CHESS East
F-Cave

NIGMS Funds Upgrade to Macromolecular Crystallography Beamlines

The CHESS wiggler stations have certainly been among the most, if not the most productive macromolecular beamlines in existence. For more than a decade MacCHESS and CHESS have pioneered many aspects of modern protein crystallography at storage rings and have helped catalyze the present biostructure revolution. Structural biology at CHESS has been tremendously successful and now utilizes three out of our four highest intensity wiggler stations. These stations are oversubscribed by about a factor of three.

To help satisfy the growing demand for crystallography facilities, the National Institute of General Medical Sciences (NIGMS) has provided funds to CHESS to upgrade the high intensity A1, F1 and F2 experimental stations. The goal of this multiyear upgrade program is to provide biological user with higher quality x-ray beams and facilities – first and foremost to deliver x-ray beam with higher intensity, better energy resolution, tunability and stability. In 1999 we are redesigned and replaced the x-ray optics room, housings, and monochromator optics on the F1 and F2 stations. A new collimating mirror filters the high power white beam and reduces the enormous heat load on the x-ray monochromator crystals. A faster computer network and more reliable software and computer equipment will enhances data collection.

Front End Optics at Wiggler Beam Lines

With the continued increase in CESR currents, the front-end x-ray optics at A- and F- wiggler lines at CHESS required considerable redesign and improvements. The F-line front-end is has been rebuilt and has a new water-cooled white-beam mirror as the first optical element. This mirror serves two crucial functions. First, it operates as a power filter so that the heat loads at F1 and F2 monochromator crystals are cut down by two-thirds. Second, the mirror can be vertically bent to make the x-ray beam more parallel, increasing the energy resolution for MAD experiments by about a factor of two at the F2 station without any significant loss of x-ray flux.

The redesigned new F-line also employs separate vacuum-compatible boxes for monochromators and mirrors to reduce the heat-load interference among crucial optical components. The double-bounce energy-tunable monochromator for F2 has been completely redesigned and will be more suitable for rapid energy changes used by MAD crystallographers. Also, longer focusing mirrors for F1 and F2 with state-of-the-art optical flatness that is at least a factor of two better than the current ones. New shielding walls of the F-cave area increase the attenuation of neutron radiation by an order of magnitude, which is necessary with the CESR current increases. A new capability was added to the F3 bend-magnet station so that focusing multilayer monochromators can be installed and operated with ease.

Optics Developments for MAD at CHESS

The optics for the F2 station have been re-designed to be optimized for work in the quickly growing field of MAD crystallography. A monochromator, along with a  collimating white beam mirror located upstream on F-line, provides many advantages for MAD experiments. The upstream mirror reduces heat load by two-thirds and increases the energy resolution at the MAD experiment to its source-size limit. A set of Si(220) crystals, when used with the upstream mirror, provides energy resolution at the core-hole limit for Se. The single rotation stage monochromator is able to change wavelengths quickly and reliably. Separated vacuum chambers for each optical element involved in MAD work greatly reduces energy drifts due to thermal 'cross-talk' between these components. A real time energy/position monitoring system quickly diagnoses and compensates for any drift in x-ray beam energy or position caused by particle beam motion.

Last Update: 2006-09-21