bluuebunny/crossref_metadata_2025 huggingface dataset:
Role of atomic oxygen produced by an electron cyclotron resonance plasma in the oxidation of YBa2Cu3O7−x thin films studied by i
n s
i
t
u resistivity measurement
Authors: Yamamoto K. , Lairson B. M. , Eom C. B. , Hammond R. H. , Bravman J. C. , Geballe T. H.
Published: July 2002

I n situ resistivity measurements have been performed to monitor the effect of activated oxygen (atomic oxygen, oxygen ions) on films subjected to an electron cyclotron resonance (ECR) oxygen plasma. The resistivity of c-axis and mixed a+c oriented YBa2Cu3O7−x films, which were deposited in situ by 90° off-axis magnetron sputtering, was measured as a function of time in an ECR oxygen plasma. The resistivity of a film in the plasma corresponds to that found in the same film subjected to higher oxygen pressure when no plasma is present. The resistivity is shown to be determined by the flux of atomic oxygen. The steady-state concentration in the film is found to depend on the kinetics of oxygen dissociation at the film surface. From the temperature dependence of the activity of atomic oxygen, we determined the activation energy for the decomposition of O2 at the surface of films with mixed a+c axis orientation and c-axis orientation to be ∼1.3 eV and ∼2.1 eV, respectively. It is proposed that in the presence of atomic oxygen, the phase diagram of oxygen content versus temperature of YBa2Cu3O7−x is changed in a way that depends on the atomic oxygen flux.
Why the effective temperature of the hot electron tail approaches the lattice temperature
Authors: Lacaita Andrea
Published: July 2002

Monte Carlo simulations of the electron distribution function in the channel of metal-oxide field-effect transistors show a tail with an effective temperature approaching the lattice temperature. This behavior was found not only when carriers are injected in thermal equilibrium with the lattice, but also for injection of monoenergetic carriers. The one-dimensional solution for both cases in the relaxation approximation is reported. The results give a quantitative explanation of why and how the tail effective temperature is due to the finite energy that the electric field can supply to the carriers on their way from source to drain.
Diffusive electrical conduction in high-speed p-i-n photodetectors
Authors: Schneider H. , Larkins E. C. , Ralston J. D. , Fleissner J. , Bender G. , Koidl P.
Published: July 2002

We report on time-resolved photocurrent measurements in InGaAs/GaAs-quantum well p-i-n photodetector structures in which the photocurrent is optically excited and electrically detected at different locations on the sample. As the electrical pulse propagates out from the point of excitation, a temporal broadening of the signal is induced by the in-plane resistance of the doped contact layers. This temporal broadening agrees quantitatively with analytical solutions obtained from the diffusion equation used to describe the lateral voltage propagation. We discuss the significance of this temporal behavior for the optimization of high-speed photodetectors. Finally, we point out the relationship between our optical-pump/electrical-probe experiments and the all-optical pump/probe experiments reported by Livescu et al.
Room-temperature growth of AlN thin films by laser ablation
Authors: Seki Kanekazu , Xu Xiangqun , Okabe Hideo , Frye Joan M. , Halpern Joshua B.
Published: July 2002

Excimer laser ablation of compressed AlN powder has been used to grow thin AlN films at room temperature on a variety of substrates. The films have a band gap of 6.15 eV as measured by UV absorption. Examination with a scanning electron microscope and an optical microscope shows that the films are smooth. The IR spectrum has an absorption characteristic of AlN. Growth rates are extremely rapid, exceeding 70 nm/min.
32 GHz metal-semiconductor-metal photodetectors on crystalline silicon
Authors: Chou Stephen Y. , Liu Yue , Carruthers T. F.
Published: July 2002

Interdigitated metal-semiconductor-metal (MSM) photodetectors with 1.2 μm finger spacing and 0.8 μm finger width were fabricated on crystalline Si substrate. The devices are transit time limited, exhibiting a measured full width at half maximum response time of 14 ps and a 3-dB bandwidth of 32 GHz. Monte Carlo simulations of Si MSM photodetector response time and bandwidth agree with experiments and predict that if the finger spacing of the Si MSM photodetectors is reduced to 25 nm, the response time can decrease to ∼1 ps and the bandwidth can increase to 440 GHz.
Influence of ion energy on the physical properties of plasma deposited SiO2 reset films
Authors: Joubert O. , Burke R. , Vallier L. , Martinet C. , Devine R. A. B.
Published: July 2002

Silicon dioxide films have been deposited using a SiH4+O2 microwave plasma excited by distributed electron cyclotron resonance. The ratio of flow rates of the reactive gas was O2/SiH4∼7. The substrate was not heated intentionally (T<150 °C). The effect of ion energy during deposition, in the 10–150 eV range, has been studied through refractive index, infrared absorption bands, chemical etch rate, and electrical measurements. For ion energies ≳50 eV, many of the film characteristics are close to those of thermal SiO2
Atomic configuration dependent secondary electron emission from reconstructed silicon surfaces
Authors: Homma Yoshikazu , Suzuki Mineharu , Tomita Masato
Published: July 2002

