Development of beamline U3A for AXAF synchrotron reflectivity calibrations

Abstract

We discuss the development ofbeamline U3A at NSLS for AXAF telescope witness mirror reflectivity calibrations in the 1 -2 keV energy range. The beamline was originally constructed as a white light beamline and has been upgraded with the addition of a monochromator to meet the needs ofthe AXAF calibration program. The beamline consists of an upstream horizontally focussing gold coated elliptical mirror, a differential pumping section, a sample/filter chamber, a monochromator and a downstream filter set. The mirror is set at a 2 degree incident angle for a nominal high energy cutoff at 2 keV. The monochromator is a separated element, scanning, double ciystal/ multilayer design having low to moderate energy resolution. A fixed exit beam is maintained through the 7-70 degree Bragg angle range by longitudinal translation ofthe second scanning ciystal. Tracking is achieved by computer control ofthe scan motors with lookup table positioning ofthe crystal rotaiy tables. All motors are in vacuum and there are no motional feedthroughs. Several different multilayer or crystal pairs are co-mounted on the monochromator crystal holders and can be exchanged in situ. Currently installed are a W/Si multilayer pair (N60, 2d=75A), beiyl (2d=15.96A), and Na-3 alumina (2d=22.53A) allowing energy coverage from 180 eV to 2000 eV. Measurements th Na-f alumina and beryl show that beam impurity less than 0. 1% can be achieved in the 1-2 keV energy range. Measured resolving powers are E/i1E60 for W/Si, 500 -800 for alumina and 1500 to 3000 for beiyl. Initial results suggest that signal to noise and beam purity are adequate in the 1-2 keV region to achieve the 1% calibration accuracy required by AXAF. This allows overlap oflr MV edge data taken on x-ray beamline X8A and with low energy data taken on ALS beamline 6.3.2.