bluuebunny/crossref_metadata_2025 huggingface dataset:
Automated superconductor measurements system
Authors: Pitsakis Michael N. , Wang Xingwu
Published: July 2002

The resistance measurement of superconductors over a 10–300 K temperature range is a time-consuming process due to the time the sample takes to reach each temperature setpoint. This article describes a method of measurement automation using dc instruments controlled by a personal computer (IBM or compatible PC) through the IEEE-488 interface with a minimum of human interaction. The system utilizes the four-point method to eliminate the effect of lead and contact resistance. The minimum measurable resistance is 1 μΩ, with a resolution of 0.1 μΩ and an accuracy of ±0.5 μΩ. The temperature range can cover 4.5–450 K using a diode sensor with resolution of 0.1 K and accuracy of ±0.5 K. The instrument can also be used to determine the critical current density of the superconductor.
Anomalous scattering studies with a four-circle diffractometer at BL-10A
Authors: Sasaki Satoshi
Published: July 2002

A four-circle diffractometer mounted on an alignment carriage has been installed at the branch beamline BL-10A for use with the synchrotron x rays at the Photon Factory. The optical design and diffractometry are described. This system was used for x-ray anomalous scattering studies on the ordering effect in a ternary system and the atomic distribution in superlattice films. A technique developed that can extract the x-ray intensity by anomalous scattering from total intensity was applied to studies on K-shell electrons in (Co, Ni, Zn)SiO3 and SrTiO3.
Soft x-ray analysis system for reflection, secondary electron, and fluorescence spectroscopy
Authors: Hirai Y. , Waki I. , Momose A. , Hayakawa K.
Published: July 2002

This article describes an UHV compatable soft x-ray analysis system for reflection, secondary electron, and fluorescence spectroscopy. It is equipped with a reflectometer with an angular accuracy of 0.01°. This is achieved with rotary encoders directly coupled to the rotation axes. At the same time, the system is equipped with an electron multiplier, a cylindrical mirror analyzer, and a Si(Li) detector, each for measuring total secondary electrons, photo- and Auger electrons, and fluorescence. Furthermore, it is possible to form multilayer films and analyze them in situ. The performance of the reflectometer has been tested on the beamline BL-8A at the Photon Factory. We present the results of reflectivity measurements for diamond-cut copper mirrors and Langmuir–Blodgett films.
Higher-harmonics suppressor for soft x rays
Authors: Waki I. , Hirai Y. , Momose A. , Hayakawa K.
Published: July 2002

We have developed an apparatus for suppressing higher harmonics contained in the soft x-ray output beam of grazing-incidence grating monochromators. It consists of eight pairs of total-reflection mirrors. Each pair serves as a low-pass filter with the cutoff energy different from one another. The eight pairs are designed to cover an energy range of 80–1600 eV with an efficiency of harmonic suppression better than 97%, while transmitting more than 50% of the fundamental photons. We have tested its preliminary performance on the soft x-ray beamline BL-8A at the Photon Factory. We present the observed transmission efficiencies and the effects of the harmonic suppressor on measurements of reflectivity and fluorescence spectra.
Constant deviation monochromator for the range 100 Å≤λ≤1000 Å
Authors: Ishiguro E. , Suzui M. , Yamazaki J. , Nakamura E. , Sakai K. , Matsudo O. , Mizutani N. , Fukui K. , Watanabe M.
Published: July 2002

A grazing incidence constant deviation monochromator with a spherical concave grating was fabricated for use with undulator radiation. It has a simple scanning mechanism with fixed entrance and exit slits, as well as fixed directions of incident and exit beams. It has been installed into an undulator beamline at IMS. Synchrotron radiation from a bending section also can be introduced into the monochromator by using premirrors. The energy resolution of the monochromator is better than 70 meV at the photon energy of 94 eV with 10-μm slits, when the bending magnet synchrotron radiation is used. The spot size of the zeroth-order light is 1.5(v)×2.0(h) mm2 at the distance of 1.85 m behind a postmirror. The photon flux of the undulator radiation behind the exit slit is approximately 1×1012 photons/s at the peak, when both the entrance and exit slits are 100 μm (ΔE=0.08 eV) and the stored current is 50 mA.
Pulsed current measurement of the resistive transition and critical current in high T
c superconductors
Authors: McGinnis W. C. , Jacobs E. W. , Rees C. D. , Jones T. E.
Published: July 2002

A pulsed current technique for measuring the critical transport properties of superconductors as a continuous function of current or temperature is described. Greatly reduced sample heating permits investigation of both the ‘‘weak link’’ and intrinsic properties of granular superconductors. Results obtained for various high Tc oxide superconductors provide an example of the technique’s application. Both intergranular and intragranular critical current densities are extracted from the data. Current-voltage measurements using the pulse method are corroborated by traditional dc measurements.
A 915 MHz/2.45 GHz ECR plasma source for large area ion beam and plasma processing
Authors: Asmussen J. , Hopwood J. , Sze F. C.
Published: July 2002

