bluuebunny/crossref_metadata_2025 huggingface dataset:
Neutral flux measurements during neutral-beam injection on Doublet III (abstract)
Authors: Lohr John , Armentrout C. J.
Published: July 2002

Neutral particle flux parallel and perpendicular to the plasma current and at energies equal to and below the injection energy has been observed with the parallel and perpendicular charge exchange spectrometers on Doublet III. Initial neutral injection is marked by a rapid increase in the high-energy neutral efflux which usually relaxes over tens of milliseconds to a lower equilibrium value. As injected power is increased by the stepped addition of more neutral beams, the measured flux is not linearly additive, often increasing slightly or not at all. For very high values of injected power, in the 5–7-MW range, the neutral particle flux is often observed in bursts correlated with the rapid fall of giant sawteeth on soft x-ray signals. In many of these shots the fishbone instability is present and is observed with the perpendicular spectrometer, however the parallel flux does not correlate with fluctuations observed with magnetic probes unless the instability terminates rapidly, in which case both a soft x-ray drop and a burst of neutrals occurs. Some aspects of these measurements have been modeled by a particle transport code with particular emphasis on changes in the neutral density profile during high-power neutral injection.
Method to determine the analysis area of x-ray photoelectron spectrometers—illustrated by a Perkin–Elmer PHI 550 ESCA/SAM
Authors: Seah M. P. , Mathieu H. J.
Published: July 2002

The area analyzed during routine x-ray photoelectron spectroscopy (XPS) measurements in a Perkin–Elmer PHI 550 spectrometer is determined by monitoring the intensity detected by the spectrometer from points on the sample surface addressed by a focused and rastered electron beam. The reference position for sample analysis is obtained using the manufacturer’s preferred procedure, originally established for Auger electron spectroscopy (AES), of moving the sample along the spectrometer axis until the correct energy is measured for a 2-keV electron beam with the analyzer operated in the AES mode. Using a sample set normal to the electron gun of the spectrometer and with the spectrometer operated in the XPS mode, the area analyzed is then determined as a function of the sample axial position. This area minimizes at the XPS focal position which appears to be 1.5 mm further from the spectrometer than the above reference position, in the particular instrument studied in Lausanne. This is attributed to inadequate manufacturing tolerances in this instrument. The analytical area has a diameter of 4 mm at the reference position, reducing to below 3 mm at the XPS focal position. This latter dimension is not sensitive to the pass energy but may be reduced to below 2 mm by use of the smallest apertures in the spectrometer. Theoretical expressions incorporating the mesh aberrations are derived which predict the above behaviors. Angle-dependent measurements, using the rotating azimuthal slit are shown to analyze an area which moves round a rather irregular path as the azimuth varies. Thus, angle-dependent studies to separate surface and bulk spectra in regular analysis are only meaningful for homogeneous samples set at the reference position. Inhomogeneities may lead to the spectra from one azimuth having no relation to those from another. The spectrometer analytical volume thus may be fully evaluated using this rastered electron beam method.
Laser/ion-beam diagnostics for potential and magnetic-field measurements in plasmas (invited)
Authors: Stern R. A.
Published: July 2002

Selected initiatives to develop sensors of the local fields, based on extensions of laser-induced fluorescence techniques, are described at both the fundamental and applied levels. Approaches discussed include the use of optical pumping (‘‘tagging’’), Stark and Zeeman effect methods, and line-narrowing techniques, such as two-photon Doppler-free schemes.
E parallel B canted detector neutral-particle spectrometer
Authors: Armentrout C. J. , Bramson G. , Evanko R.
Published: July 2002

A multichannel, mass-discriminating, neutral-particle spectrometer using parallel E and B analyzer fields has been operational on the Doublet III tokamak. The device records 60 energy channels each of hydrogen and deuterium, simultaneously, during a shot with a dynamic range in energy of greater than 20. Its unique feature is a microchannel plate detector plane set at an angle to the exit face of the magnet. This angled detector plane linearizes the columns of each mass which simplifies the detector design, and permits the magnet gap to be very small. The narrow gap minimizes figure field effects on particle trajectories and simplifies power supply and cooling design. Details are given on the design, calibration, and instrumentation of the device, as well as on its operation and experimental results.
Low-noise ac/dc current source with continuous zero crossing
Authors: Ruggiero S. T. , Schwarzbek S. , Howard R. E. , Track E.
Published: July 2002

A circuit has been developed for the measurement of the electrical characteristics of devices sensitive to extrinsic noise and intrinsic power-supply transients. The circuit comprises two active current sources running in opposition. The current can be ramped smoothly through current excursions of a maximum of ±1 A. Provision is also made for the modulation of the dc current output by an external ac source.
Multichannel spectrometer for plasma diagnostics
Authors: Carolan P. G. , Patel A.
Published: July 2002

A multichannel vacuum ultraviolet spectrometer has been constructed to provide time-resolved measurements of line radiation from a plasma. The spectrometer may simultaneously view up to 40 preselected narrow spectral bands or lines from a common viewing chord in a wide spectral region (∼60–450 nm) with the maximum frequency response limited to 80 MHz by the photomultipliers and 350 kHz by the data-acquisition system. Rapid reselection of impurity lines is facilitated by the use of multiple slits cut in a metal foil placed at the Rowland circle of the instrument. Due to the limitation imposed by the present fiber-optic coupling to the plasma the results to date are from impurity wavelength in excess of about 220 nm.
Compact time-of-flight mass spectrometer using particle-induced desorption
Authors: Summers W. R. , Schweikert E. A.
Published: July 2002

