bluuebunny/crossref_metadata_2025 huggingface dataset:
Space-resolved measurement of internal magnetic field in a bumpy torus by Li0-beam probe spectroscopy
Authors: Kadota K. , Takahashi C. , Iguchi H. , Fujiwara M. , Matsunaga K. , Fujita J.
Published: July 2002

A new method combining Li0-beam probing and spectroscopic techniques has been developed to measure local magnetic fields in a bumpy torus. A collimated thermal Li0 beam is injected into the plasma. The Zeeman pattern of the lithium resonance radiation (22S–22P, 6708 Å) is observed with a Fabry–Perot interferometer. The strength of the local magnetic field is determined from the splitting between two π components of the 22S1/2–22P1/2 transition with the spatial resolution of about 7 mm. The magnetic fields from 2 to 4 kG were measured with accuracy of ±2%. This method is applicable to plasmas of a line-integrated electron density below 5×1012 cm−2.
Observation of piezoelectric effects in strained resonant tunneling structures grown on (111)B GaAs
Authors: Campbell I. H. , Joswick M. D. , Smith D. L. , Miles R. H.
Published: July 2002

Measured current density was compared as a function of bias voltage for (111)B and (100) oriented resonant tunneling structures consisting of GaAlAs barriers and a GaInAs quantum well. The GaInAs quantum well is in biaxial compression. In the (111)B, but not the (100), oriented devices an electric field is generated inside the quantum well by the piezoelectric effect. It is observed that this strain generated electric field leads to a characteristic asymmetry in the current density of the (111)B oriented devices for positive and negative voltage bias. Calculations are presented that show how the piezoelectric generated electric field leads to the observed asymmetry in the current density of the (111)B oriented device and which are in qualitative agreement with the experimental observations.
Feasibility of alpha-particle measurement by CO2 laser Thomson scattering
Authors: Hutchinson D. P. , Vander Sluis K. L. , Sheffield J. , Sigmar D. J.
Published: July 2002

The feasibility of CO2 laser Thomson scattering from a multicomponent burning plasma has been evaluated for the measurement of the velocity distribution of D–T-produced alpha particles. The density and velocity distribution of the alpha particles from their initial energy of 3.5 MeV down to near-thermal energies may be measured by small-angle (<1°) Thomson scattering. A computer simulation of the experiment indicates that a 100-MW pulsed laser combined with a bank of heterodyne receivers will be able to measure a scattered signal from the alpha particles with a postdetection signal-to-noise ratio of 75 for an assumed alpha density of 7.5×1011 cm−3.
Magnetic suspension systems with digital controllers
Authors: Carmichael A. T. , Hinchliffe S. , Murgatroyd P. N. , Williams I. D.
Published: July 2002

Single-axis magnetic suspensions, using optical position sensing and dc electromagnets, have been developed with eight-bit-word digital controllers that replace the familiar analog phase-advance or proportional-plus-derivative circuits. Control algorithms are obtained by a simple curve-fitting approach to signals sampled at constant rates. Stable suspension has been demonstrated at sampling rates down to 75 Hz when the magnet current has series transistor regulation, and at 100 Hz in a thyristor-regulated system.
Far-infrared high-density polyethylene windows for low-temperature and moderate-pressure applications
Authors: Lim C. C.
Published: July 2002

High-density polyethylene has good spectral transmission characteristics in the range from 20–500 cm−1. This, coupled with its ease of fabrication and low cost, make it an excellent choice for far-infrared absorption cell windows which operate at room temperature. However, because of its relatively large thermal coefficient of expansion and its brittleness (at low temperatures), the usual type of polyethylene absorption cell windows are difficult to make leaktight at low temperatures, especially if there is a moderately high pressure inside the absorption cell. In this article the problems associated with the use of such windows at low temperatures and moderately high pressures are discussed and a successful window design which overcomes these problems is described. These windows have been incorporated in a cell which has been used to measure the collision-induced absorption of various nonpolar gases at low temperatures. In these experiments the cell was cycled hundreds of times at pressures up to 96.5 bar and at temperatures down to 126 K.
Prospects of centrifugation of cells, liquids, and gases at multimillion g-forces in magnetically suspended microrotors
Authors: Moroz Pavel E.
Published: July 2002

Prototypes of magnetically suspended rotors for centrifugation of cells, organic and inorganic solutions, and gases are Fe-containing glass and metallic hollow microspheres 0.1–2 mm in diameter, composite steel-glass disks up to 1 cm, and microspheres of porous steel and Fe-impregnated porous glass. Fe-coated microcapsules with cells can be used for lower centrifugal forces. Predictable applications include cell hybridization and homogenization, spinning of samples at the ‘‘magic angle’’ in nuclear-magnetic resonance (NMR), intensification of nuclear fusion by high-speed rotation of microspheres with deuterium and tritium, and other examples. Rotor contents can be examined under the microscope during centrifugation, or the spinning rotor can be frozen and its contents freeze dried for further examination.
Improvements in a new technique for measuring and mapping heat transfer coefficients
Authors: Baughn J. W. , Hoffman M. A. , Makel D. B.
Published: July 2002