We show that domains of reconstructed silicon surfaces can be imaged by secondary electrons (SEs) using an ultrahigh vacuum scanning electron microscope with a SE detector having angular resolvability. The SE images clearly show the double domain structure, alternate 2×1 and 1×2 domains on Si(100), as well as the coexistence of the reconstructed 7×7 domains and the nonreconstructed 1×1 domains on Si(111). These results demonstrate that SE emission is sensitive to the atomic configuration of the topmost layers. We call this scanning electron microscopy based technique for top layer imaging as scanning electron surface microscopy, which will evolve into a useful tool for surface characterization.
Carrier-modulated, microwave-detected Shubnikov–de Haas oscillations in two-dimensional systems
Authors: Linke H. , Kowalski B. , Ramvall P. , Emanuelsson P. , Omling P. , Oettinger K. , Drechsler M. , Meyer B. K.
Published: July 2002

It was recently shown that Shubnikov–de Haas (SdH) oscillations observed in conventional resistance measurements can be dramatically enhanced by light-induced carrier modulation [S. E. Schacham, E. J. Haugland, and S. A. Alterovitz, Appl. Phys. Lett. 61, 551 (1992)]. Here we report on a similar observation in the case of contact-free, microwave-detected SdH oscillations. In the original version of this nondestructive technique [P. Omling, B. Meyer, and P. Emanuelsson, Appl. Phys. Lett. 58, 931 (1991)], magnetic-field modulation was applied in order to enhance the sensitivity. If, instead, the carrier concentration is modulated by illumination, we show that a similar enhancement in the sensitivity of the signal is obtained. We demonstrate that very simple microwave equipment can be used for the measurements, and that the accessible magnetic-field region can be extended, allowing for contact-free transport investigations in the high magnetic-field region.
Atomic force microscope investigation of C60 adsorbed on silicon and mica
Authors: Thundat T. , Warmack R. J. , Ding D. , Compton R. N.
Published: July 2002

The morphological and frictional characteristics of C60 adsorbed on silicon and mica surfaces have been investigated using atomic force microscopy (AFM). Deposition of fullerenes by vacuum sublimation results in uniform coverage of microcrystallites with an average size between 40 and 60 nm. Small area scans on the top of these microcrystallites show disordered arrangements of molecules. Frictional measurements carried out monitoring buckling of the AFM cantilever show increased friction for C60-covered surfaces over that of clean substrates. At sufficiently high forces, the film was selectively displaced by the AFM tip, so that fine patterns could be drawn on fullerene-covered surfaces.
Room-temperature green laser emission of Er:LiYF4
Authors: Brede R. , Danger T. , Heumann E. , Huber G. , Chai B.
Published: July 2002

We report the first demonstration of a green erbium-doped crystal laser at room temperature. Excited with a pulsed dye laser, the erbium-doped LiYF4 crystal emitted on the 4S3/2–4I15/2 ground state transition. As expected from fluorescence measurements, the emitted radiation was polarized parallel to the optical axis. Laser oscillation has also been observed in erbium-doped Y3Al5O12 and Lu3Al5O12 crystals.
Low temperature current transport of Sn-GaAs contacts
Authors: Gao J. R. , Heida J. P. , van Wees B. J. , Bakker S. , Klapwijk T. M. , Alphenaar B. W.
Published: July 2002

We measure low temperature current transport properties of superconducting Sn contacts to p+-GaAs. For contacts alloyed at 450 °C, the current-voltage characteristics show a strong dependence on alloying time. The critical temperature of Sn near the superconductor-semiconductor interface decreases from 3.8 to 1.8 K as the alloying time increases from 0 to 120 s. On the other hand, a long-time alloying increases the transparency of the interface. Using the Blonder, Tinkham, and Klapwijk model [Phys. Rev. B 25, 4515 (1982)], we find that the transmission coefficient of the interface increases from 0.2 to 0.7 by alloying. However, the normal state resistance calculated using the model is much smaller than the experimental value.
Monte Carlo studies on the well-width dependence of carrier capture time in graded-index separate confinement heterostructure quantum well laser structures
Authors: Lam Yeeloy , Singh Jasprit
Published: July 2002

The total carrier capture time and the quantum well width are both important parameters affecting the graded-index separate confinement heterostructure (GRINSCH) quantum well laser modulation speed limit. However, discrepancies exist in the literature on the well-width dependence of the carrier capture times. To study this phenomenon, we have developed a Monte Carlo technique to simulate carrier relaxation in GRINSCH quantum well structures. Our results show that the carrier capture time increases with the density of carrier injection. Furthermore, depending on the concentration of injected carriers, the capture time will either decrease, remain the same, or increase with increases in the well width. At lasing conditions, the times are more or less independent of the well width up to 100 Å. We compare our calculations to published experiments and find good agreements.
Production of large diameter microwave plasma using an annular slot antenna
Authors: Ikushima Takayuki , Okuno Yoshihiro , Fujita Hiroharu
Published: July 2002

A new production method for a large diameter microwave plasma is proposed without magnetic coils. An annular slot antenna and two ring-typed permanent magnets are used for the generation of high density plasma in the circumference of a chamber with the plasma confinement and diffusing to the central region. The optimum arrangement of components in the device is examined for the production of the large diameter uniform plasma. The almost uniform electron density of about 4×1010 cm−3 is realized, and the plasma with two electron temperatures is observed. The measurement with a directional ion energy analyzer reveals that ions are almost isotropic.
Degradation mechanisms and improvement of thermal stability of CoSi2/polycrystalline Si layers
Authors: Chen Wei-Ming , Banerjee Sanjay K. , Lee Jack C.
Published: July 2002

