End Station Research Articles

Status of the Advanced Photon Source low-energy undulator test line

A Low-Energy Undulator Test Line (LEUTL) is under construction at the Advanced Photon Source (APS). Its purpose is to fully characterize innovative, future-generation undulators, and to act as a test line in pursuit of generating coherent radiation at wavelengths down to a few tens of nanometers. The line will use a high-brightness RF electron gun as its source and the APS linac to accelerate these electrons up to >650 MeV. This beam will then be directed through undulators located in a new 50 m long enclosure. In addition, there is an end station external to the radiation environment which will house the equipment necessary to directly study the light generated by the beam and undulator system. At present, the new enclosures are complete, the electron rf gun is installed and operational, and a part of the necessary transport line is installed. A prototypical undulator cell, suitable for testing the requirements of single-pass free-electron laser operation, is near completion and will be installed during the winter shutdown of 1998. This paper will describe the LEUTL project and, in particular, its capabilities for exploring the self-amplified spontaneous emission process.

Warren: a low-cost ATM home area network

This article introduces the concept of the ATM Warren. The Warren is an arbitrary mesh subnetwork of very simple ATM switches and end stations connected to the wide-area B-ISDN at one or more points. The Warren differs from other ATM networks in that both switches and end stations are designed to be implemented entirely in hardware with all control software banished to external computers.

A Multi-Anvil, High-Pressure Facility for Synchrotron Radiation Research at GeoSoilEnviroCARS at the Advanced Photon Source.

This paper describes the multi-anvil, large-volume, high-pressure facility that is being constructed at the GeoSoilEnviroCARS at the Advanced Photon Source, Argonne National Laboratory. The facility consists of multi-anvil high pressure systems at the end stations of the bending magnet and the insertion device beamline at Sector 13. Various pressure apparatus will be used to cover pressure and temperature conditions up to 40 GPa and 3000°C, with millimeter sized samples at high pressure end and centimeter sized samples at low pressure end. This national facility is open to all users and a variety of high pressure, high temperature experiments will be carried out.

Performance of the vacuum ultraviolet high-resolution and high-flux beamline for chemical dynamics studies at the Advanced Light Source

At the Advanced Light Source an undulator beamline, with an energy range from 6 to 30 eV, has been constructed for chemical dynamics experiments. The higher harmonics of the undulator are suppressed by a novel, windowless gas filter. In one branchline high-flux, 2% bandwidth radiation is directed toward an end station for photodissociation and crossed molecular-beam experiments. A photon flux of 1016 photon/s has been measured at this end station. In a second branchline a 6.65 m off-plane Eagle monochromator delivers narrow bandwidth radiation to an end station for photoionoization studies. At this second end station a peak flux of 3×1011 was observed for 25 000 resolving power. This monochromator has achieved a resolving power of 70 000 using a 4800 grooves/mm grating, one of the highest resolving powers obtained by a vacuum ultraviolet monochromator.

Approximating dependability measures of computer networks: an FDDI case study

An approximation technique is presented to evaluate the dependability of FDDI networks. This technique, based on the most likely paths to failure concept, is simple and practical. It may be applied easily to evaluate and compare the dependability of different FDDI network configurations. The effects of various network parameters on the network availability are examined. We conclude that, in order to guarantee high availability, an FDDI network backbone should be interconnected using dual-attachment concentrators. Furthermore, dual-homing configurations are required for high-availability paths between end stations and the backbone. For less stringent availability requirements, single-attachment concentrator trees with single attachment stations may suffice. We also discuss how the technique may be extended easily to more general heterogeneous networks including Token Ring and Ethernet.

Reciprocal connections between primary and secondary auditory pathways in the telencephalon of the budgerigar (Melopsittacus undulatus)

Among avian species that learn their vocalizations, budgerigars have been thought to be unusual in receiving auditory input to the vocal control circuitry of the telencephalon via an auditory component of nucleus basalis (NB), rather than via Field L2, the end station of the classical thalamofugal pathway. In the present study, however, the application of neural tracing techniques showed the two auditory pathways to be reciprocally connected within the telencephalon. The implication is, therefore, that auditory information essential for vocal learning and vocal production in the budgerigar is derived from the primary as well as the secondary auditory pathway.

