bluuebunny/crossref_metadata_2025 huggingface dataset:
Negative hydrogen ion production in the hollow cathode Penning surface-plasma source
Authors: Belchenko Yu. I. , Kupriyanov A. S.
Published: July 2002

A small hollow cathode Penning surface-plasma source (SPS) was developed and studied. The H− yield was proportional to the emission apertures area and increased over a wide range of discharge current. The H− yield, with an intensity of up to 0.95 A and an emission current density of up to 3.6 A/cm2, was obtained in a pulsed mode. With the discharge current of 20 A and a pulse duration of 60 s, an H− yield with current of 0.1 A was obtained. The H− emission current density had approximately the same value for various diameters (0.5–7 mm) and thicknesses (0.3–4.0 mm) of cylindrical emission holes, if the thickness of hole walls did not exceed the hole diameter. The H− yield extracted through the thick conical emission holes had a value 25% higher than that for a thin cylindrical hole with the same permeable diameter. Dependencies of the H− yield versus magnetic field and hydrogen feed were different from that of the standard Penning SPS. The optimal cesium coverage of the electrodes was stable for both high-current, long-pulse and low-current, dc source operation. Noticeable H− production was realized with a low-discharge voltage of 15 V. The heavy negative ions fraction was less than 1% of total negative ion yield for long-pulse operation. The yield of D− ions from deuterium discharge had a value 15% lower than that of H− ions from the hydrogen discharge. Most of the extracted H− ions are produced by conversion of fast and superthermal (E≳1 eV) atoms on the cesiated surfaces of the emission hole cones or they are due to the resonant charge exchange of anode-produced H− ions in the volume adjacent to the emission apertures.
Design of integral shutters for the beamlines at the Advanced Photon Source
Authors: Chang J. , Shu D. , Nian H. L. , Kuzay T. M. , Job P. K.
Published: July 2002

An integral shutter is a device that integrates a white-beam stop, monochromatic-beam (mono-beam) shutters, a safety stop, and a collimator into one assembly to save space in the photon beamline. Various integral shutters have been developed as standard components for the beamlines at the advanced photon source. The integral shutters are designed to be operated in white-beam mode or mono-beam mode. With regard to safety, each mode of operation is secured by locking certain devices in their up or down positions. Some of the components of the integral shutters share designs similar to the front-end shutters or fixed masks. Design details of the integral shutters are presented.
Absolute photoabsorption cross-section measurements of simple molecules in the core-level region
Authors: Itchkawitz B. S. , Kempgens B. , Köppe H. M. , Feldhaus J. , Bradshaw A. M. , Peatman W. B.
Published: July 2002

Absolute inner-shell photoabsorption cross-section measurements were obtained from a variety of simple gas-phase molecules containing low Z elements (C, N, O, F), independent of the effects of stray light, high-order light, and photoabsorption from the various optical elements. The experimental apparatus consists of (1) a compact high-order light suppressor based on the photon energy dependence of the grazing angle reflectivity of various materials which provides an adjustable cut-off energy, and (2) a gas-phase absorption cell which monitors the photon flux before and after the gas cell to yield measurements independent of the absorptions of various optical elements, response functions of the photon detectors used, and variations of the photon flux during the scans.
Facilities for spin-resolved photoemission at the SRS
Authors: Quinn F. M. , Seddon E. A. , Kirkman I. W.
Published: July 2002

Electron polarimetry at Daresbury is carried out using either a conventional high-energy Mott polarimeter or a conical retarding potential Mott polarimeter (microMott). The high-energy Mott polarimeter is a fixed feature of Station 1.2, the microMott polarimeter can be used on Stations 1.1, 5U.1, 3.3, or 6.1. This combination of beamlines, spectrometers, and polarimeters provides the research community with the capability of performing spin-resolved photoemission from both gases and solids over the photon energy range 6 to 1500 eV. First results from Ni(110) on Station 1.2 are discussed along with a preliminary test of the microMott polarimeter.
Diffraction applications using the energy dispersive beamline X6A at the National Synchrotron Light Source
Authors: Lee P. L. , Beno M. A. , Ogata C. M. , Knapp G. S. , Jennings G.
Published: July 2002

The energy dispersive beamline X6A at the National Synchrotron Light Source employs a curved crystal monochromator (polychromator) which focuses a range (∼1 keV) of x-ray energies into a narrow (100–120 μm) line image. Although this beamline was constructed primarily for time-dependent EXAFS experiments, we have begun to explore the use of this instrument for energy dispersive diffraction experiments with different types of sample including macromolecular crystals. The tunability (E=6.5 to 21 keV) and flexibility (ΔE=100–1000 eV) of the instrument makes the beamline ideal as a test bed for the application of polychromatic single-crystal diffraction techniques to different chemical or biological materials.
Simple high-pressure cell for neutron scattering
Authors: Bao Wei , Broholm C. , Trevino S. F.
Published: July 2002

A high-pressure cell, capable of 8 kbar, is developed for neutron scattering. It can be used with ILL type orange cryostats to obtain a temperature as low as 1.5 K. The simple seal design described here can easily be adopted to other high-pressure applications.
Effect of high-energy neutron flux on fiber optics in an active diagnostic on TFTR (abstract)a)
Authors: Paul S. F. , Goldstein J. L. , Durst R. D. , Fonck R. J.
Published: July 2002