The technology for producing uniform, high density (1011–1012/cm3) microwave discharges over cross sections of 50 cm2 is well established. The present challenge is to extend the high density, and electrodeless benefits of microwave discharges to produce uniform densities over an area of 300–700 cm2. Such discharges have important applications for 6 to 8-in. single wafer processing and as large surface, broad beam, high current density ion sources. The design principles for scaling the 18 cm diam MPDR ECR cavity applicator technology to 38–47 cm diam are reviewed. Microwave discharges with diameters of 20–30 cm can be created when these applicators are excited with either 2.45 GHz or 915 MHz. The design and construction of a prototype cavity applicator with a 20 cm diam discharge is described. The discharge is enclosed with a 12-pole multicusp static magnetic field produced by 2-in. by 2-in. by 1-in. rare-earth magnets. Each magnet has a pole face field strength of 3 kG. The experimental test of this plasma source in argon gas excited with 2.45 GHz energy is reviewed.
A double polarization modulation far-infrared spectrometer
Authors: Da Costa V. M. , Coleman L. B.
Published: July 2002

A new far-infrared spectrometer design is described that utilizes double polarization modulation. Based on the Martin–Puplett interferometer, this new design has high sensitivity in the region between 5 and 200 cm−1 and eliminates problems due to fluctuations in the source, interferometer drift, and reduced dynamic range in studies with small sample absorption. The new spectrometer allows, for the first time, the extension of reflection-absorption spectroscopy of ultrathin films and surface coatings into the far infrared. We present far infrared reflection-absorption data of ultrathin potassium iodide films and submicron thick polyethylene oxide films. Use of the spectrometer for far infrared dichroism studies of thin polymer films and dielectric crystals and polarization-dependent normal incidence reflectance measurements is also described.
Improving the performance of ultrafast microchannel-plate photomultipliers in time-correlated photon counting by pulse pre-shaping
Authors: Cova S. , Ripamonti G.
Published: July 2002

With ultrafast microchannel-plate (MCP) photomultipliers that produce subnanosecond pulses, the commercially available circuit modules do not provide a correct constant-fraction trigger (CFT) operation. This has a detrimental effect on the resolution obtained in time-correlated photon counting experiments. In order to circumvent this CFT limitation and better exploit the ultrafast MCP performance, a simple pulse-shaping filter has been devised and experimented with. The filter can be interposed between the MCP output and the input of any commercial CFT module, without modifying the latter. The benefit of the filter is confirmed by the experimental results. With MCP samples that produced awkward resolution curves with satellite peaks and other irregular features, the introduction of the filter regularized and narrowed the curve. Also with a setup having fairly good performance, the introduction of the filter was advantageous: the full width at half maximum (FWHM) resolution improved from 75 to 55 ps.
Quightness: A proposed figure of merit for sources of low-energy, high-charge-state ions
Authors: Schmieder Robert W.
Published: July 2002

A variety of ion sources, including the EBIS and ECRIS, are distinguished by their ability to produce low-energy ions of very high charge state. It would be useful to have some figure of merit that is particularly sensitive to this performance. I propose here such a quantity, called ‘‘Quightness,’’ which is related to brightness but which enhances the contrast between sources supplying multicharged ions of low energy. The rationale for introducing this quantity, its etymology and relationship to other figures of merit, and some representative values are presented.
Nutating subreflector for a millimeter wave telescope
Authors: Radford Simon J. E. , Boynton Paul , Melchiorri Francesco
Published: July 2002

Nutating a Cassegrain telescope’s secondary mirror is a convenient method of steering the telescope beam through a small angle. Using this principle we have constructed a high performance beam switch for a millimeter wave telescope. A low mass, graphite-epoxy laminate secondary mirror is driven by linear electric motors operated in a frequency compensated control loop. By design, the nutator exerts little net oscillating torque on the telescope structure, resulting in virtually vibration free operation. The inherent versatility of beam switching by subreflector nutation allowed us to test a variety of switching waveforms without making any hardware changes. To reduce the peak stresses on the mechanical linkage between the mirror and the motors and to attain a minimum transition time between mirror positions, we use a digitally generated driving waveform tailored to the system’s transfer function. The nutator can shift the telescope beam by 10 arcminutes, a 1.25° rotation of the 75-cm-diam secondary mirror, in an interval of 8 ms and it can sustain a switching frequency of 10 Hz.
Versatile scan generator and data collector for scanning tunneling microscopes
Authors: Cutkosky R. D.
Published: July 2002

An instrument has been constructed for generating the complex scanning and data-collection sequences required for scanning tunneling microscopy. The instrument is controlled by and returns data to a laboratory computer over an IEEE 488-bus. A very high data-collection speed was achieved through the use of a digital signal-processing microprocessor coupled to a 16-bit I/O processor.
A dual resolution noncontact vibration and displacement sensor based upon a two wavelength source
Authors: Bartlett S. C. , Farahi F. , Jackson D. A.
Published: July 2002

An optical configuration, utilizing a two wavelength source is presented. Its use as both a normal heterodyne-interferometric sensor yielding nanometer resolution, and as a subcarrier system with a much enhanced unambiguous range, but reduced resolution, are discussed. A major attribute of this system is that heterodyne signal processing has been achieved without the use of a frequency or phase shifter. Preliminary results indicate the resolution of the first configuration is comparable to that achievable in interferometric systems, while the latter shows a displacement resolution of greater than 1 mm, and vibration amplitude resolution of greater than 10 μm, over a 22-cm dynamic range.
Voltage detector and sub-micrometer focusing unit for photoemission probing
Authors: Clauberg R. , Blacha A. , Seitz H. K.
Published: July 2002