Two important improvements in a new technique for measuring and mapping local heat transfer coefficients are described. The first improvement involves the use of a new encapsulated thermochromic liquid crystal which has better stability and a narrower bandwidth than the cholesteric crystals previously used. The second important improvement is in the packaging arrangement. In this new arrangement, useful for gas flows, the liquid crystal is applied directly on the surface of an electrically conducting gold coating used as an electric heater, and is essentially in direct contact with the fluid. The encapsulated liquid crystal used in this study was applied directly to the gold surface without affecting the electrical characteristics of the gold coating. This new packaging arrangement has two advantages. First, no correction for the temperature drop across the plastic substrate is required. Second, a significant increase in the maximum detectable frequency is predicted.
Thermal magnetic noise generated by an eddy current shielded room
Authors: Stroink G. , MacAulay C.
Published: July 2002

Using a SQUID-based second-order gradiometer, we have measured the thermal magnetic noise generated by a thick aluminum plate and an eddy current shielded room used for biomagnetic measurements. The measured noise agrees with the theoretical prediction for the thermal noise fields generated by infinite conducting slabs. The noise is substantial near the walls of the shielded room, but is predicted to be less than 0.02 fT/√Hz at 1 Hz at the center of the room. This is too small to influence the biomagnetic measurements usually taken at this location.
Measurement system induced errors in diode thermometry
Authors: Krause John K. , Dodrill Brad C.
Published: July 2002

Diode temperature sensors are capable of being used at the accuracy level of a few hundredths of a kelvin. However, in order to achieve this performance, proper measurement techniques must be used. Poorly shielded or improperly grounded measurement systems can introduce ac noise which will create an apparent shift in the dc voltage reading across a diode sensor. This results in a temperature measurement error which may approach several tenths of a kelvin. The presence of the ac noise in question is not obvious during normal usage and several quick tests are outlined to verify whether or not a noise problem exists. Experimental data and derivations from theoretical p-n junction characteristics are given which correlate the ac noise level with possible voltage/temperature measurement errors. These results can be used in estimating the accuracy and performance of a temperature measurement system. Several of the more common problems which introduce noise into diode circuitry are described.
Flexible microprocessor-based digital pulse programmer for pulsed nuclear-magnetic resonance
Authors: Hale M. E. , Peemoeller H. , Sharp A. R.
Published: July 2002

A microprocessor-based pulse programmer for pulsed nuclear-magnetic resonance (NMR) based on the Intel 8086 has been developed. The pulse sequences are specified using a programming language developed specifically for this purpose. Pulse and delay timing is generated by a single timebase operating at 20 MHz, controlled by a state memory. The pulse programmer offers a high degree of flexibility at a moderate cost.
Fast λ/4 and λ/2 voltage Pockels cell driver for an internally seeded and cavity dumped regenerative laser amplifier
Authors: Dong S. , Krause W. , Völker F. , Weber H.
Published: July 2002

A krytron-based electrical circuit of a λ/4 and λ/2 voltage pulse generator for a Pockels cell incorporated in a self-injected and cavity dumped short-pulse laser source is described. The circuit supplies three independent high-tension pulses having amplitudes between 1 and 2.5 kV, fall and rise times <2 ns, and jitter <2 ns. Pulse durations and interpulse distances are adjustable.
Accelerator for ion beams using triangle-shaped accelerated waves
Authors: Kawaguchi M. , Sasahara M. , Noritake T. , Enjoji H.
Published: July 2002

An accelerator for ion beams has been designed and constructed in which ions collectively undergo acceleration in the wells of a train of triangle-shaped potential waves moving with a constant acceleration. The accelerator mentioned above is planned for investigating the conditions necessary for acceleration of ions with a mass distribution, such as cluster ions, which will be available in future fusion reactors. The method and the circuits for generations of propagating accelerated waves are described and the structure of the accelerator with an acceleration space 120 cm long is mentioned. A result is reported on a preliminary experiment for acceleration of an argon ion beam, which shows that the accelerator works well.
Differential ac method of thermopower measurement
Authors: Kettler W. H. , Wernhardt R. , Rosenberg M.
Published: July 2002

A new differential ac technique is described for rapid and continuous measurement of thermoelectric power of thin metallic ribbons over a wide temperature range. Sinusoidal heating of one thermocouple junction by means of a small resistive heater results in a measuring principle which eliminates spurious thermoelectric voltages in the lead wires and favorably benefits from ac signal processing. The resultant equilibrium temperature of the heated junction contains a constant term depending on thermal parameters of the system, and an oscillating term with a frequency-dependent amplitude. By choosing a suitable sample configuration no corrections are required for the thermal response of the system. By careful shielding of the measuring circuits and using modern lock-in amplifiers noise voltages can be reduced to less than 1 nV for measuring frequencies below 10 Hz. Measurements accurate to 1% are possible, using temperature differences smaller than 10 mK. The effectiveness of this technique is demonstrated by comparing our measurement of the thermoelectric power of an amorphous Fe80B20 alloy with measurements using conventional techniques and by studying the thermopower of an amorphous Fe90Zr10 alloy in the vicinity of its second-order magnetic phase transition.
High-precision vapor-pressure isotherms: Apparatus, errors, and results
Authors: Suter R. M. , Colella N. J. , Gangwar R. , Wang W.
Published: July 2002

