bluuebunny/crossref_metadata_2025 huggingface dataset:
A portable time of flight system for thermal and cold neutron applications
Authors: Benenson R. E. , Chen-Mayer H. H. , Sharov V.
Published: July 2002

A very small Fermi-type neutron chopper fashioned by cutting slots in a boron nitride cylinder was developed for use with a source of thermal and cold (subthermal velocity) neutrons. The original goal was to characterize spectra emerging from glass capillary fibers of less than 1 mm diameter, but other applications became apparent. For approximately 1 m flight paths, conventional nuclear electronics had to be adapted to the millisecond flight times. Both time-to-amplitude converter and multiscaling time-data storage methods were used. Data corrections for the particular geometry are reviewed and applied to the present geometry. Among examples of its potential use, the spectrum of a newly installed cold source was measured.
A scanning Auger electron spectrometer for internal surface analysis of Large Electron Positron 2 superconducting radio-frequency cavities
Authors: Benvenuti C. , Cosso R. , Genest J. , Hauer M. , Lacarrère D. , Rijllart A. , Saban R.
Published: July 2002

A computer-controlled surface analysis instrument, incorporating static Auger electron spectroscopy, scanning Auger mapping, and secondary electron imaging, has been designed and built at CERN to study and characterize the inner surface of superconducting radio-frequency cavities to be installed in the Large Electron Positron collider. A detailed description of the instrument, including the analytical head, the control system, and the vacuum system is presented. Some recent results obtained from the cavities provide examples of the instrument’s capabilities.
Novel technique for investigating the temperature effect on the diffusion coefficient of naphthalene into air
Authors: Chen Ping-Hei , Miao Jr-Ming , Jian Ching-Sung
Published: July 2002

This article describes a technique that uses a piezoelectric quartz crystal microbalance (QCM) for determining the diffusion coefficient of naphthalene into air. The QCM is placed onto the open top of a closed Stefan tube and its active surface is covered with a thin layer of solid naphthalene. Due to the markedly enhanced QCM resolution of 10−9 g/cm2 over that of the conventional digital electronic balance, the QCM in this study requires much less time than previous studies using digital electronic balances for measuring the diffusion coefficient in a binary gas system. At P=0.1013 MPa and in a temperature range from 278.25 to 315.15 K, the empirical correlations to evaluate both the diffusion coefficient of naphthalene into air at 1 atm pressure and the Schmidt number of naphthalene at various temperatures are presented. The measurement uncertainty of the diffusion coefficient of naphthalene into air with the present system is less than 3%. In addition, measured results verify that the measurement of the diffusion coefficient of naphthalene into air is only slightly affected by the length of the diffusion tube if the QCM is used in the closed Stefan tube for measuring the mass flux in the diffusion tube.
Scanning probe microscopy of NdBa2Cu3Ox thin film surfaces
Authors: Badaye M. , Ting Wu , Fukushima K. , Koshizuka N. , Morishita T. , Tanaka S.
Published: July 2002

We have found that NdBa2Cu3Ox (NBCO) thin films, fabricated by the laser ablation process, have highly stable and smooth surfaces. Clear spiral patterns with 4–5 terraces are observed all over the film area with an atomic force microscope (AFM) operating in air. We have also obtained atomically resolved image of the spiral terraces using AFM, and also using ultrahigh vacuum scanning tunneling microscope. This study suggests that NBCO film is a good candidate for device applications.
Determination of CuPt-type ordering in GaInP by means of x-ray diffraction in the skew, symmetric arrangement
Authors: Liu Q. , Prost W. , Tegude F. J.
Published: July 2002

This letter presents a simple, quick, nondestructive method for the determination of ordering in Ga0.51In0.49P layers using x-ray diffractometry. The skew, symmetric arrangement of x-ray reflection was used for this purpose enabling the measurements of all allowed (hkl) reflections. Ordered Ga0.51In0.49P layers grown by metalorganic vapor-phase epitaxy at different substrate temperatures were studied. The {1/2,1/2,1/2}, {1/2,1/2,3/2}, and {1/2,1/2,5/2} reflections of the ordering-induced monolayer superlattices have been observed. The experimental results are discussed in detail, demonstrating that x-ray diffractometry is a powerful means to evaluate ordering in semiconductors.
Simple probe for variable pressure deuterium nuclear magnetic resonance studies of soft materials
Authors: Bonev Boyan B. , Morrow Michael R.
Published: July 2002

A deuterium nuclear magnetic resonance probe in which samples can be studied at pressures up to 3 kbar is described. Characteristics of this device include simple design involving a beryllium copper pressure vessel, a modular coil assembly, and containment of the sample in a sealed polyethylene tube. The probe has been designed for operation at a deuterium frequency of 23 MHz in a 100 mm bore superconducting magnet at temperatures ranging from −20 to 100 °C. The probe has been used in isobaric and isothermal studies of phospholipid bilayer headgroup orientation, phase behavior, and molecular dynamics.
A compact ultrahigh vacuum x-ray diffractometer for surface glancing scattering using a rotating-anode source
Authors: Fujii Yoshikazu , Yoshida Kenji , Nakamura Takeshi , Yoshida Kentaroh
Published: July 2002