A new genus and species of the deep-sea family coronarctidae (Tardigrada) from a submarine cave with a deep-sea like condition

Abstract A new genus and species of the deep-sea family Coronarctidae (Tardigrada, Arthrotardigrada), collected from a sublittoral submarine cave in the French Mediterranean Sea, is described and illustrated. Tardigrades were only present in the first centimetres of the cave sediment (1.5-2 cm), where the 80 % ofmeiofauna, largely dominated by nematodes, is also concentrated. Trogloaretus trionyehes gen. et sp. n. was only identified at the stations with complete darkness, mainly at the far end station. The new genus Trogloaretus shows several characters, distinguishing it from all known Coronarctidae: presence of only one somatic cirrus (cirrus E), three claws on each leg (reduction), and an absence of large accessory spine on the fourth pair oflegs. The presence of bar shaped placoids in the pharyngeal bulb may be regarded as a plesiomorphic character. These differences involve the modification ofthe previous diagnosis ofthe family Coronarctidae in order to accommodate the new genus Trogloaretus. Ecology and geographical distribution of Coronarctidae is reviewed.

Equipment for in situ resistivity and x-ray diffraction studies during ion implantation at temperatures between 4 K and 1270 K

An instrument is presented which was designed for comprehensive in-situ analysis of phase formation and transformation during the ion implantation process. An implanter end station with heatable He-cryostat as a sample holder was built. A temperature range from 4 to 1270 K is covered by the sample holder so that temperature can be varied during implantation or subsequent annealing in high vacuum. Both x-ray diffraction and four-point resistivity measurement are installed as in-situ investigation techniques. In this way a detailed study of structural changes and defect kinetics during ion bombardment is now possible. The whole instrument has been successfully tested. Examples of carbon ion implantation in titanium and iron are given.

TGM-to-SGM conversion at NSLS beamline U7A: Recyclying of beamline components (abstract)

The U7A bending magnet toroidal grating monochromator (TGM) beamline has been converted into a spherical grating monochromator (SGM) type, without constructing any new vacuum components. That is, the mirror, slit, and grating chambers have been recycled. The inherited optical arrangement and the recycling concept prevented the use of ‘‘standard’’ SGM Kirkpatrick-Baez collecting and focusing mirrors at the front end. We show that this modification is not a serious detriment to the optical properties of the resulting beamline. Specifically, the resolution is completely unaffected and the throughput is approximately 2/3 of the ‘‘standard’’ SGM value. The flux and photon energy resolution of the U7A beamline throughout its 200–1000 eV operating photon energy range will be presented. Three end stations are being constructed for this beamline, featuring soft x-ray absorption and photoemission chambers optimized for operation in the carbon K-, oxygen K-, and transition metal L-edge ranges. Two of these end stations will be preceded by refocusing mirrors that will focus the soft x-rays to <1 mm spot size onto their samples.

Earth, soil and environmental science research facility at sector 13 of the Advanced Photon Source. I. Sector layout and optical design (abstract)

The earth, soil and environmental science component (GSECARS) of the Consortium of Advanced Radiation Sources (CARS), is designing a national research facility to be built at sector 13 of the Advanced Photon Source. The bending magnet beam will be split to allow simultaneous operation of two stations, a monochromatic (8–15 keV) side station and a multipurpose, white beam/monochromatic end station. The undulator beamline will have two white beam stations, which may operate simultaneously using a double-crystal monochromator (cryogenic Si) with a thin first crystal. In this mode, the upstream station will accept the monochromatized (4.5–22 keV) beam deflected horizontally by a third (bendable) Ge crystal, while the end station accepts the high energy component (blue beam) transmitted by the first crystal. The need for small x-ray beams and broad spectral range have led us to base the focusing aspects of the optic design on grazing incidence mirrors. Both our bending magnet and insertion device beamlines will have long (∼1 m), bendable mirrors (demagnification <11, E(cut-off) ≳70 keV; beam sizes ≳tens of micrometers). For smaller focal spots, we will use small, dynamically bent Kirpatrick-Baez mirrors (demagnification 100–400; E(cut-off) <70 keV; beam sizes ∼1 micrometer). A unique aspect of our insertion device beamline is the ability to deliver focused white beam to the sample, through the incorporation of a power management pinhole in the first optics enclosure.

