bluuebunny/crossref_metadata_2025 huggingface dataset:
Improved inverse photoemission detector
Authors: Prince K. C.
Published: July 2002

An inverse photoemission detector of the Geiger–Müller type is described, with a detection energy of 10.6 eV and resolution of 0.6 eV. The window material is MgF2 and the detecting gas is dimethyl ether, with argon as the multiplier gas. The detector offers a number of advantages compared with the conventional I2 /CaF2 detector, including a detection energy higher than that of previous detectors, insensitivity to temperature variations, and ease of handling because the detector gas is neither corrosive nor highly poisonous.
Improved fluorescence correlation apparatus for precise measurements of correlation functions
Authors: Schneider J. , Rička J. , Binkert Th.
Published: July 2002

A microscope-based fluorescence correlation apparatus for diffusivity measurements is described. The use of optical fibers offers not only the advantage of setup flexibility but also an improved quality of the illuminating beam. The achieved beam radius is as small as 0.4 μm, and the size of the observed volume amounts to only 10 μm3. The measured correlation functions obtained for noninteracting particles having diffusion coefficients in a large range form 10−12 to 5×10−10 m2/s are very well fitted by the theoretically expected hyperbolas.
Superconducting stepper motors
Authors: Moulthrop Andrew A. , Muha Michael S.
Published: July 2002

We describe modifications made on a commercially available stepper motor to enable it to operate at liquid-helium temperatures. The motor has a step angle of 6 deg and produces a torque of approximately 7×104 dyn cm. When the motor is coupled to an 88:1 reduction gear, approximately 5×104 ergs of heat are produced for each step.
Improved double fluorescence detector for x-ray absorption spectroscopy
Authors: Heald S. M.
Published: July 2002

An improved double fluorescence detector for x-ray absorption spectroscopy is described and compared to a standard filter-slit detector.
Apparatus for the measurement of compressibility isotherms of gases up to 10 kbar: Experimental data for argon at 298.15 K
Authors: Biswas S. N. , Trappeniers N. J. , Kortbeek P. J. , ten Seldam C. A.
Published: July 2002

An apparatus for the measurement of compressibility isotherms of gases up to pressures of 10 kbar and at temperatures between 273 and 350 K is described. It is based on a gas expansion method in which the pressure distortion of the experimental volume is evaluated by calibration with the measuring gas at lower pressures. The apparatus can easily be adapted for isochoric measurements over a wide temperature range. Measurements on argon at 298.15 K show that the method is capable of giving a precision of 0.02%–0.06% for the density, 0.1% for the pressure, and 2 mK for the temperature.
Compact low-energy Mott polarimeter for use in energy- and angle-resolved polarization studies
Authors: Tang F.-C. , Zhang X. , Dunning F. B. , Walters G. K.
Published: July 2002

A simple low-voltage (20-kV) UHV-compatible Mott polarimeter is described that incorporates an in-line retarding potential energy analyzer that, at incident electron energies ≤50 eV, provides an energy resolution of ≤0.5 eV. The polarimeter is very compact and is suitable for use in a wide variety of applications requiring energy- and angle-resolved polarization measurements.
Fluorescence microscope for real-time studies of Langmuir–Blodgett layer deposition
Authors: Riegler J. E.
Published: July 2002

A novel fluorescence microscope configuration for real-time observation of the Langmuir–Blodgett transfer is presented. It enables the imaging of any portion of the entire monolayer, including on the water subphase, on the substrate, or even on the meniscus. Studies are performed even while the layer is being deposited. Two sets of optical components, one for the visible and one for the ultraviolet spectrum, were implemented. Studies on a monolayer of dimyristoyl-L-α-phosphatidylethanolamine (DMPE) reveal domain growth and nucleation phenomena at the boundary between water-supported and deposited film. The performance of the instrument in the UV is demonstrated with pentadecanoic acid containing a pyrene probe.
Fabrication and calibration of integrated Cu–Cr thermocouple gauge
Authors: Kuo T. C. , Flattery J. , Ghosh P. K. , Kornreich P. G.
Published: July 2002

We report here the design, fabrication, and testing of an integrated thermocouple gauge. The gauge uses a thin-film Cr heater and a thin-film Cu–Cr differential thermocouple on a 5-×3-mm glass substrate. The thermocouple measures the difference between the heater and the substrate temperature. Calibration of the thin-film Cu–Cr thermocouple gauge was done by using a standard K-type thermocouple as reference. At a constant difference temperature the measured power input to the heater is a function of the surrounding vapor pressure. The thermocouple gauge was calibrated using a McLeod gauge with He, Ar, N2, H2O, and CO2 gases. Our measurements show that the range of the gauge can possibly be extended to the μTorr range. This gauge uses a standard thin-film processing technique for fabrication resulting in a lower cost of production. Also, small size makes this gauge versatile and unique in comparison to many commercial gauges.
Cs+ ion microsource
Authors: Liebl H. , Senftinger B.
Published: July 2002