A compact ultrahigh vacuum (UHV) x-ray diffractometer was designed and constructed using a small rotating-anode x-ray source of 18 kW. Its UHV specimen chamber is 200 mm high and 140 mm in diameter and can be evacuated up to 3×10−8 Pa. The x ray is incident into the chamber through a thin Be window, 0.2 mm thick and 30 mm in diameter. Diffracted and scattered x rays are taken out through another Be window, 0.4 mm thick and 60 mm in diameter. All the equipment, a rotating-anode x-ray source, an incident monochromator, and a two-circle diffractometer onto which an UHV specimen chamber and a conventional scintillation counter are mounted, are arranged on only one optical table, 70 cm wide and 90 cm in length. Configuration of the specimen holder in the chamber, which is designed for the surface glancing angle scatterings at present, can be controlled from outside of the vacuum. The apparatus is the best suited to in situ observations of growing crystal surfaces during the deposition. A preliminary experiment of the glancing angle scattering of mechanically polished silver polycrystal surfaces gave an order of 103 count s−1 of scattered x-ray intensity at its specular reflection angle, which is enough to derive a significant interpretation of the surface structure.
Novel bandpass electrostatic analyzer
Authors: Enloe C. L. , Agnew K. A. , Cifuentes A. F.
Published: July 2002

A novel electrostatic analyzer for energetic charged particles has been developed that has a simple geometry and has demonstrated a wide field of view (90°×4° in the prototype device). The bandpass of the device can be adjusted by changing the size of the entrance and exit apertures, and the design intrinsically retains information about the spatial distribution of the incoming particles. Comparisons between numerical simulations of the device and laboratory tests are presented.
The application of a Wien filter to mass analysis of heavy clusters from a pulsed supersonic nozzle source
Authors: Wrenger Bu. , Meiwes-Broer K. H.
Published: July 2002

A Wien filter is used for the mass analysis of small and large metal cluster ions. As the clusters are produced in a supersonic expansion source, the initial velocity obtained by gasdynamic acceleration significantly influences the measured peak positions and widths. Calculations based on the well-known theory for ions moving in crossed magnetic and electrical fields are extended to ions from supersonic expansions. They allow a mass assignment even for those (big) clusters which cannot explicitly be resolved in the Wien filter spectrum.
An up-to-date automated instrument for the characterization of microporous/mesoporous solids
Authors: Akporiaye Duncan , Plassen Martin
Published: July 2002

A high vacuum gravimetric system for measuring adsorption and desorption processes is presented. The system has been constructed using the newest technology, both with regard to the instrument hardware and software. This provides a system working over a wide pressure range, able to implement small pressure steps and monitor small weight changes, all continuously under the control of a computer through a modern graphical user-interface. The use of a microbalance allows measurements from gases and liquids with saturation pressures as low as 1 mbar. Great flexibility of the system has been maintained, both in terms of the hardware and the software, allowing easy reconfiguration to the special requirements of the particular experiment. An example is the availability of a Fourier transform infrared (FTIR) instrument which allows the simultaneous generation of IR spectra of the adsorbed surfaces species under the same pressure and temperature conditions as the isotherm develops. The function of the system is illustrated with the results from the measurement of adsorption/desorption isotherms of cyclopentane on a variety of very different adsorbents, including nonporous, microporous, and mesoporous solid oxides.
A three gun sputtering system for the deposition of superconductor/insulator multilayers
Authors: Maglic S. R. , Rippert E. D. , Yang H. Q. , Thomas C. D. , Song S. N. , Ulmer M. P. , Ketterson J. B.
Published: July 2002

A sputtering deposition system has been developed to grow high-quality superconductor/insulator multilayers specifically for use in fabricating vertically stacked Josephson junctions. A unique feature of the design is the computer control of all parameters involved in the repetitive deposition of multilayers. The computer is interfaced with stepper motors that position the substrate, and shutter wheels. Additional computer controlled stepper motors allow in situ changing of up to five contact masks. The computer is also interfaced to a gas flowmeter that controls the partial pressure of the inert and reactive sputtering gases. High-quality, reproducible multilayer films have been produced and are described. Stacked Josephson junctions have been patterned with the multilayer films and some of their electrical characteristics are presented.
Development of a depth controlling nanoindentation tester with subnanometer depth and submicro-newton load resolutions
Authors: Shimamoto Atsushi , Tanaka Kohichi
Published: July 2002

A displacement controlling nanoindentation tester was developed. It adopts a zero-balance load detection technique for measuring the application load; and an ac-modulated optical fiber displacement sensor for measuring the relative displacement between the indenter and the sample surface. The indenter is actuated by a laminated piezoelectric actuator, and the extension of the actuator is feedbacked by the relative displacement between the indenter and the sample surface. The depth controlling technique is extremely effective in suppressing the foundation-induced fluctuation and ensures 0.1 nm depth resolution in ordinary laboratory circumstances.
Technique to monitor the local temperature rise during laser irradiation of transparent dielectrics
Authors: Asbury G. , Bunton P.
Published: July 2002