A voltage detector and its connected focusing system for voltage measurements on integrated circuits by laser induced photoemission are presented. The capabilities of the system are analyzed theoretically and verified experimentally. Application to metal lines of submicrometer width and spacing is possible, combined with picosecond time resolution and a voltage sensitivity far exceeding that of electron beam probing. An excellent insensitivity to static crosstalk perturbations is demonstrated. Voltage contrast measurements and measurements of photoemission spectra have also been performed with this system.
GaxIn1−xAs multiple-quantum-wire lasers grown by the strain-induced lateral-layer ordering process
Authors: Chou S. T. , Cheng K. Y. , Chou L. J. , Hsieh K. C.
Published: July 2002

Long wavelength (∼1.55 μm) GaxIn1−xAs multiple-quantum-wire (MQWR) lasers have been grown by a single-step molecular beam epitaxy technique. The MQWR heterostructure was fabricated in situ using the strain-induced lateral-layer ordering process. The wire formation was confirmed by cross-sectional transmission electron microscopy and polarized photoluminescence spectroscopy. The 77 K threshold current densities for the MQWR laser diodes with laser cavities along [110] and [1̄10] directions show an anisotropy ratio of ∼10. Lasers with contact stripes aligned perpendicular to the quantum wire direction consistently show a lower threshold current density than those with stripes aligned parallel. The typical threshold current density for the MQWR laser with a stripe perpendicular to the quantum wires is ∼1 kA/cm2 at 300 K.
Experimental result study and design enhancement of a magnetic pulse compression circuit by using the p
s
p
i
c
e simulation program
Authors: Nehmadi M. , Ifrah Y. , Druckmann I.
Published: July 2002

Magnetic pulse compression (MPC) is widely used to drive high-power pulsed lasers such as metal vapor, excimer, and chemical lasers. A simulation program has been successfully operated for the study and enhancement of experimental results. Starting from the experimental laser voltage and current wave forms, an equivalent time-varying impedance for the laser tube has been derived. This impedance is incorporated into a simple model of the driver equivalent electrical circuit. This circuit is simulated under various changes of the MPC geometric and magnetic parameters to enhance the impedance matching between the electrical circuit and the laser tube load. Energy dissipation in the various components of the electrical equivalent circuit can be calculated by developing an equivalent circuit in the same way we developed the equivalent circuit of the load.
Automatic current control unit for electrodeposition
Authors: Scheer U. , Freitag R. , Fritz H. P.
Published: July 2002

In the course of research on the electrodeposition of ternary compound semiconductors the problem of electrolysis with up to four anodic partial current circuits arose, having different and differently changing resistances. The potential at the cathode as well as the ratio of the anodic partial currents had to be regulated. In order to handle this problem we developed an automatic electronic regulating unit, the circuit diagram of which is presented.
Diffraction grating calibration of scanning tunneling microscope piezoscanners
Authors: Poirier G. E. , White J. M.
Published: July 2002

A gold replica of a UV diffraction grating was imaged by scanning tunneling microscopy (STM) using both mechanically cut platinum and electrochemically etched W tips. The topographs are useful in calibrating x,y, and z piezocoefficients for STM piezoscanners.
Cylinder valve controller for an uninterrupted supply of cryogenic liquid
Authors: Ulvick Lisa M. , D’Evelyn Mark P.
Published: July 2002

A simple, inexpensive, solid-state controller is described which maintains an uninterrupted supply of liquid nitrogen by switching a solenoid valve from one supply cylinder to another when the first becomes exhausted. The device is used in conjunction with a commercial liquid-nitrogen level controller. The circuit uses a 7474 flip-flop as a bistable memory element, a thermistor temperature sensor, and a clock to wait an appropriate interval for the liquid-nitrogen transfer line to become cold. With minimal modification the circuit could be used with other cryogenic liquids or with compressed gases.
Reusable pressure seal for low temperature use requiring a small annular space
Authors: Clark J. C. , Chilson P. B. , Ihas G. G.
Published: July 2002

A reusable, low-temperature, super leaktight joint sealed with epoxy is presented which increases the available working area over that provided by a coventional bolted O-ring system. The seal is usable at arbitrarily low temperatures and was tested with a pressure of 70 bar with no apparent deterioration in performance. The simple method of assembly and disassembly is described and the results of various tests are discussed.
Laser-based microchemical analysis
Authors: Dovichi Norman J.
Published: July 2002

Microchemical analysis is the determination of the chemical composition of small volume samples, typically smaller than 1 mm3. The spatial coherence of the laser has been exploited by workers in many fields to probe these small volume samples. This review considers three classes of microchemical analyses: detectors for microscale separations, spectroscopic studies of minute volume samples, and laser-based microscopy. In the first case, high-sensitivity laser-based detectors are coupled with high-efficiency separation techniques to produce powerful analytical tools for submicroliter volume samples. In the second case, highly selective measurements are made on small volume samples through use of either immunological reagents or spectroscopically rich techniques. In the third case, high spatial resolution images of solid samples are created by recording a spectroscopic signal as a sample is moved with respect to a tightly focused laser beam. In each case, measurements with uniquely high sensitivity, selectivity, and spatial resolution are made possible by use of a laser beam.
Fluctuation measurements in the DIII-D and TEXT tokamaks via collective scattering and reflectometry
Authors: Peebles W. A. , Baang S. , Brower D. L. , Burrell K. , Doyle E. J. , Groebner R. J. , Lehecka T. , Luhmann N. C. , Matsumoto H. , Philipona R. , Rettig C. , Rhodes T. L. , Yu C. X.
Published: July 2002

