End Station Research Articles

Cells of the perireticular nucleus project to the developing neocortex of the rat.

The perireticular nucleus is a recently described thin sheet of small cells among the fibres of the internal capsule, lying lateral to the thalamic reticular nucleus and medial to the globus pallidus (Clemence and Mitrofanis [1992]. J. Comp. Neurol. 322:167-180). During development, the perireticular nucleus is relatively large, lying in the path of the growing corticofugal and thalamocortical axons and filling the area of the internal capsule lateral to the thalamic reticular nucleus. After these axons have formed their connections, the perireticular nucleus rapidly decreases in size, leaving only a few cells in the adult (Mitrofanis [1992] J. Comp. Neurol. 320:161-181). In this study, we aimed to investigate the connections between the developing cortex and thalamus by making injections of tracer into the cortical plate. Injections of Horse Radish Peroxidase (HRP), Wheat Germ Agglutinin bound to HRP (WGA-HRP) and 1'dioctadecyl-3,3,3',3 tetramethycarbocyanine perchlorate (DiI) were made in vivo between embryonic day (E) 18 and adult and DiI was placed in the fixed brains of rats aged between E16 and postnatal day (P)1. Between E17 and P10, the retrograde perikaryal labelling resulting from these injections revealed a transient projection from the perireticular nucleus to the ipsilateral cortical plate. No cells were labelled in the thalamic reticular nucleus. This suggests that the perireticular nucleus must be regarded as a group of cells distinct from the thalamic reticular nucleus and having a separate role in development. Comparisons between the perireticular cells and the cells of the cortical subplate suggest that both may be playing comparable roles in early development, possibly guiding fibres towards their end stations or serving to rearrange the complex mapped projections linking the thalamus and cortex.

Spectroscopy beamline at the Advanced Photon Source for the photon energy region from 0.5 to 3 keVa)

Interest in the 0.5 to 3 keV, intermediate x-ray, energy region has recently intensified as this spectral region covers, among others, the important L and M edges of transition-metal and rare-earth magnetic materials, respectively. Third-generation synchrotron facilities with their inherent high brightness have the unique potential to cover this energy region with high-resolution, high-flux x-ray beams ideal for spectroscopic studies. A 5.5-cm-period, planar undulator to be installed on the 7-GeV Advanced Photon Source will produce a high brightness source of intermediate-energy x rays. The 0.5- to 3-keV spectroscopy beamline is based on the spherical grating monochromator design that has already been shown to yield high resolution and throughput in the soft-x-ray region, below 1 keV. The beamline has been designed to cover the entire region with a peak resolving power of 6000–10 000. Photon flux at the sample is calculated to be in the range from 1011 to 1013 photons/s into a spot size of 1 mm2. A refocusing mirror will be used to further demagnify the image size at a second experimental station. As a second phase to the spectroscopy program, an elliptically polarized insertion device will be used. The polarization preserving nature of the grazing incidence optical elements in the SGM is crucial to obtain x rays of well-defined polarization. The beamline layout, together with calculations of resolution, throughput, power loading, and high harmonic suppression, will be presented. The photoemission experimental end stations for the spectroscopy station will also be briefly described.

Synchrotron X-ray absorption spectroscopy: a new tool for actinide and lanthanide speciation in solids and solution

Synchrotron-based X-ray absorption near-edge structure spectroscopy and extended X-ray absorption fine structure spectroscopy are powerful techniques to study many chemical elements in solids, liquids and gases. Information can be obtained on the speciation and complexation of lanthanide and actinide elements and other radionuclides in aqueous and non-aqueous solutions, on adsorption processes at the solid-water interface of these solutions with soils, minerals, mineral assemblies and uranium mill tailings, and on the adsorption and incorporation of these metals in biological materials. A literature review on synchrotron studies of these processes is given. The conceptual design of an experimental hard X-ray synchrotron beam line end station for the investigation of radioactive samples is described.