A bundle of 1-mm-diam fused silica optical fibers on an existing TFTR diagnostic has been exposed to 11 high-power DT discharges. Each shot subjected the fibers to a peak fast (14.7 MeV) neutron flux of ≊2×1012 n/cm2/s and a γ-dose rate of 500 rad(Si)/s for 0.75–1.0 s. The total fast-neutron fluence for these shots was ≊5×1012 n/cm2. A 15-m-long section of the bundle ran along the tokamak’s toroidal field coils and the remaining 15 m ran radially away from the reactor. Fiber luminescence at 660 nm was ≊1010 photons/s/sr/cm2/Å for the above flux (≊5%–10% of the bremsstrahlung emission), and varied linearly with DT neutron rate. Luminescence at 530 nm was 50% stronger, consistent with a Cerenkov radiation spectrum. Sensitivity to 3.5 MeV DD neutrons was ≊1/3 to 1/2 of that for DT neutrons. Fiber transmission decreased with the time integral of the neutron source rate and was reduced by 4% for the above flux. The fiber recovered rapidly: within 10 s, the transmission loss was only 2.5%. Shortly thereafter, the rate of recovery slowed to ≊0.05% per minute, but was sufficient to restore 75% of the transmission loss within two to four discharges. Recovery continued at ≊0.1% per hour and slowed overnight to ≊0.1% per day. Within the relative error of <0.2%, full transmission was recovered after five days.
X-ray imaging of uniform large scale-length plasmas created from gas-filled targets on Nova
Authors: Kalantar D. H. , MacGowan B. J. , Bernat T. P. , Klem D. E. , Montgomery D. S. , Moody J. D. , Munro D. H. , Stone G. F. , Hsing W. W. , Failor B. H.
Published: July 2002

We report on the production and characterization of large scale-length plasmas created by illuminating gas-filled thin-walled balloonlike targets using the Nova laser. The targets consisted of a 5–6000 Å skin surrounding 1 atm of neopentane which when ionized becomes a plasma with 1021 electrons/cm3. Results are presented from x-ray imaging used to evaluate the uniformity of the plasma. The most uniform plasmas were produced by illuminating the target with large converging beams that overlapped to cover most of the surface of the gas bag. An alternate focus geometry using small beam spots resulted in a less uniform plasma with low density holes in it.
Self-calibration of a thinned, backside illuminated charge coupled devices in the soft x-ray region
Authors: Li Yuelin , Tsakiris G. D. , Sigel R.
Published: July 2002

A semiempirical method of calibrating a thinned, backside illuminated charge coupled device (CCD) chip in the soft x-ray region is presented. It is based on determining the thickness of the dead layer self-consistently using the continuum emission from laser produced plasmas. The CCD camera system was coupled to a transmission grating spectrometer and recorded the spectrally resolved continuum emission from laser irradiated tungsten targets. The thickness of the dead layer was then determined by comparing the experimental spectra with the calculated quantum efficiency for a thinned CCD using a simplified model. In this way the CCD chip was semiempirically calibrated. The accuracy of the calibration in the soft x-ray range was assessed by comparing the CCD recorded spectra with those recorded by a spectrometer using the absolutely calibrated Kodak 101 photographic plates and a similar transmission grating. Based on this calibration, the CCD sensitivity is deduced to be about two orders of magnitude higher than that of the Kodak plates in this wavelength range.
Bragg resonance picture of one-dimensional fluctuation reflectometry beyond the Born approximation (abstract)a)
Authors: Chou Albert E. , Afeyan B. B. , Cohen B. I.
Published: July 2002

By using HELM1D, a numerical, one-dimensional Helmholtz equation solver, we have studied the scattering phase shifts of S-polarized O modes in fluctuation reflectometry both within and beyond the Born approximation. Comparisons are made between these numerical results and analytical expressions obtained through the use of the Born approximation. As the fluctuation amplitude increases, various peaks of the phase response evolve with distinct growth rates. This leads to steepening and distortion of the scattering phase shift due to a single wave-number fluctuation. The simultaneous coexistence of large amplitude fluctuations with nearby wave numbers complicates the task of resolving the response at each wave number.
High resolution observations of pellet emission on TFTR (abstract)a)
Authors: Mansfield D. K. , Schmidt G. , Owens D. K. , Wurden G. A.
Published: July 2002

High resolution, rapidly sampled measurements of the light emission from injected impurity pellets have recently been carried out on TFTR. Both wide and narrow views of the pellet light have been accomplished with a tightly collimated fanned array of fiber-optically coupled photomultipliers. Deep (≊100%), high frequency (40–90 kHz) modulation of the pellet emission has been observed in both neutral beam and rf heated discharges with as little as ≊1.5 MW of heating. This finding is consistent with recent work carried out on ASDEXb) with the exception that this modulation phenomenon is seen not only with hydrogenic pellets but also with lithium and boron pellets. This observation seems to point to an instability associated with the plasma surrounding the pellet rather than an instability which depends upon the atomic physics of the pellet.
Internal, nonperturbing, radio frequency wave monitor reflectometer system on the DIII-D tokamak (abstract)a)
Authors: Lee J. H. , Doyle E. J. , Luhmann N. C. , Peebles W. A. , Petty C. C. , Pinsker R. I. , Rettig C. L. , Rhodes T. L.
Published: July 2002