The design and operation of a novel Cs+ ion source are described. It consists of a heated tantalum capillary connected to a heatable reservoir containing metallic cesium. Cs vapor streaming from the reservoir through the capillary is surface ionized at its inner wall. The ions emerging from the tip of the capillary are accelerated by a strong electric field between the tip and an acceleration electrode having a central bore. The virtual size of the source is about 10 μm in diameter. The source delivered a total current of 30 μA into a solid angle of ∼0.5 sr over a period of six weeks of uninterrupted operation on a charge of 0.5 g of metallic cesium.
Combined high-pressure photocatalytic reactor–UHV system and sample transfer device
Authors: Moshfegh A. Z. , Ignatiev A.
Published: July 2002

The design and construction of a multistage high pressure photocatalytic reactor and sample transfer device with adaptation to a surface analysis chamber are reviewed in detail. The apparatus consists of four components: (i) a small stainless-steel high-pressure photocatalytic reactor with gas handling section, (ii) a gas product detection chamber with quadrupole mass spectrometer (QMS), (iii) an ultrahigh-vacuum (UHV) surface analysis system, and (iv) a bellows-type sample transfer device incorporated with a worm gear. The reactor, which has a total internal volume of ≂320 ml, is capable of operation under dynamic (flow) or static (batch) modes. It includes a sapphire view port to enable the study of the influence of UV-visible photoirradiation on low surface area (≊1 cm2) metal and metal oxide catalysts in various heterogeneous catalytic reactions. The catalyst sample can undergo any chemical process within the pressure range of from ≂1×10−9 to 2×10+3 Torr and over a temperature range of 80–1100 K. The catalyst can be positioned at three different stages for parking and loading, chemical reaction processes, and surface analysis. The sample transfer device has the ability to translate the catalyst under UHV conditions from the parking and loading stage to the surface analysis chamber (a distance of 620 mm). Before and/or after any chemical process, the surface of the catalyst can be characterized by AES, XPS, UPS, ESDIAD, and TDS techniques in the surface analysis system.
Auroral height-measuring system designed for real-time operation
Authors: Steen Åke
Published: July 2002

The altitude and altitude distribution of auroral emissions, such as the [N+2] λ427.8-nm emission, are one result of processes in the ionosphere and magnetosphere during periods of auroral activity. A bistatic height-measuring system (HMS) has been developed with the primary objective of determining the altitude and latitude of auroral emissions in the magnetic meridian plane through Kiruna, Sweden. Since significant morphological redistributions occur in the aurora within a few seconds, HMS was designed to measure auroral altitudes with a time resolution of 1.5 s. The base line between the two stations was short (13 km), which generated similar-looking meridian profiles of the measured auroral emissions. The meridian profiles were obtained with intensified photodiode arrays, operated in a monochromatic imaging mode. The hardware and software configurations of HMS and essential assumptions for the triangulation procedure are described. HMS is especially adapted to measure during periods of disturbances in auroral arcs, e.g., eastward-traveling folds. The estimated optimal accuracies of the determinations of the latitudinal position of an auroral arc and the altitude of an identified auroral point are ±0.01° and ±1 km, respectively.
High-performance GaAs polarized electron source for use in inverse photoemission spectroscopy
Authors: Kolac U. , Donath M. , Ertl K. , Liebl H. , Dose V.
Published: July 2002

The design and operating properties of a GaAs polarized electron source are presented. An electron optical system is described that passes more than 80% of the emitted electrons at 10 μA to the target under low-energy (7–20 eV) parallel beam conditions. Laser excitation can give rise to abnormal energy distributions of the photoemitted electron beam. The existence of longitudinal modes gives a possible explanation for this behavior, which can be avoided using a mode stabilized light source. The overall performance of the polarized electron source is demonstrated by inverse photoemission spectra from Ni(110).
Time-resolved doubly bent crystal x-ray spectrometer
Authors: Hockaday M. P. , Wilke M. D. , Blake R. L. , Vaninetti J. , Gray N. T. , Nedrow P. T.
Published: July 2002

X-ray spectroscopy is an essential tool in high-temperature plasma research. We describe a time-resolved x-ray spectrometer suitable for measuring spectra in harsh environments common to many very high-energy density laboratory plasma sources. The spectrometer consisted of a doubly curved Si(111) crystal diffraction element, a WL-1201 (ZnO:Ga) phosphor, a coherent fiber-optic array, and two visible streak cameras. The spectrometer design described here has a minimum time resolution of 1.3 ns with 2.8-eV spectral resolution over a 200-eV-wide bandpass in the 6–7-keV region of the spectrum. Complete system spectral throughput calibrations were done at the Cornell High Energy Synchrotron (CHESS). Details of the design and calibration results are presented.
Low-divergence, high-brightness lithium ion source for plasma diagnostics
Authors: Thomas D. M. , West W. P. , McCormick K.
Published: July 2002

