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.

First Optics Enclosure

Overview of the First Optics Enclosure (FOE)

The Integral Shutter

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

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.

The Beryllium Window

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 Bremsstrahlung Collimator

is a safety device that stops high-energy bremsstrahlung gamma rays produced in the storage ring from propagating to the experimental floor.

Thermal Dump

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

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 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 optimize the photon flux while minimizing the power loading.

The Differential Pump

isolates the vacuum in the storage ring from the vacuum in the beamline.

Source Parameters

  • X-ray source: APS undulator A, 72 periods, period length 33mm, provides continuous energy coverage from ~3keV to (theoretically) well above 100keV.
  • Electron beam size (σ values): 270μm horizontal, 8.6μm vertical.
  • Electron beam divergence (σ values): 11.4μr horizontal, 2.9μr vertical.
    • Note: The X-ray source dimensions are somewhat larger than the values above, due to radiative effects. The extent of the radiative “bloat” depends on x-ray energy, becoming negligible for high energies.
  • Bruker cryogenically cooled double crystal monochromator, using pairs of Si (111) or Si (311) crystals.
  • Energy range : 5-36keV with Si (111), 10-70keV with Si(311)
  • Bandwidth: 1.3×10-4 with Si (111), 2.8×10-5 with Si (311)
  • Bruker mirror system, consisting of vertically focusing bimorph mirror and vertically deflecting flat silicon mirror. Coated with 3 stripes, as follows:
    • SiO2 – energies below 12 keV
    • Rh – energies between 12-23 keV
    • Pt – energies above 23 keV

Theoretical Flux T​hrough The Working Aperture:

Photon Energy (keV)


Flux (phot/sec/0.1%BW)

10 1 4×1014
30 3 5×1013
50 5 7×1012
70 7 1×1012

Facility Contacts

Mrinal Bera
Anomalous Small and Wide Angle X-ray Scattering
(630) 252-0472

Wei Bu
Liquid Surface/Interface
(630) 252-0470

Natalie Chen
NSF’s ChemMatCARS Sector User and Outreach Coordinator
(630) 252-0476

Yu-Sheng Chen
Advanced Crystallography
(630) 252-0471

Binhua Lin
Executive Director and Project Manager
(630) 252-0463

Mati Meron
Beamline Optics
(630) 252-0478