multi-keV X-ray Research Articles

Multi-keV x-ray conversion efficiencies of laser-preexploded titanium foils

In the context of target design for multi-keV x-ray laser-produced experiments, the concept of exploding metallic thin foils by two laser pulses delayed in time has been tested at the OMEGA laser facility [J. M. Soures, R. L. McCrory, C. P. Verdon et al., Phys. Plasma 3, 2108 (1996)]. The first laser pulse creates an underdense plasma (ne∕nc≈0.2), and the second laser pulse heats the plasma plume which produces strong line emission from the titanium K shell (Heα at 4.7 keV and Hα at 4.9 keV). Six OMEGA beams (500-ps duration) for the prepulse and nine beams (1-ns duration) for the heating pulse irradiate one side of the foil. Different experimental conditions have been investigated in order to optimize the conversion efficiency enhancement on titanium foils. The influences of the foil thicknesses (5 and 6 μm), the delays (3, 4, and 5 ns) between the laser pulses, and the laser intensities (1.3 and 2.2×1015Wcm−2) have been tested. The absolute output power was measured by a set of filtered x-ray diodes, giving conversion efficiencies (CEs) up to 3.6% in 2π for energies above 4 keV with a preformed plasma, to be compared to the case without a prepulse where the CE is 1.5%. This double-pulse concept in this case shows an increase of CE by a factor of 2.4 for titanium thin foils. CE up to 4.9% has been reached with a laser intensity of 2.2×1015Wcm−2.

Characteristics of a multi-keV monochromatic point x-ray source based on vacuum diode with laser-produced plasma as cathode

Temporal, spatial and spectral characteristics of a multi-keV monochromatic point x-ray source based on vacuum diode with laser-produced plasma as cathode are presented. Electrons from a laser-produced aluminium plasma were accelerated towards a conical point tip titanium anode to generate K-shell x-ray radiation. Approximately 1010 photons/pulse were generated in x-ray pulses of ∼18 to ∼28 ns duration from a source of ∼300 μm diameter, athυ = 4.51 keV (K α emission of titanium), with a brightness of ∼1020 photons/cm2/s/sr. This was sufficient to record single-shot x-ray radiographs of physical objects on a DEF-5 x-ray film kept at a distance of up to ∼10 cm.

Efficient multi-keV X-ray sources from Ti-doped aerogel targets.

We have measured the production of hnu approximately 4.7 keV x rays from low-density Ti-doped aerogel (rho approximately 3 mg/cc) targets at the OMEGA laser facility (University of Rochester), with the goal of maximizing x-ray output. Forty OMEGA beams (lambda(L)=0.351 microm) illuminated the two cylindrical faces of the target with a total power that ranged from 7 to 14 TW. The laser fully ionizes the target (n(e)/n(crit)</=0.1), and a laser-bleaching wave excites, supersonically, the high-Z emitter ions in the sample. Ti K-shell x-ray emission was spectrally resolved with a two-channel crystal spectrometer and also with a set of filtered aluminum x-ray diodes; both instruments provide absolute measurement of the multi-keV x-ray emission. We find between 40 and 260 J of output with 4.67</=hnu</=5.0 keV.

X-ray scattering from solid density plasmas

Measurements of the microscopic properties of dense matter have been demonstrated by applying spectrally resolved multi-keV x-ray scattering. The scattering spectra from solid density beryllium show the inelastic Compton-down shifted feature that is spectrally broadened when heating the solid density plasmas isochorically and homogeneously to temperatures of several times the Fermi energy. The spectral shape of the inelastic scattering component provides an accurate measurement of the temperature, and the intensity ratio of inelastic to elastic scattering measures the ionization balance. These measurements extend the powerful technique of Thomson scattering [S. H. Glenzer et al., Phys. Plasmas 7, 2149 (1999)] to the x-ray regime for independent measurements of the plasma parameters of solid density and super dense laboratory plasmas. This new technique has wide applications to investigate the previously inaccessible regimes of dense matter, from Fermi degenerate, to strongly coupled, to high temperature ideal gas plasmas.