Degradation mechanisms of CoSi2/polycrystalline Si (polycide) films have been investigated. CoSi2 was formed on various silicon substrates (stacked or one-layer structures composed of polycrystalline Si 800–10 800 Å and amorphous Si 800–3000 Å). The thermal stability of these silicide films were examined using four-point probe measurement. It was found that the microstructure of the underlying silicon substrate, rather than the grain size of the CoSi2 or the silicide/polycrystalline Si interface, has the greatest influence on the thermal stability of the polycide films. The CoSi2 formed on as-deposited amorphous Si provides the maximum thermal stability. Those films are stable at 1000 °C up to 120 s, even for undoped polycide films.
Magnetic and transport properties of permalloy thin films grown by molecular beam epitaxy
Authors: Schuhl A. , Galtier P. , Durand O. , Childress J. R. , Kergoat R.
Published: July 2002

NixFe100−x thin films with x≊65%–90%, have been grown by molecular beam epitaxy on top of thin Fe/Pd multilayers. In situ electron diffraction, and ex situ x-ray diffraction indicate epitaxial growth of the films in a face-centered cubic structure, with the (011) axis perpendicular to the substrate. This has been confirmed by electron microscopy, which also reveals regions of polycrystalline growth. Although the permalloy film itself has negligible magnetic anisotropy, the in-plane uniaxial anisotropy induced in the Fe layers can be transferred to the NiFe alloy layer through a 5-Å Pd spacer layer. The high crystalline quality of the films results in bulklike transport properties; σ=25 μΩ cm, and ΔR/R=2%, for a 60-Å-thick film.
High-efficiency continuous operation HgBr excimer lamp excited by microwave discharge
Authors: Furusawa Hideki , Okada Shinsuke , Obara Minoru
Published: July 2002

The study of a HgBr excimer lamp (502 nm) excited by a microwave discharge is reported. Efficient operation in the blue-green region was obtained with a HgBr fluorescence power of 42.8 W and an intrinsic efficiency of 9.4% at a 100 kHz operation frequency is obtained when 100 mg HgBr2 and 25 Torr neon gas are introduced in a quartz discharge sphere with a 14.13 cm3 discharge volume.
Ultraviolet photoluminescence from CuAlS2 heteroepitaxial layers grown by low-pressure metalorganic chemical vapor deposition
Authors: Chichibu Shigefusa , Nakanishi Hisayuki , Shirakata Sho
Published: July 2002

Photoluminescence (PL) studies were carried out on CuAlS2 heteroepitaxial layers grown by low-pressure metalorganic chemical vapor deposition. The epilayers exhibited an intense near-band-edge PL peak at 3.525 eV (77 K) in the ultraviolet (UV) wavelength region together with PL bands at 2.76 and 2.1 eV. This near-band-edge PL peak showed the following properties: (i) the PL was strongly polarized parallel to the c axis, (ii) the peak energy varied from 3.497 to 3.525 eV at 77 K with increasing epilayer thickness from 0.49 to 0.67 μm, and (iii) the emission was observed up to room temperature. This UV-PL was tentatively assigned to an exciton-related emission, energy shifted due to the residual lattice strain.
Diamond deposition using a planar radio frequency inductively coupled plasma
Authors: Bozeman S. P. , Tucker D. A. , Stoner B. R. , Glass J. T. , Hooke W. M.
Published: July 2002

A planar radio frequency inductively coupled plasma has been used to deposit diamond onto scratched silicon. This plasma source has been developed recently for use in large area semiconductor processing and holds promise as a method for scale up of diamond growth reactors. Deposition occurs in an annulus which coincides with the area of most intense optical emission from the plasma. Well-faceted diamond particles are produced when the substrate is immersed in the plasma.
Plasma potential formation and measurement in TMX-U and MFTF-B (invited)
Authors: Grubb D. P.
Published: July 2002

Tandem mirrors control the axial variation of the plasma potential to create electrostatic ‘‘plugs’’ that improve the axial confinement of central cell ions and, in a thermal barrier tandem mirror, control the electron axial heat flow. Measurements of the spatial and temporal variations of the plasma potential are, therefore, important to the understanding of confinement in a tandem mirror. In this paper we discuss potential formation in a thermal barrier tandem mirror and examine the diagnostics and data obtained on the TMX-U device, including measurements of the thermal barrier potential profile using a diagnostic neutral beam and charged-particle energy spectroscopy. We then describe the heavy ion-beam probe and other new plasma potential diagnostics that are under development for TMX-U and MFTF-B.
Synchronous time-resolved optical and x-ray emission from simultaneous optical and x-ray streak cameras driven by a master ramp generator
Authors: Balmer J. E. , Lampert W. , Roschger E. , Hares J. D. , Kilkenny J. D.
Published: July 2002

An optical and an x-ray streak camera have been synchronized by driving the deflection plates of both cameras from the same ramp generator. The relative timing of the two cameras was calibrated by running UV light onto the x-ray streak camera. The x-ray streak camera was then used to measure the time of the x-ray emission from a laser plasma with respect to the laser pulse.
High-resolution VUV spectrometer/detector investigations of rare-earth pulsed plasma source (abstract)
Authors: Roberts J. R. , Cromer C. L. , Bridges J. M. , Lucatorto T. B.
Published: July 2002