This paper describes the design and operation of a time-of-flight mass spectrometer that uses fast, heavy ions from the spontaneous fission of Cf-252 to desorb species from the surfaces of solids. The technique provides for a simultaneous, multimass, isotope specific, elemental, and molecular surface characterization without complications due to surface charging.
Programmable laboratory interface to the IEEE-488 Bus
Authors: Hall Blair
Published: July 2002

A microprocessor-based interface is described which interfaces a wide variety of digital instruments to the IEEE-488 Bus in a very simple manner. Intended for general laboratory use the interface is simple to program and features a modular design which facilitates expansion and modification.
Heterodyne and nonheterodyne laser transceivers
Authors: Keyes Robert J.
Published: July 2002

The fundamental characteristics of heterodyne and nonheterodyne imaging laser radars are presented in terms of information content, structual complexity, and sensitivity limits. The sensitivity characteristics of heterodyne and nonheterodyne laser receivers are quantitatively compared. When feedback amplification or low-noise multiplication gain is available in the receivers, the direct detection of laser signals can approach or even surpass the sensitivity or coherent detection. The concept of ‘‘self-homodyne’’ is introduced and its potential application to laser radar measurements is addressed.
Three-dimensional atom probe analysis of a sputter-deposited Co–Cr thin film
Authors: Hono K. , Yeh K. , Maeda Y. , Sakurai T.
Published: July 2002

Three-dimensional atom probe (3DAP) was employed to study nanoscale compositional heterogeneities in Co-22 at. %Cr sputter-deposited thin films. Compositional fluctuations were visualized on a nanometer scale through a 3D reconstruction of collected atoms. Transmission electron microscopy observations of the same specimen area of before and after 3DAP analysis made it possible to scale the analyzed volume precisely. The resulting data show that a Co-22 at. %Cr thin film sputter deposited at elevated temperature was composed of two phases with a lamellarlike structure, one phase was ferromagnetic containing approximately 90 at. %Co, and the other was paramagnetic, containing approximately 60 at. %Co.
Microprocessor-based photon correlator
Authors: Noullez Alain , Boon Jean-Pierre
Published: July 2002

We present a new microprocessor-based correlation technique for photon correlation spectroscopy. We give a description of the hardware and software configurations for 256 channels. The instrument performs real-time correlations in the sampling time range 65–4.8 ms and works in batch mode for sample times between 50 and 5 μs; in the intermediate range, a concurrent mode is used to reach an efficiency comparable to real-time correlation. The present realization has the advantages of a small size and low-cost instrument. Conclusive tests are presented for the analysis of Brownian motion and cell motility measurements.
Tunneling microscope for operation in air or fluids
Authors: Drake B. , Sonnenfeld R. , Schneir J. , Hansma P. K. , Slough G. , Coleman R. V.
Published: July 2002

A tunneling microscope that is a hybrid between IBM Zurich designs and squeezable tunnel junctions has been operated in air, oil, and liquid nitrogen. Key design goals were (1) maximum rigidity and (2) minimum thermal drift. Images of individual atoms in a close packed layer have been obtained under liquid nitrogen.
Inexpensive stepping motor control system
Authors: VanBommel G. , Quinn W. R.
Published: July 2002

An easily programmable stepping motor control is based on an IBM-PC compatible parallel printer interface.
Combination closed-cycle refrigerator/liquid-He4 cryostat for e− damage of bulk samples
Authors: Johnson E. C.
Published: July 2002

A closed-cycle refrigerator/cryostat system for use in ultrasonic studies of electron irradiation damaged bulk specimens is described. The closed-cycle refrigerator provides a convenient means for long-term (several days) sample irradiation at low temperatures. A neon filled ‘‘thermal diode’’ is employed to permit efficient cooling, via liquid helium, of the sample below the base temperature of the refrigerator.
Low-noise ac/dc voltage source with continuous zero crossing
Authors: Ruggiero S. T. , Barner J. B.
Published: July 2002

We have developed an active voltage source with low-noise characteristics. The circuit was designed to drive components at constant voltage which are sensitive to extrinsic noise and power-supply zero-crossing transients.
Inexpensive home computer used as a versatile digital delay generator
Authors: Pardon A. , Peeters J.
Published: July 2002

A versatile digital delay generator is described which is built using the widely available C64 Commodore home computer. Fixed delays and delay scans from 1 μs up to 65 ms with 1-μs step size are possible. One can modify the generator program; for instance, a delay scan followed by a number of fixed delay sequences. The speed of a delay scan is adjustable over a very wide range and the accuracy of the delay generation depends uniquely on the system clock accuracy.
CO2 laser Thomson scattering diagnostic for fusion product alpha particle measurement
Authors: Richards R. K. , Bennett C. A. , Fletcher L. K. , Hunter H. T. , Hutchinson D. P.
Published: July 2002