Plasma diagnostics employing energetic lithium beams are in routine use on several present-day tokamak experiments. These measurements are constrained by the availability of a suitable lithium ion source. Necessary and/or desirable parameters include narrow energy spread, high-emission current density, simplicity, and long lifetime. The existing ion gun on the TEXT experiment uses the thermionic emitter β-eucryptite and meets the above requirements, except for being limited to a useful emission of about 4 mA. We will present design criteria and accelerator results for a new ion gun capable of 15-mA emission based on an increased emitter area. Important design considerations are the thermal and mechanical properties of the large (∼20 cm2) emitter area and the ion optics required to focus the emitted flux into a beam of ∼1-cm2 cross section. The potential improvement in the performance of both the TEXT and ASDEX diagnostic systems will be discussed.
Advances in heavy-ion beam probing
Authors: Connor K. A. , Crowley T. P. , Hickok R. L. , Carnevali A. , Schoch P. M. , Resnick J. , Simcic V. , Schatz J. G. , Heard J. , Aceto S. C. , Lewis J. F.
Published: July 2002

Recent applications of heavy-ion beam probes on such devices as the TEXT tokamak have shown the importance of increasing the capabilities of both the beam injection and detection systems. To this end we have investigated a new solid-state ion detector that will substantially improve spatial resolution. The application of the diagnostic technique on substantially larger devices will also require new electrostatic energy analyzer geometries, which are also under investigation.
Relative intensities of 2.5- and 14-MeV source neutrons from comparative responses of U-238 and U-235 detectors
Authors: Jassby D. L. , Hendel H. W. , Bosch H.-S.
Published: July 2002

The response of polyethylene-moderated U-235 fission counters is only weakly dependent on incident neutron energy, while the response of unmoderated U-238 or Th-232 fission counters increases strongly with energy. A given concentration of D–T neutrons in a mixed DT–DD source results in a unique relative detector response that depends on the parameters R14 and R2.5, where R14 is the ratio of the unmoderated U-238 and moderated U-235 detector efficiencies for a pure 14-MeV neutron source, and R2.5 is the corresponding ratio for a pure 2.5-MeV source. We have recently determined R14 and R2.5 using D–D and D–T neutron generators inside the TFTR vacuum vessel. The results indicate that, for our detector geometry, the ratio of U-238 to U-235 count rates should increase by a factor of about 3 when the fusion neutron source changes from pure D–D to pure D–T. This calibration is being applied to recent TFTR ‘‘supershot’’ data, where the uncollided neutron flux in the postbeam phase contains a high proportion of D–T neutrons from the burnup of D–D tritons.
Multichordal visible/near-UV spectroscopy on the DIII-D tokamak
Authors: Seraydarian R. P. , Burrell K. H. , Groebner R. J.
Published: July 2002

A pair of visible/near-UV spectrometers with eight viewing chords apiece have been installed on the DIII-D tokamak. Each system views a neutral heating beam and can acquire up to 250 complete spectra from each chord with 5–20-ms time resolution. Each viewing chord covers 60 Å with 0.27-Å spectral resolution, and the chords span about (2)/(3) of the plasma’s full width. By viewing Doppler-broadened spectral lines from charge exchange recombination (CER) reactions between beam neutrals and plasma ions, ion temperatures up to 4 keV have been measured, and the bulk Doppler shift of these same lines has yielded plasma rotation velocities up to 200 km/s. The constancy of temperature on a magnetic flux surface and the rigid rotor model of a flux surface have been confirmed. These instruments have also been used to measure the neutral beam deposition profile, and preliminary experimental results agree with theoretical calculations of the beam deposition profile.
Design aspects of a modular instrumentation system for thermal diagnostic studies
Authors: Rubey Wayne A. , Grant Richard A.
Published: July 2002

A laboratory instrumentation system has been developed which provides flexibility for conducting an extensive range of thermal investigations of organic materials. Test samples can be of gaseous, liquid, solid, polymeric, composite, or even multiphase nature. This modular system uses an interchangeable test-cell assembly concept for performing laboratory experiments and physical simulations. Incorporated in-line instrumental analysis techniques provide sensitive and comprehensive effluent analyses of the thermal-related degradation behavior.
Improved magnetic suspension densimeter for biochemical reactions
Authors: Gillies G. T. , Kupke D. W.
Published: July 2002

An improved version of our magnetic suspension densimeter has been developed for use with samples of aqueous systems as small as 100 μl. The instrument’s sensitivity to a change in density of the solution under test (measured as a voltage shift) is 0.1 mV≊4.5×10−6 g ml−1, with a base-line drift less than 9 μV/h. The nonlinearity of the densimeter’s response is less than 5 ppm over its calibration range. In this paper, we describe the new magnetic suspension circuit, discuss the precision limits of the instrument, and present the results of measurements made on a tetracarboxylate sequestering agent known as BAPTA which we use as a calcium-ion indicator.
A very low-noise FET input amplifier
Authors: Jefferts Steven R. , Walls F. L.
Published: July 2002

We describe the design, schematics, and performance of a very low-noise FET cascode input amplifier. This amplifier has noise performance of less than 1.2 nV/(Hz)1/2 and 0.25 fA/(Hz)1/2 over the 500 Hz to 500 kHz frequency range. With modest changes it could be extended to a wide variety of uses requiring low-noise gain in the 1 Hz to 30 MHz frequency range.
A new high-pressure cell for differential pressure-jump experiments using optical detection
Authors: Quednau Jürgen , Schneider Gerhard M.
Published: July 2002