A 1.5-m grazing incidence spectrometer with a channel electron multiplier (CEMA) and electronic readout detector has been incorporated with a rare-earth target, pulsed plasma, continuum source. The spectrometer is compact and portable while maintaining high resolution. The CEMA detector consists of a single multichannel plate (MCP) with coned-shaped input pores which are cut at a 15-degree bias to improve efficiency at grazing angles. The source is a rare-earth plasma generated by a 10-J ruby laser producing intense continuum emission for wavelengths from 170 to 5 nm. This system will be used for both stationary and transient high-resolution atomic photoabsorption spectroscopy. The pulsed plasma source itself will be investigated for suitability as a radiometric transfer standard source. Preliminary results obtained with this integrated system will be discussed.
Ion temperature measurements on the ZT-40M reversed field pinch (abstract)
Authors: Howell Robert B. , Nagayama Yoshio
Published: July 2002

A VUV seven-channel polychrometer was constructed for measuring line broadening at wavelengths from 1500 to 3000 Å. This instrument uses a cylindrical sapphire lens to expand the line image at the exit slit. The average width between channels is 0.3 Å at 1623 Å with an average channel width of ∼0.24 Å. Measurements made on the Los Alamos ZT-40M reversed field pinch yield ion temperatures up to approximately 500 eV. Measurements have been made for 0+6 1623 Å, N+5 1897 Å, and C+4 2271 Å. The O+6 provides temperature measurements primarily from the center of the plasma. The measured ion temperatures are comparable to the electron temperatures measured at the center of the discharge. The discharges used in these studies were short, the total length being ∼1.51 ms. The ions appear to be heated quickly to several hundred electron volts. For a given peak plasma current the ion temperature increases with increasing drift velocity. Some discussion of these results will be presented.
Simple phase-sensitive detector for Wheatstone bridge resistance measurements
Authors: DiBartolomeo D. , Klems J. H.
Published: July 2002

A simple and economical phase-sensitive detector circuit is described. The circuit, which was developed for use with large-area heat-flow sensors that employ resistance temperature detection, uses a synchronous rectifier driven by a square wave. It is shown that the circuit has good linearity, resolution, and immunity to external and internal noise.
High-power microwave vacuum window of fused quartz in circular waveguide
Authors: Saito T. , Kiwamoto Y. , Kariya T. , Miyoshi S.
Published: July 2002

A demountable vacuum window of fused quartz was designed and successfully used for a high-power circular waveguide system combined with 28-GHz gyrotrons for electron cyclotron resonance heating experiments in the GAMMA 10 tandem mirror. The power reflection coefficient is very low (≤0.1%) and it works satisfactorily at the transmitted power level of 120 kW with 60-ms pulse width. No problems are expected up to 200-kW transmission with 0.1-s duration.
Lithium beam Zeeman spectroscopy diagnostic development (abstract)
Authors: Weber P. G. , Wurden G. A.
Published: July 2002

A local magnetic field diagnostic, based on the Zeeman splitting of lithium atoms is under development at Los Alamos. A modified duoPIGatron ion source1 is used in conjunction with an 80-kV accelerator to produce a high-density atomic lithium beam, permitting access to plasmas with a wide range of parameters. Detection of the Zeeman pattern in the plasma will be enhanced by the use of a dye laser, either using fluorescence or intracavity absorption (ICA). While the sensitivity of resonance fluorescence is well known, that of ICA is less well understood where short time scales are involved. Experiments to study the time/concentration trade-offs in ICA have been performed on lithium vapor, and show that the sensitivity of ICA is at least equal to that of fluorescence (assuming a dark background), under conditions of submillisecond detection times. ICA is also 103 times more sensitive than single-pass absorption under these conditions. Optimization of the atomic beam and integration with the dye laser systems are in progress.
One-ampere, 80-keV, long pulse H− source and accelerator
Authors: Kwan J. W. , Ackerman G. D. , Anderson O. A. , Chan C. F. , Cooper W. S. , deVries G. J. , Lietzke A. F. , Soroka L. , Steele W. F.
Published: July 2002

The design and operation of the surface-conversion H− ion source and the 80-keV preaccelerator are discussed. Both the source and the preaccelerator, together with the transverse field focusing (TFF) matching and pumping beam transport section (presently being tested), will be parts of a negative-ion-based neutral beam line. Results from testing the source and preaccelerator have shown that the system can accelerate more than 1 A of H− ions at 80 keV continuously; the preaccelerator operates at an optimum perveance which matches the one predicted by WOLF code computer simulation. Deconditioning of the preaccelerator due to cesium contamination is a critical problem. A method has been developed to cope with this problem.
Design concepts for compact mass/energy charge exchange analyzers
Authors: Roquemore A. L. , Medley S. S.
Published: July 2002

Charge exchange diagnostics in a hostile neutron and gamma radiation environment require substantial shielding against radiation-induced noise signal. Minimizing the dimensions of the apparatus significantly reduces the shielding complexity. Conceptual designs for compact analyzers are presented. The reduced size is achieved primarily by employing high-field-strength (≤8 kG) permanent rare earth magnets to simplify magnetic field generation. In addition, a carbon foil is used in place of a gas cell to eliminate the customary analyzer vacuum pumping systems. Alternative designs employing electric and magnetic fields for mass and energy analysis will be presented that afford a reduction in volume by an order of magnitude compared with the E∥B analyzers currently in use on the tokamak fusion test reactor (TFTR).
Gas-solution microcalorimeter for determining heat binding curves
Authors: Bishop Gary A. , Parody-Morreale Antonio , Robert Charles H. , Gill Stanley J.
Published: July 2002

