S. A. Pikuz

X-ray spectroscopy of multiply-charged ions from laser plasmas

Abstract Original results are reported on the observation and identification of spectra of multiply-charged ions in the range of λ ≈ 1.5–15 A, which corresponds to transitions with a range of principal quantum number n. The main part of the review consists of tables with about a thousand spectral lines, which have been mainly observed in laser-plasma radiation, as well as in the solar corona and other laboratory sources at an electron temperature Te≈107°K. The accuracy for the wavelengths (Δλ) is the following: Δλ is equal to ≈ 0.0005 A for λ ≈ 2.5 A and it is equal to ≈ 0.003 A for λ ≈ 15 A. The spectral lines are considered for the following transitions: 1-n type for [H]-like ions (Z = 11–16)and [He]-like ions (Z = 11–26); 2-n type for [Li]-like ions (Z = 19–26), [Be]-like ions (Z = 22–34) and [Ne]-like ions (Z = 26–42); 3-n type [Co]- and [Ni]-like ions (Z = 73). The line-list contains about four hundred wavelengths for multiply-charged iron L-ions (Fe(XVII)-Fe(XXIV)) and is presented with identification of some of the transitions. The wavelengths and intensities of satellites of the [H]-like ions and [He]-like ions, which are caused by transitions from the doubly-excited autoionization states 2l2l′ and 1s2l2L′ of [He]-like ions (Z = 11–16) and [Li]-like ions (Z = 11–26), respectively, are also considered.

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.

X-ray radiation from ions with K-shell vacancies

Abstract New types of space resolved X-ray spectra produced in light matter experiments with high intensity lasers have been investigated experimentally and theoretically. This type of spectra is characterised by the disappearance of distinct resonance line emission and the appearance of very broad emission structures due to the dielectronic satellite transitions associated to the resonance lines. Atomic data calculations have shown, that rather exotic states with K-shell vacancies are involved. For quantitative spectra interpretation we developed a model for dielectronic satellite accumulation (DSA-model) in cold dense optically thick plasmas which are tested by rigorous comparison with space resolved spectra from ns-lasers. In experiments with laser intensities up to 10 19 W/cm 2 focused into nitrogen gas targets, hollow ion configurations are observed by means of soft X-ray spectroscopy. It is shown that transitions in hollow ions can be used for plasma diagnostic. The determination of the electron temperature in the long lasting recombining regime is demonstrated. In Light-matter interaction experiments with extremely high contrast (up to 10 10 ) short pulse (400 fs) lasers electron densities of n e ≈3×10 23 cm −3 at temperatures between kT e =200–300 eV have been determined by means of spectral simulations developed previously for ns-laser produced plasmas. Expansion velocities are determined analysing asymmetric optically thick line emission. Further, the results are checked by observing the spectral windows involving the region about the He α -line and the region from the He β -line to the He-like continuum. Finally, plasmas of solid density are characteristic in experiments with heavy ion beams heating massive targets. We report the first spectroscopic investigations in plasmas of this type with results on solid neon heated by Ar-ions. A spectroscopic method for the determination of the electron temperature in extreme optically thick plasmas is developed.

The determination of laser plasma electron density by K spectra of multicharged ions

X-ray spectroscopic methods for the determination of electron densities Ne>1020 cm-3 in plasmas with high electron temperatures (Te>or approximately=0.2 keV) are reviewed. The methods considered are based on the following measurements of: (i) relative intensities of resonance and intercombination lines in spectra of He-like ions; (ii) relative intensities of satellite lines in spectra of H-like ions; (iii) relative intensities of H-like resonance doublet components; (iv) Stark broadening of the lines of H-like ions. All these methods have been used in experiments on plasma heating by focusing a laser beam on plane massive targets containing elements with nuclear charge Z=12-19. The density distribution in the plasma was measured within the limits of Ne=1018-1021 cm-3. The results obtained by all the methods are compared and the limits of application of the methods are determined.