Anomalous transport in fusion plasmas remains an enigma requiring explanation. A predictive capability is highly desirable if confinement enhancement regimes such as H mode or super shots are to be extrapolated to the next phase in development of the International Fusion program, epitomized, for example in ITER. Therefore, identification of the role that electrostatic turbulence plays in confinement is a critical issue requiring detailed experimental data capable of testing and challenging existing theoretical models. This article presents microturbulence measurements obtained on the DIII-D and TEXT tokamaks utilizing heterodyne, far-infrared collective scattering, and reflectometry techniques. The experimental systems are described on both machines and emphasis placed on results obtained during the L-H transition, ELM activity, and saturated ohmic operation where ion temperature gradient driven (ITGD) turbulence is theoretically predicted to exist.
An instrument for measuring the momentum flux from atomic and charged particle jets
Authors: Cohen S. A. , Zonca F. , Timberlake J. , Bennett T. , Cuthbertson J. , Langer W. , Motley R.
Published: July 2002

We have developed an instrument to measure the momentum flux from an intense plasma stream for which the standard techniques used for low-pressure gases (<10 Torr) at room temperature are unsuitable. With a response time of < 50 ms, this device, a plasma momentum meter, can measure forces of 10−5–103 N onto surfaces of different materials immersed in dense plasmas (n≳1012cm−3). Such forces are transmitted predominantly by ionic and neutral species, with 10’s of eV’s of kinetic energy, are accompanied by high heat fluxes, and are pulsed. The momentum flux onto a biasable target plate is transferred via a suspended quartz tube onto a sensitive force transducer, a capacitance-type pressure gauge. This protects the transducer from thermal damage, arcing, and sputtering. An absolute force calibration of the PMM to 1% accuracy has been made and is described. A flat carbon target has been used in measurements of the momentum flux of He, Ne, Ar, and Kr plasmas produced in a magnetized linear plasma device.
High mass resolution isochronous time-of-flight spectrograph for three-dimensional space plasma measurements
Authors: Möbius E. , Bochsler P. , Ghielmetti A. G. , Hamilton D. C.
Published: July 2002

By combining a toroidal electrostatic analyzer with a novel cylindrically symmetric isochronous time-of-flight mass spectrometer, we have developed an instrument that simultaneously determines the three-dimensional distribution function of ions and differentiates species. The ion mass is determined to high resolution (M/ΔM≳50) from the time of flight within a harmonic field configuration defined by hyperboloid equipotential surfaces. A second conventional time-of-flight channel makes use of particles leaving the thin entrance foil as neutrals. An additional solid state detector in which the neutrals are stopped allows the total energy and thereby the ionic charge of the incident ions to be determined as well. Information from the neutral and the ion channels can be combined to determine the total mass of an incident molecular ion and the mass of one atomic fragment. This also removes the ambiguity between molecular ions and isotopic species of the same mass. A laboratory prototype has been used to demonstrate the feasibility of the principle of operation.
A surface acoustic wave oscillator-based modulator/mixer for frequency-modulated electron nuclear double resonance spectroscopy
Authors: Clarkson R. B. , Belford R. L. , Reiner C.
Published: July 2002

A device is described that provides frequency modulation to the rf signal used in electron nuclear double resonance (ENDOR) spectroscopy. Its use results in excellent spectral (signal) baseline characteristics while allowing a digital frequency synthesizer to be employed as the source of the swept rf signal. The circuit makes use of a surface acoustic wave (SAW) oscillator as the voltage-controlled frequency source of the frequency modulation, as well as rf mixers and a 5th-order Butterworth filter to produce a spectrally clean modulated frequency output. Provision for the input of a second rf frequency for TRIPLE resonance experiments also is provided. The device can be used in any frequency range with good results, as spectra from X- and Q-band ENDOR systems illustrate.
A pulsed ENDOR probehead with the bridged loop-gap resonator: Construction and performance
Authors: Forrer Jörg , Pfenninger Susanne , Eisenegger Josef , Schweiger Arthur
Published: July 2002

A probehead for pulsed electron-nuclear double resonance (ENDOR) experiments with radio-frequency fields up to 20 mT is introduced. The probehead consists of a bridged loop-gap resonator for X-band microwave frequencies surrounded by a solenoidal rf coil that generates the radio-frequency field, and serves as microwave radiation shield. A broad band and a tuned circuit for pulsed ENDOR experiments between 1–200 and 1.5–26 MHz, respectively, are described. Details of the probehead design and characteristics of the rf circuits are given. The performance of the probehead is demonstrated by pulsed ENDOR spectra in solids and liquids between 8 and 150 MHz and by an ENDOR experiment that requires a stepping of the static magnetic field strength.
Heavy beam loading measurements of an rf accelerating cavity under amplitude and phase control
Authors: Fortgang C. M. , Jachim S. P. , Geisik C. , Gutscher W. D. , Natter E. F. , Niesen J. B.
Published: July 2002