A differential pressure-jump autoclave with optical detection is described, which is capable of performing pressure jumps of about 150-bar amplitude to either lower or higher pressures within the absolute pressure range up to 2.5 kbar. The principle of a rupture diaphragm is applied and the mechanical relaxation time of the apparatus is about 0.1 ms. Optical detection either of transmitted light or scattered light under an angle of 90° can be utilized to follow the progress of a chemical reaction. A test of appliction is given for the reaction of Ni with Murexide in aqueous solution.
A new ultra-high vacuum scanning tunneling microscope design for surface science studies
Authors: Poirier G. E. , White J. M.
Published: July 2002

We have constructed a new scanning tunneling microscope (STM) designed especially for surface science studies. The novel feature of this design is a sample holder that can be backed away from the STM and then rotated about the central axis of a typically configured UHV chamber. This integrated sample holder design allows simple, rapid sample transit between scanning tunneling microscopy and a number of other surface analytical techniques. All sample motion is accomplished with a single UHV motion feedthrough. Atomic resolution images of highly oriented pyrolytic graphite and current voltage curves obtained with the STM are shown.
Piezoelectrically driven X
Yθ table for submicron lithography systems
Authors: Sugihara Kazuyoshi , Mori Ichiro , Tojo Toru , Ito Chikara , Tabata Mitsuo , Shinozaki Toshiaki
Published: July 2002

A newly designed piezoelectrically driven XYθ table has been developed for submicron lithography systems. The XYθ table was fabricated using a monolithic plate structure, joined together with flexure hinges and driven by an inchworm function. This function involves the periodic clamping and unclamping of four blocks and the expansion and contraction of piezoelectric actuators. The XYθ table can travel a long distance with fine positioning in the X, Y, and θ directions. The velocities can be controlled up to 0.5 mm/s in the X and Y directions, and 0.3×10 −2 rad/s in the θ direction by changing the inchworm function stepping rate. Positioning accuracy of less than 1 μm in the X and Y directions, and 7.5×10−6 rad in the θ direction can easily be obtained using a servo system with a 0.5-μm measuring resolution.
Magnetic needle rheometer
Authors: Chu Benjamin , Hilfiker Rolf
Published: July 2002

A magnetic needle rheometer has been developed. Its principle of operation is identical to the one of a magnetic sphere rheometer, except that the magnetic sphere is replaced by a magnetic needle. Important advantages result from this modification: (i) The lower limit of measurable viscosities (≂0.3 cP) becomes several orders of magnitude lower; (ii) analytic expressions for shear rate and shear stress have been derived; (iii) the needle can be covered by using a quartz capillary tubing, which is chemically much more inert than any magnetic material; (iv) precise determinations (±0.1%) of fluid densities, especially at high temperatures, are possible; and (v) the cost of manufacturing magnetic needles is much lower than for magnetic spheres. The device has been tested with viscosity standards.
A high-speed photomultiplier gating circuit for luminescence measurements
Authors: Yoshida Thomas M. , Jovin Thomas M. , Barisas B. George
Published: July 2002

A high-speed, normally on, gating circuit has been developed for linear-focused photomultipliers such as the EMI 9816. The gate is capable of attenuating photomultiplier response by >5000:1 with a turn-off and turn-on time of 60 and 40 ns, respectively. The circuit is compact enough to fit in a standard photomultiplier housing and has low enough power consumption to run off the photomultiplier high-voltage supply. The high speed and high extinction efficiency make this gate suitable for pulse rejection in low-light level, submicrosecond, time-resolved luminescence measurements.
Fast-responding chemiluminescent ozone analyzer for respiratory applications
Authors: Ben-Jebria Abdellaziz , Ultman James S.
Published: July 2002

With the eventual goal of measuring ozone (O3 ) uptake distribution in human lungs, we developed a fast-responding chemiluminescent O3 analyzer. As the instrument will be used to sample gases respired by human subjects, it is necessary that the reacting species be nontoxic. We chose to test ten alternative alkenes known to be biologically inert. For each of the alkene reactants, we measured the effect of reacting species flow, reaction cell pressure, and ozone inlet fraction. At fixed ozone fraction, the analyzer output reaches a well-defined maximum value at an optimum reaction cell pressure and the signal reaches a plateau value at a critical reacting flow. Operating at the optimum pressure and critical alkene flow, the ozone calibration curve is nonlinear for seven of the alkenes. It appears, however, that the calibration curve can be made linear by operating at a pressure above the optimum value. Comparison of analyzer performance among the ten alkenes indicates that the most effective reacting species is 2-methyl-2-butene. Using this vapor, the analyzer exhibited a linear calibration curve with a resolution of 20 ppb O3 and a 90% step response of 200 ms at a sampling flow of 3 mℓ/s and a reaction cell pressure of 107 Torr. By increasing sampling rate, it may be possible to improve dynamic response further.
Rapid-scanning spectrometer based on fiberoptics applied to flames
Authors: Olsson Jim O. , Lenner Magnus , Wallin Svante , Uneus Leif
Published: July 2002

