bluuebunny/crossref_metadata_2025 huggingface dataset:
A multitracer system for multizone ventilation measurement
Authors: Sherman Max
Published: July 2002

Mass transfer due to pressure-driven air flow is one of the most important processes for determining both environmental quality and energy requirements in buildings. Heat, moisture, and contaminants are all transported by air movement between indoors and outdoors as well as between different zones within a building. Measurement of these air flows is critical to understanding the performance of buildings. Virtually all measurements of ventilation are made using the dilution of a tracer gas. The vast majority of such measurements have been made in a single zone, using a single tracer gas. For the past several years LBL has been developing the MultiTracer Measurement System (MTMS) to provide full multizone air flow information in an accurate, real-time manner. MTMS is based on a quadrupole mass spectrometer to provide high-speed concentration analysis of multiple tracer gases in the (low) ppm level that are injected into multiple zones using mass-flow controllers. The measurement and injection system is controlled by a PC and can measure all concentrations in all zones (and adjust the injected tracer flows) within 2 min and can operate unattended for weeks. The resulting injection rate and concentration data can be analyzed to infer the bulk air movement between zones. The system also measures related quantities such as weather and zonal temperature to assist in the data interpretation. Using MTMS, field measurements have been made for the past two years.
A superconducting solenoid lens for spin selection and focusing of hydrogen atoms
Authors: Hershcovitch A. I. , Kponou A. E. , Meitzler C. R. , Niinikoski T. O.
Published: July 2002

Results from a novel variation on the Stern–Gerlach method for magnetic separation are presented. A superconducting solenoid lens for spin selection and focusing of a cold atomic hydrogen beam has been built and tested at Brookhaven National Laboratory. The solenoid consists of three coils connected in series, with the current in the outer two coils counter to the current in the middle coil, resulting in a large magnetic field (up to 5.2 T) with strong gradients. Beam density enhancement (focusing) of up to a factor of 10 was achieved. Excellent qualitative agreement exists with ray-tracing calculations. Quantitatively, the experimental results show a lens performance which is a factor of at least 3 better than what these calculations predict.
An x-ray image intensifier system for precision wavelength dispersive x-ray spectroscopy
Authors: Hailey C. J. , Lupton J. H. , Siegmund O. H. W. , Stewart R. E. , Ziock K. P.
Published: July 2002

We have constructed a high-resolution x-ray image intensifier (XRII) for use in atomic physics. The XRII consists of an alkali halide scintillator crystal coupled by a fiber optic to a proximity focused microchannel plate stack with a bialkali photocathode and wedge and strip readout. The useful area of the detector is 12 cm2. We have measured full width half maximum spatial resolutions at 22 keV of 300 μm and at 122 keV of 600 μm with 0.5-mm-thick and 1.6-mm-thick CsI(Na) crystals, respectively. With NaI(Tl) crystals, x-ray arrival times can be determined with sub-100 ns resolution. In this paper we present the detailed performance of the XRII as well as a brief discussion of the theory of photoelectron limited fast timing.
Raman spectrometer control with IBM-PC/XT
Authors: Interdonato S. , Majolino D. , Mallamace F. , Aliotta F. , Micali N. , Vasi C.
Published: July 2002

All parameters of a spectrometer, signal detection, and normalization of the recorded Raman signal were controlled by a compatible IBM PC/XT computer which was connected to a Spex Ramalog 5 system. By the use of a motor-driven polarizer, we are able for each single step time of the instrument, to monitor simultaneously the contributions IVV and IVH of the spectrum. Moreover, the simultaneous normalization of the signal with the intensity of the exciting laser light allows one to avoid the effects of the unwanted laser instability. The program can be requested by electronic mail.
Phase noise reduction of a 19 GHz veractor-tuned Gunn oscillator for electron paramagnetic resonance spectroscopy
Authors: Lesniewski P. , Hyde James S.
Published: July 2002

Klystrons are being replaced with solid-state microwave oscillators by designers of microwave bridges for electron paramagnetic resonance (EPR) spectroscopy. Veractor-tuned Gunn oscillators have a number of advantages, but phase noise 100 kHz from the carrier is excessive. A Pound-type dc automatic frequency control (AFC) circuit is described that reduces phase noise of a Hughes veractor-tuned 19 GHz Gunn osillator by 23 dB, resulting in a value of −117 dBc/Hz. This value is typical for a good quality external-cavity reflex klystron at this frequency. It is concluded that the oscillator with AFC exhibits sufficiently low phase noise for normal EPR spectroscopy.
Thermal conductivity measurement from 30 to 750 K: the 3ω method
Authors: Cahill David G.
Published: July 2002

An ac technique for measuring the thermal conductivity of dielectric solids between 30 and 750 K is described. This technique, the 3ω method, can be applied to bulk amorphous solids and crystals as well as amorphous films tens of microns thick. Errors from black-body radiation are calculated to be less than 2% even at 1000 K. Data for a-SiO2, Pyrex 7740, and Pyroceram 9606 are compared to results obtained by conventional techniques.
Microwave microscopy using a superconducting quantum interference device
Authors: Black R. C. , Wellstood F. C. , Dantsker E. , Miklich A. H. , Nemeth D. T. , Koelle D. , Ludwig F. , Clarke J.
Published: July 2002