A CO2 laser and xenon lamp were used to monitor the temperature rise in lithium niobate, a transparent dielectric. The CO2 laser was used to heat the sample while the xenon lamp was used to monitor the energy absorption at the band gap where the absorption is exponentially dependent upon the temperature. This technique provides a means of determining temperature rise at the laser spot with both spatial and temporal resolution. In addition, it should be applicable to many transparent dielectrics.
Powerful source of accelerated atoms for surface modification
Authors: Churkin I. N. , Volosov V. I. , Steshov A. G.
Published: July 2002

Source of accelerated atoms based on the trap with crossed fields (radial electrical and axial magnetic) is considered. Source produces simultaneously intensive (up to 20–50 mA/cm2) fluxes of accelerated (1–10 keV) atoms and slow (up to 100 eV) atoms. Accelerated atoms are formed in source volume due to the ionization of atoms sputtered from cathode surface and their acceleration by discharge radial electrical field and neutralizing inside the plasma. The features of the atomic flux formation and the atomic flux parameters are considered and discussed. Slow and accelerated atom fluxs generated by the source can be used for surface modification such as implantation and film deposition assisted by accelerated atom beam. Experiments on surface modification made with this source are considered and discussed.
Development of a multiaperture, multistage electrostatic accelerator for hydrogen negative ion beams
Authors: Watanabe Kazuhiro , Fujiwara Yukio , Hanada Masaya , Inoue Takashi , Miyamoto Kenji , Miyamoto Naoki , Ohara Yoshihiro , Okumura Yoshikazu
Published: July 2002

Voltage holding characteristics and beam optics of a multiaperture, five-stage electrostatic accelerator were investigated to demonstrate ampere class negative hydrogen ion beam acceleration up to an energy of 1 MeV for the ITER NBI. The accelerator was conditioned up to a voltage of 920 kV without beam. It was confirmed that an optimum beam perveance of the accelerator agrees well with a beam trajectory simulation. Each row of beamlet was clearly distinguished by a video camera at the optimum condition. A highest beam energy of 868 keV with an acceleration current of 19 mA for a duration of 1 s was obtained from 9 apertures of 14 mm in diameter each.
Developments at the CERN laser ion source
Authors: Haseroth H. , Kugler H. , Langbein K. , Lisi N. , Lombardi A. , Magnusson H. , Pirkl W. , Schnuriger J. C. , Scrivens R. , Tambini J. , Tanke E. , Homenko S. , Makarov K. , Roerich V. , Stepanov A. , Satov Y. , Kondrashev S. , Savin S. , Sharkov B. , Shumshurov A. , Krása J. , Láska L. , Pfeifer M. , Woryna E.
Published: July 2002

The high current, high charge-state ion beam which can be extracted from a laser produced plasma is well suited, after initial acceleration, for injection into synchrotrons. At CERN, the production of a heavy ion beam using a CO2 laser ion source is studied. The latest results of experiments with a tantalum ion beam with charge states up to 23+ and accelerated by a radio frequency quadrupole from 6.9 to 100 keV/u, are presented along with simulations of the low energy beam transport. The ion yield at the desired charge state, the pulse to pulse stability of the ion beam, and the system reliability are all of major interest. Work is under way to replace the low repetition rate free-running laser oscillator by a master oscillator and power amplifier system. The master oscillator is operational and the first results of measurements of its beam quality and stability are presented.
Measurement of negative ion beam emittance
Authors: Michaut C. , Bucalossi J. , Riz D.
Published: July 2002

The purpose of this experiment is to improve the optics of an intense H− negative-ion beam, to be used in future Tokamaks. The emittance diagnostic has been installed in the experimental setup INCA, to perform an optimization of a negative-ion injector preaccelerator. The first stage of this work consists of testing the operation of the electric-sweep scanner, to measure the beam current in the two-dimensional-phase space and to investigate the diagnostic performances. In addition to the measurement of H− angles, we can scan the angles of the fast H+ created along the beam in the transport region and test the efficiency of the electron magnetic trap installed in the second accelerator grid (extraction electrode). We also observe the presence of a neutral component. This analyzer not only provides a diagnostic of the beam divergence but also improves of the knowledge of the beam components. We studied two accelerator configurations. The first one permitted to obtain an optimal beam optics under 15 keV. Then the accelerator geometry was modified to ensure a higher optimum high voltage. We will show several experimental results performed with two accelerator configurations.
Ion beam impurity analysis of radio-frequency mass filtered broad ion beams
Authors: Schlemm H.
Published: July 2002

Broad ion beam mass filters working by a mass dependent radio-frequency acceleration of ions are a new approach to generate mass filtered broad ion beams with diameters of about 300 mm in the future. The ions are extracted from an ion source by a two grid extraction system with holes of 2.5 mm diameter followed by seven hole grids with the radio-frequency mass separator. A basic question for future successful use of this system for ion implantation is the impurity generation by sputtering of ions on the walls of the hole grids. Therefore the amount of neutral and charged impurities in the ion beam was investigated by mass spectroscopic beam analysis. It is shown that the relative amount of charged impurities in the ion beam is less than 5×10−4, and the amount of neutral impurities from sputtering is smaller than impurities created by ion-molecule interactions of the ion beam with the residual gas (basic pressure 10−8 mbar).
Noise characterization of a coherent tunable far infrared spectrometer
Authors: Viciani S. , Marin F. , De Natale P.
Published: July 2002

