bluuebunny/crossref_metadata_2025 huggingface dataset:
Time-resolved small-angle x-ray diffraction from contracting muscle
Authors: Vazina A. A. , Gadzhiev A. M. , Sergienko P. M. , Gerasimov V. S. , Korneev V. N.
Published: July 2002

This article is devoted to investigations of the mechanism of muscle contraction based on high time-resolution studies of meridional and equatorial diffraction patterns from frog sartorius muscle with the use of synchrotron radiation. Paired stimulation has been used for studying nonfatigued and fatigued muscles. The results obtained are discussed on the assumption of a noncontact mechanism of force development. Original viewpoints are presented on the role of repeated pulses in activation of fatigued muscles.
Measurement of hypersonic velocities resulting from the laser-induced breakdown of aerosols using an excimer laser imaging system
Authors: Schaub S. A. , Alexander D. R. , Poulain D. E. , Barton J. P.
Published: July 2002

In this article we describe a dual-pulse excimer-laser-based imaging system used in the determination of ejected material velocities resulting from the interaction of KrF laser radiation (λ=248 nm, pulse width FWHM=17 ns, I≊1011 W/cm2) with 20-μm aluminum particles under vacuum (P=10−5 Torr) conditions. Material velocities measured 200–400 ns after arrival of the incident pulse ranged from 450 to 1200 m/s.
Fast bevel cross sectioning of quantum-well semiconductor layers with high resolution
Authors: Honsberg M.
Published: July 2002

An improved bevel cross-sectioning method is presented which makes it possible to measure the thickness of relatively thin semiconductor surface layers. A staining procedure to enhance the contrast of the layers for two material systems, GaAs/GaAlAs and InP/InGaAsP, has been developed. Applying a newly constructed ball-lapping-apparatus, an ordinary optical microscope and a surface-profiler, relatively thin MBE-grown quantum-well layers (6.5 nm) can rapidly be measured with an accuracy of better than 10%, which is improved for thicker, normal layers (1000 nm) to better than 5%.
Reduction of statistical gain variations in a stabilized scintillation spectrometer based on a radioactive reference source
Authors: Sabol Jozef
Published: July 2002

A method has been developed to significantly suppress the effects of statistically distributed reference pulses on the gain of a stabilized scintillation spectrometer. A modified analog stabilization scheme equipped with a pulse derandomizer is proposed for this purpose. Using this method the energy resolution of the reference peak for reference pulse rate 10 s−1 improved nearly twice, namely from 7.9% to 4%.
ac bridge for high-temperature magnetic thermometry
Authors: Cho C. K. , Merson J. A. , Cale T. S.
Published: July 2002

A modified Hartshorn inductance bridge is used to follow changes in the magnetization of superparamagnetic samples in order to determine their average temperature. The thermometry is performed in the temperature range of 475–525 K. During routine experiments, the rms noise voltage in the bridge is approximately 300 nV when the primary coil is excited by a 200 mA rms current at a frequency of 47 Hz. This corresponds to a signal-to-noise ratio of 3000 and a temperature sensitivity of 0.015 K for typical samples studied.
Cuspidal pit formation during the growth of SixGe1−x strained films
Authors: Chen K. M. , Jesson D. E. , Pennycook S. J. , Thundat T. , Warmack R. J.
Published: July 2002

We have studied the formation of cuspidal pits during the growth of strained SixGe1−x alloy layers at relatively high supersaturations. The pit formation is directly linked to strain in the alloy layer, and we propose a heterogeneous formation mechanism in which the pits develop from stress-driven surface diffusion associated with a localized initial perturbation of the buffer layer surface.
Dead time correction of time distribution measurements
Authors: Esposito F. , Spinelli N. , Velotta R. , Berardi V.
Published: July 2002

We report in this article an analysis of the distortion of the time distribution due to the dead time of the detection chain. The special case of distributions coming from a pulsed source is considered and a relatively simple method for the reconstruction of the true time distribution is given. The method is applicable in both extended and nonextended dead times. It can be applied to correcting an experimental time distribution and, if the shape of the distribution is known, to deducing the true rate of events from that measured by a counter. An experimental method to simulate a pulsed source with a controllable mean production rate is also shown; the time distributions obtained from this source have been used as test distributions to prove the reliability of the reconstruction procedure.
Power stabilization of high-power CO laser by gas composition control
Authors: Kanazawa Hirotaka , Yamaguchi Naohito , Nakajima Takuro , Taira Tatsuji
Published: July 2002

Long time, stable operation of a high-power discharge-excited CO laser has been attained by controlling the laser gas composition. Firstly, stable obtainable laser output power was measured against the quantities of CO2 and of O2 added to the laser gas. Next, laser gas composition was recorded during sealed-off operation with various initial gas conditions and cooling conditions. Finally, the detractive effect of O2 (added to enhance attainable output power through discharge stabilization) of quickening CO2 generation and CO depletion, was counteracted through continuous extraction of the laser gas and parallel replacement with fresh gas of predetermined composition. The resulting stabilization of the laser gas composition reduced output power variations to ±3% at 3 kW power level.
Controlling the propagation axes of an ion laser
Authors: Guggenheimer S. C. , Wright David L.
Published: July 2002

