bluuebunny/crossref_metadata_2025 huggingface dataset:
Directional sensitivity of unplated slanted-wire probes
Authors: Samet M. , Einav S.
Published: July 2002

The directional sensitivity of unplated slanted-wire probes is experimentally investigated. It is shown that the yaw response of these probes depends on the roll angle, β, at which the plane formed by the wire and the prongs is oriented with respect to the yaw plane. At β=0°, when both planes are aligned with each other, the constant velocity characteristics are monotonic functions of the yaw angle, ψ, implying a unique correspondence between the output signals and flow direction. When the two planes are not aligned with each other, a region of yaw angles is found within which the hot-wire signals become nonuniquely related to the yaw orientation of the probe. The size of this region is shown to depend on the particular value of β; it increases with increasing β and vice versa. Problems of nonuniqueness are also found during calibrations of two- and three-wire probes. It is shown that such problems result either from improper orientation of the wires with respect to the calibration plane (in the case of an X probe) or from the arrangement of the wires on the probe (in the case of a three-wire probe) or both. To avoid nonuniqueness and ambiguous results, the use of these probes is restricted to an experimentally determined range of angular directions of the flow. However, from the current findings it appears that, in the case of a conventional three-wire probe, the limiting values of the flow angles (angular directions) are relatively small. It is concluded, therefore, that for measurements in three-dimensional or highly turbulent flows (in which the instantaneous angular directions of the flow are relatively large), an entirely new arrangement of the wires on the probe should be sought.
Mass spectrometer for measurements of relative ion concentrations in plasmas
Authors: Suszcynsky David M. , D’Angelo Nicola , Merlino Robert L.
Published: July 2002

A mass spectrometer which can be used to measure relative ion concentrations in a multi-ion component plasma has been designed for use in a strong (1–4-kG) uniform magnetic field. The spectrometer features an acceleration region which accelerates thermal ions through a series of three tantalum electrodes at a 30° angle to the B field, and a collection region in which ions are selectively collected, depending on the size of their gyroradii, by a cylindrical collector. Relative ion concentrations are determined from measurements of the collector current as a function of accelerating voltage. Results obtained using this instrument in a Q-machine device operated with a two-ion (Cs+/K+) component plasma are presented.
New and accurate technique for determination of orientation of the straight edges of single-crystal wafers
Authors: Lal Krishan , Niranjana N. Goswami S.
Published: July 2002

An x-ray traverse topograph of the specimen wafer is recorded with diffracting planes nearly parallel to the straight edge. The scan is adjusted to have the image of the straight edge on one side. A projected image of the diffracting planes is also recorded on the same photographic film in the form of a stationary topograph (a sharp line) at a short distance from the traverse topograph. The angle between the image of the straight edge and the stationary topograph is measured directly. Accuracy of ±3 arcmin is achieved. A multicrystal x-ray diffractometer or a standard x-ray diffraction topography camera can be used. A few illustrative results obtained with silicon wafers are described.
Detection of micrometer-sized pinholes in specularly reflecting films
Authors: Cornett Kenneth D. , Gibson Ursula J.
Published: July 2002

A microreflectometer system to detect micrometer-sized pinholes in specularly reflecting films has been developed. A modified compact disk player serves as an autofocusing reflectometer, with a feedback-stabilized source and a spot size on the order of 1 μm. Pinholes can be identified by the drop in signal where the reflective layer is missing. Total pinhole area in a scanned region can be determined most simply by selecting an appropriate threshold in the reflected signal (below which the presence of a pinhole is indicated), and counting the number of pixels on either side of the threshold. Additionally, changes in overall reflectance, such as those caused by the growth of a uniform oxide layer on a thin metal sample, can be detected independently of pinhole formation. This information will be of great use in studying the environmental degradation of metal and rare-earth/transition-metal (RE–TM) alloy films and the effectiveness of various protective overlayers.
Computer-controlled pulsed magnetic field gradient NMR system for electrophoretic mobility measurements
Authors: Saarinen Timothy R. , Woodward W. Stephen
Published: July 2002

A computer-controlled pulsed magnetic field gradient NMR (PFGNMR) system for making electrophoretic mobility and diffusion measurements is described. Emphasis is placed on the design and capabilities of the gradient and electrophoretic pulse generators. Various pulse sequences can be applied by the programmable gradient generator that can produce 0- to 10-A current pulses for 0 to 13 ms and continuous currents from 0 to 50 mA. The pulse areas are reproducible to within approximately 1 ppm. A pair of opposed Helmholtz coils in the probe create linear magnetic field gradients during the current pulses. Electric fields are applied across a U-tube electrophoretic cell by a 550-V constant current generator.
Measurement of infrared absorptivities and line shapes and the distortion of anvils in diamond-anvil cells
Authors: Klug D. D. , Lavergne Aurele , Whalley Edward
Published: July 2002