Hot-spot spanning tree algorithm for a bridged LAN/MAN

A bridged local area network (BLAN) is an internetwork where a lot of LANs and MANs are interconnected via bridges. The active spanning tree topology of a BLAN is to ensure that one and only one active routing path exists between each pair of end stations to resolve the frame duplication problem. A LAN is a hot-spot LAN if it has a large amount of communicating traffic load compared to other LANs. In this paper, we propose a distributed spanning tree algorithm for a BLAN with hot-spot traffic. The spanning tree constructed by our algorithm is logically rooted at the hot-spot LAN instead of the bridge with the smallest identifier. Such a spanning tree will be more practical and suitable for delivering the inter-LAN frames, and hence will obtain a better performance on end-to-end transmission delay. The effectiveness of the algorithm is evaluated by simulations. From the simulation results, we found that, compared to the standard spanning tree algorithm, the spanning tree constructed by our algorithm obtains a greater improvement in terms of end-to-end transmission delay as the traffic concentration becomes more pronounced.

End station for polarization and excitation energy selective soft x-ray fluorescence spectroscopy

An end station for soft x-ray fluorescence spectroscopy has been constructed, which includes an experiment chamber, rotatable 90° under ultrahigh vacuum conditions around the incoming synchrotron radiation beam, which is provided with a high-resolution soft x-ray spectrometer. A manipulator allowing three axes of rotation, three directions of translation, as well as LN2 cooling and resistive heating is mounted to the chamber and serves as the sample holder. Samples can be transferred under vacuum between the experiment chamber and two other chambers, one for sample preparation and another for introducing new samples and for sample storage. The end station has been used at two different synchrotron radiation laboratories (beamline BW3) at HASYLAB in Hamburg and at ALS (beamline 7.0) in Berkeley. Polarization-dependent and angular resolved, selectively excited x-ray emission studies have been made on ordered as well as nonordered systems, e.g., high-Tc superconducting systems, diamond, fullerenes, and molecular ices. The experimental system will be presented along with some recent scientific results.

Reflectometer end station for synchrotron calibrations of Advanced X-ray Astrophysics Facility flight optics and for spectrometric research applications

Preparations have been underway to construct and test a facility for grazing incidence reflectance calibrations of flat mirrors at the National Synchrotron Light Source. The purpose is to conduct calibrations on witness flats to the coating process of the flight mirrors for NASA’s Advanced X-ray Astrophysics Facility (AXAF). The x-ray energy range required is 50 eV–12 keV. Three monochromatic beamlines (X8C, X8A, U3A) will provide energy tunability over this entire range. The goal is to calibrate the AXAF flight mirrors with uncertainties approaching 1%. A portable end station with a precision-positioning reflectometer has been developed for this work. We have resolved the vacuum cleanliness requirements to preserve the coating integrity of the flats with the strict grazing-angle certainty requirements placed on the rotational control system of the reflectometer. A precision positioning table permits alignment of the system to the synchrotron beam to within 10 arcsec; the reflectometer’s rotational control system can then produce grazing angle accuracy to within less than 2 arcsec, provided that the electron orbit is stable. At 10–12 keV, this degree of angular accuracy is necessary to achieve the calibration accuracy required for AXAF. However the most important energy regions for the synchrotron calibration are in the 2000–3200 eV range, where the M-edge absorption features of the coating element, iridium, appear, and the 300–700 eV range of the Ir N edges. The detail versus energy exhibited in these features cannot be traced adequately without a tunable energy source, which necessitates a synchrotron for this work. We present the mechanical designs, motion control systems, detection and measurement capabilities, and selected procedures for our measurements, as well as reflectance data.

High-brilliance Beamline at the European Synchrotron Radiation Facilitya)

The High-brilliance Beamline at the European Synchrotron Radiation Facility is under commissioning. First official user experiments are scheduled for September 1994. During the last months the beamline optics has been installed and extensively tested. Currently, the two end stations, (a) for macromolecular crystallography and (b) for time-resolved ultrasmall-angle x-ray scattering are under construction. This article presents the final optical setup of the beamline and describes the end stations. The actual performance of the undulator, the cryogenically cooled Si-(111) channel-cut monochromator, and the toroidal mirror are discussed. All results are in very good agreement with previously published theoretical calculations. Now, at the sample position a focused monochromatic beam is available between 0.15 nm (8 keV) and 0.077 nm wavelength (16 keV). At 0.1 nm wavelength the beam size is horizontally 0.38 mm and vertically 0.75 mm (full width at half-maximum) with a photon flux density of 2.5×107 photons/s/μm2 (±30%).