The motion of the output beam from an ion laser is critical for most applications, including the pumping of other lasers. In this paper we show that for a stable ion laser cavity, the output coupler can be used to position the beam at a given point in space. In this case an actively controlled laser cavity maintains the beam position at the laser exit. For a typical ion laser with an 8 m radius output coupler optic, maintaining the output beam position reduces the total beam motion a factor of 8, 1 m from the laser. Besides reducing the total beam motion, eliminating the position offset translates to a better angular overlap of pump and a cavity modes in lasers pumped by ion lasers such as Ti:sapphire lasers.
rf-excited molecular jet plasma for reactive ion etching
Authors: Janes Joachim , Lutz Norbert
Published: July 2002

A new apparatus has been constructed combining free-jet molecular-beam technology and radio-frequency plasma production for reactive-ion etching. The beam is formed in a laval-type nozzle and is skimmed before entering the plasma chamber. The free jet enters a discharge region between two parallel plates, one of which is capacitively powered with 13.56 MHz radio frequency. The goal was to investigate the possibility of creating a high-density plasma with a linear multinozzle array for large-area wafer processing. Experiments were carried out with argon and oxygen as process gases. Jet plasma glows with lengths of about 10 cm downstream of the skimmer were detected. Jet beam profile analysis was performed measuring the distribution of dynamic pressures with the Pitot–Prandtl method.
An integrated microwave Doppler cinemometer for transport applications
Authors: Descamps P. , Bekkali M. El , Vindevoghel J.
Published: July 2002

In order to automate the driving of terrestrial vehicles it is necessary to know at any time and with the highest accuracy the values of the speed of the vehicle and of the distance covered by the vehicle; it is also necessary to know the direction of the motion relative to the ground. These values must be measured in the real-time domain and this involves that contactless and very low time-constant sensors must be used. On the other hand, the applications concerned ask for a miniaturization of the whole measurement system. For these reasons, sensors using the Doppler effect in the microwave range are particularly well convenient to these applications. We developed an X band microwave Doppler cinemometer (MDC) with a printed antenna that is built using microstrip technology.
A system to study the stability of the wires of multiwire proportional chambers exposed to a 10 G time variable force field
Authors: Ceci N. , Rainò A. , Spinelli P. , Stagno V.
Published: July 2002

We report the results of a system to test the behavior of the wires of multiwire proportional chambers (MWPC) exposed for 10 min to a uniform force field of about 10 G strength and variable in time in the frequency range 0–2000 Hz. This acceleration will be present when the chambers, mounted inside a cosmic ray spectrometer, are launched by the Space Shuttle towards the NASA Space Station ‘‘FREEDOM.’’ We have reproduced these conditions in the laboratory by an electronic device and we have found that, after repeated cycles of this treatment, the wire performance remained unchanged. This system can also be used to control the tension of the wires of a MWPC during its normal testing procedure.
Fluorescence sorting instrument for the removal of aflatoxin from large numbers of peanuts
Authors: Pelletier M. J. , Spetz W. L. , Aultz T. R.
Published: July 2002

A device capable of measuring fluorescence intensities from peanut surfaces and physically rejecting peanuts having undesired fluorescence properties is described. The device operates at a feed rate of 22 000 peanut halves per hour. The entire surface of each peanut is examined as 10 to 20 discrete spatial regions. Fluorescence intensities from each spatial region of each peanut are used to make accept/reject decisions in real time and are stored on an optical disk for off-line analysis.
Statistical analysis of interferometer detection systems
Authors: Opat Geoffrey I.
Published: July 2002

Interferometers are often used to measure small phase shifts introduced into the paths of recombining beams by some physical influence. An analysis of the associated counting statistics is presented leading to a maximum likelihood prescription for extracting the (small) phase shift. Although presented in the context of neutron interferometry, the results are easily extended to other situations involving particle counting.
Postfabrication native-oxide improvement of the reliability of visible-spectrum AlGaAs–In(AlGa)P p-n heterostructure diodes
Authors: Richard T. A. , Holonyak N. , Kish F. A. , Keever M. R. , Lei C.
Published: July 2002

Data are presented on the electrical behavior and the reliability of postfabrication native-oxide-passivated visible-spectrum AlGaAs–In(AlGa)P p-n heterostructure light emitting diodes (LEDs). The LEDs are oxidized (H2O+N2, 500 °C, 1 h) after metallization, thus sealing all exposed AlGaAs crystal at cracks, fissures, and edges against atmospheric hydrolysis without degrading their light-output characteristics. The current–voltage (I–V) characteristics of the oxide-passivated LEDs are shown to exhibit normal p-n diode behavior (∼1.9 V at 20 mA). The reliability of the oxidized devices in high-humidity conditions is greatly improved compared to otherwise identical unoxidized LEDs. The latter degrade to less than 50% of initial output power at 1500 h accelerated life test in high-humidity environments, compared to the oxidized LEDs not degrading noticeably in output power after 2500 h.
Sub-10 nm lithography and development properties of inorganic resist by scanning electron beam
Authors: Fujita J. , Watanabe H. , Ochiai Y. , Manako S. , Tsai J. S. , Matsui S.
Published: July 2002