We present results on a near-field scanning probe microwave microscope which is based on the nonlinear behavior of a YBa2Cu3O7 direct-current superconducting quantum interference device (SQUID). Our system has a spatial resolution of about 30 μm and derives its probing field from circulating currents in the SQUID loop. The frequency is set by the Josephson relation and is continuously tunable up to about 200 GHz. By imaging small patterned normal metal thin-film samples of Cu and Nb at 77 K, we have confirmed the operating bandwidth of the system and investigated the nature of the imaging process.
Laser microrefractometer
Authors: Sainov S.
Published: July 2002

A simple yet reliable laboratory laser microrefractometer is described. A detailed theoretical analysis of the errors is made. The construction permits the utilization of various lasers as light sources. Preliminary investigations on some liquids with a He-Ne laser are carried out. The results confirm the applicability of the configuration, and the practical accuracy is in good agreement with the theoretical one. The possibilities for further improvement of the device in terms of range and accuracy are discussed.
Vertical displacement of the storage ring floor due to building distortion in the Photon Factory
Authors: Katsura Tomotaro , Fujita Yutaka
Published: July 2002

The Light Source Building of the Photon Factory was found to distort so much as to induce the displacement of magnets in the storage ring. This resulted in drifting of the beam orbit. It was considered that the building was distorted by the variations of thermal stress, such as diurnal changes of the solar irradiation and atmospheric temperature. To reduce such thermal stress, the rooftop of the building was insulated with a layer of polyethylene foam. The building distortion was measured in terms of vertical floor displacements along the storage ring by using a hydrostatic level measuring system. Results of the measurement were compared with those of a model simulation based on the finite element method. Comparison between measured and simulated results showed good agreement before the insulation applied to the roof. After the insulation, the measured floor displacements reduced to about one half and were also comparable to the simulated results. A full description of the subject is given in T. Katsura, Ed., KEK Internal 90-32 (in Japanese) Jan. (1991).
A high pressure-high temperature valve packing
Authors: Costantino Marc
Published: July 2002

A rotating valve stem packing for use at temperatures at least to 400 °C and pressures to 300 MPa is described. The design is based on the unsupported area principle, with copper packing washers.
Study of an electron cold cathode tube for soft x-ray spectrometry
Authors: Legrand P. B. , Dauchot J. P. , Hecq M.
Published: July 2002

An electron gun for soft x-ray emission spectrometry (<4 keV) is described. Electrons are produced in a capacitive direct current glow discharge tube working at low pressure. The surface area struck by the electrons is about 2 cm2. The electron energy spectrum has been analyzed with a plane parallel retarding field analyzer as a function of the pressure, the voltage and the current of the discharge tube. It is shown that even at relatively high pressure (1 Pa) most of the high energy electrons flowing out of the tube have an energy close to the operating voltage of the discharge tube. Electron energy results are also correlated to electron induced x-ray emission. It is shown by the measurement of the threshold voltage of x-ray lines and of the induced background intensity that the electron beam coming out of the tube can be considered to have an energy corresponding to the applied voltage.
Electrical measurements with a SQUlD susceptometer
Authors: Wong H. K.
Published: July 2002

We describe the design of a probe that can be inserted into a SQUID susceptometer (S.H.E. model VTS-805) for electrical measurements at variable temperature and high magnetic field. This top-loading probe allows multisample measurements and rapid sample replacement without disturbing the susceptometer.
Accurate control of evaporated multilayer thicknesses by a standard quartz monitoring system
Authors: Dufour C. , Marchal G.
Published: July 2002

Multilayers were obtained by evaporation from two electron gun crucibles. The thicknesses and the evaporation rates were controlled by standard quartz monitoring systems (QMS). A method to resolve the problems of the instability and of the lack of resolution of the instrument by smoothing the information provided by the QMS is presented. With this method, the quality of the multilayers’ periodicity is improved. Si/Ge nanoscale multilayers with an accuracy of ±0.5 Å on the individual thicknesses were obtained.
Stability studies on Chinese germanium resistance thermometers designed for use in magnetic fields
Authors: Besley L. M. , Peng Lin
Published: July 2002

The stability of 15 doubly doped germanium resistance thermometers, manufactured in China and designed for use in magnetic fields, has been studied under zero magnetic field conditions while the thermometers were subjected to thermal cycling between 15 K and room temperature and between 85 K and room temperature. Resistance measurements were made on each thermometer at 15 and 20 K on the 15 K cycles and at 85 K on the 85 K cycles. The stability of the thermometers at 20 K was found to range from 1 to 300 mK. Major differences in behavior between thermometers made from n- and p-type doped germanium were observed; many of the n-type thermometers showed good stability while there were significant resistance changes for all of the p-type thermometers.
Implementation and test of a synchrotron radiation position monitor at a user beam line
Authors: Brodsky E. L. , Kleman K. J. , Rogers G. , Rioux D. , Patel R. , Höchst H.
Published: July 2002