Multi-keV x-ray conversion efficiency in laser-produced plasmas

X-ray sources are created at the Nova and Omega laser by irradiating a confined volume of Ar and Xe gas. The gas is heated by 20–35 kJ of 0.35 μm laser light and becomes a highly ionized mm-sized x-ray source which emits K-shell or L-shell x rays. The radiator is “underdense,” meaning that the initial electron density is lower than the critical density of the laser, nc∼1022 cm−3. It is heated primarily by inverse bremsstrahlung, which produces a supersonic ionization wave. In this paper, x-ray conversion efficiency and imaging from time-resolved and time-integrated diagnostics are compared over a range of experimental parameters. This work represents an important, new method for development of efficient, large-area, tailored multi-keV x-ray sources.

The X-ray microscopy project at Saga SLS

A new high resolution X-ray microscopy project has been proposed at Saga synchrotron light source, which is a third generation synchrotron light facility in Japan. Two microscopy beamlines are planned for this project. One is a scanning microscope in the water window region, and the other is a full-field imaging microscope in the multi-keV X-ray energy region. To demonstrate the feasibility of the project, the optical layout of the scanning microscope was designed. The beamline mainly consists of a 3.5 cm periodical undulator, a varied line-spacing plane grating monochorometer (600 lines/mm) and an end-station including a zone plate. Thus, the calculated X-ray properties focused on the sample position are as follows: the spot size is ∼70 nm, the monochromaticity is -2000, and the photon flux is 10 9 ∼ 10 10 photons/sec.

Femtosecond x-ray measurement of ultrafast melting and large acoustic transients.

Time-resolved x-ray diffraction with ultrashort ( approximately 300 fs), multi-keV x-ray pulses has been used to study the femtosecond laser-induced solid-to-liquid phase transition in a thin crystalline layer of germanium. Nonthermal melting is observed to take place within 300-500 fs. Following ultrafast melting we observe strong acoustic perturbations evolving on a picosecond time scale.

Recent progress in high-energy, high-resolution x-ray imaging techniques for application to the National Ignition Facility (invited)

Multi-keV x-ray microscopy will be an important laser-produced plasma diagnostic at future megajoule facilities such as the National Ignition Facility (NIF). However, laser energies and plasma characteristics imply that x-ray microscopy will be more challenging at NIF than at existing facilities. In earlier work, we concluded that target-mounted pinholes and single spherical or toroidal crystals are good options for many x-ray microscopy applications at NIF. In this article, we review the experimental progress we have made investigating these systems on the Nova and Petawatt Laser Facilities. In particular, we have performed high-resolution, high-magnification target-mounted pinhole imaging of Nova implosions, and we have obtained promising preliminary spherical-crystal data from high-intensity Petawatt experiments. We are also designing a high-energy spherical-crystal imager for use on Nova experiments.

X-ray emission from vibrating white dwarfs

view Abstract Citations (16) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS X-ray emission from vibrating white dwarfs. Katz, J. I. ; Salpeter, E. E. Abstract It had been proposed previously that regularly pulsating X-ray sources (Cen X-3 and Her X-1) may be the result of vibrating white dwarfs sending shock waves into their atmospheres. We investigate the hydrodynamics and X-ray production of such objects. The relevant parameters are discussed, and detailed numerical calculations are carried out for a series of cases. The results depend very strongly on whether the parameter values are physically realizable or not. The photospheric radiation flux cools hot atmospheric material by Compton recoil. For physically reasonable amplitudes of oscillation a mismatch between the stellar oscillation and the acoustic response of the atmosphere makes energy coupling to the atmosphere very inefficient. These two effects lead to multi-keV X-ray powers many orders of magnitude too low to explain the observations, in disagreement with earlier work. Publication: The Astrophysical Journal Pub Date: October 1974 DOI: 10.1086/153178 Bibcode: 1974ApJ...193..429K Keywords: Pulsed Radiation; Radiant Cooling; Stellar Atmospheres; Thermal Radiation; White Dwarf Stars; X Ray Sources; Astronomical Models; Atmospheric Temperature; Compton Effect; Hydrodynamics; Photosphere; Radiant Flux Density; Shock Waves; Astrophysics full text sources ADS |