The different noise contributions in a coherent tunable far infrared spectrometer were measured. On the basis of this quantitative analysis, several experimental schemes to enhance the sensitivity for spectroscopy in this spectral region are proposed. In particular, a full theoretical analysis for differential detection is developed. A double-detector scheme is theoretically analyzed and it is shown that a noise reduction of up to 17 dB is achievable with this configuration. The present work should make possible quantitative forecasting of sensitivity enhancement for new, different experimental configurations.
Navigation system for a mobile robot with a visual sensor using a fish-eye lens
Authors: Kurata Junichi , Grattan Kenneth T. V. , Uchiyama Hironobu
Published: July 2002

Various position sensing and navigation systems have been proposed for the autonomous control of mobile robots. Some of these systems have been installed with an omnidirectional visual sensor system that proved very useful in obtaining information on the environment around the mobile robot for position reckoning. In this article, this type of navigation system is discussed. The sensor is composed of one TV camera with a fish-eye lens, using a reference target on a ceiling and hybrid image processing circuits. The position of the robot, with respect to the floor, is calculated by integrating the information obtained from a visual sensor and a gyroscope mounted in the mobile robot, and the use of a simple algorithm based on PTP control for guidance is discussed. An experimental trial showed that the proposed system was both valid and useful for the navigation of an indoor vehicle.
Production techniques for rare earth and other heavy negative ions
Authors: McK. Hyder H. R. , Ashenfelter J. , McGrath R.
Published: July 2002

Current nuclear structure studies demand a wide range of heavy negative ion beams for tandem acceleration. Some of the wanted isotopes have low natural abundances and many have low or negative electron affinities. For these, gas injection or the use of hydrides, oxides, or fluorides is required to achieve usable intensities. The chemical properties of the target materials, and of the additive gases used to form molecular ions, often have detrimental effects on ion source performance and life. These effects include insulator breakdown, ionizer poisoning, and the erosion or deposition of material on critical electrodes. Methods of controlling sputter source conditions are being studied on the Wright Nuclear Structure Laboratory ion source test bench with the object of extending source life, increasing target efficiency, and achieving consistent negative ion outputs. Results are reported for several heavy ions including tellurium, neodymium, and ytterbium.
Ion optics for multiple charge exchange collisions determined by means of Monte Carlo simulation
Authors: Takeuchi T. , Yamagata T. , Yonehara K. , Arimoto Y. , Tanaka M.
Published: July 2002

A novel type of polarized He3 ion source based on “electron pumping” was recently proposed. This ion source requires multiple electron capture and stripping collisions of He+3 ions with polarized alkali atoms under a strong magnetic field (2–3 T). Since these processes may induce a serious increase in the emittance and reduction of polarized beam intensity, we investigated them in detail by using the Monte Carlo simulation. It was found that there is (1) increase in the emittance results not from angular broadening but from a beam size enlargement, (2) the phenomena under magnetic field B are simplified by a collisionless phenomenon under a weaker magnetic field (effective magnetic field) Beff defined by Beff≃(λ+0/(λ+0+λ0+))B, where λ+0 and λ0+ are mean free paths for He+3 ions and He03 atoms traveling in the alkali vapor.
Transportation of intensive ion beams (invited)
Authors: Soloshenko I. A.
Published: July 2002

This proceeding considers excitation of ion and electron oscillations in a plasma formed by the beam of fast positive ions. Linear and nonlinear stages of the oscillations developing, and the influence of these oscillations on the beam transportation properties are described. Also briefly described are some techniques for the stabilization of instabilities of electron and ion oscillations in compensated ion beams.
High-frequency modulation of the four states of polarization of light with a single phase modulator
Authors: Compain Eric , Drevillon Bernard
Published: July 2002

A method for light polarization modulation is described. It allows us to independently modulate, at a high frequency, the four components of the Stokes vector of light using a single phase modulator. It works in a double-pass configuration: the polarization of light is modulated a first time by the phase modulator, and is then modified by a coupling object before being modulated a second time by the same modulator. The coupling object consists of multiple glass plates, oriented at the Brewster angle, acting as a partial polarizer and in a right angle prism acting as a phase shifter and back reflector. Its polarimetric properties are obtained from refractive index contrast effects, which provides optimized and constant properties over a wide spectral range. The phase modulator can be either an electro-optic modulator providing a very high-frequency capability (up to 100 MHz) or a photoelastic modulator providing a wide spectral range capability. It is robust because there is no moving part and simple to implement because of the presence of one modulation. It displays a high level of sensitivity because all the components are high-frequency modulated. Two applications using this modulator in a polarimeter or in a polarization states generator are described. The four modulations, having the same fundamental frequency, are easily demodulated by numerical data processing. Optimized demodulation processing, adapted to the different kind of phase modulator is described. Its adaptation taking into account the bandwidth limitation and the variation of the sampling phase, are finally presented in the case of a photoelastic modulator.
Determination of the D/T fuel mixture using two-photon laser induced fluorescence in combination with neutral beam injection
Authors: Voslamber D. , Mandl W.
Published: July 2002

