SYNCHROTRON CRYSTALLOGRAPHY BEAMLINE X9A STRUCTURE FUNCTION STUDIES

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The NSLS, in collaboration with SPring-8, Japan, has designed, built and tested a prototype small-gap undulator, whose compactness allows it to reside between the rf cavities that exist at X9 and X29. This prototype in-vacuum undulator (IVUN), with a period of 11 mm, a minimum useful gap of 3.3 mm (maximum of 10 mm) and a magnetic field of 0.678 T is currently installed in the straight section for beamline X13. These parameters lead to a measured fundamental at 4.6 keV, second harmonic at 8.7 keV, and a third harmonic at 13.9 keV. The brightness of IVUN is comparable (slightly higher) than the X25 wiggler. Since its brightness is significantly less than that of the APS devices, the corollary is that the spectral width is greater, in fact sufficient to perform a MAD experiment around selected absorption edges if the peak energy is carefully selected. The X13 undulator will provide the basis for the design and construction of a completely dedicated small-gap undulator station for MAD data collection at the Se edge at NSLS. The availability of such a facility will greatly increase the total number of MAD days available to the scientific community and will serve as a model for the further development and implementation of small-gap undulators as major resources in structural, molecular and cellular biology.