Spectra of Be-like ions with nuclear charge Z=22,...,34 from laser-produced plasmas

Reports the classification of 220 spectral lines of Ti XIX, V XX, Cr XXI, Mn XXII, Fe XXIII, Co XXIV, Ni XXC, Cu XXVI, Zn XXVII, Ge XXIX and Se XXXI. The transitions identified are 1s22p2-1s22p3s, 1s22p2-1s22p3d, 1s22s2p-1s22s3s, 1s22s2p-1s22s3d, 1s22s2p-1s22p3p and 1s22s2-1s22s3p. These lines were emitted from laser-produced plasmas. Perturbation theory was used to calculate the wavelengths.

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.

Electron beam effects on the spectroscopy of satellite lines in Aluminum X-pinch experiments

Aluminum wire X-pinch experiments performed at the Cornell University XP pulsed power generator show detailed high resolution spectra for satellite lines of Li-like, Be-like, B-like and C-like ions. These lines, which correspond to transitions originating from autoionizing levels, are observed in the direction of the anode with respect to the hot X-pinch cross point. The intensities of such satellites are much smaller or absent in the direction of the cathode. These transitions are caused by collisions of ions with energetic electrons (5-15 keV) which are created by inductance between the hot spot and the anode. A collisional-radiative model was constructed using a non-Maxwellian electron energy distribution consisting of a thermal Maxwellian part plus a Gaussian part to represent the high energy electron beam. The shapes of the observed satellite structures are consistent with the calculated spectrum for electron temperatures between 30-100 eV, and beam densities of about 10−7 times the plasma electron density.

Nonlinear increase of X-ray intensities from thin foils irradiated with a 200 TW femtosecond laser

We report, for the first time, that the energy of femtosecond optical laser pulses, E, with relativistic intensities I > 1021  W/cm2 is efficiently converted to X-ray radiation, which is emitted by “hot” electron component in collision-less processes and heats the solid density plasma periphery. As shown by direct high-resolution spectroscopic measurements X-ray radiation from plasma periphery exhibits unusual non-linear growth ~E4–5 of its power. The non-linear power growth occurs far earlier than the known regime when the radiation reaction dominates particle motion (RDR). Nevertheless, the radiation is shown to dominate the kinetics of the plasma periphery, changing in this regime (now labeled RDKR) the physical picture of the laser plasma interaction. Although in the experiments reported here we demonstrated by observation of KK hollow ions that X-ray intensities in the keV range exceeds ~1017  W/cm2, there is no theoretical limit of the radiation power. Therefore, such powerful X-ray sources can produce and probe exotic material states with high densities and multiple inner-shell electron excitations even for higher Z elements. Femtosecond laser-produced plasmas may thus provide unique ultra-bright X-ray sources, for future studies of matter in extreme conditions, material science studies, and radiography of biological systems.

Time and space resolved measurement of the electron temperature, mass density and ionization state in the ablation plasma between two exploding Al wiresa)

We have determined the properties of plasma around and between two exploding wires using high-resolution x-ray absorption spectroscopy. Plasma densities and temperatures ranging from ≳0.1g/cm3 and a few eV to less than 0.01 g/cm3 and 30 eV have been measured in experiments at Cornell University with two 40 μm aluminum (Al) wires spaced 1 mm apart driven by ∼150 kA peak current pulses with 100 ns rise time. The wire plasma was backlit by the 1.4–1.6 keV continuum radiation produced by a Mo wire X-pinch. The spectrometer employed two spherically bent quartz crystals to record the absorption and backlighter spectra simultaneously. The transition between the dense Al wire core and the coronal plasma is seen as a transition from cold K-edge absorption to Mg-, Na-, and finally Ne-like absorption at the boundary. In the plasma that accumulates between the wires, ionization states up to C-Like Al are observed. The spectrometer geometry and ∼2μm X-pinch source size provide 0.3 eV spectral resolution and 20 μm spat...