Operational experience at the Advanced Light Source (invited)

The Advanced Light Source (ALS) has been operational for users since October 1993 when white light from a bend magnet was delivered to the Center for X-Ray Optic’s (CXRO) x-ray microprobe end station. Since then, the ALS has installed and commissioned three undulators and their beamlines (including monochromators and post-monochromator focusing optics), and eight bend-magnet beamlines, including one dedicated to machine diagnostics. Apart from one serious outage, when scheduled beam was not available to users for 17 days, the ALS has enjoyed remarkable operating statistics, with typically 95% of scheduled beam time delivered to the users. Beam quality has also been very good. With a vertical emittance measured at 0.06 nm-rad, the electron beam is kept stable to about one-tenth of its transverse dimensions, in the face of changing error fields in the insertion devices (as their main fields are varied), temperature variations, and floor vibration. The longitudinal motion of the beam, which leads to an increase in the electron beam energy spread and thence to a degradation of the undulator spectra, has recently been brought under control by the addition of an innovative feedback system. This paper focuses on those aspects of electron beam stability that we find most affect the ALS users: beam size and position, and energy spread.

Precision manufacturing using LIGA (abstract)

Our objective is the fabrication of small high-precision parts using LIGA, which can be used in a variety of industrial applications. LIGA is a combination of deep x-ray lithography, electroplating, and replication processes that enables the fabrication of microstructures with vertical dimensions several millimeters high, lateral dimensions in the micrometer range, and submicron tolerances. On beamline 10.3.2, at the Advanced Light Source (ALS), the Center for X-ray Optics (CXRO) has built an end station suitable for LIGA. The ALS is an excellent source of radiation for this application. The CXRO, in close collaboration with Sandia National Laboratory and the Jet Propulsion Laboratory, has developed the other essential process steps of mask making, resist development, x-ray exposure, and electroplating. This technology provides a powerful tool for mass production and miniaturization of mechanical systems into a dimensional regime not accessible by traditional manufacturing operations. We will present several applications that exploit the characteristics of the LIGA process: the fabrication of magnetic laminations for a high precision stepping motor; miniature octopole lens for advanced e-beam lithography; high-aspect-ratio x-ray collimating grids for astronomy; and microscopic tumblers for nuclear security.

High-resolution beamline 9.3.2 in the energy range 30–1500 eV at the Advanced Light Source: Design and performance

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.

A multichannel monolithic Ge detector system for fluorescence x-ray absorption spectroscopy

The construction and performance characteristics of a monolithic quad-pixel Ge detector designed specifically for fluorescence x-ray absorption spectroscopy (XAS) at synchrotron radiation sources is described. The detector semiconductor element has an active surface area of 4.0 cm2 that is electrically separated into four 1.0 cm2 pixels, with little interfacial dead volume. The spatial response of the array demonstrates that cross-talk between adjacent pixels is less than 10% for 5.9-keV photons that fall within 0.5 mm of the pixel boundaries. The detector electronics system utilizes preamplifiers built at LBNL with commercial Tennelec Model TC 244 amplifiers. Employing an 55Fe test source (Mn Kα , 5.9 keV), energy resolution of better than 200 eV is achieved with a 4 msec peaking time. At 0.5 msec peaking time, pulse pileup results in a 75% throughput efficiency for an incoming count rate of 100 kHz. Initial XAS fluorescence measurements at the beamline 4 wiggler end stations at SSRL show that the detector system has several advantages over commercially available x-ray spectrometers for low-concentration counting applications.