A gas-solution reaction microcalorimeter has been developed for measuring the heat produced from a macromolecule in solution when the partial pressure of a reacting ligand is changed. The accumulated result of such stepwise heat processes enables the construction of a heat binding curve: namely the enthalpy per mole of reaction site versus the logarithm of the ligand activity [Gill, Richey, Bishop, and Wyman, Biophys. Chem. 21, 1 (1985)]. The high sensitivity (1 μcal) of the calorimeter is achieved by careful twinning and closed-loop proportional control achieved through continuous computer monitoring. A 15-μl liquid sample, for example 5-mM heme hemoglobin, is held in the form of a thin layer by means of a filter paper membrane. This configuration facilitates rapid equilibrium with exposed gases and allows for the completion of a given heat process within the range of 10 min. Gas partial pressures are accurately produced by means of a precision dilution valve incorporated into the calorimeter. The automatic determination of the heat binding curve is controlled by a small microcomputer programmed to change the gas partial pressure and to measure the heat that results from the change in the gas activity. An entire binding curve can be obtained on a sample of hemoglobin with as little as 20 nmol of oxygen binding sites.
Rapid pressure measurement system utilizing the ruby fluorescence scale
Authors: Sugiura H. , Yamadaya T.
Published: July 2002

An inexpensive fluorescence spectrum measurement system for pressure measurement in a diamond anvil cell apparatus was constructed. A multichannel-type optical detector was based on a diode array image sensor and assembled to the system for rapid pressure estimation.
Wide bandwidth signal processor for removing dispersion distortion from pulsar radio signals
Authors: Hankins T. H. , Rajkowski J. M.
Published: July 2002

A hardware real-time coherent dedispersion filter based on the Reticon 5601A Quad Chirped Transversal Filter is shown to be effective for time-resolution improvement of pulsar measurements. The filter can completely remove the time distortion due to dispersive propagation through the interstellar medium. The maximum bandwidth of the filter is greater than 2 MHz, which yields an ultimate time resolution of about 0.5 μs. The immunity of such a filter to arrival time shifts due to interstellar scintillation spectral modulation makes it particularly useful for precision time of arrival measurements of the millisecond pulsar PSR 1937+214. Integrated into a system for synoptic pulsar measurements, the filter will allow us to improve the precision of extended time interval measurements beyond the current atomic standards, which, in turn, may allow setting of new limits on the existence of gravitational radiation and improve the precision of the solar system ephemeris. The principles of operation, the required support circuitry, and the results of simulations and actual telescope operation are described.
Transient space charge limited current spectroscopy method of measuring the position and concentration of trap levels in semi-insulating materials
Authors: Yuan S. H. , Pardavi-Horvath M. , Wigen P. E.
Published: July 2002

A new method is reported to measure the position and concentration of trap levels in semi-insulating materials where the regular deep level transient spectroscopy method is not applicable. In the proposed method, a transient space charge limited current (TSCLC) associated with the trap levels is measured using a capacitance balanced square wave voltage source, a voltage limiter-amplifier and a double box car averager. The TSCLC method is demonstrated on a p-type Y2.01Ca0.99Ge0.91Fe4.09O12 magnetic garnet sample ρ300=107 Ω cm. The trap level is located at 0.36 eV above the valence band edge and the concentration of the trapped holes is found to be 1013–1015 cm−3.
Circuit for studying the spatial profile of a laser beam using a closed-circuit television camera
Authors: Navathe C. P. , Narayan B. S. , Oak S. M. , Gupta B. L.
Published: July 2002

A circuit for studying the laser beam spatial intensity profile using a closed-circuit television camera (CCTV) has been developed. The camera gives an output proportional to the laser beam intensity in the form of a composite video signal. The circuit can select any scan line and the intensity variation along that line can be displayed on an oscilloscope. The circuit also generates a trigger pulse for firing the laser synchronized with the selected scan line. It can be operated in either a single-shot or repetitive mode. The circuit can be used for both pulsed and cw lasers. The dynamic range, resolution, linearity, and accuracy of measurement all depend on the CCTV camera and the oscilloscope used. The dynamic range and resolution for our particular vidicon is limited to 5 and 12 lp/mm (line pairs/mm), respectively, for a 15-ns excitation pulse and to 10 and 18 lp/mm for cw and long pulse signal.
Development of Li beam probing and laser-induced fluorescence technique for electric field measurement in a plasma
Authors: Takiyama K. , Kadota K. , Oda T. , Hamamoto M. , Ohgo T. , Kamiura Y. , Adati K. , Fujita J.
Published: July 2002

To measure local electric field in an rf-plugged sheet plasma in the RFC-XX-M open-ended machine, a spectroscopic system using a combined technique of Li-beam probing (laser blow-off method) and laser-induced fluorescence has been developed. A Li atom in the rf field can be populated to 42F by a stepwise laser pumping (22S→22P→42F) because of the Stark mixing between 42F and 42D. A cascade fluorescence of 610.4 nm (32D→22P) subsequent to the direct transition (42F→32D) was observed to estimate the rf field strength (rms) Erms. To correct the effect of electron collisions in the plasma, we observed a blue fluorescence consisting of two lines: a forbidden line of 460.2 nm (42F→22P) and an allowed line of 460.3 nm (42D→22P) induced by electron collisional transfer (42F→42D). From these intensities, we obtained Erms and electron density ne by solving numerically the rate equations, including the relevant radiative and collisional processes under the experimental conditions. Erms and ne were estimated to be 2.4 kV/cm and 3.1×1011 cm−3 near the center of the sheet plasma, respectively. It was found that the obtained Erms was enhanced by about 2.5 times with respect to the vacuum field (1 kV/cm). The obtained ne agreed well with ones by other methods. A spatial distribution of ne was also obtained from that of the Li0 resonance line (22P→22S) due to electron impact excitation. The present spectroscopic system is applicable to plasmas of ne≲1013 cm−3 and static or quasi-static electric fields of E≳400 V/cm.
Charge exchange stripping cell measurements over a wide pressure range
Authors: Colchin R. J. , Roquemore A. L. , Scott S. D.
Published: July 2002