We report the self-developing properties of an AlF3-doped LiF inorganic resist under irradiation by a scanning electron beam with an energy of 20–50 keV are reported. The self-development properties strongly depended on both AlF3 concentration and film thickness. To explain this behavior, we presented an exposure model that takes into account a balance between a carbon contamination and a diffusion process. By optimizing resist qualities, we were able to delineate 5 nm linewidth patterns with 60 nm periodicity using a 30 kV electron beam.
An analysis of the optics of a field ionization ion source for application with a scanning proton microprobe
Authors: Colman R. A. , Allan G. L. , Legge G. J. F.
Published: July 2002

This article analyzes a field ionization source for use within a pelletron accelerator which provides the primary beam for a scanning proton microprobe. The charge simulation method is used to calculate the electrostatic field, and ray tracing is used to determine optical properties. Current characteristics are taken from experimental results. Gaussian properties indicate an effective source radius of below 10−3 μm at low angles. Chromatic aberration is calculated by perturbing initial particle energies, then tracing back from field-free trajectories. Calculations indicate that at typical source voltages, the beam is never chromatically limited. Spherical aberration is also calculated and the source is found to be spherically limited above a divergence of approximately 0.1 rad. Finally, calculations indicate that a brightness of 106 A m−2 rad−2 V−1 is achieved by the source producing 150 pA of current at a tip electric field of 25 V/nm.
Measurements and modeling of helium and carbon ion plumes (abstract)
Authors: Synakowski E. J. , Bell R. E. , Johnson D. W. , Stratton B. C.
Published: July 2002

Following charge exchange between fast neutral atoms and impurities, emission from the charge exchange product can take two forms. The first is prompt radiation due to rapid cascading of the excited electron following the charge exchange event. In addition, as a result of electron impact excitation from the ground state before ionization, the impurity can subsequently radiate at the chosen wavelength. Depending on the beam-sightline geometry, plasma density, and species observed, the emission of this ‘‘ion plume’’ can rival the prompt emission, making it a potentially important consideration for ion temperature and density measurements. Direct measurements of this ion plume radiation after the charge exchange event have been made for He+ ions (n=4–3, 4686 Å) and C5+ ions (n=8–7, 5292 Å). The ratios of plume radiation to prompt charge exchange radiation for these transitions is compared to predictions from modeling, and good agreement is found. This work was supported by U.S. Department of Energy Contract No. DE-AC02-76-CHO-3073.
X-ray diagnostics for ultrashort laser produced plasma experiments (abstract)
Authors: Shepherd R. , Price D. , Nathel H. , White W. , Slaughter D. , Stewart R.
Published: July 2002

The characterization of subpicosecond laser produced plasmas is currently being investigated by the Livermore ultrashort pulse laser group. A 800-nm, 150-fs, 35-mJ laser is focused to a 7-μm spot on solid aluminum targets, producing XUV (<1 keV), K shell (1.5–30 keV), and hard (≥3.0 keV) x-ray emission. The K-shell emission is studied using a Von Hamos crystal spectrograph with a KAP crystal curved to an 80-mm radius, resulting in a calculated resolution of E/ΔE≊400. The dispersed x rays are detected with a microchannel plate intensified reticon detector which relays the images out of the chamber and displayed on a computer monitor. The hard x rays are monitored with an array of filter x-ray diodes, covering energies from 3 to 75 keV. The XUV emission is monitored with a variably spaced line grating, flat field spectrometer, and a grazing incidence spectragraph. The diagnostics will be presented along with current data from experiments. This work was performed under the auspices of the U. S. Department of Energy by Lawrence Livermore National Laboratory under Contract No. W-7405-ENG-48.
K- and L-shell absorption spectroscopy of laser-produced plasmas (invited)
Authors: Chenais-Popovics C. , Back C. A. , Renaudin P. , Audebert P. , Geindre J. P. , Gauthier J. C.
Published: July 2002

Diagnostic by Kα and Lα,β absorption spectroscopy leads to information on the ionization state, the electronic temperature, and matter density of laser-produced plasmas. In particular, a mapping of the ionic populations is possible by recording the spectra on space-resolved x-ray spectrographs. The plasma to be probed and the x-ray backlighter source are produced by different beams of the same frequency-doubled Nd laser. Kα spectroscopy probes F-like to He-like ions and Lα,β spectroscopy is a diagnostic of higher atomic number ions stripped into configurations around the Ca-like structure. Measurements of dense matter radiatively heated at temperatures around 50–100 eV in laser-irradiated multilayered targets or x-ray heated samples evidence the effect of radiative heating on the temperature gradient in the target. The space and time-resolved measurements of the corona of a low temperature aluminum plasma are presented.
Thermal ionization effects on inner-shell line emission for Au target heated by intense light ion beams
Authors: Wang P. , MacFarlane J. J. , Moses G. A.
Published: July 2002

