Matt Wallace

X-ray polarization splitting by a single crystal evaluated with synchrotron x-rays

In hexagonal crystals such as quartz, an asymmetric Bragg reflection from two equivalent internal crystal planes can separate unpolarized x-rays into two linearly polarized components. The perfectly polarized and tunable x-rays from a synchrotron are ideal to evaluate polarization spitting in detail. One unanticipated feature is that additional reflections from the crystal affect the diffraction intensity of the two polarized components, an effect that is unlikely to matter in polarization spectroscopy of radiating plasmas for which the crystal is intended.

Spatially resolved single crystal x-ray spectropolarimetry of wire array z-pinch plasmas

A recently developed single-crystal x-ray spectropolarimeter has been used to record paired sets of polarization-dependent and axially resolved x-ray spectra emitted by wire array z-pinches. In this measurement, two internal planes inside a suitable crystal diffract the x-rays into two perpendicular directions that are normal to each other, thereby separating incident x-rays into their linearly polarized components. This paper gives considerations for fielding the instrument on extended sources. Results from extended sources are difficult to interpret because generally the incident x-rays are not separated properly by the crystal. This difficulty is mitigated by using a series of collimating slits to select incident x-rays that propagate in a plane of symmetry between the polarization-splitting planes. The resulting instrument and some of the spatially resolved polarized x-ray spectra recorded for a 1-MA aluminum wire array z-pinch at the Nevada Terawatt Facility at the University of Nevada, Reno will be presented.

Characterizing a polarization splitting quartz crystal

Summary form only given. When energetic electrons inside a plasma have a preferred direction the x-rays emitted by the plasma can be polarized. Information about the electrons and the anisotropy of their velocity distribution can then be revealed by the x-ray spectrums polarization. Polarization typically measured with two crystals at a 45 degrees Bragg, can now be determined in a new way using one crystal. This crystal utilizes two sets of planes that diffract the incident x-rays in two directions that are perpendicular to each other and to the incident beam1. These diffracted x-rays are then linearly polarized perpendicularly to each other. The polarization splitting properties of quartz crystals were confirmed with the linearly polarized x-rays from the Advanced Photon Source. A crystal with surface cut [10-10] that splits polarization with [11-20] planes at 7.15 keV was among those tested. Bragg reflections at 45 degrees from the crystals [10-10] surface planes was then tested with x-rays from conical wire array z-pinches. These tests were aimed to verify the reflectivity of the planes intended for single crystal spectropolarimetric measurements in upcoming experiments.

Electron beams and x-ray emission of conical wire array Z-pinches

Summary form only given. It is well known that intense beams of energetic electrons are accelerated in z-pinches. Using magnetic deflection and Faraday cup detection we measured electron energies and the current of beams produced in conical wire array z-pinches and x-pinches. The variations in pointing and divergence of the beams reduced the accuracy of these measurements. However, the beam activity can be correlated with the x-ray emission of the z-pinches. We will present results of these measurements.

Characterization of a crystal for x-ray spectropolarimetric plasma diagnostics

Summary form only given. A well-known feature in many otherwise thermal plasmas is an energetic electron component, whose origin and properties remain to be fully understood. When the energetic electrons have a preferred direction, the X-rays created by the beam can be polarized. In turn, information about the anisotropic electron energy distribution can be obtained from the X-ray spectrums polarization, and a polarization-containing plasma radiation model. A promising way to perform the appropriate spectropolarimetry uses a crystal that contains two equivalent sets of planes under 120 degrees with each other. These diffract, for a given wavelength, an incident X-ray beam in two directions perpendicular to this beam and to each other.The diffracted X-rays are then linearly polarized perpendicular to each other. The polarization-splitting properties of a quartz crystal cut along the (10-10) plane and diffracting from two (11-20) planes were confirmed with synchrotron radiation from the Advanced Photon Source at the Argonne National Laboratory. The crystal characteristics and requirements for its use to diagnose electron beams in zpinch plasmas will be presented.

2D spatially resolved spectroscopic diagnostics using a single convex crystal

2D X-ray imaging spectroscopic diagnostics is an advanced plasma diagnostics tool, providing a way to determine the spatial dependence of plasma temperature and density (Te and ne) in hot plasmas. This can be accomplished with the usual spectroscopic diagnostics methods by taking advantage of the spatial information contained in the broad energy range spectra recorded by convex crystal spectrometers. The sensitivity of these instruments to the size of the X-ray source has long been noted, mostly as a factor leading to the reduction of the resolving power. Spectra can be spatially resolved by using a slit to create an image of the source in the direction perpendicular to the spectral dispersion. In the case of such spectra recorded by convex crystal spectrometers, it is often noted that the shape of the lines themselves, as recorded on a medium, resembles the shape of the plasma source as obtained, for example, with pinhole imaging. This provides some crude resolution perpendicular to the spectral line. We propose to use this effect for a new diagnostics technique that allows 2D spatially resolved spectroscopy of the X-ray source. Modeling the plasma emission spectrum by the PrismSPECT code allowed the identification of suitable spectral features to determine ne and Te. For an Al-Mg wire array z-pinch, the optically thin Mg lines can be used. We applied the principles of this method to get a temperature distribution map for a z-pinch from the shape of the Mg K-shell lines recorded by a convex KAP sprectrometer. The spatial resolution can be improved by deconvolving the plasma broadened line profiles from the lineshapes recorded by the convex crystal spectrometer. To obtain lineshapes with minimum instrumental broadening, a concave cylindrically bent KAP crystal spectrometer was designed.2D X-ray imaging spectroscopic diagnostics is an advanced plasma diagnostics tool, providing a way to determine the spatial dependence of plasma temperature and density (Te and ne) in hot plasmas. This can be accomplished with the usual spectroscopic diagnostics methods by taking advantage of the spatial information contained in the broad energy range spectra recorded by convex crystal spectrometers. The sensitivity of these instruments to the size of the X-ray source has long been noted, mostly as a factor leading to the reduction of the resolving power. Spectra can be spatially resolved by using a slit to create an image of the source in the direction perpendicular to the spectral dispersion. In the case of such spectra recorded by convex crystal spectrometers, it is often noted that the shape of the lines themselves, as recorded on a medium, resembles the shape of the plasma source as obtained, for example, with pinhole imaging. This provides some crude resolution perpendicular to the spectral line. We propose to use this effect for a new diagnostics technique that allows 2D spatially resolved spectroscopy of the X-ray source. Modeling the plasma emission spectrum by the PrismSPECT code allowed the identification of suitable spectral features to determine ne and Te. For an Al-Mg wire array z-pinch, the optically thin Mg lines can be used. We applied the principles of this method to get a temperature distribution map for a z-pinch from the shape of the Mg K-shell lines recorded by a convex KAP sprectrometer. The spatial resolution can be improved by deconvolving the plasma broadened line profiles from the lineshapes recorded by the convex crystal spectrometer. To obtain lineshapes with minimum instrumental broadening, a concave cylindrically bent KAP crystal spectrometer was designed.