A technique for measuring both resistive and reactive particle-beam-loading effects on an rf accelerating cavity is described. A high-power, six-port reflectometer is used to measure the complex cavity impedance, both with and without beam, as a function of cavity resonant frequency. Resistive and reactive beam loading appears as a decrease in the cavity quality factor Q and as a change in the cavity resonant frequency, respectively. An equivalent circuit model for the drive system, cavity, and beam is used to quantify these effects as a function of cavity voltage and phase, beam current, and cavity detuning. Measurements on a heavily beam-loaded two-cell drift-tube linac are compared with predictions from the equivalent circuit model and good agreement is found. The measurements are performed while maintaining constant cavity-field amplitude and phase. Thus, this technique is a nonperturbative measurement.
A completely automated flow, heat-capacity, calorimeter for use at high temperatures and pressures
Authors: Rogers P. S. Z. , Sandarusi Jamal
Published: July 2002

An automated, flow calorimeter has been constructed to measure the isobaric heat capacities of concentrated, aqueous electrolyte solutions using a differential calorimetry technique. The calorimeter is capable of operation to 700 K and 40 MPa with a measurement accuracy of 0.03% relative to the heat capacity of the pure reference fluid (water). A novel design encloses the calorimeter within a double set of separately controlled, copper, adiabatic shields that minimize calorimeter heat losses and precisely control the temperature of the inlet fluids. A multistage preheat train, used to efficiently heat the flowing fluid, includes a counter-current heat exchanger for the inlet and outlet fluid streams in tandem with two calorimeter preheaters. Complete system automation is accomplished with a distributed control scheme using multiple processors, allowing the major control tasks of calorimeter operation and control, data logging and display, and pump control to be performed simultaneously. A sophisticated pumping strategy for the two separate syringe pumps allows continuous fluid delivery. This automation system enables the calorimeter to operate unattended except for the reloading of sample fluids. In addition, automation has allowed the development and implementation of an improved heat loss calibration method that provides calorimeter calibration with absolute accuracy comparable to the overall measurement precision, even for very concentrated solutions.
Determination of depletion width of surface barrier detectors
Authors: Davis C. L. , Ouseph P. J. , O’Bryan M. Ray
Published: July 2002

A simple experimental method to determine the depletion width of a surface barrier detector is discussed. An electron spectrum of Bi207 taken with a detector having depletion width less than the range of the electrons shows an additional peak. The position of the extra peak enables us to determine the depletion width.
Application of TFTR diagnostics to study of limiter H modes (abstract)
Authors: Bush C. E. , Schivell J. , Taylor G. , Bretz N. , Cavallo A. , Fredrickson E. , Janos A. , Mansfield D. K. , McGuire K. , Nazikian R. , Park H. , Ramsey A. T. , Stratton B. , Synakowski E. J.
Published: July 2002

Circular limiter H modes with centrally peaked density profiles have been obtained on TFTR. Diagnostics used to study these unique plasmas include arrays of Dα and C ii detectors, bolometers, and Mirnov coils; x-ray imaging, charge exchange recombination spectroscopy, ECE, microwave scattering systems, and a multichannel infrared interferometer. These diagnostics have special features which allow time and space-resolved measurements during the H-mode transition and during ELMs. Microwave scattering during the H phase shows a feature in the scattered spectrum which is consistent with a poloidal rotation in the electron diamagnetic drift direction. Mirnov coil data digitized at 2 MHz show an increase in high-frequency magnetic fluctuations (60–200 kHz) during an ELM, while ECE data show 20–30 μs intense emission spikes in the outer 15–20 cm of the plasma edge.
DIII-D physics analysis database (abstract)
Authors: Bramson G. , Schissel D. P. , DeBoo J. C. , St. John H.
Published: July 2002

Since June 1986 the DIII-D tokamak has had over 16 000 discharges accumulating more than 250 Gbytes of raw data (currently over 30 Mbytes per discharge). The centralized DIII-D databases and the associated support software described earlier provide the means to extract, analyze, store, and display reduced sets of data for specific physics issues. The confinement, stability, transition, and cleanliness databases consist of more than 7500 records of basic reduced diagnostic data datasets. Each database record corresponds to a specific snapshot in time for a selected discharge. Recently some profile datasets have been implemented. Diagnostic data are fit by a cubic spline or a parabola by the in-house energy code to provide density, temperature, radiated power, effective charge (Zeff), and rotation velocity profiles. These fits are stored in the profile datasets which are inputs for the onetwo code which computes transport data.
Midplane measurements of MeV ion confinement in TFTR
Authors: Boivin R. , Kilpatrick S. , Manos D. , Zweben S.
Published: July 2002

A new detector has been designed and installed on TFTR for studying the confinement of MeV ions, especially for measuring the losses due to the toroidal field ripple. It is located just below the outer midplane where the peak in ripple-induced losses is expected. The detector consists of a scintillator [ZnS(Ag)] and collimating apertures mounted on a radially movable probe. New design features of this detector are presented along with some of the first results.
4-GHz internal MCP-photomultiplier cross correlation
Authors: Berndt Klaus W. , Lakowicz Joseph R.
Published: July 2002