A description of a CO2 laser Thomson scattering diagnostic for fusion product alpha particles is presented. Scattering calculations based on CIT plasma parameters are presented and compared to previous work based on TFTR parameters. System components are described and a proof-of-principle test in a nonburning plasma is discussed.
Stability boundaries and phase-space measurement for spatially extended dynamical systems
Authors: Simonelli F. , Gollub J. P.
Published: July 2002

Automated methods of studying the stability boundaries and phase-space dynamics of a spatially extended dynamical system are presented. The stability boundaries are determined accurately as a function of external parameters in an automated search. The amplitudes of the individual spatial modes are measured in real time in order to determine the structure of the attractors in phase space. Some control over initial conditions allows the basins of attraction and the transients leading to the attractors to be studied as well. The methods are applied specifically to interacting waves on a fluid surface, but should also be useful to other extended dynamical systems.
Apparatus for evaluating humidity-sensing characteristics of solid electrolytes
Authors: Tanase S. , Greenblatt M. , Tsai P. P.
Published: July 2002

A unique humidity-controlled apparatus has been developed to test the performance of galvanic-type humidity sensors. The system has design features including one coaxial inlet-outlet tubing and a sintered pellet for the sensor material that are improvements over previously used devices. Results of experiments show that the apparatus constructed is applicable for humidity sensing up to 1000 °C.
Gas pressure reduction circuits
Authors: Guillaume D. W. , DeVries D.
Published: July 2002

This note describes passive pressure reduction devices for use with sensitive instruments. Two gas circuits are developed which not only provide a pressure reduction under flow demand, but also limit the maximum pressure that the source can exert under a no-flow condition. The first design approach presented is a method that involves conventional orifices in a pressure divider network analogous to a voltage divider in electronics. The second method detailed, utilizing the discharge end of a jet pump, amplifies the mass flow rate of the source, reduces the source pressure at free delivery, and limits the pressure at shutoff.
A compact, bipolar, constant–current-voltage source for superconducting junction characterization
Authors: Lin M. Z. , Song S. N. , Jin B. Y. , Ketterson J. B.
Published: July 2002

A versatile, compact, constant current-voltage, bipolar power source for quasi-static or derivative measurements of the characteristics of superconducting junctions has been developed. The circuitry is based on a negative feedback strategy that is effective in maintaining constant current-voltage behavior at the junction itself and all lead resistances are included in the feedback loop. Constant currents and voltages can be delivered of up to ±0.5 A and ±0.75 V, respectively. Both fast and slow sweeps, as well as a single sweep mode, are available in variable ranges. The single sweep feature is used to avoid heating effects in low resistance junctions which are not in good thermal contact with a thermal reservoir (e.g., liquid 4 He).
Temporal behavior of neutral particle fluxes in TFTR neutral beam injectors
Authors: Kamperschroer J. H. , Gammel G. M. , Roquemore A. L. , Grisham L. R. , Kugel H. W. , Medley S. S. , O’Connor T. E. , Stevenson T. N. , von Halle A. , Williams M. D.
Published: July 2002

Data from an E∥B charge exchange neutral analyzer (CENA), which views down the axis of a neutral beamline through an aperture in the target chamber calorimeter of the TFTR neutral beam test facility, exhibit two curious effects. First, there is a turn-on transient lasting tens of milliseconds having a magnitude up to three times that of the steady state level. Second, there is a 720 Hz, up to 20% peak-to-peak fluctuation persisting the entire pulse duration. The turn-on transient occurs as the neutralizer/ion source system reaches a new pressure equilibrium following the effective ion source gas throughput reduction by particle removal as ion beam. Widths of the transient are a function of the gas throughput into the ion source, decreasing as the gas supply rate is reduced. Heating of the neutralizer gas by the beam is assumed responsible, with gas temperature increasing as gas supply rate is decreased. At low gas supply rates, the transient is primarily due to dynamic changes in the neutralizer line density and/or beam species composition. Light emission from the drift duct corroborate the CENA data. At high gas supply rates, dynamic changes in component divergence and/or spatial profiles of the source plasma are necessary to explain the observations. The 720 Hz fluctuation is attributed to a 3% peak-to-peak ripple of 720 Hz on the arc power supply amplified by the quadratic relationship between beam divergence and beam current. Tight collimation by CENA apertures cause it to accept a very small part of the ion source’s velocity space, producing a signal linearly proportional to beam divergence. Estimated fluctuations in the peak power density delivered to the plasma under these conditions are a modest 3%–8% peak to peak. The effects of both phenomena on the injected neutral beam can be ameliorated by careful operation of the ion sources.
UHV rotary manipulator with arcsecond resolution for x-ray standing-wave experiments
Authors: Gog Thomas , Durbin Stephen M.
Published: July 2002

A UHV-compatible rotary manipulator with arcsecond resolution has been constructed for use in x-ray standing-wave experiments. The manipulator is computer controlled and features two separate stepping motor drives, a ‘‘coarse’’ drive which allows sample rotations in increments of 7 arcsec with full revolution range, and a ‘‘fine’’ drive with a range of 1° and angular increments of 0.9 arcsec. The performance of the manipulator was tested under UHV conditions by recording rocking curves from a Ge(111) two-crystal monochromator in a nondispersive configuration, using Cu Kα radiation from a sealed x-ray tube. Repeated measurements taken over periods of several hours reveal excellent repeatability and precision.
Intracavity multipass system for generation of high flux of cw visible light
Authors: Anheier N. C. , Labiche M. J. , Graff M. M.
Published: July 2002