The efficiency of the stripping cell incorporated in a charge exchange analyzer has been measured over a pressure range of 1.8–130 mTorr and over an energy range of 1–130 keV/amu. In these measurements, a beam of hydrogen atoms was ionized by helium gas. As a by-product of the measurements, the scattering cross section was also measured. At the lowest pressure, the scattering cross section compared well with those measured previously; at high pressure, the cross section no longer followed an energy power law. The analyzer efficiency (defined as the fraction of the atoms that is ionized and not lost through scattering) can be modeled over the entire range of energy and pressure by including the measured scattering cross sections.
Neutral-beam diagnostic for fast confined alpha particles in a burning plasma: Application on CIT
Authors: Schlachter A. S. , Stearns J. W. , Cooper W. S.
Published: July 2002

Measurement of the slowing-down distribution for fast confined alpha particles is essential for a D–T  burning-plasma experiment. Quantitative estimates of signal level for a fast neutral-beam probe using a two-electron-capture method of measuring the alpha-particle velocity distribution are presented as applied to the proposed tokamak CIT (Compact Ignition Tokamak). The best probe is found to be a fast ground-state helium-atom beam because of its relatively good penetration into a dense plasma and because of the large cross section for two-electron capture; fast He0 can be produced in useful quantities from fast HeH+, which is sufficient to allow time-resolved measurements of the alpha-particle velocity distribution in CIT.
Accidental-coincidence corrections: Comment on ‘‘Discrepancies in accidental-coincidence corrections’’ [Rev. Sci. Instrum. 5
7, 3136 (1986)]
Authors: Smith D. , Müller J. W.
Published: July 2002

The formulas for accidental coincidence corrections published recently by DeVolpi are found to be in error and, in particular, to conflict with the results of Monte Carlo simulations and with various published exact formulas. It is shown that the traditional first-order approximate formulas are valid both for the conditions assumed by their authors, and also, at low count rates, for the conditions used by DeVolpi.
Magnetic susceptibility of some materials used for apparatus construction (at 295 K)
Authors: Keyser Paul T. , Jefferts Steven R.
Published: July 2002

The magnetic susceptibility, χ, at 295 K of a wide variety of common laboratory construction materials has been carefully measured. Only materials with well-characterized compositions are included in the final data. Materials such as Cu alloys and filled epoxies showing ferromagneticlike saturation behavior are listed with the recognition that workers will probably want to use these with great caution in precision experiments where magnetic effects may be a source of error. Susceptibility values are given for over 30 materials for which χ values are not available in the literature and which exhibit χ independent of H.
Computer-interfaced low-temperature, high-pressure flow calorimeter
Authors: Gopal P. , Zollweg J. A. , Streett W. B.
Published: July 2002

A flow calorimeter suitable for the measurement of heats-of-mixing of liquefied gas binaries is described. The calorimeter may be operated at temperatures between 77 and 300 K and at pressures up to 15 MPa. Endothermic energy effects are measured with a precision of (1.5 J/mol±1.2% HM ). The apparatus incorporates flow meters that measure mass flow rates directly. A computer data-acquisition system facilitates rapid measurements, a single heat-of-mixing measurement requiring less than 20 min. The calorimeter was tested by measuring the heat-of-mixing for the nitrogen-argon system. The calorimeter is an improvement on previous low-temperature flow calorimeters in both accuracy and speed of measurement.
Weft sensor for air-jet looms
Authors: Castellini C. , Francini F. , Longobardi G.
Published: July 2002

An optoelectronic weft stop motion for air-jet weaving looms is described. The device comprises very thin optical and optoelectronic components. It is disposed between the blades of the U-shaped channel of the loom reed in order to detect the presence of the weft yarn during its insertion into the warp shed in the weaving process. Details of the design and fabrication of the device are presented and electronic signal processing is discussed.
A simple electron-beam control circuit for FT-ICR electron impact dissociation experiments
Authors: Guan Shenheng , Jones Patrick R.
Published: July 2002

A simple electron-beam control circuit has been designed and constructed for electron-impact dissociation experiments on Fourier transform ion cyclotron resonance mass spectrometers (FT-ICR or FTMS). Two types of electron beams from a common filament are controlled by three TTL signals. The electron beam current is adjusted by varying the grid potential while the filament current is kept constant.
An amplified tunable picosecond dye laser based on an active-passive mode-locked Nd:YAG laser
Authors: Brucker G. A. , Young M. A. , Kelley D. F.
Published: July 2002