A new reflectometer system designed to monitor density fluctuations associated with rf waves has been successfully demonstrated on the DIII-D tokamak. It is a direct, internal, and nonperturbing diagnostic with access into the plasma core. This new diagnostic is motivated by a desire to improve understanding of rf wave physics issues, such as wave trajectory, heating mechanisms, rf wave deposition profile, and wave number, and is highly relevant to planned tokamaks such as ITER and TPX. This work is the first application of reflectometry to rf wave studies in a tokamak. Feedforward tracking receiver techniques are employed to remove frequency instabilities due to inherent drifts in the microwave sources and frequency pulling. In order to minimize spurious pickup of the rf pulse (∼60 MHz), heterodyne detection techniques are utilized, and all components are installed inside an rf shielding box. The system operates in the extraordinary mode (X mode) at 70 GHz. In this paper, a detailed description of the system, and data illustrating its successful operation will be presented.
High precision Wölter optic calibration facility
Authors: Morales R. I. , Remington B. A. , Schwinn T.
Published: July 2002

We have developed an off-line facility for very precise characterization of the reflectance and spatial resolution of the grazing incidence Wölter type I x-ray optics used at Nova. The primary component of the facility is a new, very versatile, high brightness x-ray source consisting of a focused DC electron beam incident onto a precision manipulated target-pinhole array. The data are recorded with a selection of detectors. For imaging measurements we use direct exposure x-ray film modules or an x-ray charge-coupled device camera. For energy-resolved reflectance measurements, we use lithium drifted silicon detectors and a proportional counter. An in situ laser alignment system allows precise location and rapid periodic alignment verification of the x-ray point source, the statically mounted Wölter optic, and the chosen detector.
Extending x-ray streak camera operation to vacuum ultraviolet wavelengths
Authors: Jaanimagi P. A. , Elton R. C. , Welch B. L. , Leng Y. , Griem H. R.
Published: July 2002

A major limitation in the use of x-ray streak cameras at longer wavelengths in the vacuum ultraviolet spectral region is the strong absorption of the radiation in the conductive thin films that are used for transmission photocathode substrates. Reflection photocathodes require off-axis illumination and hence do not couple easily to instruments such as flat-field spectrographs. We are investigating the use and optimization of an open-geometry photocathode structure consisting of a fine-mesh wire screen coated with the photoemissive material. Photons impinge directly onto this coated screen. Photoelectrons emitted from the side surfaces of the wires are accelerated into the streak tube by the applied field penetrating into the plane of the wire screen. Coatings of CsI and CuI are under study. Laser-produced plasmas, as well as discharge sources, are being used for the testing and optimization. A flat-field grazing-incidence spectrograph and a 1 m, normal-incidence spectrograph are used to cover the spectral region from 3 to 200 nm.
Lithium-ion-beam driven hohlraums for PBFA II
Authors: Dukart Raymond J.
Published: July 2002

In Sandia’s light ion inertial confinement fusion program, fusion capsules are planned to be driven with an intense x-ray radiation field produced when an intense beam of ions penetrates a radiation case and deposits energy in a foam x-ray conversion region. A first step in the program is to generate and measure these intense fields on the Particle Beam Fusion Accelerator II(PBFA II). Our goal is to generate a 100-eV radiation temperature in lithium-ion-beam driven hohlraums, the radiation environment which will provide the initial drive temperature for ion-beam driven implosion systems designed to achieve high gain. The design of such hohlraum targets and their predicted performance on PBFA II at increasing ion-beam intensities is described.
Movable ultra-high-vacuum sample mount: Heating, cooling, and temperature measurement capabilities
Authors: Jones L. A. , Wei F.-X. , Thomas D. F.
Published: July 2002

A sample mount which can be moved throughout an ultra-high-vacuum environment and through a load-lock to atmosphere is described. A sample mount holder station is also shown whereby the sample temperature can be monitored and controlled from 80 K to the sample melting point. A unique feature is that the temperature is measured with a thermocouple cemented to the sample, but the sample remains transportable. Contacts to electrically isolated side arms on the sample mount provide the correct electrical connections.
Energy dependences of absorption in beryllium windows and argon gas
Authors: Chantler C. T. , Staudenmann J.-L.
Published: July 2002

In part of an ongoing work on x-ray form factors, new absorption coefficients are being evaluated for all elements, across the energy range from below 100 eV to above 100 keV. These new coefficients are applied herein to typical problems in synchrotron radiation stations, namely the use of beryllium windows and argon gas detectors. Results are compared with those of other authors. The electron–ion pair production process in ionization chambers is discussed, and the effects of 3d-element impurities are indicated.
Versatile three-dimensional cryogenic micropositioning device
Authors: Heil J. , Böhm A. , Primke M. , Wyder P.
Published: July 2002

A simple design for a mechanically driven three-dimensional cryogenic micropositioner is presented. The design is based on a parallelogram structure constructed from leaf springs and wires. Actuation is achieved by the elastic deformation of the parallelogram by screws. Positions within a volume of roughly (2 mm)3 are attainable. The precision and reproducibility of positioning are in the μm-range. The deviations from linearity are smaller than 10% for the whole working range and the deviation from orthogonality is smaller than 3°. Calibration measurements performed on a Cu-mesh with a lattice constant of 60 μm are presented. In an experiment investigating the ballistic transport of carriers in the semimetal Bi, two such devices are used. The first one is used as a scanning unit for an optical fiber and the second one is used as micropositioner for a Cu point contact.
Production of very low energy and high brightness ion beam
Authors: Yoshikawa Takafumi , Nakamura Shin , Ueda Yoshio , Goto Seiichi
Published: July 2002