Doppler-free two-photon induced fluorescence in the Lyman-α lines of H, D, and T has been suggested previously as a local and isotope-selective diagnostic of the intrinsic neutral hydrogen densities in magnetically confined fusion plasmas. In the present article, it is shown that the diagnostic potential of this method is significantly increased if it is combined with neutral atom beams whose characteristics are such that efficient production of thermal ground state atoms via charge exchange reactions is achieved. Considerably deeper plasma regions than just the plasma edge can thus be probed and local, isotope-selective information (e.g., the H/D/T density ratios) is obtained on the more relevant ions rather than on the intrinsic neutrals. Additional diagnostic possibilities, e.g., those arising from the spectroscopic investigation of the beam particles themselves, are also discussed.
The use of a high-pressure scanning tunneling microscope as a lithography tool for modifications of amorphous hydrogenated carbon films
Authors: Schwank M. , Müller U. , Wintermantel E.
Published: July 2002

The use of a modified scanning tunneling microscope (STM) working in controlled oxygen atmospheres to create structures on the surface of a steel sample covered with 10 nm amorphous hydrogenated carbon (a-C:H) is presented. The STM lithography experiments showed the capability of producing either μm sized hills or holes depending on the oxygen pressure and the other parameters such as feedback-settings, bias-voltage, and setpoint-current. It will be shown that the hills were hollow and consisted of a locally delaminated a-C:H film induced by a dielectric breakdown between tip and sample. This explains the observed mobility and elasticity of the hills. Assuming total relaxation of the a-C:H film within the hills yielded the ratio h/d=0.07–0.1. The measured geometries of the hills were in good agreement with the estimated ratios. The resistance of a hill formed by the local delamination of a-C:H was measured, yielding a semiconducting behavior. The gap voltage and the total resistance decreased irreversibly, which was interpreted as a transformation of the a-C:H film within the hill to a more graphitic state. Holes were only created when all of the following conditions were fulfilled: (a) O2 pressure greater than 1 bar, (b) low energy density dissipated in the a-C:H surface (no dielectric breakdown), (c) positive bias voltage ⩾13 V between the sample and the tip. The Fowler–Nordheim plots log(I/U2) vs 1/U for the lithography experiments that led to holes were characteristic for field emission of electrons from the tip. From this it was concluded that the process responsible for hole formation is reactive oxygen etching. Other possible processes have been excluded experimentally and theoretically, respectively. For lithography experiments performed with the feedback system on, it was possible to find lithography parameters leading to a reproducible creation of holes.
Low-coherence lock-in interferometer for ophthalmology
Authors: Oliveira A. C. , Yasuoka F. M. M. , Santos J. B. , Carvalho L. A. V. , Castro J. C.
Published: July 2002

The measurement of short distances by interferometry using low coherence light is a potential option in the study of interfaces between intraocular elements. In this article we describe an experimental device to measure the distance between such interfaces in vitro. The procedure utilizes a Michelson interferometer to generate the probe beams together with a silicate photodetector system and a lock-in synchronous amplifier. The cornea and crystalline lens thickness of a rabbit eyeball are evaluated, as well as the human cornea in preservative solution. These tests indicate the method to be efficient, easy-to-handle, of high resolution and to present a signal-to-noise ratio of up to 12. We consider the possibility of its use in obtaining information about the degeneration of intraocular structures during the preservation process.
Multistage active vibration isolation system
Authors: Richman S. J. , Giaime J. A. , Newell D. B. , Stebbins R. T. , Bender P. L. , Faller J. E.
Published: July 2002

The major obstacle to the detection of low-frequency gravitational waves with an earth-based interferometer is seismic noise. The current design of the initial Laser Interferometer Gravitational-Wave Observatory (LIGO) receiver, now under construction, projects that ground noise will limit the operating band to frequencies above 40 Hz. In this article, we describe recent progress on the JILA active vibration isolation system. This device is being constructed to demonstrate the technology needed for useful reduction of low-frequency seismic noise in a gravitational wave interferometer. It consists of three spring-mounted stages, each of which provides both active and passive isolation. To date, all of the control loops on the first two of the three stages have been closed. Together they can reduce large vibrations by at least 70 dB in both vertical and horizontal directions at 1.5 Hz and above.
Measurement of ion charge state distributions inside electron cyclotron resonance neon and chlorine plasmas by x-ray spectroscopy (abstract)
Authors: Grübling P. , Küchler D. , Ullrich A. , Werner T. , Zschornack G.
Published: July 2002

