November 20, 2008

Design of High-Energy X-Ray Beamline X17A Progressing

The demand for experimental capabilities using high-energy x-rays has been historically high at the NSLS. Currently, the NSLS provides high-energy x-rays to users at beamline X17B1 and to the two dedicated high-pressure end stations X17B2 and X17B3. An increasing demand for beam time at these beamlines has encouraged the NSLS to evaluate use of a larger fraction of the horizontal fan of the X17 superconducting wiggler, leading to the decision to build a beamline for high-energy x-ray scattering at the A-port of X17.

X17A will be a beamline optimized for x-ray total scattering and atomic pair distribution function (PDF) experiments. A side-scattering (511) silicon Laue monochromator will be installed in the X17A path, immediately downstream of the existing X17A safety shutter, providing x-rays of 75 keV. Bending of the monochromator crystal in two directions is being investigated. If this can be done practically within useful limits, the new X17A monochromator will allow vertical and horizontal focusing of the beam to a spot size of 0.5 mm × 0.5 mm. A new experimental hutch will be built on the outboard side of the X17B1 hutch, near X16B.

The scientific focus of X17A will be the structural characterization of disordered, nanocrystalline and complex nanostructured bulk materials at ambient and extreme environmental conditions. The conceptual design for the experimental end station features a goniometer with a large accessible space at the sample position and the capability to support high loads for heavy sample environments, such as cryostats and Paris-Edinburgh type pressure cells. An automatic image-plate detector will be used to collect the total scattering data.

It is also planned to use a robotic sample changer allowing a high-throughput operation at ambient conditions and in combination with a cold gas blower in the temperature range from 80 K to 300 K. This will allow automatic measurement of a multitude of samples with variable composition, e.g. solid solutions or doped materials, and a detailed exploration of phase diagrams at low temperatures.

Prototypes of the beamline's sagittally bent crystals will be constructed and tested in the coming months. Completion is expected in 2010.

Construction of the X17A beamline will be funded by the NSLS, whereas the experimental end station will be funded through contributions from Brookhaven's Condensed Matter Physics & Materials Science Department and Columbia University.