Recent Facility Enhancements / Technical Developments

Mbar single crystal diffraction. A new single crystal diffraction technique has been developed at HPCAT, suitable for single crystal diffraction studies at Mbar pressures. The new method allows obtaining crystallographic orientations of over 100 crystallites at Mbar pressures in a coarse-grained polycrystalline samples. A few selected crystallites may be tracked using conventional single crystal structural refinement procedures. The new method opens a door for in situ studying of crystal structures of submicron crystallites in a multiphase polycrystalline sample in a diamond anvil cell. The established technique is a significant step in high pressure diffraction, which may replace the commonly used powder diffraction method in the future.

Phase contrast x-ray imaging.Understanding polymorphs in liquids is fundamental in condensed matter physics, and has attracted a lot of attentions recently. While density driven liquid-fluid transitions have been studied using x-ray absorption contrast imaging, entropy driven liquid-liquid transition have not been directly observed by any means. Using phase contrast imaging, we have successfully observed the separation of two liquid phases in liquid sulfur at high pressures.  Because the phase contrast imaging is sensitive to the refractive index change, it is particularly suitable for studying entropy driven liquid-liquid transitions.

Low Q inelastic x-ray scattering.In the current setup at HPCAT, the low Q is limited to the vicinity of 10 nm-1, due to constraints in geometry and the background from gasket materials. However, low-Q region carries rich dynamics information and is important in studying plasmons in metals, for example. Using a polycapillary optics and a confocal design, we have demonstrated the feasibility of a small Q coverage of 1.5-15 nm-1.

Materials under high strain rate.Recent enabled capabilities at HPCAT allow us to study materials behavior at various strain rates under dynamic compression or decompression. The newly installed canted undulators in combination with the new three crystal liquid nitrogen cooled monochromator deliver an order of magnitude brighter x-ray beam, significantly enhancing the time-resolved capability. The advanced detectors such as Pilatus 1MF allow x-ray measurements at a rate up to 135 Hz in continuous mode and at MHz in gated mode. New loading instruments have been developed at HPCAT for ramp loading and/or unloading at various rates. Both single event loading or unloading and multiple repetitive ramping events may be applied for studying materials properties at different strain rate conditions. Through ramp loading, the pressure changes at a rate of >50Mbar per second, equivalent to a strain rate of ~ 2-3 s-1. Using two ramp compression devices on the opposite sides of a diamond anvil cell, both compression and decompression can be controlled for the desired strain rates.

 

Supporting equipment:

Beam position monitors:Two x-ray beam position monitors have been installed at two HPCAT insertion device beamlines. This device closely monitors the condition of the x-ray beams and ensures the quality of beam delivery all the time. The monitor also provides fast position signals, allowing us to establish feedback systems both for enhancing the beam stability and for designing new x-ray controls, important in future developments in areas such as submicron probes and high energy resolution spectroscopy.

On-line Raman system.A portable optical Raman system has been re-designed to be more flexible for installing in all four HPCAT experimental stations. The established system will be first used in the 16-BM-B station in August, 2013.

New focus KB mirrors.Maximizing flux is a near future goal for 16-ID-B and 16-BM-D. The newly installed KB mirror improves the focus quality, and increases the throughput by a factor of 3, thanks to the newly available mirror polishing technology and the new benders which can accommodate longer mirrors.

Piezo driven cell.Following the development at LLNL, HPCAT has designed a piezo driven “cap” that can flexibly attach to various types of diamond anvil cells. The feasibility test is promising, allowing 1 kHz modulated pressures.