We describe an apparatus for measuring high-resolution, low-noise vapor-pressure isotherms of physisorbed films. The data can be numerically differentiated to yield precise values of the two-dimensional isothermal compressibility of monolayer films, allowing detailed analysis of phase transitions. The apparatus is a carefully implemented, automated adaptation of standard volumetric systems.
Use of thick gold foils in retarding-potential Mott polarimeters
Authors: Dunning F. B. , Tang F.-C. , Walters G. K.
Published: July 2002

Data are presented showing that thick scattering foils (or solid targets) can be used in retarding-potential Mott polarimeters without degrading their performance. Use of thick foils can simplify the design and operation of such polarimeters. A straightforward calibration procedure is described.
Scanning tunneling microscope
Authors: Park Sang-il , Quate C. F.
Published: July 2002

This article describes the design of a scanning tunneling microscope (STM) which is suitable for surface science work. Various concepts in mechanical structure and electronic circuitry of the STM have been pursued to optimize its performance. This STM has been designed especially to meet the requirement of in situ sample preparation and sample transfer in ultrahigh vacuum. The electronics of this STM are capable of taking simultaneous images with opposite polarities of tunneling voltages.
Microwave measurement of the mass of frozen hydrogen pellets
Authors: Talanker V. , Greenwald M.
Published: July 2002

A nondestructive method for measuring the mass of high-speed, frozen hydrogen pellets is described. The measurement technique is an improvement on previous methods based on the perturbation to a resonant cavity caused by a dielectric pellet passing through the cavity. In the new method, an oscillator circuit is formed with a resonant cavity in the positive feedback loop of a microwave power amplifier. An injected pellet perturbs the resonance characteristics of the cavity causing a shift in the operating frequency of the oscillator proportional to the ratio of the pellet volume to the volume of the cavity. Through digital measurement of the frequency shift the size of the pellet is determined automatically. In a ‘‘proof-of-principle’’ experiment it was shown that polyethylene pellets, with an average volume of 0.26 mm3 and velocity ≊500 m/s, caused a shift in the operating frequency of the oscillator circuit that was within 10% of the predicted value. The hydrogen pellets (of interest to us) will have 4–10× the volume of the plastic pellets. Thus with a dielectric constant of about 1.26 for frozen hydrogen, the signals in the actual experiment would be 1–2× those described here.
Density determination in the TEXTOR boundary layer by laser-ablated fast lithium atoms
Authors: Pospieszczyk A. , Ross G. G.
Published: July 2002

A method is presented which allows a determination of electron density profiles in the plasma boundary of a fusion device up to some 1013 cm−3 within about 100 μs. For this purpose, the complete attenuation of an injected lithium beam is determined by measuring its optical emission profile. The beam is generated by a ruby laser, which ablates small portions of a LiF coating with a thickness of about 1000 Å from the rear side of a glass substrate. The produced lithium atoms have velocities of 1×106 cm/s and can penetrate into the plasma until ne×l ≊1×1013 cm−2. For the measurement of the optical emission profile of the excited lithium atoms, a silicon photodiode array camera is used. The emission profile is then converted into an electron density profile with the help of the ionization rate for lithium atoms by electron impact.
Low-temperature thermometry in high magnetic fields. VI. Industrial-grade Pt resistors above 66 K; Rh–Fe and Au–Mn resistors above 40 K
Authors: Brandt B. L. , Rubin L. G. , Sample H. H.
Published: July 2002

The characteristics of twelve industrial-grade and one precision platinum resistance thermometers for temperatures from 66 to 300 K and in magnetic fields up to 19 T are described. The results from the 13 models from nine suppliers are combined to produce mean values that may be used to correct any of those thermometers for effects of a magnetic field parallel to its long axis. The correctability error at 19 T is less than ±0.3% between 66 and 110 K and less than ±0.1% above 110 K. Magnetoresistance data for Rh–Fe and Au–Mn resistance thermometers are also presented.
Automated system for relative sound velocity and ultrasonic attenuation measurements
Authors: Toulouse J. , Launay C.
Published: July 2002

In order to facilitate measurements of ultrasonic velocity and attenuation, we have developed an automated version of the phase sensitive technique with quadrature detection. The technique is outlined and the precision of relative transit time or velocity measurements that can be obtained from it is analyzed. We describe the computer-controlled experimental setup and report relative velocity and attenuation results obtained on a single crystal of pure KZnF3 . The temperature dependence of the elastic constants C11 and C44 calculated from these results agree very well with that obtained from echo overlap measurements performed on the same crystal. The relative error on the present velocity measurements is Δv/v∼10−5 .
Position sensitive detectors in (e,2e) coincidence measurements
Authors: Hayes P. , Bennett M. A. , Flexman J. , Williams J. F.
Published: July 2002