Compact monochromator for the multipurpose X3 synchrotron beamline at NSLS

A newly designed monochromator assembly for the State University of New York (SUNY) X3 beamline at the National Synchrotron Light Source (NSLS) consists of two monochromators enclosed in a single vessel, positioned at 7813 mm from the bending magnet source. It allows delivery of monochromatic radiation into two independent end stations. The first unit contains two crystals reflecting in the vertical plane, and operating in a ‘‘channel-cut’’ mode. The second of the crystals can be bent for sagittal focusing of the beam. The second monochromator unit reflects 2 mrad of the radiation fan between the A2 and B branches of the beamline at a fixed angle of 2Θ=12°, and serves the sideways experimental station A1. Four interchangeable triangular crystals, mounted on a rotary holder, provide x rays of four different energies.

First experimental results from IBM/TENN/TULANE/LLNL/LBL undulator beamline at the advanced light source

The IBM/TENN/TULANE/LLNL/LBL Beamline 8.0 at the advanced light source combining a 5.0 cm, 89 period undulator with a high-throughput, high-resolution spherical grating monochromator, provides a powerful excitation source over a spectral range of 70–1200 eV for surface physics and material science research. The beamline progress and the first experimental results obtained with a fluorescence end station on graphite and titanium oxides are presented here. The dispersive features in K emission spectra of graphite excited near threshold, and found a clear relationship between them and graphite band structure are observed. The monochromator is operated at a resolving power of roughly 2000, while the spectrometer has a resolving power of 400 for these fluorescence experiments.

Surface diffraction beamline at ESRF

A brief description of the main components of the beamline is given. The source is a standard ESRF undulator. The first active optical element is a double-crystal monochromator cryogenically cooled and sagittally focusing. The end station consists in a six-circle diffractometer and in an ultra high vacuum system with a welded beryllium window that allows incidence and exit angles up to 45°. Preliminary measurements on a Ge(001) clean surface, show that the counting rates of reflections characteristic of the surface reconstruction are of the order of 105 s−1 for standard operating conditions.

Spectroscopy beamline at the Advanced Photon Source for the photon energy region from 0.5 to 3 keV (abstract)

Interest in the 0.5–3 keV, intermediate x-ray, energy region has recently intensified as this spectral region covers, among others, the important L and M edges of transition metal and rare-earth magnetic materials, respectively. Third-generation synchrotron facilities with their inherent high brightness have the unique potential to cover this energy region with high-resolution, high-flux x-ray beams ideal for spectroscopic studies. A 5.5 cm period, planar undulator to be installed on the 7 GeV Advanced Photon Source will produce a high brightness source of intermediate energy x-rays. The 0.5–3 keV spectroscopy beamline is based on the spherical grating monochromator design that has already been shown to yield high resolution and throughput in the soft x-ray region below 1 keV. The beamline has been designed to cover the entire region with a peak resolving power of 6000–10 000. Photon flux at the sample is calculated to be in the range from 1011 to 1013 photons/s into a spot size of 1 mm2. A refocusing mirror will be used to further demagnify the image size at a second experimental station. As a second phase to the spectroscopy program, an elliptically polarized insertion device will be used. The polarization preserving nature of the grazing incidence optical elements in the SGM is crucial to obtain x rays of well-defined polarization. The beamline layout, together with calculations of resolution, throughput, power loading, and high harmonic suppression will be presented. The photoemission experimental end stations for the spectroscopy station will also be briefly described. This research was supported by the U.S. Department of Energy, BES Materials Sciences under Contract No. W-31-109-ENG-38.

VUV high resolution and high flux beamline for chemical dynamics studies at the advanced light source

An undulator beamline, consisting of VUV high resolution and high flux branch lines, devoted to chemical dynamics experiments has been designed at the Advanced Light Source. The radiation source is an undulator having a 10-cm period, and the fundamental in the energy range from 6 to 30 eV is utilized by the experiments. The higher harmonics of the undulator due to the operation at high K values is suppressed by a novel gas filter. In the first branch, high-flux 2% bandwidth radiation is directed toward an end station for photodissociation. A photon flux calculation predicts 10 16 photon/s at this end station. In the second branch, highly monochromatized radiation is sent to an end station for photoelectron spectroscopy and photoionization studies. For this purpose a vertical dispersion 6.65-m off-plane Eagle mounting was chosen for the monochromator in anticipation of achieving a resolving power of ∼ 5 × 10 4 with a 1200 grooves/mm grating and 1 × 10 5 to 2 × 10 5 with a 4800 grooves/mm grating.