We describe an intracavity multipass system (IMS) for producing very high cw flux of visible light with ion lasers. Multiple crossings of an ion beam with the extended cavity of an argon-ion laser produce effective photodetachment laser powers well over 1 kW when a high-reflectance output coupler is used. Several IMS configurations have been implemented successfully.
Concurrent pump-probe and streak camera measurements with a single mode-locked Nd:YAG laser: A picosecond absorption/emission spectrometer
Authors: Schmidt Jeffrey A. , Hilinski Edwin F.
Published: July 2002

A description is presented of a laser system that can be used for two concurrent and independent types of picosecond spectroscopic measurements. Two data-collection sybsystems, (1) a picosecond pump-probe transient absorption/emission spectrometer and (2) a streak camera system for time-dependent measurements of absorption and emission, have been developed as independent work stations within an integrated system based on a single mode-locked Nd:YAG laser oscillator which concurrently supplies each subsystem with picosecond pulses. The electronic links among the two work stations and the laser are discussed. In addition to applications involving pump-probe absorption and pulsed laser-induced emission measurements, this system can be used for picosecond-pulsed preparation-pump-probe absorption and preparation-pump emission experiments. Examples of data collected with each subsystem are presented to illustrate the complementary nature of the information that can be obtained with this versatile laser system.
A new nonclipped correlator for photon count spectroscopy
Authors: Correia Carlos , Santos Filomena P.
Published: July 2002

A circuit for photon count spectroscopy and its interface to a digital signal processor (DSP) are described. The complete circuit is housed in a standard IBM-PC board and, as it contains its own processor and memory, has a background mode of operation that releases the host system for being used in other tasks while the correlator is running. The basic autocorrelation routine executed by the DSP on data collected by the count circuit is also discussed. The use of the DSP lends the system great flexibility allowing for a high degree of customization while keeping performance to a level comparable to that of large dedicated units.
Method for measuring the stochastic properties of corona and partial-discharge pulses
Authors: Van Brunt R. J. , Kulkarni S. V.
Published: July 2002

A new method is described for measuring the stochastic behavior of corona and partial-discharge pulses which utilizes a pulse selection and sorting circuit in conjunction with a computer-controlled multichannel analyzer to directly measure various conditional and unconditional pulse-height and pulse-time-separation distributions. From these measured distributions it is possible to determine the degree of correlation between successive discharge pulses. Examples are given of results obtained from measurements on negative, point-to-plane (Trichel-type) corona pulses in a N2/O2 gas mixture which clearly demonstrate that the phenomenon is inherently stochastic in the sense that development of a discharge pulse is significantly affected by the amplitude of and time separation from the preceding pulse. It is found, for example, that corona discharge pulse amplitude and time separation from an earlier pulse are not independent random variables. Discussions are given about the limitations of the method, sources of error, and data analysis procedures required to determine self-consistency of the various measured distributions.
X-ray monochromators for circularly polarized incident radiation
Authors: Ishikawa Tetsuya
Published: July 2002

Crystal x-ray monochromators for incident circularly or elliptically polarized light waves are discussed. The amplitude ratios and phase shifts for σ- and π-polarized incident beams are calculated for various crystal arrangements. A four-crystal (+,−,−,+) arrangement is shown to be practical for delivering monochromatic circularly polarized x rays from a circularly polarized source.
Polarizing undulator with crossed and retarded magnetic fields
Authors: Onuki Hideo , Saito Norio , Saito Terubumi , Habu Mitsuhiro
Published: July 2002

A prototype of the polarizing undulator with crossed and retarded magnetic fields which was able to produce any kind of elliptically polarized synchrotron radiation from relativistic electrons was designed and constructed. This undulator was installed in a straight section of the electron storage ring, TERAS, and its radiation spectra and polarization characteristics were investigated. The experimental results proved that this device can produce linearly, elliptically, or circularly polarized synchrotron radiation and can switch its polarization quickly which would be very useful in polarization modulation spectroscopy.
Integrated inductance bridge package for ac susceptibility measurements of superconducting thin films
Authors: Polturak E. , Wilen L. , Cohen D. , Koren G.
Published: July 2002

We describe a simple integrated self-inductance bridge package for measuring the ac susceptibility of high-Tc superconducting thin films. The package has good sensitivity and baseline drift rejection, and employs mechanical clamping for easy sample interchange.
The design and application of a novel high-frequency tiltmeter
Authors: Speake C. C. , Newell D. B.
Published: July 2002

The design and construction details of a novel high-frequency tiltmeter are described. The instrument, which is based on a dumbbell suspended near its center of mass, has been used to put a preliminary limit on the magnitude of tilts in our laboratory of 1 nrad/(Hz)1/2 in the frequency range 3–10 Hz. We discuss other applications of the device and possible improvements.
A vertical force alternating-gradient magnetometer
Authors: Flanders P. J.
Published: July 2002

