First Optics Enclosure

The First Optics Enclosure (FOE), as the name implies, is the first enclosure or station the X-ray beam encounters on the experimental floor of the APS in our sector. It houses most of the beam conditioning optics, which prepare the high-power X-ray for a particular experiment.

The integral shutter is the ‘light switch’ of the FOE, controlling whether or not the beam is allowed to propegate downstream to an experiment. It can also act as a secondary thermal dump.

The Bremsstrahlung collimator is a sefety device that stops high-energy bremsstrahlung gamma rays produced in the storage ring from propegating to the experimental floor.

The Bruker Mirror System is used for (vertical) beam focusing and for harmonic rejection. It consists of two mirrors: The first is a 16-segment bimorph mirror. Differential Adjustment of voltages on the mirror segment allow for fine control of the mirror shape, providing vertical focusing at any selected location within any of the three experimental stations. Also, the mirror provides high harmonic suppression. The second is a flat silicon mirror. It provides additional high harmonic suppression and returns the beam reflected off the first mirror to horizontal (parallel to the undulator beam) trajectory.

Thermal Dump: Since most of the high-power beam is transmitted through the diamond crystals in the monocromator, a high-power beam stop is necessary to terminate the polychromatic and protect downstream components.

The L5-92 Power-limiting apertures limit the size of the x-ray beam accepted by the monochromator, thus controlling the power loading. They can be remotely controlled during an experiment in order to optimizet the photon flux while minimizing the power loading.

The Beryllium Windows is a special polished and cooled high heat-load Be window that is transparent to x-rays. X-ray beam is transmitted retaining all the original properties of the undulator. Its purpose is to isolate the vacuum in the FOE from the vacuum in the shielded beam transport.

The Bruker high heat-load Monochromator produces beam from the polychromatic beam generated by the undulator, using cryogenically cooled (LN2 temperature) silicon crystal pairs in Bragg-Bragg geometry. Si (111) and Si (311) crystal pairs are used. The energy range is 5-36 keV with Si (111), and 9-70 keV with Si (311).

The Differential pump isolates the vacuum in the storage ring from the vacuum in the beamline.