In order to produce high brightness beam at energies below 100 eV, the effects of high deceleration voltage in a triode extraction system and plasma potential have been studied. Although the application of high deceleration voltage caused beam spreading, beam brightness was increased at least up to accel–decel ratio of 80. It is found that the reduction of sheath potential of the source plasma caused the increase in beam brightness under high deceleration voltage condition. In particular, it is desirable to reduce sheath potential at the energy below 50 eV because this potential is comparable to external applied acceleration voltage.
Negative-ion sources for modification of materials (invited)
Authors: Ishikawa Junzo
Published: July 2002

The properties of negative ions, such as charging–free ion implantation and new materials syntheses by pure kinetic bonding reaction, have been shown to be promising in terms of their interaction with material surfaces. However, high-current or high-brightness negative-ion sources are required for these purposes. Several kinds of sputter-type negative-ion sources have been developed for negative-ion implantation and deposition in order to obtain high-current heavy negative ions. Recently, a microwave discharge oxygen negative-ion source for negative-ion beam deposition and a surface plasma type hydrogen negative-ion source for projection ion-beam lithography have been investigated. In this article, these negative-ion sources for modification of materials are reviewed.
Pulsed ECR source in afterglow operation at CERN
Authors: Hill C. E. , Langbein K.
Published: July 2002

A pulsed 14 GHz ECR4 source, adapted to operate in the afterglow mode, was delivered by GANIL to CERN in the framework of the Heavy Ion Facility Project. After four months of operation to commission the facility, it completed its first operational run of nine weeks at the end of 1994, providing lead ions to nuclear physics and ion cooling experiments. A very stable beam, with a useful length of over 1 ms, of 80 eμA of Pb27+ was provided by the source over this period. The operational problems experienced during the commissioning and operation, and the investigations to improve performance for the next experimental physics run are presented.
Neutralization of space charge forces using ionized background gas
Authors: Steski D. B. , Zarcone M. J. , Smith K. S. , Thieberger P.
Published: July 2002

The Tandem Van de Graaff at Brookhaven National Laboratory has delivered pulsed gold beam to the Alternating Gradient Synchrotron (AGS) and AGS Booster since 1992 for relativistic heavy ion physics. There is an ongoing effort to improve the quality and intensity of the negative ion beam delivered to the Tandem from the present Cs sputter sources. Because the beam energy is low (approximately 30 keV) and the current high, there are significant losses due to space charge forces. One of the ways being explored to overcome these losses is to neutralize the space charge forces with ionized background gas. On an ion source test bench, using three different gases (Ar, N2, and Xe), the percentage of current transported from the source to a downstream Faraday cup was increased from 10% to 40% by bleeding in gas. Bleeding in Xe resulted in the best transmission. The time dependence of the neutralization as a function of gas pressure was also observed. This system is presently being transferred to the Negative Ion Injector of the Tandem for use in upcoming heavy ion experiments.
Multiply charged ion generation from NIR and visible laser-produced plasma
Authors: Láska L. , Krása J. , Mašek K. , Pfeifer M. , Trenda P. , Králiková B. , Skála J. , Rohlena K. , Woryna E. , Farny J. , Parys P. , Wol/owski J. , Mróz W. , Shumshurov A. , Sharkov B. , Collier J. , Langbein K. , Haseroth H.
Published: July 2002

Results of experiments on ion production from Ta target using ∼350 ps pulses of the iodine photodissociation laser PERUN are presented and analysed. Ta ions with charge states higher than 45+ and with energies 8 MeV were registered in a far expansion zone (∼2 m). Theoretical interpretation of the results is possible by considering that the plasma temporal evolution follows the mechanism of two-temperature isothermal expansion.
A generation of unconventional electron beam ion sources
Authors: Kleinod M. , Becker R. , Bongers H. , Weidenmüller M. , Zipfel B. , Donets E. D.
Published: July 2002

While a high electron current electron beam ion source (EBIS) with high perveance has been proposed for its application at forthcoming TeV hadron colliders, an economical operation has been studied using oscillating electrons to reduce the collector current for low power consumptions. Results with oscillating electrons in our cryogenic EBIS with a 5 T magnetic focusing field are being discussed in relation to normal EBIS operation data considering the oscillation factor, current density, and ion yield. Our simplified EBIS/EBIT studies without magnetic focusing now span from a versatile source for the production of high current singly charged metallic ions up to the use of relativistic electron beams for the production of bare uranium. The XEBIST now works successfully with beam energies up to 10 keV. Barium ions having a charge state up to 46 have been extracted using evaporative cooling by Ar and residual gas. The extension to relativistic beam energies taking advantage of the self-focusing effect at partial space charge compensation will be presented elsewhere at this conference.
Time evolution of charge states in an electron cyclotron resonance ion sourcea)
Authors: Pardo R. C. , Harkewicz R. , Billquist P. J.
Published: July 2002