A slotted plate photodiode beam position monitor was built and installed on a user beam line. The detector is positioned in front of the first optical component of the beam line intercepting ∼3 mrad of synchrotron radiation. A 25-μm-thick Be foil strongly attenuates photons with hν<800 eV and improves the position sensitivity by reducing the vertical angular divergence of the effective photon beam by more than a factor of 10. With a 125-μm gap at 45° angle between the diode plates, the detector has a linear working range of ∼±800 μm. The vertical position sensitivity of the beam position monitor is ∼5 μm.
Performance of water jet cooled silicon monochromators in high power x-ray beams (abstract)
Authors: Berman Lonny E. , Hart Michael
Published: July 2002

We have fabricated and tested water jet cooled silicon (111) and (220) monochromators specially tailored for extended wiggler beam and concentrated undulator beam power loadings. The tests were made at the X25 27 pole, 1.1 T hybrid wiggler beam line1 at the National Synchrotron Light Source (NSLS). The wiggler-like line-type loading was produced by the direct, unfocused wiggler white beam, in which 300 W of total power in a 60-mm-wide by 5-mm-high [full width at half maximum (FWHM)] cross section were available in the experimental hutch; this represents a typical power density at existing insertion device beam lines. The undulator-like point-type loading was produced by the focused wiggler white beam, generated via reflection of a portion of the direct white beam from a toroidal platinum-coated silicon mirror, resulting in 75 W of total power in a 0.8-mm-wide (FWHM) by 0.45-mm-high (FWHM) cross section in the hutch. This will be a typical power density at next-generation insertion device beam lines.

The monochromator design consists of a thin walled silicon box whose bottom is glued to a stainless-steel water manifold; the coolant is delivered through jet tubes directed perpendicular to the underside of the top, diffracting surface of the box.2 Rectangular monochromators with multiple jets were used for the line power loading studies, and cylindrical monochromators with single jets were used for the point power loading studies. Provisions for simple adaptive corrections to compensate for the inevitable beam-induced thermal deformations, consisting of mechanisms to reverse-bend the top surface, and internal heat baffles to frustrate the cooling at the edges of the crystal (to produce an isothermal top surface), were included in the designs. These required approximate matching of the top surface dimensions to the x-ray footprint. To better understand the thermal strain fields, spatial and angular mapping of both fundamental and harmonic Bragg reflections within the beam footprint were undertaken.3 For the line power loading situation, Bragg angle variations of up to 4 arcsec across the beam footprint were observed, resulting in near-perfect performance for the fundamental.4 The harmonic was more sensitive to these strains;4 the described adaptive methods were used to correct for them.5 For the point loading situation, Bragg angle variations of over 200 arcsec were measured, causing distorted fundamental and harmonic reflectivity curves; again, ≳90% compensation was achieved via adaptive techniques.6 The detailed results show that while, for silicon at room temperature, passive crystal cooling methods are sufficient for the present unfocused insertion device beam lines, adaptive methods will have to be considered for future insertion device beam lines. This work was supported in part by th
A simple sagittal focusing crystal which utilizes a bimetallic strip
Authors: Knapp G. S. , Ramanathan M. , Nian H. L. , Macrander A. T. , Mills D. M.
Published: July 2002

A sagittal focusing monochromator which utilizes a bimetallic strip as its active focusing member has been designed and has undergone preliminary testing. The crystal bender is very easy to use as only setting the temperature of the bimetallic strip is necessary to adjust the focus. The mechanism utilizes bending rods mounted on live centers which prevent twisting of the crystal. A finite element analysis has been done on a new ribbed crystal which, based on the analysis, would have very small aberrations.
Positron versus electron-beam quality in low emittance storage rings (invited)
Authors: Marin P. C.
Published: July 2002

A brief summary of ion trapping dependence and its effects is first presented. Based on the experience of Super-ACO, the benefits at different stages of commissioning a synchrotron radiation facility with positrons are then reviewed for the running in period and later, for beam physics studies. Most important appears to be the trapping of nonconductive dust particles in electron beams and its consequences: microlosses, reduced lifetime, and beam emittance growth. A simple model based on photoionization and Möller scattering leads to several predictions which have been tested at Super-ACO. Experimental evidences are presented.
Circularly polarized synchrotron radiation from the crossed undulator at BESSY
Authors: Bahrdt J. , Gaupp A. , Gudat W. , Mast M. , Molter K. , Peatman W. B. , Scheer M. , Schroeter Th. , Wang Ch.
Published: July 2002

The first experimental results from a double undulator with crossed magnetic fields for producing circularly polarized synchrotron radiation in the vacuum ultraviolet-soft x-ray range are presented. The observed variation of the extent of circularly polarized radiation with photon energy is discussed. A strong dependence of the state and degree of polarization on the exact details of the tuning of the two undulators and the monochromator is observed. This probably accounts for the measured degree of polarization being smaller than theoretically expected.
Use of long straight sections of SPring-8
Authors: Hara M. , Nakamura T. , Takada T. , Tanaka H.
Published: July 2002