The two outgoing electrons from (e,2e) scattering processes are selected by two 180° electrostatic analyzers whose energy dispersed output spectra are detected by microchannel plates followed by resistive anodes. These detectors permit the identification of all multiple coincident events occurring within the dispersal width of the analyzers. It was found that the time difference between the two detectors for correlated events is strongly dependent on the energy of the incident electrons, which consequently causes the time coincidence window to move systematically. This behavior has been accounted for by a model that determines the time taken by an electron to go around a hemispherical analyzer. A description is given of a data collection system that can compensate for the shift in the coincidence spectra and that records all multiple coincidence events with an increase in the overall coincidence count rate of about two orders of magnitude relative to conventional non position sensitive detectors without position sensing. The performance of the system is shown for an (e,2e) spectrum of argon.
Two-color CO2 interferometer with single Bragg cell and improved vibration compensation at 3.39 μm
Authors: Innocente P. , Martini S.
Published: July 2002

A single-chord CO2 (10.6-μm) He–Ne (3.39-μm) two-color laser interferometer which has been developed for the ETA-BETA II RFP machine is presented. Compared to the usual 0.633-μm vibration compensation systems, the 3.39-μm interferometer allows faster optical path-length variations to be measured without losing fringes, can stand larger angular deflections of the beams (e.g., due to vibrations of the optic mounts) without losing alignment, and uses the same acousto-optic modulator as the CO2 system, thus minimizing the differences in the optical path of the two interferometers. The instrument has been extensively utilized on ETA-BETA II, where line density variations larger than 1020 m−2 and occurring in less than 4 μs can be routinely measured and the residual error after vibration compensation is ≊2×1018 m−2. Some further developments of the diagnostic are presented, which are presently underway or planned.
Rate control for electron gun evaporation
Authors: Schellingerhout A. J. G. , Janocko M. A. , Klapwijk T. M. , Mooij J. E.
Published: July 2002

Principles for obtaining high-quality rate control for electron gun evaporation are discussed. The design criteria for rate controllers are derived from this analysis. Results are presented which have been obtained with e-guns whose evaporation rate is controlled by a Wehnelt electrode or by sweeping of the electron beam. Further improvements of rate stability can be obtained by improved design of e-guns and power supplies.
Interrupt-driven digital controller for a magnetic suspension system
Authors: Lawson M. A. , Gillies G. T.
Published: July 2002

The hardware interrupt structure of an MS-DOSTM -based personal computer was used to enable real-time, keyboard manipulation of the control parameters of a stable, vertical magnetic suspension without halting its operation. The positions of objects suspended with this system were measured to be stable to within ±15 μm of a reference position. Stable suspensions were achieved at sampling rates as low as 45 Hz, although the system was typically operated at sampling rates of 1.0–2.0 kHz. The dynamics of the suspension were explored for several different values of proportional, integral, and derivative gains, and the system’s transient response and steady-state behavior were characterized. We present here the data resulting from those studies, as well as measurements of the suspension’s drift, empirically determined values of its second-order transfer function parameters, a discussion of the suspension’s foreground/background capabilities, a description of its algorithm, and details of its electromechanical construction.
Construction of a low-cost, servo-controlled, spark-erosion cutter
Authors: Viljoen P. E. , Bezuidenhout F. , Berning G. L. P. , Myburg G.
Published: July 2002

A low-cost, spark-erosion cutter for stain-free cutting of conducting materials in samples of specific shapes, has been built. A servo system monitors the distance between tool and sample, and advances the tool towards the sample when necessary in a controlled way. Advancement rates of between 0.4 and 3.0 mm/h are presently used but with other gear ratios for the motor it could be changed to almost any practical value. Cutting rates of typically 1–1.5 mm/h are used. The cutter works quite well, is within the financial reach of smaller laboratories, and can be built in a local machine shop.
Constructing band diagrams of semiconductor heterojunctions
Authors: Leibovitch M. , Kronik L. , Fefer E. , Korobov V. , Shapira Yoram
Published: July 2002

A novel approach for constructing the band diagrams of semiconductor heterojunctions is discussed and illustrated. It is based on a simple measurement of band discontinuities, Debye length and the width of the space–charge region at the heterojunction interface. Monitoring the changes in the surface potential during heterojunction formation makes it possible to identify the contributions of the interface states and dipole. The approach is illustrated by the results of experiments performed on the InP/In2O3 heterojunction.
Inductive detection of piezoelectric resonance by using a pulse NMR/NQR spectrometer
Authors: Choi K. , Yu I.
Published: July 2002

An inductive excitation and detection scheme of piezoelectric resonance is shown using a conventional pulse NMR/NQR spectrometer and its associated experimental techniques. This new method has advantages over the previous capacitive scheme since the measurement does not require any electrode to be attached to the sample. For a test we investigated the piezoelectric resonance observed inductively from a 3.5-MHz AT-cut quartz crystal.
Apparatus for characterizing the VUV and soft x-ray optical elements at the Photon Factory
Authors: Mitani Shichiro , Namioka Takeshi , Yanagihara Mihiro , Yamashita Kojun , Fujita Junji , Morita Shigeru , Harada Tatsuo , Sasaki Taizo , Sato Shigeru , Miyahara Tsuneaki , Koide Tsuneharu , Mikuni Akira , Okamoto Wataru , Maezawa Hideki
Published: July 2002