This paper describes a modification of the alternating-gradient magnetometer that is especially suitable for measurements from 77 to 900 K. The gradient of the alternating field, and the resulting force on the sample are made perpendicular to the magnetization of the sample and a cantilevered piezoelectric sensing element can then be located in a constant temperature environment so that the mechanical resonant frequency and gain of the magnetometer are not influenced by changes in sample temperature. The instrument has a sensitivity of 10−8 emu/(Hz)1/2 for measuring small or weakly magnetic samples, but can easily be adapted to measure relatively massive or strongly magnetic samples. Samples weighing more than 1 g and magnetic moments above 1 emu have been measured. These limits can generally be raised by using heavy piezoelectric elements and extension fibers.
Ion composition measurement techniques for space plasmas
Authors: Gloeckler George
Published: July 2002

Plasmas found in space range from the solar wind with a typical temperature of 105–106 K, ∼400 km/s bulk flow speed, and high ionization (charge states) of ions, to the hot, slowly moving plasmas in the outer magnetospheres of the giant planets, to the cold, co-rotating plasmas in inner magnetospheres. While measurements of the distribution functions of protons and electrons, which have been available for several decades of space exploration, are providing important information about the heating and acceleration mechanisms producing these plasmas, knowledge of the elemental composition and charge states of ions in these plasmas is essential for establishing their sources of origin. We review space plasma instruments and techniques, with an emphasis on hot plasma composition measurements. Starting with Faraday Cup detectors some 30 years ago, plasma instruments have evolved to the present time-of-flight systems with excellent mass resolution and three-dimensional viewing capabilities.
Characterization of a large superconducting split pair magnet for swept field measurements
Authors: Crockett A. G. , Kennedy T. A.
Published: July 2002

A Hall probe was inserted into the magnet of an optically detected magnetic resonance (ODMR) spectrometer to study residual field at zero current, homogeneity, and hysteretic effects. Residual fields were on the order of 10 mT at zero current. The magnet was homogeneous to within one part in 8000 or better over a region of 2.5 cm along its vertical axis. Several hysteresis loops were studied for field sweeps. The largest shifts were about 10 mT. Using the information collected, recommendations are made on how to improve precise field measurements for ODMR.
A fast cavity dumper for a picosecond glass laser
Authors: Oak S. M. , Bindra K. S. , Narayan B. S. , Khardekar R. K.
Published: July 2002

A fast cavity dumper for picosecond glass laser has been made. The optical and electrical characterization of the cavity dumper is described. An avalanche transistor Marx bank generator drives the cavity dumper. Up to 5 kV peak amplitude and 1.5 ns fall time negative polarity step pulses are generated by the Marx bank circuit. With a capacitive load like Pockels cell the pulse fall time increases to 4 ns. Optical switching times as fast as 2 ns (10%–90%) are experimentally measured. The contrast ratio of 1000 is obtained after a double pass through an amplifier. Single picosecond pulses are produced with an energy jitter of 10%.
Analysis and optimization of stepwise modulated TEon mode converter
Authors: Kiwamoto Y. , Honda T. , Kasugai A. , Saito T. , Miyoshi S. , Wada O. , Nakajima M.
Published: July 2002

This paper reports numerical and experimental analyses of a stepwise modulated TEon mode converter based on the mode-matching formulation. By systematic analyses, the dimensions of the TE02 to TE01 converter at 41 GHz are optimized so that a power conversion efficiency higher than 99.3% is theoretically obtained with a reflection coefficient less than 0.2%. The simple structure of the converter not only allows easy manufacturing with ordinary machining but it also enables the converter characteristics to behave well and be readily adjusted on the laboratory site. Based on the numerical analyses, a mode converter is designed and fabricated for use in the ECRH experiment on the GAMMA 10 tandem mirror. Preliminary tests show that the converter works well at a high power, above 100 kW. The transmittable power is limited by external nonaxisymmetric modes which can eventually be suppressed with efficient mode filters.
A quadratic potential time-of-flight mass spectrometer for use with slow positron ionization sources and other large-volume ion sources
Authors: Hulett L. D. , Donohue D. L. , Lewis T. A.
Published: July 2002

A time-of-flight spectrometer has been specially designed for measuring the masses of ions produced by low-energy positrons interacting with organic molecules in a Penning trap. To make the flight times insensitive to the starting positions of the ions in the trap, acceleration was done using a potential that varied as the square of the distance of the ion from the detector. The containment of the positrons in the Penning trap for extended time periods effected very long collision paths between the positrons and the molecules. The entire length of the Penning trap source could be sampled. These features produced high sensitivity, enabling the measurement of ionization processes with small cross sections. The spectrometer is useful for mass spectrometry of ions produced by processes other than positron interaction. Both large and small volume sources can be accommodated.
Devices for maintaining optical access in high-temperature coal combustion environments
Authors: Cook Robert L. , Hester Leslie R.
Published: July 2002

Advanced optical diagnostic techniques and instruments are being developed to operate successfully in the high-temperature coal combustion environments of large scale facilities. The success of these instruments depends heavily on maintaining a clear optical path into and out of the gas stream for long periods of time. The buildup of slag at the access port and contaminate fouling of the optical window require special systems to maintain the optical path. The rationale for, and design of, two such systems are presented in this article. The first system, a remotely operated window changer, provides for exchanging fouled windows for clean windows. The second system, a remotely operated slagbuster, provides for removing slag buildup in the access port. The design and operation of both systems are discussed. Parts lists, drawings, and schematics are presented also.
A short period undulator for MAX
Authors: Ahola Heikki , Meinander Tor
Published: July 2002