The production of high charge-state ions in an electron cyclotron resonance ion source has been studied as a function of time using a pulsed Nd:YAG laser to ablate heavy metal (bismuth) ions into the plasma. The time required to produce a charge state has been measured by observing the arrival time of the ions at a Faraday cup after the source analyzing magnet. The results of these measurements have been compared to a simple sequential ionization model and are found to be in good agreement with the data. The data can be used to characterize the plasma electron density, electron temperature, and neutral atom density, since these are the only three adjustable parameters in the model and are sufficient to achieve good agreement for the time evolution of all observed charge states.
3-D x-ray mirror metrology with a vertical scanning long trace profiler (abstract)
Authors: Takacs Peter Z. , Li Haizhang , Li Xiaodan , Grindel Manfred W.
Published: July 2002

The long trace profiler (LTP) was originally developed at Brookhaven National Laboratory for the specific purpose of measuring the surface figure of large cylindrical mirrors used at grazing incidence in synchrotron radiation (SR) beamlines. In its original configuration, it could measure only along one line down the center of the cylinder. A single linear profile is often sufficient to gauge the quality of the optical surface on these kinds of mirrors. For some applications it is necessary to measure the topography of the entire surface, not just along one line but over a grid that covers the entire surface area. We have modified a standard LTP to enable measurement of the complete surface of Wolter telescope optics in a vertical configuration. The vertical scanning LTP (VSLTP) is capable of producing a complete 3-D map of the surface topography errors relative to the ideal desired surface on complete segments of paraboloids and hyperboloids. The instrument uses a penta prism assembly to scan the probe beam in the longitudinal direction parallel to the mirror symmetry axis and uses a precision rotary stage to provide scans in the azimuthal direction. A Risley prism pair and a dove prism are used to orient the probe beam in the proper direction for the azimuthal scans. The repeatability of the prototype instrument is better than 20 nm over trace lengths of 35 mm with a slope measurement accuracy of about 1 microradian.
X-ray polarization detector (abstract)
Authors: Shaw Ping-Shine , Arp Uwe , Henins Albert , Southworth Steve
Published: July 2002

We designed and constructed a cylindrical gas proportional counter that can be used to analyze the linear polarization of x rays with a wide range of energy from 2 keV to 10 keV. The polarization sensitivity is based on the highly nonisotropic scattering of polarized x rays from a gas or solid target. The gas proportional counter surrounds the scattering chamber and measures the scattered x rays as a function of the azimuthal angle. The angle of scattered x rays is determined by the charge division of the anode resistive wire. This polarimeter without any moving parts can measure x rays with continuous energies. It is specially suitable for synchrotron x rays. We discuss the testing and performance of such an x-ray polarimeter.
High-resolution beamline 9.3.2 in the energy range 30–1500 eV at the Advanced Light Source: Design and performance
Authors: Hussain Z. , Huff W.R.A. , Kellar S.A. , Moler E.J. , Heimann P.A. , McKinney W. , Cummings C. , Lauritzen T. , McKean J.P. , Palomares F.J. , Wu H. , Zheng Y. , Young A.T. , Padmore H.A. , Fadley C.S. , Shirley D.A.
Published: July 2002

Bending magnet beamline 9.3.2 at the Advanced Light Source (ALS) was designed for high resolution spectroscopy with the capability for delivering circularly polarized light in the soft x-ray energy region using three gratings. The monochromator is a fixed included-angle spherical grating monochromator (SGM) and was originally used at SSRL as a prototype for later insertion-device-based monochromators for the ALS. For operation at the ALS, the toroidal pre-mirror used at SSRL was replaced by a horizontally focusing and a vertically focusing mirror in the Kirkpatrick-Baez configuration. Circularly polarized radiation is obtained by inserting a water-cooled movable aperture in front of the vertically focusing mirror to allow selecting the beam either above or below the horizontal plane. To maintain a stable beam intensity through the entrance slit, the photocurrent signals from the upper and lower jaws of the entrance slit are utilized to set a feedback loop with the vertically deflecting mirror piezoelectric drive. The beamline end station has a movable platform that accommodates two experimental chambers enabling the synchrotron radiation to be directed to either one of the two experimental chambers without breaking the vacuum. © 1996 American Institute of Physics.
Magnetic damping array implemented into a space-compatible multizone furnace for semiconductor crystal growth
Authors: Stenzel Ch. , Dold P. , Benz K. W.
Published: July 2002

For damping residual, unsteady flows in semiconductor melts a space-compatible multizone furnace including a magnetic damping array consisting of two radially magnetized permanent magnet rings has been developed. The performance of the whole system has been verified by measuring the temperature fluctuations caused by the time-dependent thermal convection in a Ga melt at 850 °C. By applying a static magnetic induction of 186 mT the fluctuations could be reduced from about 1.5 °C to less than 0.02 °C. For these high precision measurements optical fiber sensors have been used to measure the temperature in the Ga melt and to control the multizone furnace as well. A temperature constancy of ΔT≤0.03 °C in the melt could be established over a period of 16 h.
Absolute angular positioning in ultrahigh vacuum
Authors: Schief Hansjörg , Marsico Vittorio , Kern Klaus
Published: July 2002

Commercially available angular resolvers, which are routinely used in machine tools and robotics, are modified and adapted to be used under ultrahigh-vacuum (UHV) conditions. They provide straightforward and reliable measurements of angular positions for any kind of UHV sample manipulators. The corresponding absolute reproducibility is on the order of 0.005°, whereas the relative resolution is better than 0.001°, as demonstrated by high-resolution helium-reflectivity measurements. The mechanical setup and possible applications are discussed.
Laser Doppler anemometry measurements in an axisymmetric turbulent jet
Authors: Kassab Sadek Z. , Bakry Ayman E. , Warda Hassan A.
Published: July 2002

