V M Dyakin

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.

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.

Features of plasma produced by excimer laser at low intensities

A plasma, created at interaction of short-wavelength excimer laser radiation with flat targets was investigated (tlas = 12 ns, λlas = 0.308 μm, qlas = 4 – 8 × 1012 W/cm2) with the help of various x-ray spectroscopic methods. The comparison of shapes and intensities of some observable spectral lines of H-, He and Li-like ions of Na, Mg and Al with results of model calculations has allowed to determine space distributions of laser plasma parameters up to distances of 0.4 mm from the target surface. Comparison of obtained results with theoretical models of absorption of short-wavelength radiation in a plasma shows, that the absorption of short-wavelength laser radiation in a plasma (at considered values of laser flux density) is executed due to inverse bremsstrahlung process in the areas with Ne < Ne, crit..

The x-ray emission spectra of multicharged xenon ions in a gas puff laser-produced plasma

Emission spectra of multicharged xenon ions produced by a laser gas puff are observed with high spectral resolution in the 8.5-9.5 and 17- wavelength ranges. Three different theoretical methods are employed to obtain 3l- ( to 10) wavelengths and Einstein coefficients for Ni-like . For the 3d-4p transitions, very good agreement is found between the experimental wavelengths and the various theoretical wavelengths. These accurate energy level measurements can be useful for studying the Ni-like xenon x-ray laser scheme. On the other hand, several intense spectral lines could not be identified as 3l- lines of Ni-like xenon, despite the very good agreement between the wavelengths and Einstein coefficients calculated for these transitions using the three different methods.

Using x-ray spectroheliograph technique for investigations of laser-produced plasma under interaction with strong magnetic field

A dense jet of a plasma consisting of multiply charged ions was generated in the interaction of a laser plasma with a strong external axial magnetic field. It is shown that using the high-luminosity x-ray spectroheliograph technique allows to measure plasma emission spectra with 2-dimensional spatial resolution even in the cases when these spectra have small intensities. The x-ray spectroscopy and interferometry methods are used to measure plasma parameter distributions. The dependencies of Ne(z) and Te(z) measured in this paper can be used to calculate the evolution of plasma ionization state during plasma expansion. The quasihomogeneous laser jet, which appears when a laser plasma interacts with an external magnetic field can be used not only to form an active medium of a short wavelength laser, but probably also to tackle the urgent problem of transport in a laser ion injector.

The dielectronic satellites to the 2s-3p Ne-like krypton resonance lines

We present an analysis of dielectronic satellite spectra of 2p6-2s2p63p Ne-like krypton resonance lines. The satellite structure was registered with high (better than ?/?? > 3500) spectral resolution in the emission of a laser irradiated gas puff target. We perform an unambiguous identification of satellite lines caused by radiative transitions from autoionizing states of sodium-like krypton ions. A total of about 20 spectral features are identified, most of them for the first time. Very good agreement between the satellite structure calculations and experimental emission spectra is obtained.

Dielectronic 3l4l′ Na-like satellites to Ne-like krypton resonance lines

Transitions from the doubly excited 2s22p53l4l′ and 2s2p63l4l′ levels of Na-like Kr25+ were observed in spectra from plasmas produced in laser-irradiated gas-puff targets. These transitions produce satellites to n = 3–2 and n = 4–2 Ne-like Kr26+ resonance lines. High-resolution x-ray spectra were measured with a relative uncertainty of ±0.001 A by means of a spherical crystal spectrograph. A simple kinetics model was successfully used to model the experimental spectra, to assist the line identification, and to demonstrate the potential of these lines for diagnosing the plasma conditions. In addition, contributions of these lines to x-ray spectra should be taken into account in the analysis of n = 4–2 Ne-like linewidth diagnostics proposed for electron density measurements in compressed inertial confinement fusion plasmas.

Measurements of the ground-state ionization energy and wavelengths for the ( n = 4 - 10) lines of O VII

The wavelengths of the (n = 4 - 10) transitions in He-like O VII have been measured in laser-produced gas puff plasmas. The accuracy of the present measurements (1.5 - 3.0 mA) is a large improvement over previous results. In addition, the resonance transitions from the levels of He-like O VII were observed for the first time. Finally, the Rydberg series is used to determine the ground-state ionization energy of O VII. This method gives . These experimental results are compared with theoretical data calculated by different methods.

INVESTIGATION OF IONIC COMPOSITION DURING EXPANSION OF LASER-PRODUCED PLASMA BY MEANS OF X-RAY EMISSIVE SPECTROSCOPY AND MASS-SPECTROSCOPY METHODS

X-ray spectroscopy methods are used to study the evolution of the ion abundancies in a laser-produced aluminium plasma during its expansion. Plasma parameters are defined with the help of intensities and lineshapes of 3p → 1s and 1snp → 1s2 (n = 6-10) spectral lines of H-like and He-like A1 XIII, XII ions. It is shown that the most strong variation of ion abundances occurs in the plasma regions close enough to the target surface. Mass-spectrometry methods are applied to investigate the amount of ions with different charges at large (≥3000mm) distances from the target.

Interaction of laser-produced plasma clouds in vacuum and background medium

An investigation into the interaction between two plasma clouds expanding in vacuum and background gas (10>p>10-4 Torr) is described. The spatial structure of the radiation emitted by the interacting plasma clouds was determined. The radiation was in the form of spectral lines due to Be I-III and Al I-III ions and it was found that the radiation emitted by ions with a given degree of ionization was localized. A mathematical model of the process was developed and used to obtain dynamic, ionization and optical characteristics of the interacting clouds. Qualitative agreement between calculation and experiment has been achieved.