A method of obtaining parasitic e/sup +/ or e/sup -/ beams during SLAC linear collider operation

We have developed a technique that allows SLAC to provide parasitic low-intensity secondary e/sup +/ and e/sup -/ beams up to 25 GeV to End Stations A and B and to the FFTB during SLC operation. This beam was successfully used for a one-month-long experimental run in End Station A by the SLAC E146 collaboration. The experiment used 400 MeV to 25 GeV electron beams at intensities averaging one electron per pulse and 120 pulses per second. The method for producing such a beam without the need for dedicated beam time was to operate parasitically from SLC: photons produced in the SLC beam scrapers in linac sectors 28, 29 and 30 were converted to positrons and electrons in a target downstream from the SLC splitter magnet. The secondary electrons or positrons were then transported to ESA with the A-line. >

Short wavelength FELs using the SLAC linac

Recent technological developments have opened the possibility to construct a device which we call a linac coherent light source (LCLS) (C. Pellegrini et al., Nucl. Instr. and Meth. A 331 (1993) 223; H. Winick et al., Proc. IEEE 1993 Particle Accelerator Conf., Washington, DC, May 1993; C. Pellegrini, Nucl. Instr. and Meth. A 341 (1994) 326; J. Seeman, SPIE Meet. on Electron Beam Sources of High Brightness Radiation, San Diego, CA, July 1993 [1–4]); it would be a fourth-generation light source, with brightness, coherence, and peak power far exceeding other sources. Operating on the principle of the free electron laser (FEL), the LCLS would extend the range of FEL operation to much shorter wavelength than the 240 nm that has so far been reached. We report the results of studies of the use of the SLAC linac to drive an LCLS at wavelengths from about 3 to 100 nm initially and possibly even shorter wavelengths in the future. Lasing would be achieved in a single pass of a low emittance, high peak current, high-energy electron beam through a long undulator. Most present FELs use an optical cavity to build up the intensity of the light to achieve lasing action in a low-gain oscillator configuration. By eliminating the optical cavity, which is difficult to make at short wavelengths, laser action can be extended to shorter wavelengths by self-amplified-spontaneous-emission (SASE), or by harmonic generation from a longer wavelength seed laser. Short wavelength, single pass lasers have been extensively studied at several laboratories and at recent workshops (M. Cornacchia and H. Winick (eds.), SLAC Report 92/02; I. Ben-Zvi and H. Winick (eds.), BNL report 49651 [5,6]). The required low-emittance electron beam can be achieved with recently-developed rf photocathode electron guns (B.E. Carlsten, Nucl. Instr. and Meth. A 285 (1989) 313; J. Rosenzweig and L. Serafini, Proc. IEEE 1993 Particle Accelerator Conf., Washington, DC, 1993 [7,8]). The peak current is increased by about an order of magnitude by compressing the bunch to a lenght of about 0.2 ps (rms). Techniques for beam transport, acceleration, and compression without emittance dilution have been developed at SLAC as part of the linear-collider project (J. Seeman, Advances of Accelerator Physics and Technologies, ed. H. Schopper (World Scientific, Singapore, 1993 [9]). The undulator length required to saturate the laser varies from about 15 m for a 100 nm FEL to about 60 m at 3 nm. Initial experiments, at wavelengths down to about 50 nm are planned using the 25-m long Paladin undulator now located at LLNL. In a proposed future LCLS R&D facility the short wavelength light pulses are distributed to multiple end stations using grazing-incidence mirrors. About 10 14 photons per pulse can be produced at a 120 Hz rate, corresponding to average brightness levels of about 10 21 photons/s/mm 2/mrad 2 within 0.1% BW and peak brightness levels of about 10 31 photons/s/mm 2/mrad 2 within 0.1% BW. Peak power levels are several hundred megawatts to several gigawatts. Electron energies required range from about 500 MeV for the 100 nm FEL to about 7 GeV for 3 nm.