An apparatus dedicated to characterizing the VUV and soft x-ray optical elements was fabricated, and a preliminary test on its performance was made in the soft x-ray region with a grasshopper monochromator at the Photon Factory. The results demonstrated that quantitative evaluation of diffraction efficiency of a grating could be easily performed using the apparatus.
Performance of a tuneable secondary x-ray spectrometer
Authors: Brennan S. , Cowan P. L. , Deslattes R. D. , Henins A. , Lindle D. W. , Karlin B. A.
Published: July 2002

An efficient, high-resolution secondary x-ray spectrometer is critical to studies of x-ray-excited fluorescent x-ray emission spectra. Even with the highest available incident flux of x rays, the signal count rate can become unacceptably low when dispersed by an analyzing crystal. This problem is most serious in studies of gas targets, or at low energies where fluorescence yields are low. We have characterized the performance of a spectrometer based on the Rowland circle geometry with a variable-radius curved (Johann) analyzing crystal. A position-sensitive detector was used so that counts at a range of points on the Rowland circle corresponding to different wavelengths can be recorded in parallel. The efficiency of the spectrometer permits the observation of weak processes, such as subthreshold elastic and elastic x-ray scattering from gases. Energy resolution at low energies is sufficient to allow observations of spectral peak widths which are narrower than lifetime broadening widths. Polarization dependence of the fluorescence can also be studied.
SUNY X3 beamline at NSLS
Authors: Phillips James C.
Published: July 2002

The State University of New York (SUNY) beamline at National Synchrotron Light Source [NSLS] has been moved to the X3 port during the NSLS Phase II shutdown. Additional floorspace and new equipment have enabled several changes and additions to the line to be made. There will be four sets of optics with independent operation. These will feed a short wavelength crystallography station, an x-ray spectroscopy station, a time-sharing crystallography/SAXS station, and a surface science chamber. The new design of the line is presented.
Development of compact synchrotron light source for x-ray lithography (abstract)
Authors: Mandai S. , Hoshi Y. , Kohno Y.
Published: July 2002

Ishikawajima-Harima Heavy Industries Co., Ltd., (IHI) has developed a prototype compact synchrotron light source for x-ray lithography of semiconductors. It consists of 45-MeV linear accelerator as an electron injector and an 800-MeV synchrotron. Peak wavelength of synchrotron radiation is around 10 Å. The basic parameter of the synchrotron is as follows: (1) Beam current: more than 50 mA; (2) Beam life: more than 1 hr; (3) Circumference: 23.5 m; (4) Bending magnet: 1.33 T, 90° sector laminated core; (5) rf system: 178.5 MHz tetrode power supply. Our synchrotron is a so-called low-energy injection accelerator and various difficult problems such as ion trapping, vacuum, Touscheck effect will occur. So, we provide ion cleaning electrodes inside the vacuum chamber to avoid ion trapping. Also, we have adopted a trapezoidal magnet excitation method as an injection scheme to stimulate gas desorption of the vacuum chamber. The beamline extracted from the bending magnet will be used for various research subjects which include x-ray lithography, photoelectron spectroscopy, EXAFS, fluorescence analysis, and so on. This machine will be completed by the end of 1988 and is scheduled to use synchrotron radiation in the spring of 1989.
Perspectives on micropole undulators in synchrotron radiation technology
Authors: Tatchyn Roman , Csonka Paul , Toor Arthur
Published: July 2002

Micropole undulators promise to advance synchrotron radiation (SR) technology in two distinct ways. The first is in the development of economical, low-energy storage rings, or linacs, as soft x-ray sources, and the second is in the opening up of gamma-ray spectral ranges on high-energy storage rings. In this paper the promise and current status of micropole undulator (MPU) technology are discussed, and a review of some practical obstacles to the implementation of MPU’s on present-day storage rings is given. Some successful results of recent performance measurements of micropole undulators on the Lawrence Livermore National Laboratory linac are briefly summarized.
Liquid gallium cooling of silicon crystals in high intensity photon beams (invited)
Authors: Smither R. K. , Forster G. A. , Bilderback D. H. , Bedzyk M. , Finkelstein K. , Henderson C. , White J. , Berman L. E. , Stefan P. , Oversluizen T.
Published: July 2002

The high-brilliance, insertion-device-based photon beams of the next generation of synchrotron sources (Argonne’s APS and Grenoble’s ESRF) will deliver large thermal loads (1–10 kW) to the first optical elements. Considering the problems that present synchrotron users are experiencing with beams from recently installed insertion devices, new and improved methods of cooling these first optical elements, particularly when they are diffraction crystals, are clearly needed. A series of finite element calculations were performed to test the efficiency of new cooling geometries and various cooling fluids. The best results were obtained with liquid Ga metal flowing in channels just below the surface of the crystal. Ga was selected because of its good thermal conductivity and thermal capacity, low melting point, high boiling point, low kinetic viscosity, and very low vapor pressure. Its very low vapor pressure, even at elevated temperatures, makes it especially attractive in UHV conditions. A series of experiments were conducted at CHESS in February of 1988 that compared liquid gallium-cooled silicon diffraction crystals with water-cooled crystals. A six-pole wiggler beam was used to perform these tests on three different Si crystals, two with new cooling geometries and the one presently in use. A special high-pressure electromagnetic induction pump, recently developed at Argonne, was used to circulate the liquid gallium through the silicon crystals. In all experiments, the specially cooled crystal was used as the first crystal in a two crystal monochromator. An infrared camera was used to monitor the thermal profiles and correlated them with rocking curve measurements. A second set of cooling experiments were conducted in June of 1988 that used the intense, highly collimated beam from the newly installed ANL/CHESS undulator. Tests were performed on two new Ga-cooled Si crystals and compared with the standard water-cooled Si crystal. One of the crystals had cooling channels at two levels in the crystal that allowed one to actively control the shape of the crystal surface. The second one had rectangular cooling channels located just beneath the diffraction surface. Both crystals showed major improvements over the water-cooled crystal.
Advances in mercuric iodide energy dispersive x-ray array detectors and associated miniaturized processing electronics (invited)
Authors: Iwanczyk J. S. , Dorri N. , Wang M. , Szawlowski M. , Warburton W. K. , Hedman B. , Hodgson K. O.
Published: July 2002

