Detailed diffraction imaging of x-ray optics crystals with synchrotron radiation.

Rocking curve topography at the Advanced Photon Source's beamline 1-BM measures the x-ray reflection from large (many cm2) flat crystals on a sub-mm scale with microradian angular resolution. The (011̄1) reflection at 8 keV is uniform across the crystal and close to theory for three thick quartz wafers well-polished with increasingly finer grit. However, the reflection is non-uniform for some ∼0.1 mm thin, bendable crystals that are made flat by optical contact with a flat substrate. These thin crystals are bent to serve in certain x-ray diagnostics of plasmas, and similar non-uniformities could then occur in bent crystals as well. The same detail in x-ray reflection in bent crystals is unachievable with the existing topography setup: One way to get the desired resolution is with a standard microfocusing approach.

On evaluating x-ray imaging crystals with synchrotron radiation.

Bent crystals used in diagnostics of plasmas combine x-rays diffracted from across the crystal. Therefore imperfections in the resulting 1-D spectrum or 2-D image are not the best way to find out why one particular crystal may differ in its performance from another and what, if anything, to do about it. Instead, here we want to measure the diffraction locally, with the necessary resolution. Nominally monochromatic and unidirectional radiation from the synchrotron's standard x-ray optics proved to be insufficient for the purpose. Here much better radiation comes from the x-ray topography setup at the x-ray optics testing beamline 1-BM at the Advanced Photon Source, thanks to a specially designed quartz conditioning crystal. Some worrisome features in a bent crystal's diffraction have thereby disappeared, while minor fabrication flaws remain highly visible.

Spatial resolution of a spherical x-ray crystal spectrometer at various magnifications.

A high spatial resolution of a few µm is often required for probing small-scale high-energy-density plasmas using high resolution x-ray imaging spectroscopy. This resolution can be achieved by adjusting system magnification to overcome the inherent limitation of the detector pixel size. Laboratory experiments on investigating the relation between spatial resolution and system magnification for a spherical crystal spectrometer are presented. Tungsten Lß2 rays from a tungsten-target micro-focus x-ray tube were diffracted by a Ge 440 crystal, which was spherically bent to a radius of 223 mm, and imaged onto an x-ray CCD with 13-µm pixel size. The source-to-crystal (p) and crystal-to-detector (q) distances were varied to produce spatial magnifications (M = q/p) ranging from 2 to 10. The inferred instrumental spatial width reduces with increasing system magnification M. However, the experimental measurement at each M is larger than the theoretical value of pixel size divided by M. Future work will focus on investigating possible broadening mechanisms that limit the spatial resolution.

Spherical quartz crystals investigated with synchrotron radiation.

The quality of x-ray spectra and images obtained from plasmas with spherically bent crystals depends in part on the crystal's x-ray diffraction across the entire crystal surface. We employ the energy selectivity and high intensity of synchrotron radiation to examine typical spherical crystals from alpha-quartz for their diffraction quality, in a perpendicular geometry that is particularly convenient to examine sagittal focusing. The crystal's local diffraction is not ideal: the most noticeable problems come from isolated regions that so far have failed to correlate with visible imperfections. Excluding diffraction from such problem spots has little effect on the focus beyond a decrease in background.

Compact focusing spectrometer: visible (1 eV) to hard x-rays (200 keV).

A low-cost spectrometer that covers a wide range of photon energies can be useful to teach spectroscopy, and for simple, rapid measurements of the photon spectrum produced by small plasma devices. The spectrometer here achieves its wide range, nominally from 1 eV to 200 keV, with a series of spherically and cylindrically bent gratings or crystals that all have the same shape and the same radius of curvature; they are complemented by matching apertures and diagnostics on the Rowland circle that serves as the circular part of the spectrometer's vacuum vessel. Spectral lines are easily identified with software that finds their positions from the dispersion of each diffractive element and the known energies of the lines.

A novel zirconium Kα imager for high energy density physics research.

We report on the development and characterization of a zirconium Kα imager for high energy density physics research. The imager consists of a spherically bent quartz crystal operating at 15.7 keV photon energy. We compare the performance of the imager in terms of integrated reflectivity (R(int)) and temperature dependent collection efficiency (η(Te)) to that of the widely used Cu Kα imager. Our collisional-radiative simulations show that the new imager can be reliably used up to 250 eV plasma temperature. Monte Carlo simulations show that for a 25 µm thick tracer layer of zirconium, the contribution to Kα production from photo-pumping is only 2%. We present, for the first time, 2D spatially resolved images of zirconium plasmas generated by a high intensity short pulse laser interacting with Zr solid targets.

X-ray spectropolarimeter.

We have constructed a novel single-crystal x-ray spectropolarimeter that separates spatially the two perpendicularly polarized components of an x-ray beam. We have tested this device by using an x-ray tube, and confirmed its performance to be satisfactory as expected from its design.