The present study was performed to investigate experimentally some aspects related to the characteristics of turbulent jet flow using laser Doppler anemometry (LDA) as a measuring technique. It includes the following: (1) investigation of the effect of the velocity bias on the experimental results of the mean and fluctuating velocities, (2) study of the effect of upstream conditions on the mean and turbulent velocity profiles at the jet exit plane, (3) measurement of the decay rate of the center line longitudinal mean velocity and compared results with empirical correlations, (4) examination of the achievement of self-preservation of the jet flow, (5) investigation of whether the flow is approaching isotropy, (6) measurement and documentation of the distribution of the radial mean as well as turbulent velocity profiles. The axial and radial velocity components were measured simultaneously at the same location of the flow using a 5 W argon-ion laser Doppler anemometry. The LDA operated in the fringe Pattern mode, in two-component colors, and in the backscattering detection mode. The present study was carried out for the Reynolds number Ree=104 (based on the nozzle exit diameter D and the center line longitudinal mean velocity at the nozzle exit diameter Ue) up to an axial distance of 45D. In addition, seven cases of initial upstream conditions were investigated. The obtained results revealed that no correction for the velocity bias is needed when the turbulence intensity is low (below 15%). Further, the mean velocity profiles cannot uniquely identify the state of a jet flow. In addition, the effect of the upstream conditions is pronounced mainly in the near field region. Meanwhile the jet flow approaches a certain degree of isotropy in the far field.
A novel technique for a narrow line selection and wideband tuning of Ti:Al2O3 and dye lasers
Authors: Deneva M. , Stoykova E. , Nenchev M.
Published: July 2002

We have developed a novel simple technique for a wide gain laser narrow line selection and tuning using classical interferometric selectors (Fabry–Perot interferometer, interference wedge). Its most important advantage is that selection and tuning need only one thick interferometer instead of a combination of a thin (5 μm) and a thick (∼100 μm) one as in the conventional approach. This makes tuning much simpler without having to synchronize two tuning elements and the system as a whole essentially cheaper. The computer simulation and the experimental test have shown that the proposed technique is highly competitive compared with traditional interferometers with thicknesses of 30–70 μm. It assures a spectral resolution of less than ∼0.01 nm and tuning in the wide region (≥100 nm), in particular, it completely covers the spectrum of the dye solution and that of the Ti:Al2O3 crystal. Besides enlarging the tuning region, the linewidth is narrowed and the spectral purity of emission is increased. Using a qualitative interferometer with transmission close to unity a high efficiency can be reached.
A radio frequency compensated emissive probe
Authors: Kang Jungwon , Carlile Robert N. , O’Hanlon John F.
Published: July 2002

We discuss a technique for using an emissive probe to measure accurately the time-invariant plasma potential in a rf generated plasma, usually used in plasma processing. With an emissive probe, a short length of filament, heated to thermionic emission, is immersed in the plasma. We have introduced into each lead of the filament two LC circuits, one resonant at 13.6 MHz, the fundamental rf frequency, and the other at 27.2 MHz, the first harmonic. With the LC circuits in place a single peak of di/dv versus v occurs with a maximum at the time-invariant plasma potential. The inflection point method of measuring this potential described by Smith, Hershkowitz, and Coakley [Rev. Sci. Instrum. 50, 210 (1979)] in a dc plasma is now operative. The estimated error in measuring this potential is ±3.5%.
Simultaneous third and fourth harmonic mode-locking of a Q-switched flashlamp-pumped Nd:YAG laser
Authors: Andreoni Alessandra , Bondani Maria , Di Trapani Paolo , Amati Sabrina , Cavalcabo’ Guglielmo , Zanzottera Eugenio
Published: July 2002

A single-rod, high pulse-energy, Nd:YAG laser is presented that is actively mode-locked simultaneously at the third and fourth harmonics of the round-trip frequency and Q-switched after a prelasing period. The output consists of highly stable pulses, separated by the round-trip time, of about 90 ps duration and 1 mJ energy.
A description of cryogenic temperature sensor characteristics by the weighted orthonormal polynomial expansion method: Germanium and platinum thermometer calibration test data approximation
Authors: Bogdanova Nina B. , Terzijska Bonka M.
Published: July 2002

We consider a new approximation of T=f(R) and R=g(T) functions for germanium (GRT) and platinum (PRT) cryogenic resistance thermometers from 1.2 to 85 K and from 14 to 325 K, respectively, using the weighted orthonormal polynomial expansion method (OPEM). The main aspect in this description is an evolving new type of weighting function referred to the specific material characteristics of the investigated cryogenic resistance temperature sensors. The OPEM fitting errors for GRT and PRT characteristics in the considered approximation within the whole useful temperature ranges determine the perspectives of our method in cryogenic thermometry. The proposed OPEM description of R and T functions of the investigated thermoresistors defines the hopefulness of our algorithm with respect to both the calibration of GRT and PRT sensors and the automation of thermal measurements at low temperatures. The demonstrated values of the OPEM fitting errors with the R function approximation as well as the evaluation of the first derivative dR/dT allow the OPEM to be successfully used for a generation of the interpolation tables with the resistance thermometer calibration.
Method for calculating the induced voltage in a vibrating sample magnetometer detection coil system
Authors: Xu Xiaonong , Sun Aimin , Jin Xin , Fan Hongchang , Yao Xixian
Published: July 2002