In order to deduce the experimental beam conditions from the observed x-ray line emission spectrum of high Z elements, atomic radiative data for transition energies and oscillator strengths, ion-atom impact ionization cross sections, Coster–Kronig yields, and fluorescence yield are needed. In this paper, we report on calculations to study the dependence of these atomic data on ionization stage. It has been found that proton impact ionization cross sections decrease slowly with increasing ionization stage, and the fluoresence yields have discrete jumps when the dominant Auger, Coster–Kronig transitions become energetically forbidden. Our study indicates that thermal ionization effects are not important for the dominant K-, L-, and M-line emissions for plasmas with Te ∼ 102 eV.
Electronics for microchannel plate detectors of a Thomson scattering system
Authors: Bassan M. , Pasqualotto R. , Sardella A. , Giudicotti L.
Published: July 2002

We describe electronics developed for the operation of multianode microchannel plate (MCP) photomultipliers in a multipoint Thomson scattering system. A pulsed, digitally programmable high voltage power supply with current feedback and a built-in protection circuit has been designed to bias the detector in safe conditions, taking into account the nonlinear behavior of the MCP resistance. The 180-V photocathode voltage is switched by a fast, current driven, optically coupled metal-oxide-semiconductor field-effect transistor. Gating pulses with 10-ns rise time and 50–500-ns programmable duration are generated with negligible noise at the output anodes.
Short wavelength interferometer for ITER
Authors: Snider R. T. , Carlstrom T. N.
Published: July 2002

There is a need for a real time, reliable density measurement compatible with the restricted access and radiation environment on International Thermonuclear Experimental Reactor (ITER). Due to the large plasma path length, high density and field, refraction, and Faraday rotation effects makes the use of contemporary long wavelength (≳50 μm) interferometers impractical. In this paper we consider the design of a short wavelength vibration compensated interferometer which allows operation without a prohibitively large vibration isolated structure and permits the optics to be conveniently mounted directly in or on the tokamak. A density interferometer design for ITER incorporating a 10.6 μm CO2 interferometer with vibration compensation provided by a 3.39 μm HeNe laser is discussed. The proposed interferometer design requires only a small intrusion into the ITER tokamak without a large support structure, refraction and Faraday rotation problems are avoided, and it provides a density resolution of at least 0.5%. Results are presented from an interferometer installed on the DIII-D tokamak incorporating essential elements of the proposed ITER design including 10.6 and 3.39 μm lasers, a retroreflector mounted on the vacuum wall of the DIII-D tokamak and real-time density feedback control. In this paper we consider a short wavelength interferometer design that incorporates vibration compensation for use on ITER. Our primary concern is to develop an interferometer design that will produce a reliable real time density monitor. We use the ITER conceptual design activity report as the basis of the design.
Proton beam targets shot on PBFA-II
Authors: Derzon D. K. , Aubert J. H. , Schneider D. A. , Assink R. A. , Sawyer P. S. , McNamara W. F.
Published: July 2002

In recent proton beam experiments on PBFA-II, foam-filled gold targets and gas-filled spherical exploding pushers were shot as physics targets. Surrounding these targets were gold foils used to characterize the beam. The target fabrication and characterization are presented in this paper.
A simple unfold method for Rutherford scattering, intense ion-beam spectrographs
Authors: Fehl D. L. , Leeper R. J. , Kensek R. P.
Published: July 2002

Elastic Rutherford scattering with subsequent momentum analysis has become a powerful tool for analyzing intense, pulsed light-ion beams for inertial confinement fusion studies. The ion spectrum is obtained by mathematical inversion of the data. This paper reports a product-integration solution to the inverse problem which is readily adapted to rapid data analysis and is simpler in form than reported previously. While this approach introduces some unphysical (negative) components into the solution, these are often negligible. Discussed here are the unfold method together with its accuracy and precision.
A proton activation diagnostic to measure D–3He reaction yields
Authors: Lierzer J. R. , Wenzel K. W. , Petrasso R. D. , Lo D. H. , Coleman J. W. , Li C. K. , Hsieh E. , Bernat T.
Published: July 2002

We are developing activation diagnostics for monitoring energetic charged-particle fluxes in space and laboratory plasmas. More immediately, we plan to use activation to measure the time-integrated proton flux from D–3He fusion reactions in Alcator C-MOD, providing a measure of the time-averaged D–3He fusion rate. We demonstrated the technique’s feasibility by inducing significant gamma activity in a titanium sample exposed to D–3He protons created in our Cockcroft–Walton generator. The titanium target received a fluence of 5.5×109 protons at 14.7 MeV (of order what a 3-cm2 target should receive from one shot in Alcator C-MOD) and became activated by the48Ti(p,n)48V reaction. The activity’s spectrum from a high-purity germanium (HPGe) detector showed the characteristic 0.984- and 1.312-MeV lines of 48V. The measured activity agreed reasonably well with theory. An absence of activity at those energies before D–3He activation eliminated background or D–D product-induced activity as the gamma source. We intend to repeat the experiment with a chromium target to evaluate that material’s diagnostic potential.
Diagnostics for ITER; A status report (invited)
Authors: Young K. M.
Published: July 2002