Review of secondary ion mass spectrometry characterization of contamination associated with ion implantation

Contamination associated with ion implantation is reviewed with an emphasis on secondary ion mass spectrometry (SIMS) characterization. Specific examples are provided using SIMS as a tool to detect and resolve contaminant problems. This study of contamination is organized according to the path of the ion beam through an ion implanter, starting with the source and continuing to the end station. The source material, ion source components, and vacuum system can produce contaminant mass interferences that may not be eliminated by mass filtration in the implanter. A table of possible mass interferences is provided. The mass resolution of the implanter may be insufficient to remove adjacent masses and therefore may permit additional contaminants in the mass-analyzed ion beam. Charge exchange and molecular ion dissociation due to poor vacuum can occur at several locations in the implanter, especially after mass separation but before final acceleration. Detailed examples of BF2 dissociation are presented. Collisions of the ion beam with end station components result in low energy deposition of contaminants that can be driven into the target by the ion implanting beam. The fluence of the species of interest can be in error. Examples of multiple contaminant sources are also provided.

ATM local area networks

LAN emulation offers a best-effort, connectionless, packet transfer service at the MAC sublayer, implemented on top of a connection-oriented ATM network LAN emulation using switched virtual connections requires address resolution to locate the destination end station followed by connection establishment to the resulting ATM address. Address resolution may be implemented by a broadcast technique or by an address server. The broadcast method is the simplest for small networks but a combination of both is probably better. The use of the MAC address to identify an end station, with dynamic binding to its current physical location in the ATM network, allows the ATM LAN segment to be viewed as a virtual LAN. The virtual LAN model permits end stations to move and change physical location while maintaining connection to the same ATM LAN segment. This greatly simplifies the management of large data networks. >

Vibration Control Characteristic of Rotating Disk System for Ion Implanter Equipped with Magnetic Bearing.

The end station of an ion implanting machine contains a rotating disk on which several semiconductor wafers are mounted to be exposed uniformly to ion beams of dopants. The recent trend of using higher beam energy and higher rotational speed of the disk requires a sufficient capability of suppressing rotor vibrations in a high-vacuum environment. To meet this requirement, a new system using a magnetic bearing has been developed. Two methods of unbalance force cancellation and automatic balancing were tested against a large amount of unbalance oscillation force, with satisfactory results of reducing vibration amplitude and bearing force fluctuation, respectively.

Interconnecting high-speed LANs and backbones

Transparent source routing, an algorithm that exploits the best features of the transparent spanning tree and source routing algorithms for medium-access-control (MAC) bridges used in local area network (LAN) interconnections, is presented. The scheme uses optimal routes, is transparent to end stations, and reduces bridge processing overheads. Aspects of the existing transparent spanning tree and source routing algorithms are described. A comparison of the new scheme with the two existing schemes is presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A new high energy implantation facility for materials research at the CRN, Strasbourg

A 5 MV implanter has been installed at the Centre de Recherches Nucléaires (CRN) of Strasbourg in collaboration with Vivirad-High-Voltage in the framework of the European Network on Ion Beam Processing of Semiconductors. This single-ended Van de Graaff is built using a new concept of discrete electrodes and is equipped with a microwave ion source. A first beam line with an electrostatic scanning device has been constructed. The end station containing a goniometric wafer holder is coupled with the 4 MV accelerator to allow in situ implantation and analysis by nuclear techniques. The possibility of low temperature operations and control is also available. The performance of the machine will be reported and applications in material modification and analysis will be described. Particular attention will be paid to effects of high energy implantation in semiconductors (range, defects, amorphization-recrystallization). Further developments and applications in other fields will be presented.

Computer-controlled scanning and acquisition system for atmospheric PIXE

A dedicated end station has been developed to allow convenient spatially-resolved trace element analysis in air using proton-induced X-ray emission. The system is able to scan over three-dimensional surfaces while maintaining a constant air gap through the use of an optical surface profiler. The scanning stage provides movement of several inches for all three axes, allowing the system to have a dedicated load position which is stepped away from the proton collimator. Specimens can be viewed directly at the computer display while in the specimen load position. This allows scan areas, lines and points to be specified directly on the video image prior to acquisition. The PC-based acquisition system is capable of acquiring an entire 1024-point spectrum at each of up to 10000 spatial points. Elemental maps can be generated quickly, since all data is stored in RAM.