A numerical method for obtaining the vibrating sample magnetometer (VSM) sensitivity functions due to a uniformly magnetized sample in the shape of ellipsoid, cuboid or cylinder, and then calculating the induced voltage in a VSM detection coil systems is presented. The induced voltage, which depends on the equilibrium position and amplitude of the sample in three-dimensional space, and depends on the geometric parameters of both sample and detection coils, is calculated from the viewpoint of magnetic charges. This numerical method is more accurate than others, which use dipole moment approximation without taking into consideration the sample shape and size. By using this method, the induced voltage, for which the shape and size effects of the sample must be taken into account, can be calculated if there is knowledge of geometric parameters of the sample and coils. The formulas for calculating the correction coefficient are also given for samples whose shape errors should be considered. Our results provide rigorous theoretical guidance for the exhaustive study of the VSM working principle, for accurate measurement of the sample magnetic moment, and for optimum design of configuration, position, and orientation of VSM pickup coils.
A high current pulse generator for magnetizing thin magnetic films
Authors: Ting Joseph W. , Rubins Daniel J. , Huang D.-J. , Erskine J. L.
Published: July 2002

A bipolar, high-current (10 000 A) pulse generator, used to magnetically saturate thin films during spin-polarized electron and dynamic response measurements, is described. Bipolar operation is achieved by discharging a bank of capacitors through selected pairs of high-power silicon-controlled rectifiers connected to a coil in an H bridge configuration. The pulse generator can be controlled either manually or by means of a computer.
Cleaning and outgassing studies of machinable tungsten for beamline safety shutters
Authors: Liu C. , Ryding D. , Nielsen R. W. , Kruy T. L. , Kuzay T. M.
Published: July 2002

Machinable tungsten blocks are used as safety shutters in the front ends and the beamlines at the Advanced Photon Source (APS). The machinable tungsten used is characterized as a UHV-compatible metal by the vendor and was developed through a joint research effort with the APS. However, because of the inherent porosity in the sintered tungsten metal, it may present a vacuum problem and has to be subjected to strict vacuum testing before it is put on the beamlines. We have chosen specially heat-treated machinable tungsten with a density of 18 g/cm3 for safety shutters. In-house-developed, environmentally friendly vacuum cleaning procedures were used. In this paper, we present results of thermal outgassing tests for machinable tungsten safety shutter sets. Each set consists of five blocks and has a total area of 4500 cm2. A cleaning procedure using alkaline detergent ultrasonic washes, deionized water rinses, and a 500 °C vacuum furnace baking was used before outgassing measurements. Outgassing rates 10 hours after initial pump down at room temperature reached ∼1.60×10−10 Torr⋅l⋅s−1⋅cm−2 for machinable tungsten and ∼1.56×10−10 Torr⋅l⋅s−1⋅cm−2 for the stainless steel vacuum chamber. The outgassing rate of machinable tungsten 24 hours after an in situ 48 h bake at 160 °C is also comparable to that of the stainless steel vacuum chamber. The importance of a 500 °C vacuum furnace baking has been confirmed by outgassing studies for machinable tungsten sets that were not subject to vacuum furnace baking.
Experience with ray-tracing simulations at the European Synchrotron Radiation Facility (invited)
Authors: Sánchez del Río Manuel
Published: July 2002

The ESRF is the first operational third-generation synchrotron radiation hard-x-ray source. Since the beginning of its construction (1988), the ray-tracing technique proved to be an essential computer tool for beamline optics design. The optical systems of most beamlines have been simulated by ray tracing in order to optimize the optics, fully understand their properties, and check if operation performances were as expected. In this paper, a short compilation of the experience with ray tracing and optics simulation codes at the ESRF, as well as some other in-house developments, is presented.
A review of methods for experimentally determining linear optics in storage rings
Authors: Safranek J.
Published: July 2002

In order to maximize the brightness and provide sufficient dynamic aperture in synchrotron radiation storage rings, one must understand and control the linear optics. Control of the horizontal beta function and dispersion is important for minimizing the horizontal beam size. Control of the skew gradient distribution is important for minimizing the vertical size. In this paper, various methods for experimentally determining the optics in a storage ring will be reviewed. Recent work at the National Synchrotron Light Source X-Ray Ring will be presented, as well as work done at laboratories worldwide.
Investigation of low-frequency beam motion at the Advanced Photon Source
Authors: Kim S. , Decker G. , Doose C. , Hogrefe R. , Mangra D. , Merl R. , Milton S.
Published: July 2002

The storage ring of the Advanced Photon Source has relatively tight tolerance requirements for beam stability. The tolerances of the rms beam motion in the insertion device straight sections are set to be less than 4.4 μm and 17 μm in the vertical and horizontal planes, respectively, in a bandwidth of 4–50 Hz. Sources of beam motions have been investigated for mechanical vibrations of the magnets and vacuum chambers induced by ground motion and water systems and for power supply ripple. Horizontal beam motions in a bandwidth of 9–12 Hz have been significantly reduced by inserting viscoelastic damping pads between the girder supports and pedestals, and by welding the magnet cooling headers to the ceiling of the storage ring tunnel. Current ripple of S1A sextupoles has been identified as a source of beam motion in a bandwidth of 5–8 Hz. The eddy current induced by the ripple field in the sextupole produced a vertical dipole field to drive the beam horizontally. After modification of the sextupole power supplies, the beam stability requirements have now been met even without activating the feedback system.
Status and projected performance of the Duke FEL lab soft x-ray source
Authors: Johnson L. , Madey J.M.J. , Straub K.D. , Litvinenko V.N.
Published: July 2002