Energy dispersive x-ray spectroscopy of Kα transitions of neon and chlorine ions inside an electron cyclotron resonance (ECR) plasma is used to analyze the ion charge state distribution (CSD) inside the plasma. Basing on a computer code describing time dependent and stationary solutions of the balance equations for the CSD in ECR plasmas (considering single and multiple ionization and charge exchange processes, radiative recombination, vacancy cascades, and electron shake-off) and considering atomic properties (fluorescence yields, transition rates, x-ray energy shifts, x-ray production cross sections) of ions with different charge states, an approximation of simulated x-ray spectra to measured ones is possible. Thus the result we get is the corresponding CSD and information about the electron energy distribution function in the low energy region in the plasma.
Multiframing Mach–Zehnder interferometer for spatiotemporal electron density measurement in a field-reversed configuration plasma
Authors: Ye Maofu , Jiang Deyi
Published: July 2002

Interferometric measurement is used to establish the spatially and temporally resolved electron density distribution in high β plasma experiments. However, a series of interferograms are recorded separately on different shots. In order to avoid shot-to-shot data variation, we have developed a multiframing Mach–Zehnder interferometer system to produce multiframe interferograms on a single field-reversed configuration (FRC) plasma shot. In this interferometer system, a continuous wave He–Ne laser is used to illuminate the interferometer and the interferograms at various instances are recorded photographically by a rotating mirror framing camera at framing rates of 0.7–2.9 MHz. A simple electromechanically operated optical shutter with opening time of 300 μs was developed in our lab to gate the laser light to prevent both the considerable attenuation of laser light intensity and multiple exposure of the interferograms. The precise timing of the interferograms relative to FRC plasma discharge is determined with two optical fiber glasses pointed separately towards the first and the last microlenses in the framing camera to pick up their laser light pulse signals. Twenty-eight consecutive FRC plasma interferograms were recorded successfully on Kodak T-MAX 400 film in the first half discharge period of 10 μs with this system. From these interferograms, the spatiotemporal evolution of plasma density can be evaluated.
Feasibility studies of two-dimensional edge turbulence measurements by laser induced fluorescence
Authors: Skinner C. H. , Zweben S. J. , Levinton F. M. , McChesney J.
Published: July 2002

Edge turbulence is a key factor in the performance of fusion devices but is not well understood even after many years of research. We assess the feasibility of using laser induced fluorescence to obtain two-dimensional images of turbulent structures in the plasma. Based on theoretical expectations of density fluctuations arising from turbulence and calculations of level populations in He-like and noble gas ions we show that high signal/noise ratios (S/N>100) may be expected for experimental conditions in the magnetic reconnection experiment and on the National Spherical Torus Experiment at PPPL. Schemes include exciting the ion emission lines such as B IV 282.3 nm or Kr II 441.8 nm by a tunable laser.
Characteristics of a novel ion energy spectrum f(E∥,E⊥) analyzer in measurements of plasma flow in a magnetic mirror throat
Authors: Okubo M. , Mizuguchi N. , Okada S. , Goto S.
Published: July 2002

The new ion energy analyzer is developed to measure the energy distribution function f(E∥,E⊥) of ions lost along the confinement magnetic field [M. Okubo et al., J. Plasma Fusion Res. 70, 1102 (1994)]. The end-loss ions have larger E⊥ components compared with their E∥ components in the magnetic mirror throat. In this case, the ion energy distribution function is distorted because of the incident angle dependency of the retarding grid transmission. We try to compensate a measured energy distribution function by calculated grid transmission functions.
Modeling of passive charge exchange emission in The Joint European Torus (abstract)
Authors: Tunklev M. , Breger P. , Hellermann M. v. , König R.
Published: July 2002

Passive charge exchange (PCX) between neutral deuterium entering the plasma from the walls and ionized light impurities in a Tokamak Fusion Plasma have been investigated, and a comparison between the synthetic spectra and the experimental data is performed. In the core light impurities are fully stripped and may only be detected by the use of charge exchange recombination spectroscopy. Using a multichord spectrometer viewing various radial points from the edge to the plasma center intersecting the neutral beam injection path, a strong localized signal from active charge exchange (ACX) will be detected during the deexcitation process in the plasma ion. However, it is well known that passive charge exchange emission from neutral deuterium in the plasma blends the signal, and since calculations of particle densities are performed on the ACX, it is therefore of crucial importance to separate the ACX from the PCX. The spectra from the PCX component will carry line of sight integrated information about the plasma rotation velocity and the ion temperature throughout the plasma. By taking an initial estimate of the radial emissivity for the PCX into account as well as the ion temperature and plasma rotation profiles, one may perform the line integrated emission calculation over the various viewing lines through the plasma, and reconstruct a synthetic spectra for each viewing line. Since the emissivity is given by the reaction rate cross section and the densities of the participating ions one may, by inserting the synthetic emission into the measured spectra and performing a nonlinear least squares fit of the intensity, establish a more accurate assessment of the D0 density. The investigation shows good agreement between the experimentally observed PCX and the theoretical model, both in wavelength position and in spectral shape. The accuracy on the absolute value of the measured neutral density will be 50%, depending on the model of the decrease of the neutrals from the wall, and the error in the charge exchange cross section.
Inframetrics infrared scanner upgraded to a 12-bit digital thermography system for heat load measurements at nuclear fusion experiments
Authors: Denner T.
Published: July 2002

