CT imaging of small animals using monochromatized synchrotron x rays

Rats and chicken embryos were imaged in vivo with a prototype Multiple Energy Computed Tomography (MECT) system using monochromatized x rays from the X17 superconducting wiggler at the National Synchrotron Light Source. The CT configuration coated of a horizontal low-divergence, fan-shaped beam, 70 mm wide and 0.5 mm high, and a subject rotating about a vertical aids. A linear-array high-purity Ge detector with 140 elements, each 0.5 mm wide and 6 mm thick, was used with a data acquisition system that provides a linear response over almost six orders of magnitude of detector current. The dual photon absorptiometry (DPA) algorithm was applied to images of the rat head acquired at 20 and 45 keV to obtain two new images, one representing the low-Z, and the other the intermediate-Z clement group. The results indicate that the contrast resolution and the quantification accuracy of the images improve stepwise; first, with the monochromatic beam and, second, the DPA method. The system is a prototype for a brain scanner

Old Wine in New Bottles-The SPEAR Control System Upgrade

The control systems for the SPEAR storage ring and injector were designed almost two decades ago and have worked reliably for us. Both systems are heavily dependent on the OpenVMS operating system and CAMAC. The realtime data reside in shared memory on a single computer for each control system. In order to use more modern client tools while preserving our investment in the hardware and software, we have installed an EPICS Portable Channel Access Server (CAS) on the control computers. The CAS will serve the existing realtime data as EPICS Process Variables (PVs) and allow us to use client tools like dm2k and IDL running on other workstations to more easily build new operator interfaces and develop accelerator physics programs. The CAS will also provide the infrastructure to help integrate new hardware controlled by EPICS Input/Output Controllers (IOCs).

Applications of heat pipes for high thermal load beam lines

The high flux beam produced by insertion devices often requires special heat removal techniques. For the optical elements used in such high thermal load beam lines, the required precision demands a highly accurate design. Heat pipe cooling of critical elements of the X-1 beam line at the National Synchrotron Light Source is described. This method reduces vibrations caused by water cooling systems and simplifies the design. In some of these designs, deposited heat must be transferred through unbonded contact interfaces. A pinhole assembly and a beam position monitor designed for the X-1 beam line both transfer heat through such interfaces in an ultrahigh vacuum environment. The fundamental design objective is that of removing the heat with minimal interface thermal resistance. We present our test method and results for measuring the thermal resistance across metallic interfaces as a function of contact pressure. The design of some devices which utilize both heat pipes and thermal contact interfaces will also be described. 12 refs., 8 figs

A water-cooled mirror system for synchrotron radiation

This paper describes the design and performance of a directly-cooled soft x-ray mirror system which has been developed at Lawrence Berkeley Laboratory for synchrotron radiation beam lines in which mirror thermal distortion must be minimized for acceptable optical performance. Two similar mirror systems are being built: the first mirror has been installed and operated at the National Synchrotron Light Source on the X-17T mini-undulator beam line and will be moved to the permanent X-1 beam line when a new, more powerful undulator is installed there. The second system is being built for installation at the Stanford Synchrotron Radiation Laboratory on Beam Line VI, where the total absorbed power on the mirror may be as high as 2400 W with peak absorbed power density of 520 W/cm/sup 2/. Direct cooling by convection is achieved using internal water channels in a brazed, dispersion-strengthened copper and OFHC copper substrate with a polished electroless-nickel surface. A simple kinematic linkage and flexural pivot mounting provide for mirror positioning about two rotational axes that coincide with the optical surface. Surface figure metrology, optical configurations, and tolerancing are also discussed. 11 refs., 8 figs

X-ray holographic microscopy experiments at the Brookhaven synchrotron light source

Soft x-ray holographic microscopy is discussed from an experimental point of view. Three series of measurements have been carried out using the Brookhaven 750 MeV storage ring as an x-ray source. Young slits fringes, Gabor (in line) holograms and various data pertaining to the soft x-ray performance of photographic plates are reported. The measurements are discussed in terms of the technique for recording them and the experimental limitations in effect. Some discussion is also given of the issues involved in reconstruction using visible light

In-Situ Shearing Interferometry Of National Synchrotron Light Source Mirrors

In situ mirror distortion measurements were made with a lateral shearing interferometer on three mirrors in beam line X17T at the National Syn203hrotron Light Source. Lateral shearing interference is insensitive to vibrational motion in five of the six degrees of freedom, so it is well-suited for investigations in the synchrotron radiation (SR) environment. No distortion was seen in an uncooled silicon carbide mirror and in a colled copper alloy mirror on X17TB, but a change in the radius of an uncooled electroless nickel-plated aluminium cylinder mirror of about 6.2% was observed on X17TA. Angular vibrations in the 2 to 3 arc second range were easily observed on one of the beam lines, as was an overall mirror rotation in the arc second range

High flux photon beam monitor

We have designed two photon beam position monitors for use on our x-ray storage ring beam lines. In both designs, a pair of tungsten blades, separated by a pre-determined gap, intercepts a small fraction of the incoming beam. Due to photoemission, an electrical signal is generated which is proportional to the amount of beam intercepted. The thermal load deposited in the blade is transferred by a heat pipe to a heat exchanger outside the vacuum chamber. A prototype monitor with gap adjustment capability was fabricated and tested at a uv beam line. The results show that the generated electrical signal is a good measurement of the photon beam position. In the following sections, design features and test results are discussed

An automatic beam steering system for the NSLS X-17T beam line using closed orbit feedback

Initial observations of motion of the undulator radiation in the NSLS X-17T beam line clearly indicated that the beam had to be stabilized in both directions to be usable for the planned soft x-ray imaging experiments. The low frequency spectra of beam motion contained peaks in the range from dc to 60 Hz and at higher frequencies. A beam steering system employing closed orbit feedback has been designed and installed to stabilize the beam in both planes. In each plane of motion, beam position is measured with a beam position detector and a correction signal is fed back to a local four magnet orbit bump to dynamically control the angle of the radiation at the source. This paper describes the design and performance of the beam steering system

Undulator based scanning microscope at the National Synchrotron Light Source

A second generation scanning soft x-ray microscope is under construction, designed to utilize the dramatic increase in source bightness available at the soft x-ray undulator. The new instrument is expected to reduce image acquisition time by a factor of about 100, and to improve resolution, stability, and reproducibility