The protocol agreement allowing the design of the International Thermonuclear Engineering Reactor (ITER) to proceed will be signed early this year. There is already a small U.S. Program evaluating diagnostic capability for this device and there will shortly be an international effort on diagnostics to ensure satisfactory integration of the diagnostic systems with all the complex systems that will be developed for this large ignited tokamak. The diagnostic studies, at least initially, will depend heavily on the output information provided by the conceptual design activity (CDA). ITER provides a very large plasma (R=6.0 m, a=2.15 m) with high average density (<ne≳∼1.0×1020 m−3), and temperatures (<Te≳∼<Ti≳≥10 keV). It is highly elongated and could have primarily noninductive current drive so that its pulse length can be very long (t≤2 weeks) to allow significant blanket testing in its technology phase. These parameters lead to considering new diagnostic methods for some measurements. A set of specifications for the diagnostic measurements were developed, and a corresponding set of diagnostic instruments was proposed during the CDA. The specifications for spatial and temporal measurement of the plasma parameters are very similar to those achieved on present day large tokamaks, where, on the whole, the access to the plasma is much more open and there is a negligible radiation background in which the diagnostics have to perform.

The specifications require that many diagnostic signals participate in the control of complex fuelling, heating, and current drive schemes, so it is clear that the diagnostic design issues for these burning plasmas must be addressed early in ITER’s design life. This is particularly true because penetrations through the first wall are at a premium and only small holes can be tolerated because of radiation streaming. The needs for Research and Development, necessary to demonstrate the feasibility of diagnostic techniques for the ITER plasma parameters and the radiation environment were also addressed. In the area of radiation impact on diagnostic components, some priorities have been set and testing programs have been started. This report will address the present activities on diagnostics in the U.S. Program to address some of the problems left over from the CDA.
Reconstruction of current density distributions in the CDX-U tokamak
Authors: Hwang Y. S. , Forest C. B. , Darrow D. S. , Greene G. , Ono M.
Published: July 2002

Magnetic diagnostics are used to reconstruct current density profiles in noninductively driven plasmas in the CDX-U tokamak. The boundary magnetic fields are measured by 32 pickup coils and three flux loops attached at different poloidal positions inside the CDX-U vessel; in addition, internal magnetic probes are also used. Significant eddy currents are measured on the thick aluminum vessel and accounted for in the analysis. Two-dimensional current density distributions and magnetic flux contours are reconstructed from these measurements using a least-square-error technique. A finite element description of plasma currents is useful for general magnetic geometries which evolve from open field lines to closed flux surfaces. By increasing the number of elements, a converged current density distribution is obtained.
New reflectometer systems for the DIII-D tokamak (abstract)
Authors: Doyle E. J. , Kim K. W. , Burns S. , Nguyen X. , Peebles W. A. , Rhodes T. L.
Published: July 2002

During a machine vent in December 1991, two new reflectometer systems were successfully installed and tested on the DIII-D tokamak. The first is an X-mode broadband system primarily intended for density profile measurements, utilizing BWO sources and covering Q and V frequency bands (33–50 and 50–75 GHz). The second system is an adaptation of a pre-existing inside launch (high field side) ECRH waveguide to provide an inside launch reflectometer capability at the same frequencies and polarization as an outside launch fixed frequency O-mode system. The new systems will have a dual role in both directly supporting the DIII-D physics program, and also acting as flexible and adaptable test beds for the development of reactor relevant reflectometer systems, such as required for ITER. Specific examples of planned measurements include investigation of possible in/out plasma asymmetries at the L–H transition and ELMs, and demonstration of routine and reliable density profile measurements. It is expected that preliminary data from the inside launch system will be available by the time of the conference. This work is supported by the U. S. Department of Energy under Grant No. DE-FG03-86-ER53225 and General Atomics subcontract SC120536 under DOE Contract No. DE-AC03-89ER51114.
Measurements of electron parallel momentum distributions using cyclotron wave transmission (abstract)
Authors: Boyd D. A. , Skiff F. , Colborn J. A.
Published: July 2002

The method of cyclotron wave transmission for measuring the electron parallel momentum distribution is studied in a lower-hybrid driven tokamak plasma. Questions of resolution, sensitivity, and technique are addressed. Measurements are made of the suprathermal distribution produced by current drive as well as the incremental changes in the distribution function produced by short pulses of lower-hybrid waves. The results indicate that cyclotron wave transmission is well suited for studies of electron velocity space phenomena and may be used to detect the effect of diagnostic perturbations. This research was supported by the U. S. Department of Energy.
Generalization of linac mode spectrum and fitting procedure
Authors: Shanker O.
Published: July 2002

An earlier report presented a method for analytically extracting the intercavity coupling constants from the measured mode spectrum of a side-coupled standing wave linear accelerator. The method required that the linac stack be terminated by half cavities at either end. We extend the work to include all other possible terminations. The results derived here are used to analyze the mode spectrum of a linac tube fabricated at our institution.
Digital images from your old scanning electron microscope
Authors: Dubson M. A. , Zhu Qifu
Published: July 2002

We describe an inexpensive procedure for obtaining digital images from a scanning electron microscope (SEM) which produces only analog output. Using a 286-class PC and a 20 kHz A/D board, and with no modification of our SEM, we record digitized SEM images with a resolution of 512×480 pixels.
Magnetic-spiker sustainer discharge excitation of a wide aperture small-gap TEA-CO2 laser
Authors: Taylor R. S. , Leopold K. E.
Published: July 2002

