January 12, 2006

X25 Cryo-Capable Mini-Gap In-Vacuum Undulator Installed in the X-Ray Ring

Some of the X25 MGU project staff gathered around the newly assembled device in the Magnetic Measurements Facility prior to its move to Bldg. 725 (NSLS).

At the start of 2004, beamline X25's programmatic focus shifted completely to monochromatic macromolecular crystallography, following 14 years of operation as a mixed-use high-brightness beamline. Thus, the NSLS was presented with an opportunity to renovate the beamline, as well as the radiation source, to optimize them for a dedicated macromolecular crystallography program. To this end, the BNL Macromolecular Crystallography Research Resource (PXRR), a collaboration between the BNL Biology Department and the NSLS, submitted a funding request in late 2002 as part of its proposal to the National Institutes of Health's National Center for Research Resources and the Department of Energy's Office of Biological and Environmental Research (DOE BER) to renew its five-year grant. The proposal was well received, and $2.2M in funds was awarded by DOE BER beginning in late 2003, to be dispensed over the course of three fiscal years.

January 12, 2006: The new X25 MGU installed in the NSLS x-ray ring.

During the December 2005 shutdown, the original hybrid wiggler, which served as the radiation source for beamline X25 since its inception in 1990, was replaced by a custom-designed in-vacuum miniature-gap hybrid undulator. At a photon energy of 6.3 keV, the new radiation source will be 15 times brighter than the old one, and will be six times brighter at a photon energy of 10.5 keV. Its design consists of 0.99 meter-long planar hybrid magnet arrays with a period length of 18 mm (55 periods total) and a minimum attainable gap of 5.6 mm, with a corresponding maximum deflection parameter, K, of 1.5. The NdFeB-type permanent magnet material, which has been used in this insertion device, can have a higher magnetic field and a higher radiation resistance simply by cooling: Operation at 150K will likely produce a 13-14% higher magnetic field (and higher K), resulting in a larger photon energy tuning range. Therefore, this undulator design also incorporates a provision for cryogenic operation, which might be pursued in the future. Unlike previous miniature-gap undulator designs in use at the NSLS, the one now implemented for X25 will be continuously tunable from 2 to 20 keV by employing all harmonics up through the 9th. The undulator vacuum and gap separation system was manufactured by Advanced Design Consulting of Lansing, New York. In conjunction with the installation of the undulator, certain components in the front end of the beamline, and the active interlock system that protects the x-ray ring exit chamber, were upgraded in order to be able to cope with the much higher power density of the undulator beam.

X-ray burns taken using original wiggler (top) and the new undulator (bottom), in the same location, show that the undulator beam is much smaller than the wiggler beam, as expected.

In addition to the new radiation source, upgrades to the beamline optics will also be implemented in order to exploit the properties of the new source. The current double crystal monochromator will be replaced by one that incorporates cryogenic cooling of the first crystal and sagittal bending of the second crystal to permit horizontal focusing. It will be followed by a new bendable mirror, containing multiple coating stripes, to permit vertical focusing.

Further information about the X25 upgrade can be found at http://www.px.nsls.bnl.gov/x25/upgrade/.

ARTICLE BY: Lonny Berman, for the entire X25 undulator project team