We have performed sinusoidal and pulsed internal cross correlation within a Hamamatsu model R2024U gatable microchannel-plate photomultiplier (MCP-PMT) by biasing and modulating the gating mesh which is located 0.2 mm behind the photocathode. The light source used was a sync-pumped and cavity-dumped dye laser. Near the photocathode center, no effective high-frequency photocurrent modulation was achieved. However, for a circular area near the photocathode edge, useful modulation up to 4.5 GHz, the frequency limit of our amplifier, was obtained. The modulation frequency response is characterized by resonances caused by the gating mesh which represents a strong disturbance with respect to the modulation-cable termination. The shortest measured rise time for pulsed modulation was 178 ps at 700 nm. The measured pulse response is a ‘‘mirror image’’ of a response curve as observed normally because the gating pulse is sampled by the δ-like photoelectron pulse. From this observation it can be reasoned that an even higher gating speed seems to be feasible by using a better mesh construction. We have utilized the internally cross-correlated R2024U to perform frequency-domain fluorometry test measurements. Using etalon glass plates instead of fluorescent samples, delay times as short as 6 ps have been measured with an accuracy of 1 ps.
An analytical expression for the Radon transform of Bessel basis function in tomography
Authors: Wang Ling , Granetz Robert S.
Published: July 2002

Based on a previously simplified formula [Wang and Granetz, Rev. Sci. Instrum. 62, 842 (1991)], the Radon transformation of Bessel basis functions in 2-D tomography is further reduced to an analytical series expansion in terms of sinusoidal functions with known coefficients. Because there is no integration it is simpler and faster to compute than the previous expression.
Background effects in electron stimulated desorption ion angular distribution (ESDIAD) measurements on Si(111)-(7×7)
Authors: Wallace R. M. , Taylor P. A. , Dresser M. J. , Choyke W. J. , Yates J. T.
Published: July 2002

The background effect in electron stimulated desorption ion angular distribution (ESDIAD) measurements due to soft x-ray production on Si(111)-(7×7) is investigated. We find that the background intensity from a Si(111)-(7×7) surface varies linearly with incident electron beam energy and current density. It is also found that the elimination of the background effect (by subtraction) plays a crucial role in both quantitative and qualitative interpretations of digital ESDIAD measurements on silicon, as well as to similar measurements on other surfaces.
A broadband plasma radiation detector with spatial resolution based on the optical scanning of the fluorescence of a phosphor
Authors: Zurro B.
Published: July 2002

A detector which converts the line-integrated plasma radiation profile to visible light within a selected spectral range, by means of a film of sodium salicylate, is presented. The phosphor fluorescent emission is spatially scanned by a rapidly vibrating mirror and detected by a filtered photomultiplier, allowing one to measure the time evolution of plasma radiation profiles in real time. A detailed description of the detector, calibration method, and its performances in the TJ-I tokamak are included.
Semiautomated analysis of clay samples
Authors: da F. Costa Luciano , Leng Xiaoling , Sandler Mark B. , Smart Peter
Published: July 2002

Important information about physical characteristics of clays can be inferred from the distribution of the orientations of straight lines in photographs of cross sections of its samples. This article describes the development of a semiautomated system for clay analysis that is based on the application of computer vision techniques. Due to the inherent complexity of these techniques, two strategies have been used in order to reduce the execution time: an effective technique, the binary Hough transform, is applied for detection of straight lines and the transputer is used to enhance the system processing power. The article includes the characterization of the clay analysis application, the description of the binary Hough transform for detection of straight line segments, the presentation of the semiautomated system, and a complete illustrative example.
Passive microelectrode arrays for recording of neural signals: A simplified fabrication process
Authors: Peckerar Martin , Shamma Shihab A. , Rebbert Milton , Kosakowski John , Isaacson Peter
Published: July 2002

A new process for the fabrication of microelectrode arrays is developed that is fully compatible with standard integrated circuit fabrication schedules. The process involves two innovations: the use of initially thin silicon substrates (50 μm), and the use of sputtered SiO2 as a plasma etching mask. The finished electrode array consists of a very thin silicon substrate (<20 μm) that provides a mechanically stable carrier for the electrodes. The electrode metal conductors are sandwiched between two layers of polyimide films that adhere firmly to the substrate. Small electrode interface and contact windows are made with lithographically limited minimum feature sizes. Dry plasma etching is employed both to open the windows and to thin the substrate. For the former, we have determined the appropriate etching conditions and thicknesses necessary for SiO2 to be a viable mask in this step. For the latter step, the electrode profile is first etched to the final desired substrate thickness from the front (with the same oxide as the mask), and the wafer is then turned over and fully etched until the electrodes separate. Using initially thin wafers simplifies considerably this final etch.
An arrangement of two reflective photodetectors for measuring all four Stokes parameters of light
Authors: Azzam R. M. A.
Published: July 2002