The SPring-8 project is in progress in Japan. The main facility is an 8 GeV storage ring dedicated to synchrotron radiation [H. Kamitsubo et al. (this conference)]. The main feature of the ring is in the free straight sections 30 m long. In this paper the design of the long straight sections and how to use them is described. The long free straights are achieved through two phases to make the commissioning of the ring smooth. In the second phase, the long free straight sections are available. These long straight sections have the following potential to realize (1) extremely high brilliance, (2) multiundulators with broadband, and (3) free electron lasers. The emittance of the stored electron beam can be reduced to subnano m rad at 4 GeV with damping wigglers. Three-order higher brilliance can be obtained around 4 keV. With these optics, three-dimensional simulation was performed for free electron lasers (FEL). The calculated gain was not so large in the practical peak current level.
Simultaneous scanning of the revolver undulator and monochromator at BL-19A of the Photon Factory
Authors: Kakizaki A. , Ohkuma H. , Kinoshita T. , Harasawa A. , Ishii T.
Published: July 2002

The revolver undulator beam line BL-19A at the Photon Factory has been constructed to be dedicated to the solid-state research and laid out for photon energy from 20 to 250 eV. To cover a wide spectral range by the maximum intensity of a first harmonics of undulator radiation, the simultaneous scanning of the undulator magnet gap and the monochromator has been accomplished in the normal user beam time. A displacement of the positron beam induced by scanning the undulator magnet gap are corrected using vertical and horizontal steering magnets at both ends of the undulator. The degradation of the beamline by the high heat loading was considerably reduced by adopting SiC substrate mirrors and gratings.
Chromaticity correction for the VUV and soft x-ray ring at the Photon Factory (abstract)a)
Authors: Kobayashi Yukinori , Kamiya Yukihide
Published: July 2002

We will present a method of chromaticity correction for a high brilliant SR ring. This method has been successfully applied to a low emittance ring, the VUV and soft x-ray ring, which is one of the future plans of the Photon Factory. As a result, we have obtained a sufficiently wide dynamic aperture, more than 40 mm in both transverse directions.
Superconductor-normal-superconductor junctions for programmable voltage standards
Authors: Benz S. P.
Published: July 2002

Series arrays of Nb–PdAu–Nb Josephson junctions were fabricated with characteristics ideally suited for application in programmable voltage standards and D/A converters with fundamental accuracy. Large arrays of junctions with applied microwave power showed constant voltage steps with current amplitudes as large as 7 mA. A novel coplanar waveguide design enabled uniform microwave power coupling to a five-segment array of 8192 junctions, so each segment had constant voltage steps over the same bias range. The 8192-junction device generated 1.1 mA steps at 186 mV with 11 GHz power and a maximum constant voltage step of 260 mV at 15.34 GHz.
Interdiffusion induced enhancement of one-dimensional level separation in quantum wires
Authors: Sallese J. M. , Carlin J. F. , Gailhanou M. , Grunberg P.
Published: July 2002

We have calculated the effect of alloy interdiffusion on the one-dimensional energy confinement of (Al,Ga)As/GaAs crescent shaped quantum wire structures. We show that the energy splitting between excited states may be greatly enhanced by the interdiffusion mechanism.
Nonuniform heating effects on thermal diffusivity measurements by the laser-pulse method: Influence of detector position
Authors: Fabbri L. , Scafè E.
Published: July 2002

Laser-pulse method is a well-known technique for measuring thermal diffusivity of solids and is based on several assumptions, i.e., adiabatic conditions, short laser-pulse length, temperature independence of thermal properties, and uniform heating of sample surface. However, very little has been published on the nonuniform heating effect that can limit the accuracy of measurements of several percent. In this paper the solution of heat equations under particular nonuniform conditions has been presented. Moreover, a heuristic model has been introduced in order to describe nonuniform heating effects arising under a general laser energy distribution. In both cases a good agreement with experimental results has been obtained.
A code for calculating spectral line shapes in tokamaks and assisting in experimental data interpretation
Authors: Zurro B. , Burgos C.
Published: July 2002

A code for calculating the actual spectral line shapes in magnetically confined plasmas of the tokamak type is described. The code determines the resulting line shape averaged along the line-of-sight of the spectrometer, starting from prescribed thermal temperature, ion emissivity, and flow profiles, for a plasma immersed in a magnetic field. In addition, the influence on the impurity linewidths of nonthermal fluctuating velocities due to fluctuating electric fields and to possible magnetic fluctuations is also included. Typical applications of the code to spectral data analysis in the TJ-I tokamak are given.
Hard x-ray diagnostics for laser fusion plasmas analysis
Authors: Miquel J-L. , Bourgade J-L. , Schirmann D. , Veaux J. , Gex J-P. , Cavailler C. , de Mascureau J. , Frotté V. , Trochet R.
Published: July 2002

Two diagnostics for the study of hard x-ray emission produced by plasmas during inertial confinement fusion experiments, are described: (i) a hard x-ray spectrometer to measure the high-energy tail of the spectrum, with eight spectral bands in the 50–400-keV range, by fluorescence and simple filter techniques; (ii) a time-integrated pinhole imaging device using a microchannel plate converter tube and a 7.5-μm-thick tantalum photocathode adjusted for a mean spectral sensitivity around 200 keV. Adjustment and test of these diagnostics have been performed with a pulsed hard x-ray generator using a plasma focus device. Absolute calibration of the spectrometer detectors (scintillator Photomultiplier) was obtained on an x-ray tube with fluorescent emission lines (10–100 keV) and with a cobalt radioactive source at 1.23 MeV.
A magneto-optic imaging probe for continuous magnetic field profiles
Authors: Dimonte Guy
Published: July 2002