A rapid-scanning optical spectrometer based on fiberoptic probes, used to measure radical emission in low-pressure premixed laminar flames, is presented. Emission spectra and intensity profiles as a function of height above the burner have been recorded for OH, CH, and C2 in an ethylene/oxygen/nitrogen flame (14% C2 H4 , 64% O2 , 22% N2 ), stabilized at 5 Torr on a sintered stainless-steel burner. The emitted light was guided from the flame reactor to the spectrometer by fused silica optical fibers. Rapid scanning (100 scans/s) eliminates the effects of turbulence and temporal signal fluctuations, as 104 –105 scans over a preset spectral window are collected and signal averaged within a few minutes. The technique is discussed and compared to classical methods in flame spectroscopy.
Measurement of adsorbed F atoms on a HF treated Si surface using infrared reflection absorption spectroscopy
Authors: Yamada Yoshiyasu , Hattori Tadashi , Urisu Tsuneo , Ohshima Hisayoshi
Published: July 2002

Si(111) surface treated with HF solution was studied using Fourier transform infrared reflection absorption spectroscopy for the observation of Si–Fx bond absorption and x-ray photoelectron spectroscopy for the identification of the adsorbates on the Si surface. Two absorption peaks were observed in the range of 905–925 cm−1, and they were assigned to Si–F2 symmetric stretching mode at 918 cm−1 and Si–H2 bending mode at 910 cm−1. The absorption peak of Si–F2 distinctly decreased with de-ionized water rinse, though the Si–H2 peak hardly changed. The absorption peak of Si–F was not observed in all spectra. This result indicates that F atoms selectively adsorbed at a step region rather than on a terrace region on Si(111) surface after HF treatment.
A new detection scheme for Fourier transform-ion cyclotron resonance spectrometry in Penning traps
Authors: Schweikhard L. , Blundschling M. , Jertz R. , Kluge H.-J.
Published: July 2002

A new detection scheme for Fourier transform-ion cyclotron resonance (FT-ICR) studies is proposed and initial experimental results are presented. While in conventional FT-ICR, the difference of the transient signals from two opposite electrodes is recorded and Fourier transformed, it is also possible to use the sum of these signals. In this way resonances are observed at the harmonic of the reduced cyclotron frequency 2 ν+ as well as ν+−ν− and ν++ν−, the later being important for accurate mass measurements. The experiments were performed with a Penning trap in an electromagnet.
A flexible high-energy toroidal grating monochromator at Bessy
Authors: Bernstorff S. , Braun W. , Mast M. , Peatman W. , Schroeter T.
Published: July 2002

A toroidal grating monochromator, the HE-TGM-2, designed for medium high resolution and high transmission in the spectral range 100–730 eV, has been installed and tested at the Berlin electron storage ring BESSY. Having a conventional configuration, namely a prefocusing mirror and an entrance slit, the resolution of the HE-TGM-2 is essentially independent of the source size and position of the stored electron beam. Gas phase photoionization spectra of free atoms and molecules as well as photoemission experiments on solid surfaces have been used to characterize this monochromator.
A trial construction of a secondary electron multiplier with ring-shaped dynodes
Authors: Inaba S.
Published: July 2002

A box-grid type of secondary electron multiplier with ring-shaped dynodes has been constructed. In this multiplier, since the area of the later dynode becomes larger, output current shows no saturation by the space-charge effect at high current (70 μA).
Ultrasoft (C,N,O) x-ray fluorescence detection: Proportional counters, focusing multilayer mirrors, and scattered light systematics (invited)
Authors: Fischer D. A. , Colbert J. , Gland J. L.
Published: July 2002

Ultrasoft x-ray detection is discussed as applied to the fluorescence yield near edge spectroscopy (FYNES) technique. We describe a progression of improved ultra-high vacuum compatible soft x-ray proportional counters for FYNES measurements. The importance of energy dispersive detection is discussed and examples shown. Scattered light background problems are quantified and compared for several real samples. Finally, focusing multilayer mirror collection is introduced for reducing scattered light background and improved elemental differentiation in the fluorescence signal.
Simple, high-voltage, square pulse generator for ion beam deflection in a neutron generator
Authors: Tomić Davor
Published: July 2002

A fast rise time, low repetition rate, high-voltage, square pulse generator with double-diffused-metal-oxide-semiconductor (DMOS) switching is described. It has been developed for ion beam deflection at an electrostatic deflector in a beam guide system of a neutron generator. The features of the generator are: 1.7 kV amplitude, variable frequency from 2 to 50 Hz, variable width from 0.5 to 5 μs, and 125 ns delay. Output pulses are free of overshoot and backswing with rise and fall times of approximately 45 ns and 5 μs width.
4He cryostat with sample interlock for analysis of superconducting materials and devices
Authors: Askew T. R. , Flippen R. B. , Swartz E. T.
Published: July 2002

We have constructed 4He cryostats which accept samples up to 1.5 in. diam and can be inserted into storage Dewars having large diameter necks. These cryostats are constructed from simple and inexpensive parts, allow temperature controlled operation from 4.2 to 300 K, provide for rapid thermal cycling, and have a load/lock system to prevent exposure of the samples to air or water and to protect lab occupants from toxic materials. Design and construction details are presented and temperature control performance is discussed. Although the cryostat is designed for analysis of superconducting devices, it is useful whenever samples of several cubic inch volume need to be analyzed over a wide cryogenic temperature range with thermal stability and environmental control.
An easy to construct, economical, safe, high-pressure magnetic pump for pressures to 140 MPa suitable for circulation of supercritical fluids
Authors: Drake Bruce D. , Dunbar Michael T. , Smith Richard L.
Published: July 2002