Magnetic-spiker sustainer technology has been used to generate pulsed TEA-CO2 laser outputs of ∼2 J from ultrawide aperture (8 cm), small electrode gap (1 cm) discharges with a laser efficiency of 10.6%.
Control of the neutron detector count rate by optical imaging
Authors: Roquemore A. L. , Johnson L. C.
Published: July 2002

The signal processing electronics used for the NE451 detectors on the TFTR multichannel neutron collimator are presently showing saturation effects at high counting rates equivalent to neutron yields of ∼1016 n/s. While nonlinearity due to pulse pileup can be corrected for in most present TFTR experiments, additional steps are required for neutron source strengths above ∼3×1016 n/s. These pulse pileup effects could be reduced by inserting sleeves in the collimator shielding to reduce the neutron flux in the vicinity of the detectors or by reducing the volume of detector exposed to the flux. We describe a novel method of avoiding saturation by optically controlling the number neutron events processed by the detector electronics. Because of the optical opacity of the ZnS-plastic detectors such as NE451, photons from a proton-recoil scintillation arise from a spatially localized area of the detector. By imaging a selected portion of the detector onto a photomultiplier, we reduce the effective volume of the detector in a controllable, reversible way. A prototype system, consisting of a focusing lens, a field lens, and a variable aperture, has been constructed. Results of laboratory feasibility tests are presented.
The general purpose two-circle diffractometer on Station 9.1, Daresbury Laboratory
Authors: Bushnell-Wye G. , Cernik R. J.
Published: July 2002

Station 9.1 at Daresbury Laboratory houses a general purpose two-circle diffractometer which can be variously configured for high or low angular resolution. Being only 16 m from the tangent point of the 5-T wiggler magnet, it receives a high flux and is therefore ideally situated for experiments on both crystalline powders and liquid and amorphous systems. Both capillary and flat-plate geometry are available, and experiments can also be performed using grazing incidence from surfaces. A choice of monochromators can maximize the flux or provide stable wavelength control for measurements exploiting anomalous dispersion. High- and low-temperature sample environments are available in addition to controlled atmospheres for in situ investigation of chemical reactions.
Evaluating the accuracy of optical-streak-camera sweep rates using uncertain data
Authors: Montgomery D. S. , Lerche R. A. , Laumann C. W. , Wiedwald J. D. , Drake R. P.
Published: July 2002

A number of optical streak cameras are routinely operated for experiments at the Lawrence Livermore National Laboratory Nova laser facility. We report results from a study of the accuracy and reproducibility of the sweep rate. The sweep rates, measured using a 3 GHz pulse generator, vary by ±1.3% rms for data collected routinely over a several month period. Using statistical analysis, we develop an analytic model describing the effect of noise on our measurement technique in order to estimate the actual variation in the sweep rate. Numerical simulations of the effect of noise on the uncertainty of our measurement technique show close agreement with the model. By applying this model, we estimate that the sweep rate is reproducible to at least ±1.2%, and that the measurement technique contributes ±0.5% uncertainty. Other data are presented which support this estimate.
A field portable scanner for analysis of thin layer chromatography plates based on multiwavelength image processing
Authors: Aldridge Paul K. , Callis James B. , Burns David H.
Published: July 2002

A field portable, multiwavelength, digital image processing system for the analysis of thin layer chromatography plates is described. The imaging module consists of a two-dimensional charge coupled device detector, a xenon strobe light source, a stepper driven filter wheel for wavelength selection, and hardware to digitize images. The instrument is controlled by a laptop computer resulting in a compact device the size of a 6-in. thick briefcase. As a representative application, software has been developed for the automated analysis of sulfa residues in pork products by thin layer chromatography (USDA SOS-test). Response to analyte concentration is linear over two and one half orders of magnitude with a correlation coefficient of 0.9998. Detection limit is 80 pg for sulfamethazine spotted on a plate.
A liquid-helium-cooled absolute reference cold load for long-wavelength radiometric calibration
Authors: Bensadoun Marc , Witebsky Chris , Smoot George , De Amici Giovanni , Kogut Al , Levin Steve
Published: July 2002

We describe a large (78 cm) diameter liquid-helium-cooled blackbody absolute reference cold load for the calibration of microwave radiometers. The load provides an absolute calibration near the liquid-helium (LHe) boiling point, with total uncertainty in the radiometric temperature of less than 30 mK over the 2.5–23-cm wavelength (12–1.3 GHz) operating range. Emission from those parts of the cold load not immersed in LHe is ≤25 mK and the reflection coefficient is ≤3.5×10−4. This cold load has been used at several wavelengths at the South Pole, Antarctica and at the White Mountain Research Station, California to calibrate spectral measurements of the cosmic microwave background radiation. For the instruments operated at 20-, 12-, 7.9-, and 4.0-cm wavelength at the South Pole, the total corrections to the LHe boiling-point temperature (∼3.8 K) were 48±23, 18±10, 10±18, and 15±16 mK, respectively. In operation, the average LHe loss rate was ≤4.4 ℓ/h, allowing day-long periods of operation without a LHe fill. The boiloff rate is not strongly dependent on the radiative load at the aperture, yielding very stable operation and radiometric performance. Design considerations, radiometric and thermal performance, and operational aspects are discussed. A comparison with other LHe-cooled reference loads including the predecessor of this cold load is given.
Development of a transient internal probe diagnostic
Authors: Spanjers G. G. , Galambos J. P. , Bohnet M. A. , Jarboe T. R. , Christiansen W. H. , Wurden G. A. , Wright B. L. , Smith R. J.
Published: July 2002

