Test Results of GSECARS Large KB Mirror Focusing System
On Friday August 24th 2001 on GSECARS sector 13 we successfully double focused a 12.7 keV x-ray beam produced by APS Undulator “A” to a size of 61.4um x 13.4mm fwhm (H x V) using the GSECARS designed “Large KB Mirror Focusing System”. The total flux density gain was equal to 1,232 with an ion chamber current (when using the 3rd harmonic) of approximately 5 mA!
The de-magnification in the horizontal and vertical direction was 10.9 and 7.5 respectively. Assuming the FWHM source size to be 700 mm x 45 mm (H x V) the geometric ideal focus size would be 64 mm x 6.0 mm. Based on our focusing tests we are perfectly focusing the beam in the horizontal and in the vertical have a mirror with an effective figure error of 0.4 mrad. It is interesting to note that the vertical mirror was measured using the APS LTP to have a rms slope error of 0.8 mrad over its 700mm optical surface indicating the rms value represents an upper limit to mirror performance with some of the surface “waviness” helping to match the proper figure when bent.
We operated both mirrors at an incidence angle of 2.5 mrad. At this angle the horizontal mirror with its optical length of 1.0 m has an available entrance aperture of 2.5 mm. We defined the beam in front at the mirror with slits to width of 1.0 mm (the FWHM size of the horizontal source divergence at the mirror located at 46.6m is 2.3 mm) about 74% of the beam. The horizontal focus resulted in a flux density gain of 28. The vertical mirror has an optical length of 0.7 m resulting in an available entrance aperture of 1.76 mm. The beam was slit to 1.0 mm effectively collection 100% of the vertical divergence at the mirror located 44.6 m from the source. Plots of horizontal and vertical scans through the beam show the profiles fit well to a Gaussian line shape indication that there is very little tail coming from the main focus and we are doing a good job at imaging the source (there is a weak diffuse scattering cross centered on the focused beam caused by the few Angstrom RMS surface roughness, that can be remove by placing “clean-up” slits close to the sample.)
Image of double focused 12.7 keV Undulator “A” beam: 61.4 mm wide by 13.4 mm tall. The image was produce by projection the beam onto a thin YAG single crystal that produces visible imaged with a 20X objective coupled to 1k x 1k cooled CCD camera with an effective resolution of about 3 mm. About 74% of the full undulator harmonic is included in the focused beam.
GSECARS ID SOE (13ID-B) showing GSECARS designed “Large KB Mirror Focusing System”. The vertical mirror is 1m long with an optical aperture 0.7m long, the horizontal mirror is 1.2m long with optical aperture 1.0m long both mirrors are enclosed in a UHV environment (<10-9 torr.) The mirrors are internally water-cooled capable of accepting white beam, with a pair of bending holes through the width of each end of the mirrors. These holes are used to apply a linear bending moments profile to length of the mirror with the GSECARS UHV mirror bender allowing the optic to be dynamic figured.