A commercially available Inframetrics Scanner (Modell 760) has been upgraded to 12-bit resolution in order to derive heat fluxes on tokamak devices (TEXTOR-94). The temperature resolution is high enough to detect—at the same camera settings—the small sawtoothing heat flux modulation and the large disruptive heat fluxes. Eight new boards have been developed and installed at TEXTOR-94 to perform the measurement, transmit the data from the experiment to the control room, and store the data in a PC. To ensure reliable data transmission, the data stream (1.1 MSPS) is transferred via optical fibers from the camera to the PC in the control room. The PC receives timing information from the TEXTOR-94 timing system such that a synchronization of the camera clock and the experimental clock is guaranteed. The new system includes a time reference to correct a small frequency drift of the original Inframetrics scanner. This feature permits to compare the heat flux with signals from other TEXTOR-94 diagnostics during fast events like disruptions for which the camera can also be operated in the fast line scan mode.
A self-contained, portable variable-pressure hydrostatic cell for use in low gauge pressure electromagnetic, ultrasonic, and photoacoustic studies
Authors: Oakley Barbara , Wright Forrest , Barber Gary , Latcha Michael , Kobus Chris , Grim Pamela
Published: July 2002

A simple, manually adjustable hydrostatic cell for electromagnetic, ultrasonic, and photoacoustic studies in absolute pressure ranges from 40 kPa to 5.5 MPa is described. The cell consists of two 3-mm-thick quartz windows enclosing a 1.3-cm-diameter hole bored through a 2.54-cm-long cube block of stainless steel. Four 3-mm-diameter counterbored and taper-threaded holes on the cube walls provide minimally intrusive, chemically inert ports for temperature and acoustical monitoring. Pressure is easily varied within the cell by means of a stainless steel threaded shaft with an O-ring seal at the end, situated inside a matched internally threaded housing. An example of photoacoustic waveforms acquired under conditions of varying hydrostatic pressure is provided.
New microhumidity field-effect transistor sensor in ppmv level
Authors: Chakraborty Supratic , Hara Kazuhiro , Lai P. T.
Published: July 2002

An integrated humidity sensor able to detect and measure a very low humidity concentration and higher relative humidity (RH) levels as well with the possibility of industrial application has been designed and fabricated using very large scale integration technology where thin porous Al2O3 film acts as humidity sensing material. The porous structure of Al2O3 has been obtained by anodic oxidation of a thin film of Al in sulfuric acid. During anodic oxidation, a few top atomic layers of Ta are also oxidized into Ta2O5 whose properties affect the normal sensing properties of Al2O3 and a better quality of sensor with higher sensitivity and speed is obtained. The gate insulator structure of the field-effect transistor is SiO2/Si3N4/Ta/Ta2O5/Al2O3. The device is basically an enhancement mode metal–oxide–semiconductor field-effect transistor. The drain current ID of the device is measured at constant gate and drain voltages at 25 °C and found to be sensitive up to less than ∼1 ppmv moisture concentration. The response time of the sensor in ppmv level is less than 1 s. The device is also found to be very sensitive at higher RH levels and shows a linear dependency on RH. The response and recovery times of the sensor are 2 and 6 s, respectively.
Instrumental aspects of x-ray microbeams in the range above 1 keV
Authors: Dhez P. , Chevallier P. , Lucatorto T. B. , Tarrio C.
Published: July 2002

X-ray microscopy has the capability of looking into normally opaque samples with high resolution. X rays are sensitive to elemental, structural, and chemical content and thus can provide microscopic maps of the composition and structure of a sample. X-ray microscopy has seen great growth in the last two decades in the number and types of operating instruments as well as their capabilities. This growth is due to two developments. The first is the development of high-brightness second- and third-generation synchrotron light sources that can be used with small-aperture optics. The second is a revolution in x-ray optics. In addition to the extension of commonly used visible optics, such as Fresnel zone plates and multilayer mirrors, into the x-ray regime, there has also been a dramatic improvement in grazing-incidence optics fabrication. In the range up to a few keV, Fresnel zone plates offer the highest resolution, which is below 100 nm in several instruments. Recent developments in fabrication may lead to their application at higher energies; for now, however, sub-μm diffractive microfocusing at higher energies is usually achieved by Bragg–Fresnel optics, Fresnel optics operated in reflection using either crystal planes or multilayer coatings. Although these offer very high resolution, they have small collection apertures and limited wavelength range of operation. The Kirkpatrick–Baez mirror combination remains the most popular and versatile microprobe in the x-ray regime. These systems can operate over a very broad energy range and several facilities are now operating with micron-scale resolution. We will discuss these and some newer types of x-ray focusing schemes.
A calibration method of a radio frequency magnetic probe
Authors: Yang J. G. , Choi J. H. , Kim B. C. , Yoon N. S. , Hwang S. M.
Published: July 2002

We demonstrate a simple calibration method of a rf magnetic probe by utilizing a two port network analysis method. The sensitivity (V/G) of the probe is determined by measuring the scattering parameters of S11 and S21. The magnetic field generated by the Helmholtz coil is calculated from S11 and the probe sensitivity is obtained from S21. The measured probe sensitivity is 0.1–0.6 V/G in the frequency range of 1–15 MHz.
Liquid nitrogen auto fill for temperature controlled cryogenic traps
Authors: Dennis Paul F. , Etchells Alex , Blomfield David
Published: July 2002