There are important areas of synchrotron radiation research which would strongly benefit from the availability of energy dispersive detector arrays with high energy resolution and good spatial resolution. The goal of this developmental project is to produce a several element mercuric iodide (HgI2) submodule, which can later be multiplied and grouped into larger arrays of 100–400 elements. A prototype five-element HgI2 array detector was constructed and tested using a synchrotron radiation beam at SSRL. An energy resolution of 280 eV (FWHM) has been obtained for the MnKα line at 5.9 keV. Miniaturized processing electronics were developed in parallel with array advancement. To date, we have completed the hybridized preamplifier and finished breadboarding a computer controlled amplifier. The system integration aspects of large array detectors were studied, producing a conceptual design for both the detector array and its computerized data-acquisition and analysis system.
Challenge to precise magnetic Compton-profile measurements (invited)
Authors: Sakai N. , Shiotani N. , Ito M. , Itoh F. , Kawata H. , Amemiya Y. , Ando M. , Yamamoto S. , Kitamura H.
Published: July 2002

Recent developments of the insertion devices have made it possible to utilize intense hard x rays for precise Compton-profile measurements. A Compton profile of Si (110), which is measured using 29.5-keV synchrotron-radiation x rays, is shown as an example of a precise measurement having a momentum resolution of 0.084 a.u., the best resolution ever achieved. A promising plan is presented on magnetic electron Compton-profile measurements using circularly polarized 60-keV x rays from a newly developed multipole wiggler in the 6-GeV accumulation ring at KEK as an elliptically polarized source.
Magnetic-field study in a compact helical system
Authors: Yamada H. , Matsuoka K. , Okamura S. , Ida K. , Nishimura K.
Published: July 2002

Implementation of the designed magnetic field in the compact helical system torsatron device has been verified both experimentally and numerically. A misalignment of the outer two sets of poloidal field coils has been identified both quantitatively and qualitatively. A magnetic-field-mapping experiment has indicated that closed magnetic surfaces have been successfully achieved up to 95% of the outermost surface and that islands exist on the m=2 and 3 major rational surfaces. The experimental results and the computational analysis consistently explain that these islands are mainly caused by the ambient field resulting from magnetization of the building structure. The m=2 island width is estimated to be several millimeters during regular plasma heating experiments when the toroidal field is more than 1 T.
Novel microwave device for nondestructive electrical characterization of semiconducting layers
Authors: Druon C. , Tabourier P. , Bourzgui N. , Wacrenier J. M.
Published: July 2002

A microwave measurement technique, using a novel cell which enables the sheet resistance (R⧠), the carrier density (n), and the mobility (μ) of epitaxial layers to be measured, is proposed. The system, controlled by a microcomputer, performs this characterization by measuring galvanomagnetic effects. The sample is only lightly pressed on the cell. The electrical contacts between the sample and the cell are capacitive. This method is thus nondestructive and requires no technological process. The data treatment necessitates knowledge of factors which are determined from a calibration procedure made only once. For the GaAs samples reported here, the accuracy is better than 5% for R⧠, 15% for μ, and 20% for n.
Intrinsic optical fiber temperature sensor based on the differential absorption technique
Authors: Appleyard A. P. , Scrivener P. L. , Maton P. D.
Published: July 2002

A microprocessor-based instrument for temperature measurement has been developed based upon the intrinsic temperature sensitive absorption properties of a neodymium doped optical fiber. The accuracy and repeatability of temperature measurement are investigated with respect to the stability of environmentally sensitive system components. In the light of these investigations a prototype instrument employing novel compensation techniques has been developed. Accuracy and repeatability have been determined to be better than ±1 °C over a 20–200 °C temperature measurement range with the potential of increased range and accuracy for temperatures down to −100 °C.
Automatic control system of the PIG ion source for the U-400 cyclotron
Authors: Kutner V. B. , Subbotin V. G. , Sukhov A. M. , Tretyakov Yu. P. , Fefilov B. V. , Kasyanov A. A. , Rybin V. M.
Published: July 2002