A folded-path two-detector photopolarimeter for measuring all four Stokes parameters of light is described. The light beam, whose state of polarization is to be measured, strikes the two (windowless and reflective) detector surfaces at oblique incidence and with noncoincident planes of incidence. After reflection from the second detector, the beam is folded back on itself by a mirror and the feedback is interrupted periodically with a light chopper. This intermittent feedback causes square-wave modulation of the two detector outputs which provides a 4×1 current vector I. The unknown 4×1 Stokes vector S of incident light is determined by S=A−1 I, where A is a wavelength-dependent 4×4 instrument matrix which is fixed by calibration. Based on an explicit expression for det A, all potential singularities of A are investigated and are found to be readily avoidable. Optimum parameters are also specified that make A as far from singular as possible by maximizing its determinant.
Multichannel time-correlated single photon counting: Spectroscopy and time-gated imaging using a resistive anode photomultiplier tube
Authors: Courtney Scott H. , Wilson William L.
Published: July 2002

A multichannel single photon counting detection system for steady state, time-resolved luminescence spectra, time-gated imaging, or time-gated Raman is described. This system, which has approximately 80 ps time resolution, is based on a microchannel plate photomultiplier with a position-sensitive anode (Mepsicron). This detector can operate at very low light levels with excitation wavelengths from 200 nm to the near infrared. For time-resolved luminescence applications, the system simultaneously collects 1024 decays of up to 1024 spectral channels. The measured time dispersion for spectral bandwidths greater than 100 nm are shown to be negligible.
Water-cooled quasi-doubly bent crystal monochromator for Compton scattering experiments
Authors: Kawata Hiroshi , Sato Masato , Iwazumi Toshiaki , Ando Masami , Sakai Nobuhiko , Ito Masahisa , Tanaka Yoshikazu , Shiotani Nobuhiro , Itoh Fumitake , Sakurai Hiroshi , Sakurai Yoshiharu , Watanabe Yosiyuki , Nanao Susumu
Published: July 2002

Commissioning and performance of a water-cooled quasi doubly bent crystal monochromator for Compton scattering experiments are described. The monochromator consists of an array of twenty singly bent crystals. Each crystal is half immersed in liquid Ga-ln alloy contained in a water-cooled holder. This is necessary because the monochromator must be able to withstand heat load of 4 kW from synchrotron radiation from an ellipsoid multipole wiggler at the 6.5 GeV accumulation ring. The alignment procedure for twenty singly bent crystals is described in detail. Its performance is as follows; the focused beam size of 60 keV x rays is about 3 mm (vertical) and 8 mm (horizontal). The flux is 6×1012 photons/s at stored currents of 30 mA and the energy resolution is 88 eV for 60 keV x rays. Heating of various adjusting mechanisms by Compton scattered x rays from both the absorber used to suppress low energy x rays and the monochromator crystals is found to be a very serious problem for designing a high energy x-ray beamline.
An experimental apparatus to study chemisorption at surfaces by He diffractive scattering, ultraviolet photoemission, and metastable deexcitation spectroscopies
Authors: Canepa M. , Guarnaschelli C. , Mattera L. , Polese M. , Terreni S. , Truffelli D.
Published: July 2002

An experimental apparatus designed to study structural and electronic properties of surfaces is described. Ultraviolet photoemission (UPS) and metastable deexcitation spectroscopies (MDS) have been implemented in order to obtain information on electronic states in the valence-band region with different surface sensitivity. The supersonic metastable beam source is fully described and characterized by time-of-flight measurements while the characteristics of the apparatus have been tested in the study of the Ag(110) surface, clean and following the dissociative chemisorption of oxygen. Exploiting the surface sensitivity of MDS, measurements as function of the oxygen coverage allow a direct correlation between work function increase and the population of the s-p bands of the substrate near the Fermi edge. Oxygen-induced states around 7.5 eV, difficult to observe in UPS because of strong contributions from the d bands of the substrate, are also detected.
Computer-assisted magnetic core loss measurements on single strips of metallic glass
Authors: Khachan J. , Delamore G. W.
Published: July 2002

Core loss measurements on single strips of Allied Corporation’s METGLAS 2605S-2 were made using a sinusoidal magnetizing field H(t). The contribution to the core loss from the harmonics present in the flux density B(t) were eliminated numerically by using a digital storage oscilloscope to accumulate the H(t) and dB(t)/dt data which were then down loaded into an IBM/AT computer, where the numerical analysis was carried out. The measured core losses at 50, 400, and 1000 Hz are in good agreement with those obtained using the more conventional sine flux condition.
Plasma erosion rate diagnostics using laser-induced fluorescence
Authors: Gaeta C. J. , Turley R. S. , Matossian J. N. , Beattie J. R. , Williamson W. S.
Published: July 2002

We have developed and demonstrated an optical technique for measuring the sputtering rate of a molybdenum surface immersed in a xenon plasma. This approach, which may be useful in real-time wear diagnostics for ion thrusters, relies on laser-induced fluorescence to determine the density of sputtered molybdenum atoms.
Laser-prearc railgun: Development for the application to a fuel pellet injector of a nuclear fusion reactor
Authors: Tamura H. , Sawaoka A. B. , Oda Y. , Onozuka M. , Kuribayashi S. , Shimizu K.
Published: July 2002

The laser-prearc railgun, that utilizes the phenomenon of laser-induced arc formation, was constructed and tested with plastic pellet projectiles. We envision our railgun as especially well suited as a solid hydrogen pellet injector for magnetic confinement fusion. The system consisted of a gas gun for preacceleration of a pellet and a railgun for its primary acceleration. A Q-switched ruby laser was used to induce electrical breakdown of propellant helium gas behind a dielectric pellet in the railgun. The present railgun was shown to accelerate a plastic pellet up to a velocity of 2.4 km/s.
A capacitive detector to test the principle of equivalence in a free fall experiment
Authors: Pace E. , De Martini F. , Melchiorri F.
Published: July 2002