The transient internal probe (TIP) diagnostic is a novel method for probing the interior of hot magnetic fusion plasmas. In the TIP scheme, a probe is fired, using a two-stage light gas gun, through a hot plasma at velocities up to 5 km/s, and makes direct, local measurements of the internal magnetic field structure. The data are relayed to the laboratory optical detection system using an incident laser that is directed through a Faraday rotator payload acting as a magneto-optic sensor. Ablative effects are avoided by minimizing the probe size, limiting the time that the probe is in the hot plasma, and encasing the probe with a diamond cladding. The degree to which the diamond probe cladding is susceptible to ablative effects will determine the plasma density and temperature regime in which the TIP diagnostic can be used. If the TIP suffers significant ablation it is an indication that the diagnostic is not usable on this hot and dense of a plasma (or that greater velocity must be imparted to the probe to further minimize the time that it is in the plasma). A quantitative experimental study of the ablation rates of diamond is planned as part of the TIP development. The integrated TIP system will be functional in 1992 and installed on the Helicity Injected Torus (HIT) [T. R. Jarboe, Fusion Tech. 15, 9 (1989)] at the University of Washington.
Resonant tunneling through ErAs semimetal quantum wells
Authors: Brehmer D. E. , Zhang Kai , Schwarz Ch. J. , Chau S.-P. , Allen S. J. , Ibbetson J. P. , Zhang J. P. , Palmstro/m C. J. , Wilkens B.
Published: July 2002

Resonant tunneling is observed in double barrier resonant tunneling diodes with semimetallic ErAs quantum wells. Magnetic field dependence distinguishes two different resonant channels while the thickness dependence of the voltage for resonant tunneling strongly suggests that the electrons tunnel through hole states in the semimetal quantum well.
Heating stage for in situ studies of thin-film reactions
Authors: Schwarz R. B. , Rubin J. B.
Published: July 2002

We describe a method for measuring and controlling the temperature of thin ceramic plates which are used as substrates for the deposition of thin films in high vacuum. The ceramic plates have an embedded platinum resistor which acts as both heating element and thermometer. The temperature of the substrate is controlled by an electronic feedback circuit. This arrangement enables accurate measurements of the thin-film temperature. In addition, the system has a fast response time and excellent long-term temperature stability. We describe an application where the temperature control system is combined with ac resistance measurements to study the kinetics of a solid-state interdiffusion reaction in Ni-Zr multilayers.
A piston-actuated shock-tube, with laser–Schlieren diagnostics
Authors: Hurst S. M. , Bauer S. H.
Published: July 2002

The essential construction features of a piston actuated shock tube are described, and its advantages relative to the conventional use of diaphragm ruptures for shock initiation are listed. Typical operational parameters are presented to illustrate the levels of reproducibility achieved. Tests with He and N2 drivers into ∼99% Ar (1.0%–0.1% reagent) covered shock speeds from 1.539±0.002–0.8143±0.002 mm/μs, corresponding to 2390–847K incident shock temperatures. Application of this tube for recording postshock front density gradients of the endoergic dissociation of ethane and the exoergic condensation of iron atoms via the laser–Schlieren technique is described.
A compact gas scintillation proportional counter for ultrasoft x rays
Authors: Maeyama Satoshi , Sugiyama Munehiro , Oshima Masaharu , Shimizu Kazuaki , Shoji Takashi
Published: July 2002

A gas scintillation proportional counter has been developed for measuring ultrasoft fluorescence x rays. This counter is high-vacuum compatible for connecting to the ICF-70 flange of a vacuum chamber. A Mylar window of 0.6-μm thickness and 12-mm diameter is utilized for the entrance of the ultrasoft x rays. The counter has a large entrance window of approximately 100 mm2 and an energy resolution high enough to separate C Kα and O Kα radiations. This counter is applicable to not only x-ray fluorescence analysis, but also to fluorescence-yield extended x-ray absorption fine structure measurement of ultralow-Z elements.
Calibration of a Mott electron polarimeter: Comparison of different methods
Authors: Mayer S. , Fischer T. , Blaschke W. , Kessler J.
Published: July 2002

The accuracy of the calibration of a Mott polarimeter with a recently suggested method that uses an auxiliary target is compared with the accuracy obtained with the classical double-scattering experiment in its improved form. It turns out that the former method is affected by depolarization of the polarized incident beam in the auxiliary target. This systematic error source can, however, be eliminated by performing an additional asymmetry measurement.
Measurements of internal heat transfer in germanium resistance thermometers
Authors: Besley L. M. , Hai Lu
Published: July 2002

