T.A. Shelkovenko

High-performance x-ray spectroscopic devices for plasma microsources investigations

X-ray spectroscopy with high spectral (up to Δλ/λ = 10−4) and spatial resolution (up to 1 μm) is discussed. Devices based on crystals, diffraction and Bragg-Fresnel elements and their applications in Z- and X-pinches and laser plasma experiments are described.

Flat and Spherically Bent Muscovite (Mica) Crystals for X-ray Spectroscopy

Essential parameters for the application of crystals to quantitative X-ray spectroscopy are the upper wavelength limit and the quantitative reflection properties (intrinsic resolving power, luminosity) of the crystal. Due to the large lattice constant, muscovite, a mica group mineral, can be used in the wavelength range up to about 2nm. Muscovite crystals can be bent to small radii of curvature due to their favourable cleavage and elastic properties. Characteristic reflection properties at reflections 002 – 00 24 were investigated theoretically and experimentally. The integrated reflectivity was calculated for various reflections of perfect flat as well as spherically bent muscovite crystals with curvature radii R = 100 and R = 186mm. It was measured for flat crystals in the reflections 00 10 – 00 26 using CuKα- and MoKα-radiation from X-ray tubes and compared with calculations for both perfect and mosaic crystals. Available high-quality muscovite crystals have a mosaic structure with a mosaic spread of about 1 arcmin. This mosaic spread limits the spectral resolving power for high reflection orders.

Phase-contrast x-ray radiography using the X pinch radiation

The application of the X pinch x-ray source for phase-contrast x-ray radiography of low absorption materials is demonstrated. The X pinch is a source of radiation in the 1-10 keV x-ray band with extremely small size and short pulse duration. The small source size provides high spatial coherence of the imaging x-ray beam, enabling it to be used to image low absorption, low contrast objects with excellent spatial resolution. Images with spatial resolution better than 3 micrometers of exploded, insulated 25 micrometers W wire and biological objects are presented. The advantages of the X-pinch over other x-ray sources are discussed.

Radiative properties of hot dense X-pinch

Abstract A high luminosity spectrometer with a spherically bent mica crystal has been used to obtain H- and He-like spectra of Al and Si ions in X-pinch plasma with high spectral (λ/Δλ ∼ 3000) and spatial (∼ 30 μm) resolution. The electron density (up to 2.1024 cm-3) and the temperature (up to 950 eV) in the “hot point” were measured by means of X-ray spectroscopy methods. The estimates show, that the emission of K-line radiation can be up to 1 J, the power being 109 W). The total energy emitted in the spectral region 5–100 A is about 1 kJ.

Ray-tracing for a monochromatic x-ray backlighting scheme based on spherically bent crystal

The properties of a monochromatic x-ray backlighting system based on a spherically bent crystal were investigated. Simulations of spatial resolution for spherically bent crystals with different radius of curvature and for several wavelengths of incidence radiation were done using the ray-tracing method. Test experiments were carried out to demonstrate the high spatial resolution using the incoherent soft x-ray radiation produced by laser- and x-pinch plasmas. Both experimental and theoretical results show that a spatial resolution of at least 4 μm can be obtained in a field of view ranging from a few mm to cm. The narrow spectral band of the diffracted beam (Δλ/λ ~ 3 × 10−4), the high efficiency of the presented scheme and the possibility of significantly reducing the self radiation of the studied object make it one of the most promising backlighting systems. This scheme permits the essential reduction of requirements of the source of radiation and could be a less costly alternative to using x-ray lasers for such purposes.

X-pinch source characteristics for x-rays above 10 keV

X pinch radiation produced by electron beams accelerated in the X pinch minidiode ranging in energy from 10 to 100 keV has been studied and used to image a variety of different objects. The experiments have been carried out using the XP pulser (470 kA, 100 ns) at Cornell University and the BIN pulser (280 kA, 120 ns) at the P.N. Lebedev Physical Institute. This electron-beam-generated x-ray sources geometric, temporal and spectral properties have been studied over different energy ranges between 10 and 100 keV. The imaging was carried out in a low magnification scheme, and spatial resolution of a few tens of μm was demonstrated.

X pinch: a source of 1- to 10-keV x rays

Several methods of using the X pinch as a source of x-ray radiation for the radiography of dense plasmas and other objects are presented. These methods do not use pinholes, instead taking advantage of the small source size and short x-ray emission duration of the X pinch radiation. Detailed measurements of the emission characteristics of X pinches made using different wire materials and in different energy ranges using a set of x-ray diagnostics with high temporal and spatial resolution are presented. Several applications of the X pinch are discussed.

Transitions from Na-like and Mg-like autoionizing levels of multicharged molybdenum ions in an X-pinch plasma

A superdense X-pinch plasma was used to investigate the emission spectra of multicharged molybdenum ions in the spectral region 4.4 – 5.0 A. A comparison of the experimental data obtained with results of theoretical calculations allowed the identification of a number of spectral lines caused by radiative decay of autoionizing levels of Na- and Mg-like ions. The wavelengths of the identified spectral lines were measured with a relative accuracy of about ±0.001 A. These measurements provide important tests of radiative emission models of dense plasmas.

Small size X-pinch radiation source for application to phase-contrast X-ray radiography of biological specimens

The X pinch is a very small size radiation source in the 3-10 keV X-ray band. As such, it has been used successfully to obtain high resolution images of /spl les/2 min thick biological samples ranging from small bugs (flies, beetles, etc.) to a small piece of mouse intestine. The X pinch source size as a function of the X-ray energy is important because it directly determines the spatial resolution of the imaging system. Furthermore, a small source size can provide high spatial coherence of the imaging X-rays, enabling their use for imaging low absorption, low contrast objects with excellent spatial resolution by a method called phase-contrast imaging. In order to determine the source size, several structures have been micro-fabricated that involve gold on a membrane that is transparent to the X-rays. If these structures are imaged in point projection radiography, a finite source size will cause penumbral blurring. Therefore, the shape of the shadow image pattern depends on the source size of the X-rays, the energy band of the X-rays, the shape and material used for the structures, and the geometry of the experiment. The experimental results must be compared with wave-optics calculations for the expected image pattern as a function of all of the above parameters, but especially the source size. The several conditions for phase-contrast imaging are discussed. Examples of high-resolution images of biological objects are presented.

FSSR mica spherical crystal spectrometer with CCD detector for high-resolution x-ray spectroscopy of femtosecond laser produced plasma

The use of the FSSR mica spherical crystal spectrograph with CCD detector to study satellite structures of 1s2–1s2p transitions of [He]-like Al ions and fine structure of Kα-lines is presented. It is shown that the FSSR spectrograph is more suitable for study of laser plasma with high spectral and spatial resolution than other types of spectrographs and the use of this spectrograph gives the possibility to measure the sizes of the x-ray sources and the intensity of the dielectronic satellites.