The infrared transmission of diamond and other transparent anvil apparatuses that contain absorbing samples, has been calculated as a function of frequency for planar anvils that are inclined to one another or that are distorted into parabolic shapes. At frequencies where the samples are completely transparent, the height of the interference fringes decreases with increase of frequency at nearly the same rate for both parabolically distorted and inclined anvils for which the maximum difference in optical path length of the sample is the same. Hence, the distortion of anvils in a typical experimental configuration have been measured up to a mean pressure on the anvil faces of 60 kbar. They are consistent with the predictions of elasticity theory that distortions occur at the rate of about 20 μm in 500 kbar. The predicted effect of such distortions on the absorbance, integrated area, and time autocorrelation function of the dipole moment is insignificant in a well-designed experiment, and so all these properties can now be measured accurately at high pressures.
X-ray diagnosis of high-density compression of Ar-filled polymer shell targets (abstract)
Authors: Richardson M. C. , Bradley D. K. , Jaanimagi P. A. , Delettrez J. , Epstein R. , Hooper C. F. , Mancini R. C. , Kilcrease D.
Published: July 2002

Time-resolved x-ray diagnosis is the only practical approach at present to examining the change of fuel and shell conditions during the final stages of compression of laser fusion targets. Time-resolved spectroscopy of lines emitted by the fuel or shell elements can provide information about the time history of the density, temperature, and integrity of the target. We report on time-integrated and time-resolved x-ray measurements of compressed polymer shell targets filled with Ar, or mixtures of Ar/Kr, directly irradiated by the 24-beam 2-kJ, UV (351-nm) OMEGA laser. These include x-ray photography, time-resolved and spaced-resolved x-ray spectroscopy, and x-ray diode measurements. Picosecond x-ray spectroscopy of the K shell emission from Ar has been studied, and detailed modeling and Spark Broadening analysis of the H-like and He-like line emission made. The results are compared with predictions of hydrodynamics code simulations of the implosions. From this analysis, a consistent history of the density and temperature of the compressed target is inferred. This work was supported by the U.S. DOE Office of Inertial Fusion under agreement No. DE-FC08-85DP40200 and the Sponsors of the Laser Fusion Feasibility Project at the Laboratory for Laser Energetics.
X-ray pulse perturbations by line-of-sight closure effects (abstract)
Authors: Harrach R. J. , Gee M.
Published: July 2002

In experiments with intense x-ray pulses, perturbations of the signal in traversing a diagnostic line-of-sight channel connecting source and detector can be large, requiring detailed computations to infer true characteristics of the signal. These perturbations fall in the most difficult class, being highly nonlinear (especially with respect to frequency) and time dependent. They cause the transmission of collimators and vacuum windows to change continuously as these apertures heat, ionize, and expand under intense irradiation; similarly the fluorescence efficiency of a scattering foil, the transmission of a filter, the reflectivity of a multilayer mirror, etc., can change significantly over the x-ray pulse duration. We discuss the problem of modeling x-ray transport through the ablation plasmas created by the intense signal, focusing on the questions: What are the sources of systematic error in our calculations that limit our ability to correct for aperture closure effects and how can the size of perturbations be minimized by careful design of the line-of-sight channel? This work was performed under the auspices of the U. S. DOE by the LLNL under Contract No. W-7405-ENG-48.
Time-resolving x-ray diagnostics for ICF (invited)
Authors: Jaanimagi P. A. , Bradley D. K. , Duff J. , Gregory G. G. , Richardson M. C.
Published: July 2002

X-ray streak cameras, which can be coupled to a large variety of spectroscopic or imaging devices, provide an important research tool for studying laser fusion plasmas. Generally, several of these instruments are deployed simultaneously on a given experiment to furnish a comprehensive data set of the x-ray emission spectrum and target hydrodynamics. Of particular importance is the ability to do quantitative analysis with the data set. This allows meaningful comparisons to be made with simulations. The sophistication of the hydrodynamic and atomic physics codes is such that qualitative analysis is insufficient. Various simple parameters in these codes are bench-marked against experimental measurements before more detailed calculations are performed. As in all diagnostic systems the range of linear response must be well defined. In this article we will discuss some of the constraints inherent in streak camera systems and how they affect the acquisition and analysis of the experimental results. Examples illustrating our current capabilities for diagnosing experiments on the OMEGA laser fusion facility will be presented.
Image analysis and data-acquisition techniques for infrared and CCD cameras for ATF
Authors: Young K. G. , Hillis D. L.
Published: July 2002

A multipurpose image processing system has been developed for the Advanced Toroidal Facility (ATF) stellarator experiment. This system makes it possible to investigate the complicated topology inherent in stellarator plasmas with conventional video technology. Infrared (IR) and charge-coupled device (CCD) cameras, operated at the standard video framing rate, are used on ATF to measure heat flux patterns to the vacuum vessel wall and visible-light emission from the ionized plasma. These video cameras are coupled with fast acquisition and display systems, developed for a MicroVAX-II, which allow between-shot observation of the dynamic temperature and spatial extent of the plasma generated by ATF. The IR camera system provides acquisition of one frame of 60×80 eight-bit pixels every 16.7 ms via storage in a CAMAC module. The CCD data acquisition proceeds automatically, storing the video frames until its 12-bit, 1-Mbyte CAMAC memory is filled. After analysis, transformation, and compression, selected portions of the data are stored on disk. Interactive display of experimental data and theoretical calculations are performed with software written in Interactive Data Language.
ATF data system
Authors: Wing W. R. , Baylor L. R. , Bell J. D. , Burris R. D. , DeVan W. R. , Greenwood D. E. , Kannan K. L. , Ketterer H. E. , Mankin J. B. , Overbey D. R. , Stewart K. A. , Sumner J. N. , Young K. G.
Published: July 2002