New end station for the study of gases, liquids, and solid films at the MAX laboratory

A new end station equipped with a very high-resolution SES-200 electron energy analyzer has been constructed for the study of gases and soft molecular materials. The analyzer is rotatable around the direction of the photon beam, allowing angular-dependent studies. The system has been built in a way allowing the investigation of free molecules and atoms, metal vapors, liquid interfaces as well as solid films. The first electron spectroscopy results for gases, liquids, and polymer films are presented.

On the Simultaneous Optimization of Server and Work Allocations in Production Line Systems with Variable Processing Times

The allocation of servers and the allocation of work are two important decision variables in designing production line systems. Previous studies of each variable in isolation have found that throughput is maximized by using an allocation that gives preferential treatment to interior stations (especially center stations) over the two end stations. In this paper we study the simultaneous optimization of server and work allocations and obtain some surprising results of a different nature. One key finding is the L-phenomenon, whereby the throughput is maximized by assigning all extra servers over one per station to just one of the end stations and then adjusting the work allocation so that this station has by far the greatest amount of work per server. Another key finding is the multiple-server phenomenon, whereby extra servers add far more throughput per server than the initial one-per-station servers. Both findings have important implications for the design of some production line systems in ways that will greatly improve their efficiency. Similar conclusions are drawn when lower and/or upper bounds are imposed on the number of servers per station and the number of stations is included as a decision variable.

Fluorescence detected soft XAS and MCD - applications to bioinorganic systems

Recent developments in synchrotron radiation sources and end stations make x-ray magnetic circular dichroism a feasible experiment for metalloproteins. This paper describes the experimental apparatus and some results that indicate the promise of the technique.

High resolution soft X-ray bending magnet beamline 9.3.2 with circularly polarized radiation capability at the Advanced Light Source

Bending magnet beamline 9.3.2 at the Advanced Light Source (ALS) was designed for high resolution spectroscopy in the soft x-ray energy region, covering a range from 30 eV to 1500 eV with three gratings. The monochromator itself is a standard fixed included angle 55 m spherical grating monochromator and was originally used at the Stanford Synchrotron Radiation Laboratory (SSRL) as a prototype for later insertion device based monochromators for the ALS. For operations at the ALS, the toroidal pre-mirror used at SSRL to vertically focus onto the entrance slit and horizontally focus onto the exit slit was replaced by two separate crossed mirrors (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 rotatable platform (through 60°) that accommodates two experimental chambers, enabling the synchrotron radiation to be directed to either one without breaking vacuum.

Ion optical system for transport and deceleration of highly charged ions

An ion optical system which transports the highly charged ions of an ECR ion source to a RBS end station of a 2 MV Van de Graaff beam line is described. The highly charged ions are focused and decelerated in a four-electrode lens to a spot size of about 5 mm on the grounded target. The system transports ion currents of 0.1–50 μA with 90% transmission to final kinetic energies of q*(10–10 000) eV (q being the charge state of the ion).

End-station performance under leaky bucket traffic shaping

The shaping of traffic at its source is a prominent congestion control solution in ATM networks. The with a is a very popular traffic-shaping approach. By sizing the leaky bucket and spacer parameters, an end station shapes its traffic to conform to a good behaviour contract with the network. The leaky bucket delays the transmission of a selected number of cells, while the spacer forces a minimum time distance between transmitted cells. When a contracted transmission rate is close to the traffic generation rate of the end station, this traffic stream will utilize most of the bandwidth available on its virtual connection. The high utilization of such a connection leads to large queues of frames and cells at the end station, with high adverse consequences for end-to-end delay and jitter. Based on the negotiated traffic parameters and source traffic characteristics, we study, through simulations, the contribution of the leaky bucket plus cell spacer subsystem to the delay and jitter in an end station. We also study the distribution of the size of the bursts of cells leaving the end station and entering the network. Finally, we derive the theoretical upper bound for the size of bursts of the cells.