An automatic control system is described for the multiply charged ion source of the U-400 cyclotron based on CAMAC apparatus and microprocessor controllers. The system allows the automatic tuning of the ion source to the necessary regime, including the automatic start-up of discharge, determination of the necessary parameters of sputtering, and the automatic search for a maximum beam current for given discharge parameters. The system performs the tuning of the ion source to the quasioptimal regime in 10–15 min with up to 5% deviation from the preset parameters. It is possible to stabilize the beam current within 3% using the automatic correction of the discharge regime.
Pulse radar technique for reflectometry on thermonuclear plasmas
Authors: Hugenholtz C. A. J. , Heijnen S. H.
Published: July 2002

A new method to measure density profiles of thermonuclear plasmas with fast pulse radar is proposed. A number of important benefits of pulse radar above the generally used swept frequency reflectometry are given. A test bench experiment at 34 GHz, using pulses with 1.5-ns rise and fall times, showed that a spatial accuracy of about 1 mm can be reached. With ultrafast (200 ps) microwave pulses it is perhaps possible to perform a direct measurement of the density gradient of the plasma from the broadening and the modification of the shape of the reflected pulse.
Triple-axis goniometric magnetotransport measurement system with 0.02° angular resolution
Authors: Iye Yasuhiro
Published: July 2002

A system useful for magnetotransport measurement on highly anisotropic materials is described. One type of cryostat can rotate a sample about two horizontal axes over an angular range of ∼±15° with a resolution of ∼0.02°, while another can rotate it about one axis over a wider range with a resolution of ∼0.1°. These sample holders are rotated about a vertical axis by a computer-controlled stepping motor with a 0.0036°/step resolution in a horizontal magnetic field generated by a 7 T superconducting split-coil magnet. A few examples of measurements recently made by use of this system are given to illustrate the system’s performance.
Experiments to trap dust particles by a wire simulating an electron beam
Authors: Saeki Hiroshi , Momose Takashi , Ishimaru Hajime
Published: July 2002

Motion of trapped dust particles has been previously analyzed using high-energy bremsstrahlung data obtained during dust trapping in the TRISTAN accumulation ring. Because it is difficult to observe the actual motions of dust particles trapped in an electron beam due to the strong synchrotron light background, we carried out experiments to trap sample dust particles with a Cu wire simulating an electron beam. A negative potential was slowly applied to the wire using a high voltage dc power supply. Motions of dust particles trapped by the wire were recorded with a video camera system. In an experiment using a Cu wire (1.5 mm in diameter) with no magnetic field, the charged dust particle made vertical oscillation about the wire. In another experiment using the same wire but with a vertical magnetic field (0.135 T) simulating a bending magnetic field, both vertical and horizontal oscillating motions perpendicular to the wire were observed. Furthermore, it was found that the dust particle moved in the longitudinal direction of the wire in the bending magnetic field. Therefore, it is expected that charged dust particles trapped by the electric field of the electron beam oscillate vertically where there is no magnetic field in the TRISTAN accumulation ring. It is also expected that trapped dust particles where there is a bending magnetic field oscillate horizontally and vertically as the particle drifts in a longitudinal direction along the ring.
An active vibration isolation system for inertial reference and precision measurement
Authors: Nelson Peter G.
Published: July 2002

We describe an active low-frequency vibration isolation system based on an earlier instrument developed at the Joint Institute for Laboratory Astrophysics (JILA). Several modifications, which have led to improved transient response, temperature stability, and a greatly reduced size, are discussed. We also comment on how the performance of the system is limited by sensor noise, mechanical resonances, and cross couplings between the different degrees of freedom.
Measurement of light impurity densities and Zeff in JET using x-ray tomography
Authors: Weisen H. , Pasini D. , Weller A. , Edwards A. W.
Published: July 2002

In the vast majority of plasmas produced in the JET tokamak the x-ray emission at energies above about 1 keV is dominated by bremsstrahlung radiation from the background deuterium ions, and both bremsstrahlung and recombination radiation from one or two light impurity species such as beryllium and carbon. Under these circumstances local values of impurity densities and concentrations, or alternatively of the effective charge Zeff of the ion mixture, are derived from tomographic measurements of the local x-ray emissivity at energies above 1–3 keV, in conjunction with measurements of electron density and temperature profiles. These calculations are performed using the intrinsic emissivities due to the impurity ions. The emissivities into the relevant energy bands, determined by the detector and filter characteristics, were calculated assuming coronal ionization equilibrium, and tabulated as a function of electron temperature. This method offers a good spatial and temporal resolution, and is successfully applied to most plasma conditions where the relative proportions of impurities are known. We also present a detailed sensitivity study to assess the effects of errors in the input data, and a comparison with established methods based on visible bremsstrahlung measurements, and charge exchange spectroscopy.
A new generation of integrated multichannel single-particle detectors (invited)
Authors: Hatfield J. V. , Comer J. , York T. A. , Hicks P. J.
Published: July 2002

Monolithic integrated circuit (IC) detectors have been developed which consist of an array of electron sensing anodes and a corresponding array of amplifiers and counters all integrated onto a single chip. The anodes are fabricated on the surface of the chip over a thick dielectric film. The IC is mounted with a microchannel plate multiplier so that it counts individual charged particles and photons. The detector chip is so designed that it can be used in hybrid configurations. The active anode area can, therefore, be arbitrarily extended by abutting individual detector chips side by side, under the control of a customizing gate-array chip. Quad-detector chip sets are currently in use.
Sensitivity calibration of surface barrier diodes for soft x-ray observation of plasma
Authors: Sakurai M. , Shimazu Y. , Asakura N.
Published: July 2002