Heat transfer processes through the solid materials and the filling gas in germanium resistance thermometers from three manufacturers have been investigated experimentally at temperatures from 4.2 to 120 K. The experimental results agree with a published theoretical analysis. The heat transfer coefficient for these thermometers is found to vary by a factor of 50 for different types and different temperatures. In some thermometers, conduction through the gas is greater than that through the solid leads and the influence of contamination of the gas at temperatures between 45 and 65 K is very significant. However, in other thermometers solid conduction is the dominant heat transfer mechanism. It is suggested that solid conduction should be enhanced in the design of germanium resistance thermometers for use in the liquid-nitrogen temperature range.
Multifunctional cell for measurements of temperature, distance, and refractive index as for determining optical calibration factors in rotating systems
Authors: Cölfen H. , Holtus G. , Borchard W.
Published: July 2002

The method of measuring temperatures in rotating systems developed by Borchard and Hermanns is applied to the routine use in analytical ultracentrifugation. The temperature measuring device is built into a so-called counterbalance cell which is used for distance calibration as well as for a correct mass balance of the rotor. Now it is possible to measure temperatures with high precision of better than 0.1 °C in high-speed rotating systems at a defined place which is the location of the measuring cell in an analytical rotor. In the main part a temperature measuring cell consists of a differential refractometer system having refractive indices with different temperature dependences, therefore a light beam passing straight through the cell is refracted proportional to a temperature difference relative to a known temperature where the system is isorefractive. The displacement of the light beam can be measured by means of an optical system which is able to detect the refraction of a light beam. The described device can be generally used for temperature and refractive index measurements in a large field of applications. Two simple detection systems suitable for general applications are suggested. In case of a Schlieren or Rayleigh interference optical system the multifunctional cell can be used as a calibration cell if the temperature is measured with an independent detection system.
A Preston tube calibration chart
Authors: Kassab Sadek Z.
Published: July 2002

A simple calibration chart is presented for correlating the Preston tube reading directly with the friction velocity. This chart provides a quick and easy way to obtain the friction velocity (an important scaling velocity in turbulent flow studies) and consequently the wall shear stress. In addition the chart overcomes most of the drawbacks of previous Preston tube calibration methods. A comparison between friction velocities obtained using the chart and the corresponding values obtained from Patel’s calibration shows a good agreement with a maximum difference of 5%.
Self-rectifying electron beam melter for pendant-drop containerless processing
Authors: Pyun D. S. , Collings E. W.
Published: July 2002

A self-rectifying electron beam melting technique is described. Utilizing an ac power supply, in contrast to the more usual dc supply, the in situ self-rectifying approach offers a simple and very inexpensive means of producing metallic pendant drops for use in containerless melt-processing experiments.
Large off-axis epoxy paraboloids for millimetric telescopes and optical light collectors
Authors: Alvarez Donald L. , Dragovan Mark , Novak Giles
Published: July 2002

Large, off-axis epoxy paraboloids with high surface accuracy (26 μm rms) were generated by spinning a bowl containing a long cure time, low viscosity epoxy. This note also describes procedures for generating and measuring meter-class surfaces.
An optical fiber multiplexing system using Fabry–Perot cavities
Authors: Wang Qi
Published: July 2002

An optical fiber multiplexing sensing system with Fabry–Perot interferometers is proposed. A white light source and multimode fibers are used in the system. A theoretical result for the central maximum optical transmittance peak’s half width is given. In the proposed system, a primary servoloop and a secondary servoloop are applied in order to lock the reference cavity’s spacing on the sensing cavities’ spacing. The system is suitable for a multisensor system with a slowly varying signal.
Low Z impurity ion extraction from Tokamak Fusion Test Reactor ion sources
Authors: Kamperschroer J. H. , Grisham L. R. , Newman R. A. , O’Connor T. E. , Stevenson T. N. , von Halle A. , Williams M. D. , Wright K. E.
Published: July 2002

Tokamak Fusion Test Reactor (TFTR) deuterium neutral beams have been operated unintentionally with significant quantities of extracted water ions. Water has been observed with an optical multichannel analyzer. These leaks were thermally induced with the contamination level increasing linearly with pulse length. Up to 6% of the beam current was attributed to water ions, corresponding to an instantaneous value of 12% at the end of a 1.5 s pulse. A similar contamination is observed during initial operation of ion sources exposed to air. Operation of new ion sources typically produces a contamination level of ∼2%, with cleanup to undetectable levels in 50–100 beam pulses. Approximately 90% of the water extracted from ion sources with water leaks was deuterated, implying that there is the potential for tritiated water production during TFTR’s forthcoming DT operation. It is concluded that isotope exchange in the plasma generator takes place rapidly, most likely as the result of surface catalysis. The primary concern is with O implanted into beam absorbers recombining with tritium, and the subsequent retention of T2O on cryopanels.
High-temperature uniaxial stress apparatus for semiconductor defect symmetry determination
Authors: Yang S. , Lamp D.
Published: July 2002

A mechanical apparatus designed for use in deep level transient spectroscopy (DLTS) experiments and capable of applying more than 5 GPa pressure to a semiconductor crystal sample at temperatures from 300–450 K is described. This compound lever system applies a temperature-independent stress to the sample throughout the temperature range of interest. As an illustration of this device’s application, the initial result of a uniaxial stress DLTS experiment on EL2 in n-GaAs is given. EL2 is found to split under the [100] uniaxial stress, denying the AsGa and AsGa–Asi models.