A simple new design for a high-pressure magnetic pump is described. The pump requires minimal machining, requires no lubricant or seals, and uses no special alloys, resins or polymer components, internally. The pump described could circulate supercritical carbon dioxide and methanol mixtures satisfactorily and could achieve pumping rates of 200-cm3/min water at atmospheric pressure and 30-cm water head. The pump is assembled primarily from commercially available parts at a total 1989 cost of approximately $300 plus the cost of the motor and drive.
An efficient high-repetition-rate fast-pulsed gas valve
Authors: Corat E. J. , Trava-Airoldi V. J.
Published: July 2002

In this work we present an alternate concept of a fast-pulsed valve which is convenient for molecular-beam spectroscopy and gas puffing in plasma assemblies. The valve operates at repetition rates up to 100 Hz with repetitive high-intensity 100-μs FWHM pulses. Its efficient closed magnetic circuit with low power consumption permits a high-repetition-rate operation. The very light mass-spring assembly allows for rather narrow repetitive pulses. The valve has a small size and is self-sealed for use with corrosive gases. A fast PVDF pyroelectric detector was used for diagnosis.
Simple prism coupling technique to measure the refractive index of a liquid and its variation with temperature
Authors: Shenoy M. R. , Roy Sukhdev , Thyagarajan K.
Published: July 2002

We present a simple and novel prism coupling technique for the measurement of the refractive index of a liquid and its variation with temperature, which is typically ∼10−4/°C. The proposed experimental setup is based on a simplified version of the conventional critical angle method, and uses components easily available in an undergraduate laboratory. Experimental details and results of the measurements carried out on water and ethyl alcohol are reported, along with a discussion on the various sources of error. The measured values of the refractive indices and their temperature dependence are in good agreement with the standard values. Errors in the measured values of refractive index and its variation with temperature are less than 0.1% and 10%, respectively. The most attractive feature of the proposed technique is the simplicity of the experimental set up, which consists only of a prism and a light source (preferably a laser source).
Analysis of the expected resolution of the electron-cyclotron emission crossed-sightline magnetic field diagnostic
Authors: Hanson G. R. , Thomas C. E.
Published: July 2002

The local value of the magnetic field B(r) inside the plasma in magnetic fusion experiments is a quantity of considerable interest. Given information about plasma density and temperature it can be used to calculate the poloidal magnetic field, or given a zero current device (or the current profile) the local value of beta. The time history B(,t) can be used to infer the level of magnetic fluctuations in the plasma. The poloidal magnetic field and the level of magnetic fluctuations are particularly interesting quantities, since they are difficult to measure, and are both important for understanding particle and energy transport in magnetic fusion experiments. In fact, to date, no measurement of the local value of the total magnetic field or its time variation has been made in a high temperature plasma. Previous measurements have been confined to relatively cold plasmas where probes could be used, or have inadequate resolution to distinguish the value of the field with plasma present from its vacuum value. It has been recently suggested that crossed-sightline correlation of electron-cyclotron emission might be used to infer B(rx,t) at the crossing point rx in the plasma of the two sightlines. The equations and techniques necessary to simulate this proposed diagnostic are developed below, and the results of a numerical simulation of the diagnostic resolution for both TEXT and CIT are presented.
Fully automated system for simultaneous measurement of thermal conductivity and heat capacity from 4 to 300 K
Authors: Kwok R. S. , Brown S. E.
Published: July 2002

A fully automated system which is capable of measuring specific heat and thermal conductivity simultaneously from liquid helium to room temperature is presented. Thermal conductivity is measured by a steady-state longitudinal heat flow technique, and specific heat by a thermal relaxation method. A numerical simulation of the one-dimensional heat flow equation is used to examine the basic operational principle. The method is tested using GE 214 fused quartz and AISI 304 stainless-steel rods, and the results compare favorably with values quoted in the literature.
The Marshall Space Flight Center Drop Tube Facility
Authors: Rathz Thomas J. , Robinson Michael B. , Hofmeister William H. , Bayuzick Robert J.
Published: July 2002

A description of the structural and instrumentation hardware and the improved experimental capabilities of the 105-m Marshall Space Flight Center Drop Tube Facility is described. The structure comprising the Drop Tube Facility is designed to provide a high-vacuum facility in a vertical orientation. The low-gravity environment obtained during free-fall and the containerless materials processing capabilities are discussed. Two furnaces, an electron-beam and an electromagnetic levitator, are used to melt metallic samples in a process environment ranging from 10−6 Torr to 1 atm. Specifics of the vacuum control and gas delivery systems are provided. The experimental instrumentation and data acquisition systems used to perform predrop and in-flight measurements of the melting and solidification process are discussed. Typical experimental results are presented as an indicator of the performance of the Drop Tube Facility.
A containerless-melting twin-roller melt-spinning system
Authors: Wright R. N. , Korth G. E. , Sellers C. H.
Published: July 2002