The data system for the advanced toroidal facility (ATF) is a logical extension of the system used for the Impurity Studies Experiment ISX-B. Based on the ISX-B concepts and hardware, it extends them to provide support for long-pulse or steady-state operation of ATF. The system is now network based rather than shared memory based and can dynamically add or remove processors. The hardware consists of a pair of VAX 8700 CPUs and an assortment of MicroVAX front ends. This hardware acquires all data, generates all control waveforms, and provides trending and logging services for the safety interlock and control systems. These systems are based on programmable logic controllers (PLCs) which are independent of the data system. The software consists of three major components: a master scheduling and monitoring system (SAMS) that provides synchronizing services and allocates files and memory; a signal-based data and file management package (DMG) that provides data access services; and the ORNL CAMAC driver package. All diagnostics are supported by data acquisition and analysis software (either generic or specialized) that is based on and shared by these services.
Conceptual design of the physics support portion of the CIT instrumentation and control system
Authors: Sauthoff N. R. , Stark W. , Rauch W. , Randerson L. , Fleming G.
Published: July 2002

The conceptual design of the data handling system for the Compact Ignition Tokamak (CIT) takes advantage of the recent and upcoming advances in the technologies of database management systems, workstations, networking, and front-end processing. The software configuration of a diagnostic’s front-end signal conditioning, data acquisition, and data reduction by means of filling in tables and specifying ‘‘objects’’ for the data transformations will provide a more powerful tool for efficient application ‘‘programming.’’ The maintenance of an audit trail of chains of transformations (input data and processes) will permit identification and recalculation of results which are affected by modifications of calibrations and processing.
Toward a nonintrusive measurement of current density in a reversed field pinch plasma (abstract)
Authors: Evans D. E. , Wilcock P. D.
Published: July 2002

Understanding of the RFP plasma will be materially advanced by a knowledge of its magnetic field or current density profiles. A nonintrusive means of measuring these is offered by Thomson scattering, which, to demonstrate the principle, has been performed at 90° in the poloidal plane of HBTX at three locations: the center, and ±16 cm either side of center along a horizontal diameter. Laser light scattered at any one of these locations is dispersed into two broad wavebands whose intensity ratio depends on Te and on the poloidal component of the electron drift velocity vθ, so a pair of measurements, one at each of the eccentric positions, is needed to determine Te and vθ independently. Typical results for constant current 200-kA plasmas for which average jz ∼1 MA m−2 are, 1.5 ms after initiation of the current: Te =255 eV, vθ =0.55 m/μs, and using ne ∼1.5×1019 m−3, jθ =2.1 MA m−2. At 2.5 ms, Te =455 eV, vθ =2 m/μs, ne ∼1×1019 m−3, and jθ =3.2 MA m−2. At 4.0 ms, Te =475 eV, vθ =1.1 m/μs, ne ∼0.9×1019 m−3, and jθ =1.5 MA m−2. The direction of jθ deduced from scattering agrees with that known for the prevailing HBTX wiring configuration.
High-resolution 14-MeV neutron spectrometer
Authors: Pillon M. , Bastistoni P. , Bertalot L. , Martone M. , Podda S.
Published: July 2002

A neutron spectrometer based on both the track position identification and the energy measurement of recoiling protons from a hydrogenous radiator is proposed. The expected performance limits of this spectrometer with regard to energy resolution, efficiency, and counting rate are evaluated for five different configurations. The results show the possibility of deriving an optimized spectrometer design with an energy resolution up to 1% at 14 MeV. In particular, the application of the spectrometer for the ion temperature measurement on the Next European Torus is presented.
Ion cyclotron emission spectroscopy as an α-particle monitor
Authors: Moses K. G. , Sperling J. L. , Dooling J. C. , Chu C.
Published: July 2002

Since 1981, we have proposed and investigated spectral analysis of the harmonics of ion cyclotron emission (ICE) as a means of monitoring the energy content of α particles confined in a magnetic fusion device. A pair of crown probe antennas have been constructed for TFTR to collect ICE spectra and will be installed on that device in the near future. The design of this ICE spectroscopy system is described. Also, some calculations of ICE electromagnetic fluctuations in the ICRF, due to newborn α particles with a distribution function appropriate to typical fusion reactor parameters, are discussed. The calculated emission spectra are quite distinct from that of blackbody radiation.
Atomic parameters for dielectronic satellite spectra of hydrogenlike iron
Authors: Bhalla C. P. , Karim K. R.
Published: July 2002

Theoretical atomic parameters for the dielectronic satellite lines of the Fe xxvi resonance line are presented. These satellite lines correspond to radiative transitions from states with electron configurations 2lnl′ for n=2, 3, and 4. A comparison of our calulations, based on the Hartree–Fock–Slater atomic model, with those obtained with the Z-expansion technique and with the scaled multiconfiguration Thomas–Fermi model shows reasonable agreements for n=2, but systematic and sometimes significant differences in F*2 values for n=3 and 4 satellites are found between our results and those obtained with the Thomas–Fermi model.
Upconverting Tm3+ doped Ba–Y–Yb–F thin film waveguides for visible and ultraviolet light sources
Authors: Chwalek James M. , Paz-Pujalt Gustavo R.
Published: July 2002