A hybrid undulator for generation of high brilliance synchrotron radiation in the photon energy range of 60–600 eV at the 550 MeV electron storage ring MAX in Lund, Sweden has been designed and built at the Technical Research Centre of Finland in close collaboration with MAX-lab of Lund University. At the rather modest electron energy of MAX this photon energy range can be reached only by an undulator featuring a fairly short period and the smallest possible magnetic gap. Even then, higher harmonics (up to the 13th) of the radiation spectrum must be utilized. An optimization of the magnetic design resulted in a hybrid configuration of NdFeB magnets and soft iron poles with a period of 24 mm and a minimum magnetic gap of 7–10 mm. A variable-gap vacuum chamber allows reduction of the vacuum gap from a maximum of 20 mm, needed for injection, down to 6 mm during stored beam operation. A special design of this chamber permits a magnetic gap between pole tips that is only 1 mm larger than the vacuum gap. Adequate field uniformity was ensured by calibration of magnets to equal strength at their true operating point and verification of the homogeneity of their magnetization. Magnetic measurements included Hall probe scans of the undulator field and flip coil evaluations of the field integral.
Measurement of helium gas in a deuterium environment
Authors: Finken K. H. , Dippel K. H. , Baek W. Y. , Hardtke A.
Published: July 2002

The detection of helium in a deuterium gas environment (both mass 4) is an important task in the field of nuclear fusion physics. To fulfill this purpose a detector has been developed which is based on spectroscopic measurement techniques. For the excitation of the helium and deuterium atoms different electron sources have been tested. Most sources had to be rejected because they either produce a disturbingly high background light level or cannot be operated reproducibly after venting or are mechanically not stable enough. The best line emitting light source has been found to be a Penning gauge. The light is collected in an optical fiber bundle, transferred away from the tokamak experiment to an area more easily accessible, split by interference filters into Dα light and the light of a strong He i line, and detected by photomultipliers. Unfortunately broad spectral lines from the deuterium molecule superimpose the strongest He i lines and have nearly the same intensity as the helium lines at a He concentration of about 5%. Therefore, some effort is necessary to deduce the partial pressures of helium and deuterium. A method is described which yields the calibration factors for the observed nonlinear pressure response of the spectral lines. The lower limit for the determination of the helium concentration presently amounts to about 1%–2%; the time resolution of the system is of the order of a few milliseconds.
Cleaning of carbon contaminated vacuum ultraviolet-optics: Influence on surface roughness and reflectivity
Authors: Müller B. R. , Feldhaus J. , Schäfers F. , Eggenstein F.
Published: July 2002

The loss of transmission of optical elements by irradiation is a big problem of all synchrotron radiation laboratories. A major reason for the reduced transmission is the contamination with graphitic carbon that is due to adsorbed and cracked hydrocarbons. In accordance with earlier experiments at other storage rings, a cleaning procedure was developed at BESSY which consists of an oxygen discharge suspended by an rf cavity. The atomic oxygen that is created in the plasma reacts with the carbon to CO and CO2 and dissolves from the surface. The investigations focused on the items: (a) influence of the cleaning procedure on the reflectivity, (b) its influence on the surface roughness of the optical element, and (c) transfer of the procedure to other elements (e.g., vacuum ultraviolet detectors, diodes, different substrates). For an in-situ check of the cleaning efficiency, the reflectivity of gold-and carbon-coated test samples was measured before and after cleaning using the BESSY HE-TGM 2 beamline. The microroughness was investigated employing different surface sensitive techniques like scanning electron microscopy, scanning tunneling microscopy, and interferometry.
Optimization of undulators for a SX-700 Instrument: Finite element coupled to ray tracing
Authors: de Castro A. R. B. , Reininger R.
Published: July 2002

The flux and total power of the insertion devices to be installed in the XUV beam line at DORIS III have been optimized under the constraint of preserving the source size limited resolution of the monochromator. This was achieved by interactive redesign of undulators, mirror geometry, and mirror coatings. Coupled finite-element analysis and ray tracing were employed, taking into account the absolute power irradiated by each insertion device and its spatial, angular, and spectral distribution. The angular and spectral dependence of coating reflectivities and realistic thermal boundary conditions as imposed by the manufacturer of the water-cooled substrates were also considered. A specific example, showing the advantage of coating the first mirror with SiO2 instead of Au for the low-energy range of the monochromator is discussed in detail.
A new energy dispersive x-ray monochromator for soft x-ray applications
Authors: Blank H. , Neff B. , Steil St. , Hormes J.
Published: July 2002

Energy dispersive x-ray monochromators allow time-resolved XANES and EXAFS measurements in the millisecond time scale. With this technique it is possible to study changes, during chemical reactions and phase transitions, in the structure of chemical substances within the environment of the absorbing atom. The instruments used up to now are not built for use under vacuum and are thus restricted to experiments above 4 keV. An energy dispersive monochromator is described which is currently being built at the Bonn 3.5 GeV electron stretcher and accelerator (ELSA). The purpose of this monochromator is to be able to measure downwards in energy at least to the sulfur K edge at 2.4 keV. The problems which had to be solved are (i) the construction of a windowless vacuum chamber for the Bragg crystal, the sample, and the detector, (ii) the short distance between the crystal and the sample, and (iii) the small radius of curvature of the Bragg crystal. Furthermore, the monochromator has to be rapidly tuned with ease to different energies.
The high energy spherical grating monochromator−A new source of soft x rays at Daresbury (abstract)
Authors: Surman M. , Cragg-Hine I. , Singh J. , Bowler B. , Padmore H. A. , Norman D. , Johnson A. L. , Atrei A. , Walter W. K. , King D. A. , Davis R. , Purcell K. G. , Thornton G.
Published: July 2002