Magnetic field profiles are measured continuously in space and time using Faraday rotation in magneto-optic glass. A line focused laser beam which undergoes Faraday rotation within the glass element is imaged in one dimension through a polarizer and onto a streak camera. The system is described and used to characterize an exploding diamagnetic plasma cavity.
ITER x-ray diagnostic studies
Authors: Hill K. W. , Young K. M. , Bitter M. , von Goeler S. , Hsuan H. , Hulse R. , Ku L.-P. , Stratton B. C. , Krieger A. S. , Parsignault D. , Franco E. D.
Published: July 2002

Present-day tokamak x-ray imaging (XIS) and pulse height analysis (PHA) diagnostics will require special shielding and x-ray optics to permit use on fusion reactors without prohibitive noise and detector damage from neutrons and gamma rays; x-ray curved-crystal spectrometers (XCS) may work with extensive shielding and collimation, but radiation damage of crystals and attainment of adequate impurity concentrations for ion-temperature measurement are concerns. We consider the use of one or more reflections at grazing incidence from x-ray mirrors or from Bragg layered synthetic microstructures (LSM) to decouple the x-ray diagnostic from the direct fusion neutron beam. We present calculations of expected x-ray line brightnesses from ITER and total instrument throughput. We also consider the use of hollow glass capillaries embedded in radiation shields to precede the XIS detector and reduce the ratio of neutron plus gamma radiation to x rays by a factor of ∼0.01 or better. Compatibility of capillary schemes with the PHA and XCS are discussed.
Comparison of experimental results and calculated detector responses for PBFA II thermal source experiments
Authors: Derzon M. , Aubert J. , Bailey J. , Carlson A. , Chandler G. , Derzon D. , Dukart R. , Humphreys R. , Hunter J. , Johnson D. , Matzern K. , Mix P. , Moats A. , Olson R. , Pantuso J. , Rockett P. , Ruiz C. , Sawyer P. , Torres J. , Hussey T.
Published: July 2002

We performed experiments using proton beams to heat foam-filled cylinders on the Particle Beam Fusion Acceleration II. Preliminary analysis of these diagnostic results provides reasonable agreement between prediction and experiment. The diagnostic package allowed us to benchmark target response as well as diagnose driver performance. Soft x-ray images, both time and space resolved, and the results of broadband spectral measurements on bolometers and x-ray diodes provide qualitative agreement with LASNEX predictions of target features such as Au motion and soft x-ray emission profile. The analysis is consistent with a total beam deposition of 40–50 kJ and power depositions of approximately 180 TW/g. Estimates of target motion confirm the ability of the foam to retard wall motion.
Lithium pellet deposition and penetration in TFTR
Authors: Sergeev V. Yu. , Marmar E. S. , Snipes J. A. , Terry J. L. , Park H. , Mansfield D. K. , Bell M. , McCune D.
Published: July 2002

The electron deposition resulting from the injection of Li pellets into Tokamak Fusion Test Reactor, measured by a multichannel (10) infrared interferometer, is compared with that deduced from the pellet ablation cloud emission, measured by a filtered diode array which views the pellet from behind. By assuming that the ablation rate Ṅ(r) is proportional to the pellet cloud emissivity, which is dominated by Li+ line emission in the 548.5±5 nm bandpass of the interference filter, the post-pellet, line averaged density perturbations along the interferometer chords were calculated and compared with those measured. Good agreement is observed. The experimental ablation rate profiles obtained using the emissivity have also been compared with predictions of the theoretical models. There is an agreement between the time history of the emissivity and the predicted ablation rate at the plasma edge where the electron temperature values are less than 1–1.5 keV. When the pellet penetrates more deeply, the experimental Ṅ(r) values are systematically smaller than those predicted. This points out the necessity of taking into account plasma shielding and/or precooling of the target plasma during pellet injection in the ablation model.
Neural networks and their diagnostic applications
Authors: Bishop Chris
Published: July 2002

Neural network techniques offer a wide range of new opportunities for the analysis of data from plasma diagnostics. In particular, the class of neural network known as the multilayer perceptron provides a general purpose approach to nonlinear data transformation between multidimensional spaces. In this paper, we outline the principles of the multilayer perceptron, and illustrate its application to plasma diagnostics using two examples. The first of these concerns the extraction of line shape parameters from spectral data, and offers considerable improvements in speed compared with conventional approaches. The second application involves deconvolution of line integral data from a multichannel interferometer, allowing the extraction of more detailed density profiles than obtained by conventional Abel inversion.
Cautions in using x-ray measurements derived from broad spectral response functions to determine the peak voltage of flash bremsstrahlung sources
Authors: Fehl D. L. , Baldwin G. T. , Lorence L. J.
Published: July 2002

Because a direct measurement of the voltage (V) in pulsed power bremsstrahlung sources can be difficult, the energy spectrum of x rays emitted is sometimes used to infer V. Both the voltage and current in such sources vary with time. Moreover, for modern x-ray simulators with multiple cathodes, multiple voltages may exist simultaneously. We demonstrate here how such sources lead to systematic errors in several types of simple-to-field x-ray voltage measurements, especially those with broad spectral response functions, when calibrated against constant-potential bremsstrahlung spectra.
Heavy ion and fusion particle stopping power in inertial confinement fusion (abstract)
Authors: Li C. K. , Petrasso R. D.
Published: July 2002