An amplified tunable picosecond dye laser has been constructed which is pumped by an active-passive mode-locked Nd:YAG laser. The laser is tunable from 555 nm to >700 nm. It provides a maximum of 2-mJ pulses with pulse widths of ∼17 ps (FWHM). The tuning range can be extended by frequency doubling and/or mixing with the residual 1064-nm pulses. The dye laser is very stable and relatively inexpensive to construct.
Soft-x-ray imaging with the 35 period undulator at the NSLS
Authors: Buckley C. , Rarback H. , Alforque R. , Shu D. , Ade H. , Hellman S. , Iskander N. , Kirz J. , Lindaas S. , Mcnulty I. , Oversluizen M. , Tang E. , Attwood D. , DiGennaro R. , Howells M. , Jacobsen C. , Vladimirsky Y. , Rothman S. , Kern D. , Sayre D.
Published: July 2002

In the summer of 1988, the National Synchrotron Light Source installed a 35 period soft-x-ray undulator. We are using this device as a radiation source for a beamline designed for soft-x-ray imaging experiments that require high brightness for practical operation. We present the design philosophy and implementation of this beamline. Preliminary characterization of the beamline and undulator indicate that the central intensity of the undulator is within a factor of 2 of design. We have measured an intensity of more than 1015 photons/s/0.1% BW/mrad2 at 36 Å. The monochromator has achieved its design resolving power of 2000.
Super-ACO: Results on a positron low emittance ring (invited)
Authors: Besson J. C. , Certain P. , Dael A. , Damany A. , Juan P. , Labeque A. , Level M. P. , Marin P. C. , Michaut J. , Monet-Descombey C. , Nghiem P. , Sommer M. , Souchet R. , Zyngier H.
Published: July 2002

The dedicated VUV radiation source Super-ACO is part of the Orsay synchrotron radiation complex. The construction of this 800-MeV positron storage ring was started in 1982, and the first beam was stored on March 18, 1987. Super-ACO is expected to accommodate up to six undulators. The first, a 3.2-m-long optical klystron has already been operated between 500 and 800 MeV. A 1.3-m-long undulator has been recently installed. The experience gained during the three periods of operation is presented. From March to October 1987 measurements were taken of the machine properties in the low emittance regime, as well as performances in single and multibunch operation. In March 1988 the optical klystron was tested together with the commissioning of two beamlines out of a bending magnet. Starting from May 1988 two undulators and six beamlines progressively operated.
A shock tube with tunable, pulsed laser-based diagnostics
Authors: Gray Jeffrey A.
Published: July 2002

This article describes a unique shock tube that is interfaced with a short-pulse, Nd:YAG-pumped, tunable dye-laser system to provide real-time information on transient chemical species. The tube’s internal bore (38.1-mm-diam) accomodates 18 optical diagnostic ports. Pressure-driven shock waves are generated in a double-diaphragm driver section and are timed in the driven section by HeNe laser schlieren detectors. Incident shock speeds range between 1000 and 1500 m/s and are reproducible to ±5 m/s. Individual pulses from the laser and the gate for a photodiode array detector are synchronized with the arrival of shock fronts at the viewing station. Laser-induced fluorescence (LIF) imaging experiments demonstrate the diagnostic power of the new apparatus. One-dimensional (1D) LIF images are recorded in shocked mixtures of ethane, oxygen, and argon by propagating the tunable laser beam along the shock tube’s axis and collecting fluorescence from the OH radical on the 1D detector. The detection sensitivity limit for OH by LIF in this shock tube is approximately 4×1011 radicals/cm3 (0.1 ppm).
A four-probe ac apparatus for the high-resolution conductivity measurement of ceramic oxides at high temperatures
Authors: Plomp L. , Booy A. , van Roosmalen J. A. M. , Cordfunke E. H. P.
Published: July 2002

A simple nonbridge four-probe ac apparatus has been developed for the measurement of the electrical resistances of ceramic oxide samples in the range from 0.1 mΩ up to 1 Ω. Use of platinum press contacts enables performance up to 1000 °C in oxidant gas atmospheres on pressed pellets as well as on thin layers on a substrate. The method allows for high-resolution measurements, 0.1% or better, at low measuring currents, typically 100 μA, and is insensitive to noise and environmental electromagnetic signals. The apparatus is relatively inexpensive and can be operated automatically by means of a personal computer. Results on the conductivity of platinum and of mixed lanthanum strontium manganite are given as an example.
Metal coating of organic thin films for thickness measurements by a stylus method
Authors: Mitsuya Munehisa , Imazeki Shuji
Published: July 2002

The metal coating on the surface of organic thin films has been examined to measure their surface profile by using a scanning stylus on them. The thickness of a Langmuir–Blodgett film has been successfully obtained by covering a sample with a platinum layer some nm thick. The network of the deposited overlayer is considered to be responsible for an increase in mechanical strength sufficient to endure a stylus load.
Lignin analyzer based on pyrolysis-mass spectrometry of pulp in hydrogen or helium
Authors: Shakkottai P. , Kwack E. Y. , Lawson D.
Published: July 2002

