospheric conditions
Authors: Hars Gyorgy , Meuzelaar Henk LC.
Published: July 2002

A tubular ion conduit has been constructed, which transports ions by convection by means of a carrier gas. Typical inlet pressures are in the 10–100 Torr range, with outlet pressures as low as 10−3 Torr. The 20–30 cm, 1–2-mm-i.d., capillary tube, made of an electrically insulating material, is surrounded by a specifically configured pair of helical electrodes (“helical dipole”), which are supplied with symmetrical voltages in the tens of volt amplitude and in 1 MHz frequency range. The vibrational average force field generated reduces the tendency of ions to hit the inner wall of the tube. This way ions can be transported with minimal loss. Previously, known ion guides are operated under molecular flow (high vacuum) conditions only, as opposed to the method described here, where the carrier gas enters under viscous flow conditions and exits as molecular flow. In addition, existing ion guides are stiff in contrast to the flexible construction described here, which can be easily and inexpensively manufactured. The ion conduit is expected to have important applications in connecting ambient or near-ambient pressure electrospray ionization or atmospheric pressure ionization type ion sources to mass spectrometers, while reducing pumping requirements, e.g., field portable equipment. Furthermore, the device may provide a means for connecting electron multiplier detectors to near ambient pressure analyzers such as ion mobility spectrometers.