June 18, 2008

X18A Outfitted with New Equipment

Beamline X18A, originally a scattering and diffraction participating research team (PRT) beamline, is undergoing its first major upgrade in 20 years, with a new energy-scanning monochromator, a new control system and a replacement for its focusing mirror. It is also becoming a facility beamline. This upgrade was done, in part, to satisfy the needs of a new contributing user group from the Synchrotron Catalysis Consortium. X18A will have the ability to perform x-ray absorption spectroscopy measurements, as well as the ability to perform absorption and diffraction on the same samples. It will maintain its full scattering and diffraction capabilities. The ability to perform absorption spectroscopy will help with the oversubscription of general users on X18B.

The new X18A monochromator with adjustable beam stop to the right

Former X7B focusing mirror installed in the X18A mirror bender and chamber

The new monochromator is a Si(111) channel-cut design similar to that at X18B. It will allow accurate scanning of the energy from about 5-40 keV in order to satisfy the new spectroscopy users of the beamline. The original platinum-coated bent, cylindrical focusing mirror was replaced by a similar rhodium-coated one from X7B with a smaller cylinder radius in order to raise the energy cutoff from 12 to 25 keV. The control system for X18A has been upgraded to a PC-based system running SPEC and EPICS. The PC controls a VME crate, which contains motor indexers and scalers. Stepping motors controlling the Huber diffactometer, diffractometer table, and in-hutch slits have been replaced by new stepping motors with built-in microstepping drivers. The beamline will be capable of performing quick-EXAFS measurements like X18B with spectra collected on time scales of seconds. This method is useful for measuring short-term kinetics.

The Lithium Battery Group, from BNL, is also a contributing user group at X18A and will continue to make use of the beamline’s diffraction capabilities.