A system is described to produce rapidly solidified ribbons of high-purity aluminum doped with controlled amounts of impurities. The system levitation melts the aluminum and drops the liquid onto twin copper rolls under vacuum or a controlled gas atmosphere. By avoiding a crucible for melting and a ceramic orifice for collimating the melt, contamination by low levels of impurities is eliminated. The cooling rate for this method of solidification is estimated to be similar to that of gas atomization and the ribbons formed are suitable for direct mechanical property testing and microstructural characterization.
A high-duty-cycle long-pulse electron gun for electron accelerators
Authors: Ebrahim N. A. , Thrasher M. H.
Published: July 2002

We describe the design and operation of a long-pulse (200–300 μs), high-duty-cycle (5%–6%), 8-mm-diam dispenser cathode, electrically isolated, modulating Wehnelt electron gun for applications in a high-average-power electron linear accelerator. The electron optics design was optimized with computer modeling of the electron trajectories and equipotentials. The gun performance was established in a series of experimental measurements in a test stand. Excellent pulse-to-pulse emission current reproducibility and electron-beam pulse profile stability were obtained.
A phototube constant current circuit design used in phase modulated spectroscopic ellipsometry
Authors: Vasseghi Koorosh , Yue Kintak , Blanco Julio R.
Published: July 2002

A simple differential integrator circuit is described for use with a Kepco OPS 1000B high-voltage power supply. The circuit maintains a constant phototube output dc current as incident light changes intensity during a spectroscopic measurement. The dc level is maintained better than ± 50 μV. The response time constant of the circuit is 1.6 ms, thus attenuating noise components as high as 0.6 kHz. However, the circuit is insensitive to the high-frequency signal components (50 and 100 kHz) normally measured in phase modulated spectroscopic ellipsometry. This circuit design can be used as explained with most phototubes without any changes. The high-voltage bias is easily computer controlled.
An ‘‘on’’-gated photomultiplier circuit for the determination of phosphorescence lifetimes
Authors: Piton Mark C. , Panning Wolfgang , Winnik Mitchell A.
Published: July 2002

An ‘‘on’’-gated photomultiplier circuit is described which possesses a cutoff ratio >103 by switching dynodes 1 and 3 of a nine-stage side-on phototube (Hamamatsu models 1P28, R955, etc.). ‘‘On’’-gate delay and gate-width times are continuously variable between 150 ns and 10 ms. The ‘‘ringing’’ usually observed after the gate opening in similar circuit designs, due to the propagation delay in the dynode chain and the capacitive coupling between the anode and the switched dynodes, has been greatly reduced using a ‘‘spike compensator’’ circuit. When −1000 V was applied to the anode of the phototube, the resulting output of the circuit was linear 80 ns after the unit was triggered. The circuit will also operate as an ungated photomultiplier.
Performance of a high-current metal vapor vacuum arc ion source
Authors: Shiraishi Hiroshi , Brown Ian G.
Published: July 2002

The operational characteristics of a metal vapor vacuum arc ion source have been studied. The beam current has been measured as a function of ion source extraction voltage (5–80 kV), arc current (50–250 A), metal-ion species (Ti, Ta, and Pb), and extractor grid spacing (0.89 and 0.38 cm). The measured beam current ranged up to 700 mA. The parametric variation of beam current is compared to that expected from the Child–Langmuir equation and excellent agreement is found.
Numerical study of neutral beam probe spectroscopy for edge fluctuation measurements
Authors: Komori A. , Nagai S. , Morisaki T. , Kawai Y.
Published: July 2002

A thermal neutral beam probing combined with a spectroscopic technique is numerically demonstrated to be available to the measurement of local electron-density fluctuations in edge plasmas, although the spatial attenuation of the beam due to the electron-impact ionization is not negligible. It is found that the fluctuations are accurately measured in the region where the density is lower than (4–6) × 1012 cm−3, and that this critical density decreases slightly for the fluctuations which propagate in the beam direction with phase velocities comparable to a thermal speed of the beam. Some results of the beam probe mounted on the TEXTOR tokamak are also described and good agreement is found between numerical and experimental results.
Neutral beam probe for edge plasma analysis in tokamaks
Authors: Saravia E. , Castracane J. , Woo J. T.
Published: July 2002

A neutral beam diagnostic system has been designed to do simultaneous space potential and density measurements in the tokamak plasma edge to complement existing probe diagnostics. Rapid radial profiles are possible by computer control of the energy and the injection angle of the neutral beam. A particular application under consideration is the Tokamak de Varennes, which is presently being upgraded to operate either as a limiter or as a divertor machine. In this application, an ion gun is used to produce a Tl+1 beam that can be steered radially and toroidally to scan the plasma edge. The ion beam is neutralized downstream in a charge-exchange cell and the resulting Tl neutral beam is injected through a side port into the plasma. Singly charged Tl ions produced in the plasma exit through a top port of the tokamak and are collected by an electrostatic energy analyzer. Numerical simulations of the trajectories show that beam energies between 40 and 55 keV are sufficient to probe the plasma edge radially from 23 to 29 cm with a few millimeters resolution. The use of a neutral beam allows measurements in a tokamak edge plasma with BT∼1.0 T with a reduction in beam energy by more than a factor of 3 compared to the use of ion beams. Details of the beam probe hardware and the Tokamak de Varennes application are presented.
Application of TFTR diagnostics to study of limiter H-modes
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.
Time-resolved, simultaneous density, temperature, and absorption measurements in dense laser-produced plasmas
Authors: Kearney K. J. , Mostovych A. N. , Stamper J. A.
Published: July 2002