We report the results of Tm3+ doped Ba–Y–Yb–F thin film planar waveguides in glassy form, which produced red, green, blue, and ultraviolet upconverted luminescence when pumped by infrared radiation at λ=960 nm. The films of nominal composition BaYYbF8 doped with 1% Tm have been deposited with both thermal and e-beam evaporation techniques on substrates of fused silica, Si, and GaAs. Planar waveguiding was demonstrated for the films deposited on fused silica. Optimal deposition conditions with respect to the ability of the films to produce upconverted luminescence and low propagation loss are discussed.
Multiple electrode potentiostat
Authors: Harrington M. S. , Anderson L. B. , Robbins J. A. , Karweik D. H.
Published: July 2002

A general purpose multiple electrode potentiostat is described which allows the execution of novel electrochemical experiments. The potentiostat independently controls the potentials and measures the currents at multiple (up to eleven) working electrodes using a single auxiliary electrode and a single reference electrode. It is designed for either stand-alone operation or performance under the direction of a computerized data-acquisition and control system, and it is capable of implementing either stepped potential or scanned potential programs. A modular design consisting of a backplane data and control bus with slots for each independent component provides the means for relatively simple maintenance and facile expansion for arrangements employing additional working electrodes. Current sensitivities of 1 mA/V to 100 nA/V in five ranges are selectable with additional sensitivities of 10 nA/V, 1 nA/V, and 100 pA/V available through the use of a preamplifier.
High-resolution low-voltage electron optical system for very large specimens
Authors: Shao Zhifeng , Lin P. S. D.
Published: July 2002

This article introduces an unconventional electron optical probe forming system which is particularly suitable for low beam voltages and very large specimens, such as semiconductor wafers which also require a large angle tilting. The system can produce an electron probe of less than 20 Å for a nontilting specimen at 1-kV beam voltage with a working distance of 2.5 mm. The particular design allows a large volume of free space below the specimen which may be used to accommodate a complicated transporting mechanism.
Synthesizers’ phase noise in frequency-domain fluorometry
Authors: Barbieri Beniamino , De Piccoli Fabio , Gratton Enrico
Published: July 2002

The influence on the final phase and amplitude determination of the phase noise of frequency synthesizers used in frequency-domain fluorometry is analyzed. It is shown that the phase noise exactly cancels out due to the differential method used for the phase measurement. The only consequence of the phase noise is the detuning of the cross-correlation frequency with respect to the center of the filter used to analyze the cross-correlation signal. This detuning can have severe adverse effects on the phase and modulation values. By using higher values of the cross-correlation frequency, these effects can be minimized. The performance of different synthesizers is tested and compared. The results support the general prediction that the noise of the synthesizer has little influence on the phase noise of actual measurements.
Millisecond time-resolved x-ray diffraction on liquid-crystalline phase transitions using infrared laser T-jump technique and synchrotron radiation
Authors: Kriechbaum Manfred , Rapp Gert , Hendrix Jules , Laggner Peter
Published: July 2002

An erbium laser (λ=1.5 μm) with a pulse energy of 2 J delivered in 2 ms was used for rapid heating to investigate the kinetics and structural mechanism of the thermotropic phase transitions of a phospholipid/water system by fast x-ray small-angle powder diffraction. The phase transitions were induced by a single laser pulse, leading to a T jump of about 10 °C and the structural relaxations following the T jump were detected in 1-ms resolution. The results show that the transition at 29 °C (Lβ-Lα) is at least as fast as the heating time (2 ms) and that the lamellar/hexagonal transition around 57 °C (Lα-HII) is considerably slower with a half-time of the order of 100 ms.
Luminescence excitation in BaF2-BaCl2 and BaF2-BaBr2 synchrotron radiation
Authors: Mikhaylin V. V. , Terekhin M. A.
Published: July 2002

Luminescence excitation spectra in barium fluorohalides have been studied using synchrotron radiation of the SIBERIA-I electron storage ring in the energy range from 4 to 35 eV. The energy position of edge and core exciton formation as well as that of the electronic excitation multiplication threshold have been established. These luminophors find their practical application in the novel image-plate technique.
Scanning x-ray fluorescent microanalysis of rock samples
Authors: Baryshev V. B. , Gavrilov N. G. , Daryin A. V. , Zolotarev K. V. , Kulipanov G. N. , Mezentsev N. A. , Terekhov Ya. V.
Published: July 2002

Results are given concerning the two-dimensional scanning microanalysis of microsections of metallographic specimens of rocks. The monochromatized or white SR beam from a wiggler magnet installed at the electron storage ring VEPP-3 (2 GeV, 20 kG, 100–200 mA) was used for fluorescence excitation. The working energies ranged from 8 to 35 keV. Without focusing x-ray optics, the spatial resolution was 60 μm with the monochromatic beam and 30 μm with the white SR beam. The minimum detectable concentration of the elements (within the Fe-Sr region) is 10 ppm for 1–3 s exposures per point.
Instrumentation for x-ray photoacoustic imaging and depth profiling
Authors: Masujima T. , Shiwaku H. , Yoshida H. , Sano T. , Amemiya Y. , Kawata H. , Kataoka M. , Hoshi M. , Nagoshi C. , Uehara S. , Imai H. , Ando M.
Published: July 2002

