Von Hamos Geometry Research Articles

Mapping the ionization state of laser-irradiated Ar gas jets with multiwavelength monochromatic x-ray imaging

Two-dimensional monochromatic images of fast-electron stimulated Ar Kα and He-α x-ray self-emission have recorded a time-integrated map of the extent of Ar(≈6+) and Ar(16+) ions, respectively, within a high density (10(20) cm(-3) atomic density) Ar plasma. This plasma was produced by irradiating a 2 mm wide clustering Ar gas jet with an ultrahigh intensity (10(19) W/cm(2), 50 TW) Ti:sapphire laser operating at 800 nm. Spherically bent quartz crystals in the 200 (for Kα) and 201 (for He-α) planes were used as near-normal incidence reflective x-ray optics. We see that a large (830 μm long) region of plasma emits Kα primarily along the laser axis, while the He-α emission is confined to smaller hot spot (230 μm long) region that likely corresponds to the focal volume of the f/8 laser beam. X-ray spectra from a Bragg spectrometer operating in the von Hamos geometry indicate that the centroids of the Kα and He-α emission regions are separated by approximately 330 μm along the laser axis.

Evolution of elastic x-ray scattering in laser-shocked warm dense lithium

We have studied the dynamics of warm dense Li with near-elastic x-ray scattering. Li foils were heated and compressed using shock waves driven by 4-ns-long laser pulses. Separate 1-ns-long laser pulses were used to generate a bright source of 2.96 keV Cl Ly- alpha photons for x-ray scattering, and the spectrum of scattered photons was recorded at a scattering angle of 120 degrees using a highly oriented pyrolytic graphite crystal operated in the von Hamos geometry. A variable delay between the heater and backlighter laser beams measured the scattering time evolution. Comparison with radiation-hydrodynamics simulations shows that the plasma is highly coupled during the first several nanoseconds, then relaxes to a moderate coupling state at later times. Near-elastic scattering amplitudes have been successfully simulated using the screened one-component plasma model. Our main finding is that the near-elastic scattering amplitudes are quite sensitive to the mean ionization state Z[over ] and by extension to the choice of ionization model in the radiation-hydrodynamics simulations used to predict plasma properties within the shocked Li.

Spectrally resolved X-ray scatter from laser-shock-driven plasmas

We report spectrally resolved X-ray scattering data from shock compressed foils illustrating the feasibility of X-ray Thomson scattering experiment on a sub-kilo joule laser system. Sandwich targets consisting of CH/Al/CH were shock compressed using ∼1 ns laser pulses. Separate 270 ps laser pulses were used to generate an intense source of Ti-He-α (1s2-1s2p1P) radiation which was used as a probing source of 4.75 keV photons. The spectrum of scattered photons was recorded at a scattering angle of 82° with a CCD fitted spectrometer using a PET crystal in von-Hamos geometry. Although spectral resolution was used to separate the scatter from any background, the resolution was limited by source broadening. The relative level of scatter at different times in the sample history was measured by varying the delay between the shock driving beams and the back-lighter beams. We have compared the scatter spectra with simulations based on two different models of the L-shell bound-free contribution.

Chemical effects in the Kβ X-ray emission spectra of sulfur

In this work our previous study about chemical effects in the Kα spectra of S compounds employing high-resolution X-ray spectroscopy has been extended to the Kβ emission spectra. The measurements were performed with a wavelength dispersive single crystal spectrometer operated in the von Hamos geometry having an energy resolution comparable to the natural linewidth of the measured Kβ X-ray lines. The target fluorescence was produced by irradiating the samples with the bremsstrahlung from an X-ray tube. The energies and widths of the main components in the Kβ emission spectrum are given for different sulfur compounds (sulfide, sulfite, sulfate). The measured energy shifts between the Kβ lines of the compounds and elemental sulfur are presented as a function of the sulfur oxidation state and compared with the results obtained from the former Kα measurements.

Ion-induced X-ray studies with a high luminosity von Hamos crystal spectrometer

A high-resolution, high-efficiency, von Hamos geometry, Bragg crystal X-ray spectrometer has been developed and mounted on a beamline at the Holifield Heavy Ion Research Facility at the Oak Ridge National Laboratory. Measurements have been made of K and L X-rays emitted from a variety of targets and projectiles. Instrument performance characteristics are reported here along with spectra from fast projectile ions and very low intensity target emission — areas of measurement for which this spectrometer is especially suitable.

Advances in High-Resolution Studies of the Chemical Effects in the Molybdenum L Heavy-Ion-Induced X-Ray Satellite Emission (HIXSE) Spectra*

AbstractHigh-resolution measurements of the molybdenum L heavy-ion-induced X-ray satellite emission (HIXSE) spectra of a series of Mo alloys and compounds have been obtained with a new, high-efficiency, high-resolution Bragg crystal spectrometer in the von Hamos geometry. The improved resolution (5 eV at 2.3 keV) is sufficient to reveal the LnMm configuration lines in the Lα and Lβ hypersatellite bands. Both sets of lines exhibit the same trend in the variation of the relative yield distribution with the chemical environment as was observed for KLn lines of lower Z targets. Difference spectra, using elemental molybdenum as a subtrahend, enhance the systematic variation. These results confirm the analysis and conclusions of lower resolution studies. They also indicate a potential for even greater sensitivity to the chemical environment.