In this article we report the characteristics of the new High Energy Spherical Grating Monochromator beam line on the SRS. The instrument, which has no entrance slit, was designed to provide high photon flux with small spot size, in the energy range covering the 1s binding energies of carbon, nitrogen, oxygen, and fluorine. Radiation from a bending magnet is horizontally focused onto the exit slit by a long, Pt-coated meridian cylinder (R=299 m, 2 mrad horiz. aperture, 2° glancing angle). The light is vertically diffracted and focused by one of three interchangeable spherical gratings (1050, 1500, and 1800 lines mm−1) operating in negative order. Finally, the light is refocused by an ellipsoidal mirror. The photon flux, determined with copper and carbon photocathodes, is presented for the three gratings. Useful flux is obtained in the range 250–1200 eV, with intensity maxima for each grating at 600, 700, and 800 eV of 11, 9, and 5×1010 photons s−1 per 100-mA stored beam into a band pass of 0.05%. The influence of contaminants which are present on the optical elements is discussed, together with details of beam line operating conditions which minimize the build up of such contaminants. Photoabsorption and photoemission measurements indicate a high (up to 30%) second order and some third order light content. Resolution determinations obtained from photoabsorption measurements are presented. Although features as narrow as 250 meV have been resolved, the resolving power of the instrument is found to depend strongly on stored beam current. We suggest this may be due to electron beam (i.e., source) blow-up. We critically discuss the suitability of the new facility for surface EXAFS of low Z adsorbates, in particular above the carbon, nitrogen, and oxygen 1s edges, using examples from recent studies which have been undertaken on the beamline.
Photoconductivity and luminescence measurements in liquids exposed to 4–6-keV x rays
Authors: Sham T. K. , Kristof P. , Holroyd R. A.
Published: July 2002

Conductivity measurements have been made on liquid hydrocarbons and solutions of tetramethyltin in hydrocarbons exposed to 4–6-keV x rays. It is found that although the free ion yield of the pure liquid at 6-keV photon energy is in agreement with previous measurements the ion yields at x-ray energies below 6 keV are lower than predicted by theory. The ionization current at the Sn L3 edge of solutions of tetramethyltin in 2,2,4,4-trimethylpentane (TMP) and toluene exhibits an inverted edge jump at various concentrations as expected from theory. Luminescence yield at the Sn L3 edge for a solution of tetramethyltin in toluene also exhibits the same inversion behavior, in general accord with previous results and the current understanding of edge jump behavior studies in liquids.
Compact UHV valve with field replaceable windows
Authors: Johnson Erik D. , Freeman John , Powell Forbes
Published: July 2002

There are many applications in synchrotron radiation research where window valves can be usefully employed. Examples include gas cells for monochromator calibration, filters for high-order light rejection, and as vacuum isolation elements between machine and experimental vacua. Often these devices are fairly expensive, and have only fixed (i.e., nonremovable) windows. The development of a new type of seal technology by VAT for their series 01 valves provides a gate surface which is free from obstructions due to internal mechanical elements. This feature allows a threaded recess to be machined into the gate to receive a removable window frame which can carry standard size Luxel thin-film windows. The combination of these features results in a DN 40 (2.75-in. conflat flange) valve which provides a clear aperture of 21-mm diameter for the window material.
Monochromator alignment technique
Authors: Tsang King-Long , Tseng Ping-Chung , Chen Ching-Iue , Song Yen-Fang , Chung Shinchun , Dann Tang-Eh , Lin Hsueh-Feng , Huang Liang-Ren , Chang Chu-Nan
Published: July 2002

A simple and high precision technique is developed for the monochromator alignment. The alignment setup is composed of two He/Ne lasers, a penta-prism, a flat mirror, and other common alignment aids. The alignment principle and the setup is described. An example of how to align Synchrotron Radiation Research Center 1-m-Seya monochromator is presented as well.
Backreflection x-ray standing waves and crystal truncation rods as structure probe for epilayer–substrate systems
Authors: Hashizume H. , Sugiyama M. , Niwa T. , Sakata O. , Cowan P. L.
Published: July 2002

Backreflection x-ray standing waves (BRXSW) and crystal truncation rod (CTR) scatterings have been used to probe the structure of heteroepitaxial CaSrF2 crystals on GaAs(111)B substrate. Coupled with the film-thickness information obtained from x-ray Fresnel reflectivity data, the combined x-ray standing wave and BRXSW data suggest one or both of the F and As layers missing from the heteroepitaxial interface. The CTR data support a missing F layer and interface (Ca, Sr) atoms occupying the T sites on GaAs(111) surface.
Total reflection of x-rays from vacuum-evaporated platinum mirrors in photon energy from 1.8–8 keV
Authors: Goto S. , Taguchi T. , Okamura S. , Hisatsugu T. , Kimura T.
Published: July 2002