A proposed photoacoustic imaging by a scanning focused x-ray beam has been investigated. The experimental setup and its current performance are shown using model samples. The current spatial resolution, 0.5 mm, by this method is limited by detector sensitivity or photon flux. For the study of the nondestructive three-dimensional analysis of atomic components, the computer system has the commands to estimate the average values of the signal amplitude and phase at the desired areas. Layered samples were measured for demonstration.
Studies on Si(111) 7/8  ×  7/8 -Bi and -Ag surfaces by x-ray diffraction under nearly normal incidence
Authors: Takahashi T. , Nakatani S. , Okamoto N. , Ishikawa T. , Kikuta S.
Published: July 2002

X-ray intensity versus energy (I-E) curves were measured in order to obtain the rod profiles. The three-dimensional surface structures of Si(111) 7/8  ×  7/8 -Bi and -Ag were analyzed. The adsorption sites with respect to the crystal were derived from the intensity changes along the integral-order rods especially near the Bragg points by utilizing the interference effect between the x rays diffracted from the adsorbed layer and the bulk crystal. The positions of the surface Si atoms were studied by using the interference effect between the x rays diffracted from the adsorbed layer and the surface Si layer.
X-ray diffraction study under pressure using an imaging plate (abstract)
Authors: Shimomura O. , Takemura K. , Ohishi Y. , Kikegawa T. , Fujii Y. , Matsushita T. , Amemiya Y.
Published: July 2002

Synchrotron radiation (SR) has been proved to be a powerful tool for x-ray study under pressure. So far, an energy dispersive method has been used because the intensity of the monochromatized beam is not strong enough for the very small sample under pressure, even if SR is used. In order to perform an angle-dispersive method under pressure, we need to use one- or two-dimensional detectors. Recently, a photostimulable fluorescence plate, named an imaging plate (IP), has been successfully used as an x-ray detector at the Photon Factory. We tried to combine a diamond anvil cell with SR and IP. Exposure time on IP for the diffraction from Ag in a diamond anvil cell at 22 keV is shorter than that on an x-ray film by a factor of 50. Resolution of IP (180 μm) is not a severe problem where IP is apart from the sample by 150 mm. Data on IP are digitally treated, so that it is easy to integrate the intensity along the Debye ring. Then, the reliability becomes more than 10 times better than a one-dimensional scan. Accuracy in determination of lattice constants and integrated intensity will be presented.
Spectral properties of segmented undulators for the 7-GeV Advanced Photon Source
Authors: Shenoy G. K. , Viccaro P. J. , Alp E. E.
Published: July 2002

The effect of nonzero particle beam emittance and magnetic field errors on the on-axis spectral brightness (BT0) of long undulators is discussed. It is shown that the quadratic dependence of BT0 on the number of undulator periods, N, is reduced by emittance to Nx with 1≤x<2. Further reductions in the intensity result from random magnetic field errors present in the undulator. An approximate model for the intensity of the central core of radiation of the principle harmonics is discussed and the results compared to those from Monte Carlo-type calculations where emittance is explicitly accounted for. An estimation of the effects of random field errors on the on-axis brightness in the presence of nonzero particle emittance is made. For the particular case of undulators proposed for the 7-GeV Advanced Photon Source, the results indicate that 5-m-long devices segmented into two sections will provide the required spectral intensity of a single long undulator when both emittance and magnet errors are considered.
Ion-surface interaction system (ISIS) for the study of redeposited materials: An application of decelerated ion beams with quartz-crystal microbalances
Authors: Youchison D. L. , Nahemow M. D.
Published: July 2002

The ion-surface interaction system (ISIS) is a facility developed for the study of redeposited fusion impurity control surfaces. It was designed to investigate variations in the sputtering yield and surface binding energy caused by alterations to the surface microstructure. ISIS can create redeposited films similar to that found on tokamak limiters continuously sputtering a target at incident energies representative of a tokamak edge plasma. A duoplasmatron ion source is used to produce well-focused, mass-analyzed 30-keV particle beams of H+ to Xe+ with fluxes of 1E15 to 7E15 ions/cm2 s. These beams are decelerated to the 100–1000 eV range before target impact with currents from 50 to 900 μA. The sputtered neutrals are ionized, accelerated to the incident sputtering energy, and deposited onto another target substrate in a controlled background. The deposited film is then sputtered in situ to determine changes in sputtering yield and surface binding energy. The sputtering and redeposition of the ionized sputtered particles is monitored via a unique dual quartz-crystal-microbalance apparatus. As many as eight samples are accommodated in this apparatus by a carousel arrangement that facilitates the redeposition while permitting the exchange of crystals (targets) under vacuum. Targets may be either bulk samples or films evaporated onto planar 4.4-MHz AT-cut quartz crystals. The system is complete with computerized data acquisition, residual gas analysis, and multiple current transducers.
An interrupted field time-of-flight (IFTOF) technique in transient photoconductivity measurements
Authors: Kasap S. O. , Polischuk B. , Dodds D.
Published: July 2002

An interrupted field time-of-flight (IFTOF) technique that enables displacement-current-free measurement of the photocurrent in the conventional transient photoconductivity experiment is described and implemented. During the drift of the photoinjected charge carriers across the sample, the applied field is removed at time T1 and reapplied at time T2=T1+ti, where ti is the interruption time. During the interruption period ti, the charge carriers interact with the deep traps so that the recovered photocurrent when the field is reapplied at T2 = T1 + ti indicates the concentration of carriers remaining in the transport band. Although the IFTOF technique has a number of distinct advantages for studying charge trapping and release processes in high-resistivity solids, it has generally not been adopted as a convenient experiment since the sample capacitance results in large displacement currents at switching.