Previous magnetic field measurements on the entrance half of the NIST undulator showed errors that resulted in a beam path deflection of 5.2 mm [Wallace et al., Nucl. Instrum. Methods A 331, 759 (1993)]. Pole height variations as much as .009’’ gave rise to field errors of up to 2% at a gap of 20 mm. We report on our effort to rebuild the NIST undulator through a series of in-situ and off-line measurements and modifications. Initial results indicate that at 40 Å, a brightness of 2.5×1018 (ph/sec/mm2/mrad2/A/0.1% BW) can be achieved. Commissioning of the undulator will take place in January 1996.
Redesigned front end for the upgrade at CHESS (abstract)
Authors: Headrick Randall L. , Smolenski Karl W.
Published: July 2002

We will report on beamline front-end upgrades for the 24-pole wiggler beamlines at CHESS. A new design for primary x-ray beamstops based on a tapered, water-cooled copper block has been implemented and installed in the CHESS F beamline. The design uses a horizontally tapered ‘‘V’’ shape to reduce the power density on the internal surfaces and internal water channels in the block to provide efficient water cooling. Upstream of the beam stops, we have installed a new photoelectron style beam position monitor with separate monitoring of the wiggler and dipole vertical beam positions and with micron-level sensitivity. The monitor’s internal surfaces are designed to absorb the full x-ray power in case of beam missteering, and the uncooled photoelectron collecting plates are not visible to the x-ray beam. A graphite prefilter has been installed to protect the beryllium windows that separate the front end from the x-ray optics downstream. The redesigned front end is required by the upgrade of the Cornell storage ring, now in progress, which will allow stored electron and positron currents of 300 mA by 1996, and 500 mA by 1998. At 500 mA, the wiggler power output will be over 32 kW.
A diamond-window XAFS cell for studies of high-temperature, high-pressure aqueous solutions
Authors: Fulton John L. , Pfund David M. , Ma Yanjun
Published: July 2002

We describe a method to collect x-ray absorption fine structure (XAFS) spectra of ions in a supercritical water solvent. Supercritical water (SCW), at temperatures above water’s critical point of 374 °C, is an interesting solvent for chemical reactions and hazardous waste destruction due to the high solubility of organics and the aggressive oxidizing environment. XAFS may provide a better understanding of the solvent environment in SCW. The XAFS cell used in these studies was composed of a block of high-nickel alloy, Hastelloy C-22, containing two windows for transmission of the x-ray beam and a single optical view window. All internal wetted surfaces were platinum plated. The maximum operating conditions for this design were 500 °C and 700 bar. The x-ray transmission windows consisted of CVD (chemical vapor deposition) diamond windows (3 mm diameter ×0.5 mm thick) that were brazed to the tip of a standard 1/4-in. high-pressure, coned-shape fitting. Spectra are reported for strontium and rubidium ions in a supercritical water solvent. This cell design could be used for a variety of other solvent systems at high temperatures and high pressures.
A system for single-crystal elastic and inelastic x-ray scattering studies of condensed gases at pressures to 300 MPa and temperatures to 4 K
Authors: Venkataraman C. T. , Simmons R. O.
Published: July 2002

A versatile system, operating at pressures to 300 MPa and temperatures to 4 K, has been designed and used for a variety of elastic and inelastic x-ray scattering studies of single crystals of condensed gases. Sintered Be sample cells of volumes 15–30 mm3 are used. Pressure generation is clean and well controlled. Excellent temperature control allows monitoring of phase transitions associated with solidification and melting. The system has very low background and, combined with the high-intensity of synchrotron radiation, is well suited to studies of low-intensity signals. It has been used for 4He in q-dependent studies of fcc lattice dynamics and diffuse scattering and to study thermal defect properties through lattice parameter measurements. In addition, its application to inelastic scattering studies of hcp 4He at 1.5 eV and 10 meV resolution have yielded results about electronic and phonon excitations, respectively. The system can also be used to study other crystalline compounds; in particular, an application has been made to lattice parameter measurements on C2F6.
Deconvolution of 3d transition metal L-edge EXAFS and magnetic EXAFS signals
Authors: Kemner K. M. , Chakarian V. , Idzerda Y. U. , Elam W. T.
Published: July 2002

Due to the closely overlapping L-edge EXAFS regions for the ferromagnetic 3d metals, their analyses have not generally been attempted. Similarly, although analysis of L-edge magnetic EXAFS (MEXAFS) is desirable because of the enhanced amplitude of the signal compared to K-edge MEXAFS, such experiments on the ferromagnetic 3d metals have also not been attempted. In order to address this problem, we describe the use of an iterative Van Cittert deconvolution approach to isolate the LIII-edge from the LII-edge EXAFS and MEXAFS signals for Fe, Co and Ni thin films. The deconvoluted LIII-edge EXAFS data are in agreement with theoretically generated LIII-edge data, thus demonstrating the validity of this approach. Results from the deconvolution of the MEXAFS data also qualitatively agree with previously published MEXAFS data on the same elements at the K-edge. The results for the Fe EXAFS and MEXAFS data will be presented here.