In inertial confinement fusion (ICF), the energy deposition of, first, heavy ions in the hohlraum and, second, charged fusion products in the plasma pellet is an essential issue. This can be quite subtle because the targets experience a series of phase transitions (solid→gas→partially ionized plasma→fully ionized plasma) and, most importantly, charged particle energy deposition depends on whether the charged particles are in the ‘‘fast,’’ ‘‘intermediate,’’ or ‘‘slow’’ regime, which depends on the plasma temperature. (The regime is defined as xi/e=vi2/vthe2. vi is ion velocity and vthe is electron thermal velocity. xi/e≫1, xi/e∼1, and xi/e≪1 correspond to fast, intermediate, and slow regimes, respectively.) A physical model based on the theory of binary interactions and plasma collective effects is being applied to the stopping power in these different regimes, especially in the transition regime (xi/e∼1), which is almost always ignored. From this model, we describe the physical picture of the evolution in energy deposition in both holhraum and the compressed pellet. Taking the typical ICF parameters for holhraum−ion energy ∼1 MeV/amu, electron density ∼1024 cm−3, and plasma temperature from a few eV to 1 keV −the scale sizes for both collisional energy exchange and electron plasma wave damping have been estimated and the energy relaxation rates of both mechanisms calculated. The significance of nuclear stopping and electron degeneracy effects will also be considered for fusion products in the core of pellet plasma. Finally, we briefly extend this model to the Solar core. This work was supported by U. S. Department of Energy Grant No. DE-FG02-91ER54109 and LLNL Subcontract B116798.
Preparing diagnostic data for the s
n
a
p transport code
Authors: Murphy J. A. , Scott S. D. , Towner H. H.
Published: July 2002

This paper describes the program snapin which is used to prepare data for transport analysis with the snap code. The data input to snap includes diagnostic profiles [ne(R), Te(R), Ti(R), vφ(R), Zeff(R), Prad(R)] and measurements such as total plasma current, Rmajor, beam power, gas puff rate, etc. snapin reads in the necessary TFTR data, allows editing of that data, including graphical editing of profile data and the selection of physics models. snapin allows comparison of profile data from all diagnostics that measure a quantity, for example, electron temperature profiles from Thomson scattering and electron cyclotron emission (ECE). A powerful user interface is important to help the user prepare input data sets quickly and consistently, because hundreds of variables must be specified for each analysis. snapin facilitates this by a careful organization of menus, display of all scalar data and switch settings within the menus, the graphical editing and comparison of profiles, and step-by-step checking for consistent physics controls [J. Murphy, S. Scott, and H. Towner, The snap User’s Guide, Technical Report PPPL-TM-393, Princeton Plasma Physics Laboratory (1992)].
A simple and efficient low-temperature sample cell for infrared spectrophotometry
Authors: Bruno Thomas J.
Published: July 2002

It is often helpful in infrared spectrophotometry to contain a liquid sample in a cell that is maintained at a subambient or nearly cryogenic temperature. Volatile samples and solvents being studied can vaporize and form bubbles in conventional liquid sample cells, especially under the influence of the infrared radiation from the source in a continuous-wave instrument. This will result in the formation of spikes on the spectra. In addition, some analytes are thermally labile and must be protected from warming while the spectrum is recorded. An easily constructed cell cooled with a vortex tube can solve many of these problems, and is in many ways an improvement over commercial devices. In this note, such a cell is described and its application to volatile alternative refrigerants is discussed.
Particle reflection and TFTR neutral beam diagnostics
Authors: Kamperschroer J. H. , Grisham L. R. , Kugel H. W. , O T. E. , Newman R. A. , Stevenson T. N. , von Halle A. , Williams M. D.
Published: July 2002

Determination of two critical neutral beam parameters, power and divergence, are affected by the reflection of a fraction of the incident energy from the surface of the measuring calorimeter. On the TFTR Neutral Beam Test Stand, greater than 30% of the incident power directed at the target chamber calorimeter was unaccounted for. Most of this loss is believed due to reflection from the surface of the flat calorimeter, which was struck at a near grazing incidence (12°). Beamline calorimeters, of a ‘‘V’’-shape design, while retaining the beam power, also suffer from reflection effects. Reflection, in this latter case, artificially peaks the power toward the apex of the ‘‘V,’’ complicating the fitting technique, and increasing the power density on axis by 10%–20%; an effect of import to future beamline designers. Agreement is found between measured and expected divergence values, even with 24% of the incident energy reflected.
Long range constant force profiling for measurement of engineering surfaces
Authors: Howard L. P. , Smith S. T.
Published: July 2002