The present paper describes a Schering-type bridge network that is excited by a switchable floating high-voltage supply. Recently available high-voltage complementary TMOS transistors were used to switch voltages as high as 500 V. Trigger signals to initiate the various IFTOF events were simply and economically generated from TTL logic gates and IC timers while the required time delays were obtained via clocked digital countdown techniques. The IFTOF method was successfully applied to the examination of hole trapping processes in chlorinated a-Se:0.3%As xeroradiographic-type films for which the conventional TOF measurement indicated essentially trap-free photocurrent. Using the IFTOF technique, it is shown that over a time scale far exceeding the conventional TOF transit time, the photoinjected hole concentration under low field conditions decays almost exponentially with a well-defined trapping time τ. Furthermore, by interrupting the electric field while the photoinjected charge packet is at different locations in the film, it is shown that the IFTOF technique may be used to examine the dependence of the trapping time on the distance into the film. IFTOF is therefore a valuable technique for studying trapping inhomogeneities in amorphous semiconductor films. It is expected that the simple displacement-current-free IFTOF technique described in this paper, with further improvements, may be applied to study charge carrier trapping and release kinetics in a wide variety of high-resistivity solids.
A very-low-inductance triggered multichannel surface switch
Authors: Buzzi J. M. , Doucet H. J. , Jones W. D. , Lamain H. , Rouillé C.
Published: July 2002

Triggered surface switches built on planar lines ranging in width from a few cm up to 40 cm, and having from 1 to 39 current channels, have been measured to have inductances of the order of a few nH. Such low inductances guarantee that this type of switch, which is suitable for use in very-fast-current-rise-time, multi-kA, multi-kV circuits will not, itself, set a lower limit on the current rise time of the circuit. The formation of the channels is in the range of 20–100 ns and the jitter can be as low as 1–2 ns.
A simplified double-tuned 31P-1H circuit for NMR i
n v
i
v
o spectroscopic experiments
Authors: Leroy-Willig Anne , Bittoun Jacques , Kan Siew , Gonord Patrick
Published: July 2002

A simplified time-shared double-tuned 31P-1H probe was designed primarily for 31P signal observation and 1H field shimming purposes. The pulsed 1H current is impeded from reaching the 31P channel by a length of cable whose length combined with that of the quarter-wavelength cable in the 31P circuit is equal to an odd number of quarter-wavelengths at the 1H frequency. An analysis shows that this scheme may lead to a lower Q and a slight power on/off probe detuning for the 1H channel. An experimental evaluation of the normalized sensitivity shows that there is only a slight drop in performance of the order of 10% with respect to a commercial single-frequency unit.
Efficient generation of multigigawatt rf power by a klystronlike amplifier
Authors: Friedman M. , Krall J. , Lau Y. Y. , Serlin V.
Published: July 2002

This article addresses the new development of high-power rf klystronlike amplifiers using modulated intense relativistic electron beams. Development of these amplifiers follows earlier research in which the interaction between a high-impedance (120-Ω) intense relativistic electron beam and a low-power rf pulse resulted in the generation of coherent bunches of electrons with excellent amplitude and phase stabilities. In the present experiment a low-impedance (30-Ω) large-diameter (13.2-cm) annular electron beam of power ∼8 GW was modulated using an external rf source (magnetron at 1.3 GHz) of 0.5 MW power. The interaction of the modulated electron beam with a structure generated a 3-GW rf pulse that was radiated into the atmosphere. The self-fields of the intense beam provided significant electrostatic insulation against vacuum breakdown at the modulating gaps and at the rf extraction gap.
Simple modification of Varian E-line microwave bridges for fast time-resolved EPR spectroscopy
Authors: Forbes Malcolm D. E. , Peterson John , Breivogel Christopher S.
Published: July 2002

Modification of the popular Varian E-line series of electron paramagnetic resonance (EPR) spectrometers for fast direct detection EPR spectroscopy is described. The overall time response and signal reproducibility of the spectrometer is improved by changing the values of two capacitors in the microwave bridge preamplifier circuit, with no alteration of instrument performance in normal field-modulated experiments. The rise times are slew rate limited for large input signals. There is a propagation delay of 40 ns before any preamplifier response is observed. Signal-to-noise ratios for the direct detection EPR experiment with the modified and unmodified bridges are comparable. A test of the modified bridge using a biradical, formed within 20 ns by laser flash photolysis, shows a signal decay consistent with that measured by optical methods, in contrast to the unmodified circuit. Other factors influencing the time response of the experiment are discussed. While the preamplifier rise time is still the limiting factor, spectra as close as 70 ns to the laser flash can now be measured with adequate signal-to-noise ratios.
Microcomputer-controlled, programmable current source for NMR measurements at very low temperatures
Authors: Skyba Peter
Published: July 2002