We describe the principle of operation and construction of an inexpensive, reliable system for the automated dispensing of liquid nitrogen from a single supply Dewar to multiple cryogenic traps. The system can be run under full computer control and in conjunction with existing designs of traps will allow unattended operation over long duty periods combined with programmed temperature cycles.
Investigation of a microwave differential cavity resonator device for the measurement of humidity in gases
Authors: Rouleau J. F. , Goyette J. , Bose T. K. , Fréchette M. F.
Published: July 2002

A resonant cavity based microwave differential device has been developed as a sensor for the measurement of small quantities of water vapor in gases. The presence of a contaminant is assessed by induced variations in the relative permittivity due to a shift in the resonant frequency of the measuring resonator. The measured output signal is related to the difference in the reflection coefficients of the measuring resonator and the reference one. A simple modeling approach of the system shows the proportionality between the difference of the reflection coefficients of the cavities and the variation in the dielectric constant. The evaluation of the minimum detectable change in the permittivity is possible using the Clausius–Mossotti equation for a binary gas mixture at a given concentration and pressure. The detection threshold is then determined by taking into account the signal-to-noise ratio of the differential setup. The estimation of the limit of detection for some practical moisture contaminated gases yields values in the low ppm level at T=293 K and atmospheric pressure. Experimental data suggest a detection threshold of 6 ppm for moisture.
Compact high-temperature cell for Brillouin scattering measurements
Authors: Sinogeikin Stanislav V. , Jackson Jennifer M. , O’Neill Bridget , Palko James W. , Bass Jay D.
Published: July 2002

A compact ceramic high-temperature cell for Brillouin spectroscopy was designed and tested. The cell can be mounted onto a three- or four-circle goniometer and allows collection of the full set of elastic constants of minerals to temperatures in excess of 1500 K from samples with dimensions of 100×100×20 μm or smaller. As a test of the instrument the single-crystal elastic constants of MgO were measured to 1510(10) K, and are found to be in excellent agreement with earlier independent results. The high-temperature cell should be useful for other types of spectroscopic measurements, and is especially useful in situations where spectral properties vary with the scattering geometry.
Fast impedance spectroscopy: General aspects and performance study for single ion channel measurements
Authors: Wiegand Gerald , Neumaier Klaus R. , Sackmann Erich
Published: July 2002

In the present work, we propose a novel technical approach in time domain impedance spectroscopy enabling both enhanced time and current resolution by an improved data analysis and hardware setup. We introduce nonstationary time-to-frequency conversion methods such as short-time Fourier transform and wavelet transform resulting in an improved time resolution. The combination of a time domain impedance spectrometer with a patch-clamp amplifier enables the resolution of gigaohm impedance at low perturbation signal amplitudes. A fast impedance spectroscopy (FIS) setup is presented which is optimized for biophysical application of single ion channel measurements in supported biomembranes. The applicability and performance of the technique is first evaluated by simulations. It is then verified by measurements on model circuits which exhibit the characteristic key properties of single ion channel measurements. Here, FIS improves the time resolution by about three orders of magnitude down to milliseconds. The general aspects derived in this work are also valid in other fields, where the spectral information of a perturbation applied on a system and its response is analyzed, e.g., mechanical impedance spectroscopy and microrheology.
NSTAR Xenon Ion Thruster on Deep Space 1: Ground and flight tests (invited)
Authors: Marcucci M. G. , Polk J. E.
Published: July 2002

After having been in development for many years at the Glenn Research Center (formerly the Lewis Research Center), the national aeronautics and space administration-designed, 30 cm, ring-cusp, xenon ion engine was launched on the Deep Space 1 (DS1) spacecraft on 24 Oct. 1998 from the Kennedy Space Center in Florida. It has since accumulated 2200 h of in-space thrusting at input power levels ranging from 0.52 to 1.96 kW, has successfully enabled the spacecraft to fly by the asteroid Braille in July 1999, and is now thrusting DS1 along a trajectory towards its comet destinations in 2001. The design, assembly, test, integration, and operation of this thruster comprise a unique path of technical determination, artful design choices, persistent engineering and analysis, and mastery of vacuum chamber operations. The testing program over the development years, the assembly and integration periods, and the flight operational period thus far have shown that the project test philosophy of segregating effects against unique causes proved itself most useful. The 8000 h life test, the culmination of the pre-launch ground test plan, not only met its goals but surpassed them with margin. This article will explain the thruster test program from beginning to end, illustrating the technical and programmatic decision making along the way. It will justify the use of engineering models as an inexpensive method of determining answers to key design questions and will explain why testing of the thruster alone only solved a portion of the system operations task. The highlight of the test program proved to be the vacuum firing of the ion engine during the spacecraft’s solar thermal vacuum test. A comparison of the preflight data with postflight data shows that high confidence was warranted for executing a successful flight to the asteroid and beyond.