A new instrument bridging the gap between atomic force microscopes (AFMs) and stylus profiling instruments is described. The constant force profiler is capable of subnanometer resolution over a 15-μm vertical range with a horizontal traverse length of 50 mm. This long traverse length, coupled with the possibilities of utilizing standard radius, diamond measurement styli, make the force profiler more compatible with existing profiling instrument standards. The forces between the specimen and a diamond stylus tipped cantilever spring are sensed as displacements using a capacitance bridge. This displacement signal is then fed through a proportional plus integral controller to a high stability piezoelectric actuator to maintain a constant tip-to-sample force of approximately 100 nN. Much of the sensor head and traverse mechanism is made of Zerodur glass-ceramic to provide the thermal stability needed for long travel measurements. Profiles of a 30-nm silica step height standard and an 8.5-μm step etched on Zerodur are presented.
Correlation of photon beam motion with vacuum chamber cooling on the NSLS x-ray ring
Authors: Johnson Erik D. , Fauchet Anne-Marie , Zhang Xiaohao
Published: July 2002

The NSLS x-ray ring exhibits a direct correlation between photon beam motion, and distortion of the ring vacuum chamber induced by fluctuations in the cooling system. We have made long term measurements of photon beam vertical position, accelerator vacuum chamber motion, process water temperatures, and angular motions of the magnets around one superperiod of the NSLS x-ray ring. Short term transients in water temperature cause deflection of the ring vacuum chamber which have in turn been shown to induce very small angular rotations of the magnets, on the order of 10 μrad. A larger and more difficult to correct effect is the drift in beam position over the course of a fill. This problem has been shown to be related to the thermal gradients that develop across the vacuum chamber which, as a consequence of the configuration of the chamber cooling, depend upon stored current. Orbit simulations based upon the measured rotations are in agreement with the observed beam motions, and reveal that certain patterns of correlated motions of the magnets can produce much larger errors than random motion or concerted motion of all the magnets. During the course of these measurements global orbit feedback was installed, and found to significantly reduce the orbit errors which could not be corrected at their source.
A photoemitted electron-impact ionization method for time-of-flight mass spectrometers
Authors: Cheng P. Y. , Dai H. L.
Published: July 2002

A simple and efficient electron-impact ionization method for time-of-flight mass spectrometers is described. This method utilizes the photoelectrons emitted from the accelerating electrode surfaces upon UV laser irradiation as the electron source. Since no modification of the spectrometer is required, it provides a convenient way to perform electron-impact ionization in a time-of-flight mass spectrometer originally designed for laser ionization. The detection sensitivity (∼109/cm3) and mass resolution (∼150) achieved by this method in our apparatus are sufficient for diagnostic purposes for cluster beam experiments. The observed ion intensities suggest that the photoelectron current density produced is comparable to those generated by conventional thermionic emission electron sources. This technique is generally applicable as an ionization method in time-of-flight mass spectrometers and is particularly useful when the available lasers are not suitable for photoionization detection due to wavelength or intensity limitations.
Calibration of atomic-force microscope tips
Authors: Hutter Jeffrey L. , Bechhoefer John
Published: July 2002

Images and force measurements taken by an atomic-force microscope (AFM) depend greatly on the properties of the spring and tip used to probe the sample’s surface. In this article, we describe a simple, nondestructive procedure for measuring the force constant, resonant frequency, and quality factor of an AFM cantilever spring and the effective radius of curvature of an AFM tip. Our procedure uses the AFM itself and does not require additional equipment.
Computerized thermogravimetric reactor with video microscopy imaging system for coal pyrolysis and combustion studies
Authors: Matzakos Andreas N. , Zygourakis Kyriacos
Published: July 2002

We present the development of a novel thermogravimetric reactor with in situ video microscopy imaging capabilities (TGA/VMI) and discuss its use for studying coal pyrolysis and combustion. Our design combines a long working distance optical microscope and video recording equipment with a computer-automated microbalance reactor. The TGA/VMI apparatus allows for simultaneous thermogravimetric measurement of reaction rates and direct viewing or video taping of structural transformations that may accompany the heterogeneous reactions. Reactor temperature is controlled by a digital algorithm combining feedback with model-based feedforward control. With its computer control and custom-built furnace, our reactor can achieve high heating rates (up to 50 °C/s) and temperatures (1000 °C) with excellent accuracy, stability, and reproducibility. We present some experimental results from our studies on coal pyrolysis and gasification to demonstrate the capabilities of the apparatus and suggest other potential applications.
Pulsed laser-induced damage threshold studies of thin aluminum films on quartz: Simultaneous monitoring of optical and acoustic signals
Authors: Lai Yau-Ming , Cheung Nai-Ho
Published: July 2002

Simultaneous measurements by two techniques for in situ laser-induced damage threshold (LIDT) detection, based on optical diffraction and acoustic measurements, were demonstrated. Pulsed Nd:YAG laser (532 nm) ablation of 25-nm-thick aluminum films on quartz was studied as a test case. The two probes gave consistent LIDT values, and were sensitive and simple to operate. For above-threshold ablation, the diffraction and acoustic signals were found to be strongly correlated, rendering them useful not just for threshold detection, but for studying ablation dynamics as well.
High-voltage variable resistor for ion energy spectroscopy
Authors: Gay T. J. , Irby V. D. , Yallaly S. P.
Published: July 2002

A high-voltage variable resistor was designed, built, and implemented to modify an ion-energy spectrometer for the study of ion–atom collisions in which the projectiles change charge. The resistor is remotely switchable from 0 to 2050 MΩ and has a voltage rating of 200 kV. The design criteria and the electrical and mechanical details of the apparatus are discussed. The design and construction of an ancillary device, comprising two precision resistive-divider voltmeters, are also discussed.
Gold-coated tungsten tips for scanning tunneling microscopy
Authors: Fried Glenn A. , Wang X. D. , Hipps K. W.
Published: July 2002

