First SwissFEL Mirror Units ready to take X-rays
On May 11, 2017 the vacuum chambers of the first two offset mirrors have been closed eventually with the final gold- wire gasket and pumped down to ultra- high vacuum (goal: 1e-9 mbar). These mirrors are the key elements to switch the X-rays between the experimental stations. In pink beam mode they are the only optical elements for the X-rays on their way from the undulator to the Alvra experiment.
The optical surface of the mirrors is 630 mm long, the material is single crystal silicon with two coating stripes- on one side a bilayer B4C/SiC and a bilayer B4C/Mo on the other side. The mirrors have an almost perfectly flat surface (radius > 1000 km, rms figure error < 3 nm). The mirrors are mounted in a two-element mechanical bender to bend them to a cylindrical shape (minimum radius about 10 km). The whole setup is adjustable by remote control in 5 degrees of freedom with micrometer and nanoradian precision inside ultra high vacuum.
During the last months the mirror units with all their sub-components have been extensively tested on air and in vacuum. We measured the quality of the mirror substrate after delivery, then the mirror has been mounted in a motorized mechanical bender. The bender system has been calibrated with a Long-Trace Profiler in the metrology laboratory at SLS. In parallel the vacuum chamber and granite support structure has been installed at the final position in the optics tunnel of the Aramis beamline. On February 17, 2017 we installed the first bender mechanics in the vacuum vessel (see picture). Afterwards followed an intensive debugging and commissioning period of the internal and external wiring and controls system, the final survey and test of all functions in vacuum with a preliminary viton gasket.