The reflectivity of commercially available vacuum-evaporated platinum mirrors in photon energy was measured from 1.8–8 keV. The measured reflectivity was compared with that calculated using a graded refractive index model. For the two mirrors measured, assuming an rms surface roughness of 1.6 and 3.4 nm gave good fit of the measured to calculated reflectivity. These values are almost identical to the roughness measured by scanning tunneling microscopy. Using this model, the reflectivity of conventional vacuum-evaporated platinum mirrors in the few-keV range could be explained.
H−-conversion aided detection of low-energy H0 fluxes from the TORTUR tokamak in a time-of-flight analyzer
Authors: van Toledo W. , van Buuren R. , Donné A. J. H. , de Kluiver H.
Published: July 2002

A time-of-flight spectrometer has been developed to examine the velocity distribution of the hydrogen charge-exchange particles emitted from the TORTUR tokamak. To investigate the scrape-off layer, the spectrometer has been made sensitive to low-energy hydrogen atoms. This has been done by converting the hydrogen atoms into more easily detectable negative hydrogen ions on a cesiated monocrystalline tungsten surface. This detection technique enables examination of the neutral particle flux in a large energy range (5–2000 eV). Typical examples of time-of-flight spectra recorded during TORTUR discharges will be shown.
Instrumentation for high-precision x-ray optics at the synchrotron radiation source ‘‘Zelenograd’’
Authors: Kazimirov A. Yu. , Kovalchuk M. V. , Kreines A. Ya. , Mazurenko S. N. , Shilin Yu. N.
Published: July 2002

The high-precision x-ray optics station is to be installed on one of the five branches of the wiggler beamline at the new dedicated synchrotron radiation source ‘‘Zelenograd.’’ It is intended for the precision x-ray diffraction measurements using different methods which have been developed in the last decade for the structure studies of nearly perfect crystals and interfaces. The station consists of the double-crystal monochromator unit, the main goniometer with the crystal analyzer, the slit system with ion chambers, and the control and data acquisition system. The design of principal units and modules of the station is treated. The x-ray optics schemes which can be implemented on the station are described. The control and measuring system for x-ray experiments is presented.
Supermodulus effect in a Au/Ni superlattice studied by a diamond anvil cell and SR x ray
Authors: Konishi H. , Fujii Y. , Hamaya N. , Kawada H. , Ohishi Y. , Nakayama N. , Wu L. , Dohnomae H. , Shinjo T. , Matsushita T.
Published: July 2002

Elastic and thermal properties of Au/Ni superlattices have been investigated by x-ray diffraction on a synchrotron radiation source at the Photon Factory. An elastic response of [Au(10 Å)/Ni(10 Å)]50 to hydrostatic pressure generated by a diamond anvil cell has been measured in the layer-stacking direction. Its compressibility obtained from the pressure dependence of its superlattice period (Λ vs P) shows an anomalously small value compared with either bulk Au or Ni metal. Linear thermal expansions has also been measured by a similar method (Λ vs T). A significant anisotropic behavior between the layer-stacking and in-plane direction was found in both [Au(10 Å)/Ni(10 Å)]50 and [Au(4 Å)/Ni(4 Å)]210.
The status of beam lines for macromolecular crystallography at the Siberia-2 storage ring
Authors: Kusev S. V. , Raiko V. I. , Skuratovskii I. Ya.
Published: July 2002

An overview is presented of the x-ray optics of the four macromolecular crystallography beam lines under construction at the storage ring SIBERIA-2, Moscow. The four workstations are to utilize isomorphous replacement, anomalous dispersion, reflections energy profile, and the Laue technique. The instrumentation details, the results of ray-tracing analysis, and the use of an area detector are discussed.
A small angle x-ray scattering workstation for National Laboratory for Synchrotron Light
Authors: Bernardes L. A. , Tolentino H. , Rodrigues A. R. D. , Craievich A. , Torriani I.
Published: July 2002

A versatile, modular, and high-vacuum compatible small angle x-ray scattering workstation is under construction at National Laboratory for Synchrotron Light. It will use a wiggler source to be installed in the 1.15-GeV UVX2 electron storage ring. The white beam is monochromatized by Bragg reflection using a silicon triangular-shaped, asymmetrically cut and bent crystal. The movements required for θ rotation, crystal bending, and tilting are performed by an external goniometer and two specially designed translation stages, respectively. The x-ray wavelength will cover the range 1 Å<λ<2 Å and can be varied by θ rotation of the whole monochromator crystal and housing and 2θ rotation of the monochromatic beam path setup. The monochromator, secondary shutter, slits, sample holder, beam stopper, and detection system are stepping motor driven and computer controlled.
A new method for spectroscopy of liquid surface waves over the frequency range from 500 Hz to 40 kHz
Authors: Sakai K. , Kikuchi H. , Takagi K.
Published: July 2002

A simple method has been developed for measuring the propagation of liquid surface waves over a frequency range from 500 Hz to 40 kHz. A new type of electromagnetic wire transducer was successfully employed to generate liquid surface waves at such high frequencies. Surface waves were detected by an optical probe with spatial resolution as high as 30 μm, which determined the high-frequency limit of the measurement.