Relative sensitivities of surface barrier diode detectors used for soft x-ray imaging of plasma emission were calibrated using synchrotron radiation as a calibration source. The variation of responses among 33 detectors against monochromatized light in the soft x-ray region were measured at the calibration beam line BL5B of UVSOR. The response of detectors against pulsed incident radiation (20 μs) was stored and averaged by a boxcar integrator. The calibration factors obtained at this experiment were applied to correct the soft x-ray emission profiles measured from a high-temperature plasma.
A diffractometer for grazing incidence x-ray diffraction study of Langmuir monolayers (abstract)
Authors: Matsushita Tadashi , Iida Atsuo , Takeshita Kunikazu , Saito Kazuhiro , Kuroda Shin-ichi , Oyanagi Hiroyuki , Sugi Michio , Furukawa Yukito
Published: July 2002

We report the design and performance of a diffractometer which is used on the 53 pole wiggler beamline at the Photon Factory for grazing incidence x-ray diffraction study of monolayers spread on the surface of water. It is a simple two-circle (ω-2θ) diffractometer. A Langmuir trough is mounted on a vertical translation stage on the ω axis. A one-dimensional position sensitive detector is vertically mounted on the 2θ arm with a 50-mm-high Soller collimator (0.1° resolution) in front of it. With this position sensitive detector, the intensity distribution along the Bragg rod is simultaneously recorded during the 2θ scan. A saggitally focusing Si(111) double-crystal monochromator is used to monochromatize and horizontally focus the x-ray beam. X-ray beams are then reflected downward and vertically focused by a bent mirror. The grazing incidence angle of the x-ray beam to the surface of water is also controlled by adjusting this mirror. The instrumental angular resolution in the horizontal plane was measured to be 0.17°. With this diffractometer, we studied the structure of arachidic acid monolayers spread on surfaces of (i) pure water, (ii) 10−4 M Cd2+ solution, and (iii) 10−4 M cyanine dye solution. By analyzing the x-ray intensity distribution along the Bragg rod using a simple model proposed by Kjaer et al. [K. Kjaer, J. Als-Nielsen, C. A. Helm, P. Tippman-Krayer, and H. Möhwald, J. Phys. Chem. 93, 3200 (1989)] we obtained the following conclusions. In the case on pure water, molecules tilt toward the nearest neighbors at low surface pressures and stand upright at higher pressures. In the presence of Cd2+, molecules stand upright even at a very low pressure. In the presence of cyanine dye in the water, molecules tilt toward the next nearest neighbors at low pressures and stand upright at higher pressures.
Operation of a dynamically bent sagittally focusing double crystal monochromator for XAFS studies
Authors: Lamble G. M. , Heald S. M.
Published: July 2002

The X-11A beamline at the NSLS has been upgraded to include a dynamic sagittally focusing second crystal in the monochromator, currently operating in the range 5.5–11 keV. The monochromator maintains a constant focus at the sample by adjustment of the bent crystal radius during the XAFS scan. The monochromator accepts 3.3 mrad of horizontal radiation and a spot size of ∼1.5 mm2 is achieved at the sample. The sagittally focusing mechanism in the monochromator is described and the results are presented of intensity profiles, spatial stability, and energy resolution between the energy ranges 6 and 10 keV, where the system performs most favorably. Intensity gains over unfocused operation are substantial and XAFS studies of dilute fluorescence samples reveal the expected S/N improvements, without any introduction of additional noise from the bending process. The mechanism operates with close to 100% efficiency between the energy ranges 6 and 8 keV. Bending errors hinder the performance at higher energies and also preclude effective harmonic rejection, by piezocrystal detuning, over the entire energy range.
Performance of an integrated materials science station (abstract)
Authors: Dobson B. R. , Dent A.
Published: July 2002

Station 9.3 on Daresbury Synchrotron Radiation Source (SRS) was constructed as an integrated facility for Materials Science investigations. The station will eventually be able to carry out scanning extended x-ray-absorption fine structure (EXAFS), energy dispersive EXAFS, and powder diffraction measurements. In addition, there will be a number of different sample presentations and environments available such as high-temperature/pressure catalysis, reflectivity, high pressure. The scanning EXAFS monochromator and vertically focusing mirror is the first part of the instrument to be completed. The performance of the monochromator is demonstrated paying attention to its stability and accuracy. Two modes of operation are demonstrated: high aperture, high resolution and variable resolution, and vertical focusing. Some results from the use of the reflectivity rig are presented demonstrating one of the sample presentation techniques. In addition, results from measurements using a high pressure cell are included.
Efficient helium-free multi-joule TE-CO2 laser using spiker-sustainer excitation
Authors: Bhadani P. K. , Sylvan A. , Harrison R. G.
Published: July 2002

A highly efficient multi-joule output TE-CO2 laser has been developed using a spiker-sustainer excitation method. With helium-free laser gas mixtures 5-J laser pulses have been produced at a pressure of 400 mbar with an energy output efficiency of 22.6%. The addition of small amounts of hydrogen to the gas mix has been found to enhance laser performance.