The construction and electrical characteristics of a programmable, microprocessor-controlled current source are described. The source is suitable for supplying superconducting nuclear magnetic resonance magnets as well as for general applications. The source has a bipolar output with maximum output current ±5 A/±10 V with stability better than 5×10−5 and the current step 160 μA. The rate of excitation of the output current may be varied from 2 ms to 9.999 s per step, with 1 ms resolution. The source is fully programmable via HP-IB bus.
Poloidal magnetic field measurement system in JT-60
Authors: Nishino Nobuhiro , Kubo Hirotaka , Sakasai Akira , Koide Yoshihiko , Akaoka Nobuo , Sugie Tatsuo , Tsukahara Yoshimitu , Ito Takao , Takeuchi Hiroshi
Published: July 2002

A diagnostic system using a helium beam for local poloidal magnetic field measurements (Zeeman polarimeter system) has been constructed. The Zeeman spectrum of the helium 31P-21S line was observed in JT-60. The intensity and energy of the neutral helium beam were up to 0.6 A and 200 keV, respectively. Resolution of the Zeeman polarimeter was 0.01 nm which was realized by using a Littrow-type spectrometer. Photon counting efficiency was 0.065. Moreover, an in situ wavelength calibration could be done, using an Ar laser, within an error of 0.001 nm.
Cryopumping of atomic hydrogen
Authors: Luppov V. G. , Mertig M. , Roser T. , van Guilder B. S. , Vuaridel B. , Melnik Yu. M. , Prudkoglyad A. F.
Published: July 2002

The pumping speed for the cryopumping of an atomic hydrogen beam was measured. Measurements were made for cryocondensation, cryosorption, and differential pumping. The pumping speed for atomic hydrogen was observed to be much smaller than the pumping speed for molecular hydrogen. It is believed that this is due to the energy released during the recombination of the atomic hydrogen.
A high-frequency sinusoidal phase-modulation interferometer using an electro-optic modulator: Development and evaluation
Authors: Minoni U. , Sardini E. , Gelmini E. , Docchio F. , Marioli D.
Published: July 2002

An optical interferometric instrument for the measurement of distance and position is presented. The system is based on a high-frequency sinusoidal phase-modulation interferometer. Phase modulation of the laser beam in one of the two interferometer arms is obtained by means of an electro-optic modulator operating at frequencies up to 10 MHz. The electronic unit performs synchronous demodulation of the signal coming from the photodetector. The resulting signals are fed to an up-down counting logic that is interfaced to a personal computer. The performance of the instrument has been evaluated by means of a system calibration against a reference high-precision commercial interferometer. The overall accuracy of the system resulted to be within 80 nm, at target speeds up to 1 m/s. In this article, the optical setup, the electronic equipment, and the calibration results are presented.
A simple two-stage cascading spark gap for ultraviolet preionized transversely excited atmospheric CO2 lasers
Authors: Tou T. Y. , Low K. S. , Tan B. C.
Published: July 2002

A simple trigatron spark-gap chamber is modified to accommodate two cascading high-voltage breakdowns, separated by the time lag of the second spark formation. The time lag is employed as a temporal delay for synchronizing the ultraviolet preionization and the main discharge in the transversely excited atmospheric CO2 laser. Owing to prompt triggering and in situ preionization of the second breakdown, reliable delay up to 500 ns is possible by simply varying the separation of the second spark-gap electrode to that of the first spark gap.
An exact analysis for beam centroid position monitors used in pulsed intense relativistic electron-beam experiments
Authors: Rienstra W. W. , Haworth M. D.
Published: July 2002

Azimuthal arrays of B-dot loops are often used to measure the time-resolved beam centroid location of a pulsed, intense relativistic electron beam propagating in a metallic drift tube. A new analytical analysis is presented which can solve for the beam centroid position exactly, even for large radial displacements near the drift tube wall. This exact method is compared with the traditional first-order analysis.
Absolute values of ac susceptibility for rectangular prism specimens
Authors: Mrachkov J. , Kirov M.
Published: July 2002

Absolute values of ac susceptibility of specimens shaped as a rectangular prism are obtained by numerical calculations of the magnetic field created by the specimen. The obtained values for superconducting samples are compared with the expected value.
An improved infrared technique for sorting pecans
Authors: Graeve Thorsten , Dereniak Eustace L. , Lamonica John A.
Published: July 2002

This paper presents the results of a study of pecan spectral reflectances. It describes an experiment for measuring the contrast between several components of raw pecan product to be sorted. An analysis of the experimental data reveals high contrast ratios in the infrared spectrum, suggesting a potential improvement in sorting efficiency when separating pecan meat from shells. It is believed that this technique has the potential to dramatically improve the efficiency of current sorting machinery, and to reduce the cost of processing pecans for the consumer market.
Advanced viscometric thermometer: Steady and unsteady state temperature measurement in electric or magnetic fields
Authors: Seyed-Yagoobi Jamal
Published: July 2002