The lignin content of wood, paper, pulp, or other materials containing lignin (such as filter paper soaked in black liquor) is readily determined by flash pyrolysis of the sample at approximately 550 °C in a reducing atmosphere of hydrogen or in an inert atmosphere of helium followed by a rapid analysis of the product gas by a mass spectrometer. The heated pyrolysis unit as fabricated, comprises a small platinum cup welded to an electrically heated stainless-steel ribbon with control units for programmed short duration (1.5 s, approximately) heating and for continuous flow of hydrogen or helium. The pyrolysis products enter an electron-ionization-mode mass spectrometer for spectral evaluation. Lignin content is obtained from certain ratios of integrated ion currents of many mass spectral lines, the ratios being linearly related to the Kappa number or Klason lignin. The Kappa number can be obtained from a few milligram sample in 3 min which is at least ten times faster than a Kappa number determination by the Standard Chemical Method. The present instrument can measure Kappa numbers in the whole range from 0 to 200 without any readjustments.
Controlled levitation of a large magnet above superconductors
Authors: Takamori Takeshi , Boland John J. , Dove Derek B.
Published: July 2002

The levitation of a permanent magnet over a type-II superconductor may be modified and controlled by the addition of a variable magnetic field to the magnet-superconductor system. Using this scheme, levitation of a magnet of significantly larger mass was established by the direct interaction of the additonal field with the levitating magnet.
Design and performance of a vapor transport cell for operation onboard the Space Shuttle Orbiter
Authors: Debe M. K. , Poirier R. J. , Schroder F. S. , Cook E. L. , Follett G. J.
Published: July 2002

The experimental reactor cell designed and developed for the growth of films and crystals by closed cell physical vapor transport on the Space Shuttle Orbiter is discussed. The cell design has been proven by over 60 experiments, including 18 on two space flights, to be very satisfactory from the standpoints of minimal power use at operating temperatures of 400 °C, mechanical vibration resistance and approximation to ideal steady-state growth conditions. The performance realized is closely related to the assembly and cell preparation procedures which affect internal outgassing into a critical vacuum insulation region. The results of thermal performance studies of the cell as a function of this gas composition and pressure, as well as actually measured power and temperature relationships occurring during ground control and flight thin film growth experiments are presented. The cell design is presented in detail and the important aspects of the cell preparation and assembly identified.
Factors affecting emittance measurements of ion beams
Authors: Tsai C. C. , Akerman M. A. , Becraft W. R. , Dagenhart W. K. , Haselton H. H. , Schechter D. E. , Stirling W. L. , Whealton J. H. , Donaghy J. J.
Published: July 2002

The emittances of hydrogen and deuterium negative ion beams produced by volume ion sources have been measured in a transverse plane normal to the beam trajectory. The extraction voltage was varied from 10 to 40 kV, and the transverse magnetic field in the Penning discharges was varied from 0.1 to 0.2 T. Measurements were made on beams with current densities up to 60 mA/cm2 at Oak Ridge National Laboratory with an emittance scanner originally developed at Los Alamos National Laboratory. The beam profile at the scanner can be used to improve the accuracy of the emittance measurements. Other factors affecting emittance measurements are discussed. This analysis may be applicable to other ion sources.
Application of a sine transform method to experiments of single-photon-decay spectroscopy: Single exponential decay signals
Authors: López R. J. , González F. , Moreno F.
Published: July 2002

In this article we present as an experiment in single-photon-decay spectroscopy an alternative method to that based on the measurement of the probability distribution function, Pf(t), of the time intervals for the time of arrival of the first photon after the excitation pulse. We propose the measurement of the sine transform of Pf(t), which gives a maximum when the fluorescence signal is of the single exponential decay type. The existence of this maximum allows us to determine very accurately the value of the decay constant using a number of measurements which is lower than that required to establish a Pf(t) that is accurate enough to draw the same conclusions. A theoretical model of the error is studied and is compared by means of a computer simulation with the usual method of measuring Pf(t). An experiment is performed using a TMMC crystal to verify the validity of the theoretical predictions and of the simulation results.
Status of the ECR ion source at the Uppsala cyclotron
Authors: Ekström C. , Hemryd B. , Holm S. , Renberg P.-U. , Thuresson L. , Wessman D. , Arnesen A. , Hallin R. , Heijkenskjöld F. , Nordgren J. , Vogel O.
Published: July 2002

The room-temperature ECR ion source at The Svedberg Laboratory, Uppsala, is being used as injector for the Gustaf Werner cylcotron as well as for atomic-physics experiments. In November 1990 the first heavy-ion beams from the ECR ion source were accelerated in the cyclotron. Nuclear-physics experiments have now taken data using beams of He2+, O5+, and N6+. The transmission through the cyclotron is typically 5%. The present energy record is 450 MeV N6+. The energy of the heavy-ion beams will be increased further by acceleration in the CELSIUS storage ring. Examples of atomic-physics experiments in preparation are emission spectroscopy of highly ionized atoms, in particular, to study the transitions between Rydberg states, and studies of electron transfer processes in collisions of slow multicharged ions with atoms. The studies of yrast transitions are of interest in the field of x-ray lasers and one motivation for the electron transfer studies is the importance of these phenomena in astrophysics and fusion research.
The 10-GHz NEOMAFIOS upgraded electron cyclotron resonance ion source
Authors: Ludwig P. , Geller R. , Melin G.
Published: July 2002

After the successful development of the first NEOMAFIOS source, an ECRIS for highly charged ions at 8 GHz with a magnetic configuration obtained only with FeNdB permanent magnets, the building of an upgraded NEOMAFIOS at 10 GHz has been achieved. This source started operating a few months ago and already delivers in dc regime quite interesting results. Such a source is convenient for high voltage platforms because of its very low electrical power consumption about 6 kW. In addition its tuning is exceptionally easy because of its perfect reproducibility and stability.