We describe a system of capacitive transducers applied to two free falling objects with the aim of detecting differential accelerations due to nonNewtonian components. The two objects have a cylindrical shape to minimize the systematic errors and they fall in a microgravity condition inside a vacuum tube released by a stratospheric balloon at an altitude of 40 km. The calibration of the capacitive transducers performed in laboratory has shown that it is possible to detect differential accelerations Δa ≲ 1.4 × 10−10 m s−2.
High-frequency fatigue testing of ferroelectric memory capacitors
Authors: Kisler Y. , Smith I. W.
Published: July 2002

Fatigue testing of typical process-development ferroelectric capacitors requires application of controlled high-frequency waveforms to a capacitor (in the nF range) whose impedance at frequencies of interest is only a few Ω. Only experimental setups which have been designed with this fact in mind will give meaningful results. We analyze a range of typical setups and give the maximum fatigue frequency for each. A simple, standard setup may only allow frequencies of 20 kHz (109 cycles in an overnight run). A well-optimized setup will work at frequencies in the MHz range, allowing reaching 1011 cycles in an overnight run.
Kevlar support for thermal isolation at low temperatures
Authors: Roach Pat R.
Published: July 2002

A cryogenic support has been developed that rigidly attaches two U-shaped aluminum beams to each other with strands of Kevlar. The Kevlar creates a very strong and stiff coupling between the beams while allowing only a very small heat to flow between them. Measurements at room temperature and at 77 K confirm the stiffness and strength of the support
Lock-in rate-window thermomodulation (thermal wave) and photomodulation spectrometry
Authors: Mandelis Andreas , Chen Zhuohui
Published: July 2002

The application of the rate-window concept, familiar from deep level transient spectroscopy, to thermomodulation and photomodulation problems via lock-in detection has been investigated. Theoretical analysis of the newly adapted technique to these problems is presented and experimental photopyroelectric and photomodulated optical reflectance results are discussed. The utilization of the lock-in analyzer as a signal transient filtering system and as a dual-gate boxcar integrator equivalent with transient thermal wave signals is examined. Optimal instrumental conditions for use with thermal and electron-hole plasma analysis methodologies are presented, and experimental results with aluminum foil, crystalline and ion-implanted Si illustrate the potential of this measurement methodology for nondestructive thermal and electronic spectrometric evaluation of condensed phases and electronic materials.
Compact, combined scanning tunneling/force microscope
Authors: Anselmetti D. , Gerber Ch. , Michel B. , Güntherodt H.-J. , Rohrer H.
Published: July 2002

We have built a combined scanning tunneling and scanning force microscope. Owing to the compact design of the instrument with Nomarski type of interferometry for lever deflection sensing, we achieved excellent stability with a total rms noise of 0.03–0.04 Å in a frequency bandwidth of 0.01 Hz–2 kHz and a spectral noise density of 2.0×10−4 Å/ √Hz at higher frequencies (≳2 kHz) using cantilevers with compliances of ∼150 N m−1. Simultaneous measurement of constant current contours, the acting forces, and the system compliance allows separation of sample topography from electronic and elastic effects.
Programmable CCD imaging system for synchrotron radiation studies
Authors: Brizard Christine , Rodricks Brian
Published: July 2002

A real-time imaging system for x-ray detection has been developed. The Computer Automated Measurement and Control (CAMAC)-based system has a charge coupled device (CCD) as its active detection element. The electronics consists of a CAMAC crate based dedicated microprocessor coupled to arbitrary wave form generators, programmable timing and analog-to-digital converter modules. The hardware flexibility achievable through this system enables us to use virtually any commercially available CCD. A dedicated CAMAC-based display driver allows for real-time imaging on a high-resolution color monitor. An optional front end consisting of a fibre-optic taper and a focusing optical lens system coupled to a phosphor screen allows for large area imaging. Further, programming flexibility, where the detector can be used in different readout modes, enables it to be exploited for time-resolved experiments. In one mode, sections of the CCD can be readout with millisecond time resolution and in another, the use of the CCD as a storage device is exploited resulting in microsecond time resolution. Three different CCDs with radically different readout timings and waveforms have been tested. The CCD characterized for uniformity, charge transfer efficiency, linearity and sensitivity is the TC215.
Time-resolved XEOL spectroscopy of new scintillators based on CsI
Authors: Belsky A. N. , Vasil’ev A. N. , Mikhailin V. V. , Gektin A. V. , Shiran N. V. , Rogalev A. L. , Zinin E. I.
Published: July 2002

Spectral and kinetic properties of the fast intrinsic ultraviolet luminescence of CsI single crystals either pure or doped by Br, Cl, Rb, or K, studied under different types of excitation at temperatures from 80 to 550 K, are presented. Since conventional models of intrinsic luminescence in their ‘‘pure’’ form fail to explain the observed properties of the UVL, a new one should be worked out taking into account collective interaction of neighboring excitations and defects, created by ionizing particles, which form clusters of excitations. It has been shown that luminescence decay time can be controlled by doping with homologs.