The viscometric thermometer is one of the few simple and inexpensive methods of temperature measurement in the presence of electric or magnetic fields. This work further improves our previous viscometric thermometer design so it now measures the temperature distributions in both steady and transient states with a response time of a few seconds or less.
An ultrasoft x-ray fluorescence detector for EXAFS measurements on low-Z elements
Authors: Maeyama Satoshi , Oshima Masaharu , Shoji Takashi , Yamamoto Hikoshi
Published: July 2002

An ultrahigh vacuum compatible x-ray detector has been developed for measuring the extended x-ray absorption fine structure (EXAFS) of low-Z elements (C,N,O) by fluorescence yield detection. The detector is a type of gas scintillation proportional counter, with a better energy resolution than conventional gas proportional counters. Two Mylar windows of 0.6 μm thickness and 36 mm diameter in series, in combination with a differential pumping system, were utilized for the entrance of ultrasoft x-ray fluorescence. The energy resolution (full width half maximum) of 46% at 183 eV was confirmed by measuring the boron Kα pulse height distribution curve. Fluorescence yield EXAFS spectra, with high signal-to-background ratios, were obtained above O and N K edges of thin SiO2 and Si3N4 films for the first time by using this detector. These results demonstrate that the newly developed detector with improved energy resolution is extremely useful for fluorescence yield EXAFS measurements of low-Z atoms on the surface and in the bulk.
Probe measurements in the REPUTE-1 reversed field pinch
Authors: Ji H. , Toyama H. , Yamagishi K. , Shinohara S. , Fujisawa A. , Miyamoto K.
Published: July 2002

A four-channel triple-probe and magnetic-probe array, a complex probe which consists of three types of probes and two eight-channel magnetic-probe (poloidal and toroidal) arrays, has been installed in the revised field pinch University of Tokyo experiment (REPUTE-1) reversed field pinch (RFP) device. Mean and fluctuation parts of plasma parameters, including the three components of magnetic fields, three components of electric fields, electron density, electron temperature, and space potential, are measured in 0.5a≲r≤a region. The triple-probe method and the electric field measurement are described in detail, and effects due to the fast electrons, etc., are discussed. Some experimental examples obtained in the REPUTE-1 RFP plasma are given, and the detailed results will be published elsewhere.
A flange-mounted UHV-compatible axial fatigue apparatus using a piezoelectric actuator
Authors: Sriram T. S. , Fine M. E. , Chung Y. W.
Published: July 2002

The design and construction of a flange-mounted ultra-high vacuum compatible fatigue apparatus using a piezoelectric actuator is described. This apparatus is capable of operation under ambient pressures down to 10−9 Torr. Push-pull fatigue tests can be performed under load, total strain, and plastic strain control at frequencies up to 100 Hz. Control of the fatigue tests and data acquisition are done using standard fatigue control electronics and software.
An apparatus for vapor pressure measurements of organic solids using a computer controlled null-detector
Authors: Tobaly P.
Published: July 2002

An apparatus is described for the measurement of vapor pressures of low volatility solids and liquids by a static method in the range 10−2–100 mm Hg and 30 °C–300 °C. The method consists in inserting between the pressure gauge (here a capacitance manometer) and the product to be tested, a membrane that is maintained in equipressure by a suitable control loop. Experimental problems related to this arrangement are discussed. A test of the apparatus with a known product (benzoic acid) has been performed. The results have been found to be in good accordance with data found in the literature.
A simple multipurpose data-acquisition program for PC-IBM
Authors: Antonino Grasso , Rosario Gangemi , Ulderico Wanderlingh
Published: July 2002

A basic program is described that runs on any PC-IBM. This program allows data acquisition either from most interfaciable devices (by means of IEEE 488 or RS 232), or suitable cards such as the 8255. During acquisition, recorded data can be processed and displayed, and several commands can be executed so as to modify the acquisition itself in real time. The set of commands forms a sort of programming language and an ASCII file of such commands can be executed. Some applications, already in use in our laboratory, are also described.
Thermocouple butt-welding device
Authors: Secco R. A. , Tucker R. F.
Published: July 2002

A simple and inexpensive device to make electric or gas-welded butt-join thermocouples is described. It allows for junction bead size control by means of a spring-loaded moveable block with adjustable travel. The device has been successfully tested with thermocouple wire diameters of 125, 250, and 375 μm and should also be able to accommodate smaller and larger wires with very minor modifications.
Electro-optic tensor of KTiOPO4 measured with a Fizeau interferometer
Authors: Wang B. L. , Liu X. Q.
Published: July 2002

A KTiOPO4 crystal block was used as a Fizeau interferometer. We modulated the interference pattern formed by the primary reflections from the front and rear surfaces of the crystal by the application of an electric field. The modulation is detected via a Faraday cell. In this way we measured the unclamped linear electro-optic tensor with high precision.
Suspension and thermal link of an ultralow temperature gravitational wave antenna
Authors: Coccia E. , Fafone V. , Modena I.
Published: July 2002

We discuss here the use of a mechanical suspension for the new generation of resonant gravitational wave antennas, cooled at temperatures below 0.1 K. The crucial problem of these detectors is the isolation from all external mechanical vibrations in the presence of the unavoidable solid thermal link with a dilution refrigerator. Measurements of the mechanical transfer function performed with two types of suspension-thermal link configurations are reported. This study has led to the design of the suspension and thermal link of the first ultralow temperature antenna of the Rome group ‘‘Nautilus.’’