Electrochemically etched tungsten scanning tunneling microscope (STM) tips are dc sputter coated with 20 nm of gold (0.04 nm/s and 10 mTorr of argon). Transmission electron microscope (TEM) images of typical etched tips and gold-coated etched tips are presented. The gold layer forms as a series of spherical sections having a mean height of 6.7 nm and mean width of 19.6 nm. STM images are reported for the uncoated W tips, and for gold-coated graphite after coating the tip with gold. We also provide scanning electron microscopy (SEM) and STM images of the surface of a thin CuTCNQ film. The STM image taken with a gold-coated W tip compares very well to the SEM image of the same sample. Gold coating provides a relatively inexpensive and easy way to produce chemically stable tips of well known electronic structure for use in ambient atmosphere STM studies of morphology (structures ≥10 nm) where atomic resolution is not required.
Analysis of internal heat transfer in germanium resistance thermometers
Authors: Hai Lu , Besley L. M.
Published: July 2002

A theoretical analysis of internal heat transfer processes and their variation with temperature over the range 4.2–100 K is made for a typical commercial germanium resistance thermometer. It is shown that the proportion of the heat transfer occurring through the solid materials in the thermometer compared to that taking place in the gas trapped in the thermometer capsule varies substantially with temperature. The factors influencing heat transfer include the construction and the size of the thermometer, the thermal properties of materials, and the position of the germanium crystal within its capsule. Where heat transfer through the gas in the capsule is important, any changes in the composition of the gas play a significant role through the consequent changes in its thermal conductivity.
Broadband four-channel cryogenic wafer probing system for automated coplanar on-chip measurements
Authors: Höfer G. J. , Jäger F. , Kratz H. A.
Published: July 2002

An automated measurement system for cryogenic wafer probing is described. The system has been designed for up to four simultaneous broadband on-chip measurements in the temperature range from 4 to 300 K. Special requirements for superconducting samples have been taken into consideration. Most of the measurements needed for characterization of superconducting thin films and circuits can be done with a high degree of precision in the low- and high-frequency region. Details of the design are presented and the system performance is discussed.
Active optoelectronic system for stabilizing pulsed laser output energy at the fourth-harmonic frequency
Authors: Papayannis A. , Ancellet G. , Conrad J. L. , Laqui C. , Pelon J.
Published: July 2002

A feedback loop using an optoelectronic system has been tested successfully for the stabilization of the output energy at the fourth-harmonic frequency of a Nd-YAG laser (266 nm). The system presented includes an optical device to monitor the laser output energy at the nonconverted wavelengths and an electronic circuitry to optimize the laser output energy at the fourth-harmonic frequency. This optimization is achieved by the real-time correction of the frequency quadrupling laser crystal angle with respect to the input beam, using a stepping motor oscillating around the optimum crystal position. Results show that the present system provides a laser output energy stability better than ±15% for a long-term operation at the fourth-harmonic frequency, and keeps the locking even during the warming phase, immediately after the laser turning on. This system was designed for automatic LIDAR operations in field experiments, but its principle of operation can also be applied to any type of harmonic generator for either solid-state or dye laser.
Acousto-optic scanning and interfering photon density waves for precise localization of an absorbing (or fluorescent) body in a turbid medium
Authors: Knüttel A. , Schmitt J. M. , Barnes R. , Knutson J. R.
Published: July 2002

In most optical methods proposed for imaging an absorbing object embedded in a turbid medium, data are collected using a single source and detector scanned mechanically across the surface of the medium. In our setup, we exploited destructive interference of diffusive photon density waves originating from two sources to localize an absorbing (or fluorescent) body in a scattering medium. A frequency-domain instrumentation is described that scans several laser-beam spots across the surface of a turbid medium using 1D (or 2D) acousto-optical deflectors. An additional acousto-optic deflector is used to establish arbitrary phase shifts for the interfering photon-density waves. A destructive interference pattern was created to laterally localize an absorbing (or fluorescent) body in the reflection and transmission modes. In some experiments the destructive interference pattern was altered by modulating the individual beam intensities to improve sensitivity and ameliorate surface texture problems. The experimental results were retrieved from a gated intensified CCD camera at 246 MHz modulation frequency. Results indicate that less than a 1 mm displacement of a small object embedded 10 mm in a medium with optical characteristics similar to bloodless skin tissue can be detected.
A selective polishing approach for the fabrication of bonded-wafer silicon-on-insulator
Authors: Yamada A.
Published: July 2002

A new polishing machine has been constructed for the fabrication of bonded-wafer silicon-on-insulator (bonded-wafer SOI) through a numerically controlled polishing technique. The polishing machine is equipped with 32 small-area tools which produce the variation of polishing pressure over a wafer surface. The tools do not rotate. Instead, the wafers being polished perform an oscillatory motion. A tool removal profile which was adequate for selectively polishing one place on a wafer without affecting its neighboring areas was obtained. As a result of its test operation, the initial thickness deviation of σ=380 nm of the top Si layer of a bonded-wafer SOI sample has been improved to σ=48 nm.