We describe an optical diagnostic setup which permits simultaneous spatially and temporally resolved measurements of temperature and density from cold, dense laser-produced plasmas. Such information is necessary to investigate the physics of strongly coupled plasmas. The plasma is created in a slab geometry such that the transverse slab dimension is approximately one optical depth of the probing radiation in thickness. To perform the measurements the 2nd harmonic (λ=0.527 μm) of a mode-locked Nd:glass laser (τpulse=300–500 ps) is split into two orthogonally polarized beams. One of the beams measures plasma electron density using polarization wave front interferometry. The other beam uses a set of fast (τ=350 ps) photodiodes to measure single-frequency optical absorption. Plasma electron temperature is determined from time-resolved absolute emission measurements combined with the optical absorption measurements via Kirchoff’s law. This technique avoids the difficulties involved in spectroscopic temperature measurements, where the spectral intensities and line profiles are affected by the physics of the cold, dense plasma. A set of timing fiducials allows the entire set of diagnostics to be synchronized in time, while an accurate, self-referenced alignment system assures that all diagnostics sample the same region of plasma volume.
A new shear apparatus for small angle neutron scattering (SANS) measurements
Authors: Kalus J. , Neubauer G. , Schmelzer U.
Published: July 2002

A new shear apparatus for small angle neutron scattering experiments was developed. Compared to other instruments two new experimental degrees of freedom are characteristic for this apparatus: (i) there is only one shear cell and not two as in other shear apparatus, and (ii) the angle α between the incident beam of neutrons and the vector of the velocity gradient of the sheared solution can be changed between 0° and 50°. This gives the possibility to test the anisotropic distribution of nonspherical particles, like micelles, in much more detail than with the other shear apparatuses. For example the symmetry of the scattering pattern of rodlike micelles is reduced from point group 2 mm for α=0 to point group 2 for α≠0, which is shown in an experiment performed with rodlike micelles of Cetylpyridiniumsalicylate.
A passive probe for electrostatic charge density measurements
Authors: Miaoulis Ioannis N. , Abedian Behrouz
Published: July 2002

A probe has been developed to detect space charge density in flow streams. The probe not only measures the average space charge at a point, but also very small amplitude fluctuations up to 1 kHz. This electrostatic probe has a simple design and consists of a miniature central electrode and a hollow aerodynamically shaped shielding electrode for minimal flow disturbance. The high-frequency response of the probe and its simple design would make it desirable in many applications. Results of tests in a charged turbulent free jet flow of kerosene indicating the probe capabilities are presented.
Simple overdense rf plasma source
Authors: McWilliams R. , Edrich D. , Platt R. C. , Sheehan D. P.
Published: July 2002

A simple, gas-fed, radio-frequency-driven plasma source is described. By use of lower hybrid waves, noble gas plasmas were produced with electron densities up to 1012 cm−3 over a range of magnetic fields from 400 G to 1.5 kG and rf frequencies from 2–220 MHz.
PPPL Lorentz orbit code
Authors: Felt J. , Barnes Cris W. , Chrien R. E. , Cohen S. A. , Heidbrink W. W. , Manos D. , Zweben S.
Published: July 2002

A code that integrates the Lorentz force equation has been developed to trace a single charged particle’s trajectory under the influence of toroidally symmetric magnetic fields found in tokamaks. This code is used primarily to design and estimate the efficiency of charged fusion product probes, which detect escaping energetic ions such as the 1 MeV tritons, 3 MeV protons, 15 MeV protons, and 3.5 MeV alphas created in TFTR. This interactive code has also been used as a teaching tool to illustrate classes of orbits such as trapped and passing, as well as subtle orbital motions, e.g., precession of banana orbits in tokamaks, or orbits in dipole magnetic field configuration. This paper describes the code as well as recent modifications which (1) include Shafranov shifts of the magnetic surfaces, (2) use more realistic current density profiles, and (3) allow modeling of the detector and limiters.
QCS: Driving automatic data analysis programs for TFTR
Authors: Gibney Thomas R.
Published: July 2002

QCS (Queue Control System) executes on the VAX Cluster, driving programs which provide automatic analysis of per-shot data for the TFTR experiment at PPPL. QCS works in conjunction with site-specific programs to provide these noninteractive user programs with shot numbers for which all necessary conditions have been satisfied to permit processing. A typical condition is the existence of a particular data file or set of files for a shot. The user provides a boolean expression of the conditions upon which a shot number should be entered into a private Queue. The user program requests a ‘‘ready-to-process’’ shot number through a call to a specially provided function. If the specified Queue is empty, the program hibernates until another shot number is available.