Kenneth M. Skulina

Tabletop x-ray microscope using 8 keV zone plates

We describe the implementation of an 8 keV microscope that operates with a conventional x-ray source in our lab. Samples are scanned pixel-by-pixel through a focused x-ray spot produced by a phase-modulating zone plate fabricated with the sputtered-sliced technique. The micro- focused x-ray source uses a Cu target and produces 8 keV photons that are detected with a Si(Li) spectroscopy system. The microscope currently achieves 10 µm resolution.

Hard x‐ray sputtered‐sliced phase zone plates

Al/Cu sputtered‐sliced phase zone plates, designed to operate with a focal length of 18 cm at 8.05 keV, were tested at the Stanford Synchrotron Radiation Laboratory. First‐, second‐, and third‐order peaks are measured, along with a defocused condition. The first‐order focusing efficiencies ranged from 13% to 19% for the two lenses presented here. Monte Carlo simulations are compared to the data.

Performance comparison of hard x-ray plates fabricated by two different methods

Two types of fabrication methods have been developed to fabricate Fresnel zone plates for focusing x-rays in the 5 - 25 keV energy region. These two fabrication methods are discussed in terms of spatial resolution and focusing efficiency, which are two important parameters that characterize the performance of a Fresnel zone plate. Experimental characterization of the zone plates fabricated by the two methods are described and the results are discussed.

8 Kev X-Ray Zone Plates

Sputtered-sliced transmissive x-ray zone plates consisting of concentric rings of Al and Cu have been fabricated and tested using the 8.04 keV k-a line from Cu. Due to the need for high aspect ratios for this 1.54 A radiation, magnetron sputtering onto a rotating opaque central wire was chosen as the fabrication method. Both the fabrication technology and initial results are presented.

Neutron reflectivity measurements of titanium—beryllium multilayers

Abstract Some of the best neutron supermirrors currently in production are made of alternating layers of nickel and titanium, with carbon added to the Ni to eliminate preferential growth. Reflectivities of 75–95% in the θc-2θc range are currently obtained from the Ni/C-Ti system. The Ti-Be multilayer system is presented here as a possible alternative to the Ni/C-Ti system. Titanium is one of the few elements which has a negative neutron scattering length, while beryllium has a relatively large positive scattering length. This makes for bilayer structures which have excellent neutron contrast, a necessary requirement of supermirror devices. Single-bilayer-spacing Ti-Be multilayers were prepared by magnetron sputtering onto 2mm thick silicon (001) substrates. Depositions were made with 10–80 bilayers at two different bilayer thicknesses of approximately 90 and 110 A. Bulk layers of Ti and Be were also prepared to determine the scattering length density of each deposition component. The samples were measured at the Intense Pulsed Neutron Source (IPNS) at Argonne National Laboratory on the POSYII reflectometer. First order Bragg peak reflectivities of up to 64% were observed. Data from the two bulk depositions and one multilayer deposition have been fitted using a genetic algorithm developed at IPNS. For the bulk depositions, the scattering length densities of Ti and Be depositions are −2.2 × 10−6 and 10.3 × 10−6 A−2, respectively. In addition, results clearly indicate the presence of a 50 A thick oxide layer on the bulk Ti deposition. The neutron scattering length density profile obtained from the neutron reflectivity measurements are in good agreement with XPS analysis of the oxide film which showed a mixture of TiO2 and Ti2O3.

Demonstration of a time-integrated short line of sight neutron imaging system for inertial confinement fusion.

The Neutron Imaging System (NIS) is an important diagnostic for understanding implosions of deuterium-tritium capsules at the National Ignition Facility. While the detectors for the existing system must be positioned 28 m from the source to produce sufficient imaging magnification and resolution, recent testing of a new short line of sight neutron imaging system has shown sufficient resolution to allow reconstruction of the source image with quality similar to that of the existing NIS on a 11.6 m line of sight. The new system used the existing pinhole aperture array and a stack of detectors composed of 2 mm thick high-density polyethylene converter material followed by an image plate. In these detectors, neutrons enter the converter material and interact with protons, which recoil and deposit energy within the thin active layer of the image plate through ionization losses. The described system produces time-integrated images for all neutron energies passing through the pinhole. We present details of the measurement scheme for this novel technique to produce energy-integrated neutron images as well as source reconstruction results from recent experiments at NIF.

Performance results of the high-gain Nd:glass engineering prototype preamplifier module (PAM) for the National Ignition Facility (NIF)

We describe recent, energetics performance results on the engineering preamplifier module (PAM) prototype located in the front end of the 1.8 MJ National Ignition Facility laser system. Three vertically mounted subsystem located in the PAM provide laser gain as well as spatial beam shaping. The first subsystem in the PAM prototype is a diode pumped, Nd:glass, linear, TEM00, 4.5 m long regenerative amplifier cavity. With a single diode pumped head, we amplify a 1 nJ, mode matched, temporally shaped (approximately equals 20 ns) seed pulse by a factor of approximately 107 to 20 mJ. The second subsystem in the PAM is the beam shaping module, which magnifies the gaussian output beam of the regenerative amplifier to provide a 30 mm X 30 mm square beam that is spatially shaped in two dimensions to pre- compensate for radial gain profiles in the main amplifiers. The final subsystem in the PAM is the 4-pass amplifier which relay images the 1 mJ output of the beam shaper through four gain passes in a (phi) 5 cm X 48 cm flashlamp pumped rod amplifier, amplifying the energy to 17 J. The system gain of the PAM is 1010. Each PAM provides 3 J of injected energy to four separate main amplifier chains which in turn delivers 1.8 MJ in 192 frequency converted laser beams to the target for a broad range of laser fusion experiments.

High-gain preamplifier module (PAM) engineering prototype for the National Ignition Facility (NIF) laser system

We describe recent results and developments in the preamplifier module engineering prototype located in NIFs front end or Optical Pulse Generation system. This prototype uses the general laser design developed on a physics testbed and integrates NIF type packaging as well as controls and diagnostics. We will present laser, mechanical and electrical hardware designed and built to data as well as laser energetics measurements.

Experimental characterization of Fresnel zone plate for hard x-ray applications

A series of experimental measurements was conducted for the characterization of a transmission circular zone plate. The zone plate (ZP), with a primary focal length of 40 cm for 8 keV photons, was illuminated by monochromatized synchrotron x rays. Focusing efficiency of the ZP was measured as a function of x-ray energy between 5 - 1 keV, from which the ZP thickness was determined. Focal spot sizes at the first, second, and third order focus were measured, and they agreed very well with the calculated values. Images of a 1000 mesh/inch gold grid were also obtained at the three focal planes. The grid scans indicated that the spatial resolution is about 2 (mu) in the image obtained at the third order focus.

A mechanical thickness scale for opaque parts

A method for measuring the thickness of opaque parts to within 4 μm by inserting a small scale into the part or along side has been developed. A combination digital and analog scale is used to determine the length of the scale when viewed from the edge. This scale should be useful for applications where only one surface is exposed during machining or polishing, and where the side is also inaccessible.