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Light Source

The up to now most elaborate beamline system at BESSY II was necessary for providing EMIL with a wide energy range from 80 to 10000 eV.

A canted double undulator system serves as a light emitter in the storage ring:

  • The soft-X-ray range from 80 to 2300 eV is covered with an APPLE II undulator UE48. This undulator type can provide helical polarised radiation.
  • For tender X-rays from 2000 to 10000 eV a cryogenic, in-vacuum undulator CPMU17 was developed.

The central component of the soft-X-ray branch is a collimated Plane Grating Monochromator  (PGM) equipped with two blazed reflexion gratings. Steering and focusing of the photon beam are performed with a variety of pre- and post monochromator mirrors, so that 4 experimental stations (SISSY-1, SISSY-2, CAT, PEEM) can be served with soft X-rays.

For the tender X-ray branch from 2000 to 10000 eV, a newly developed liquid nitrogen cooled UHV- Double Crystal Monochromator (DCM) is installed. Alternatively, a PGM can be brought into the beam path for using the very intense first harmonic of the CPMU17 in the range from 700 to 1600 eV.

All mirror chambers are of the constant-strut-length hexapod type, a variant of the very stable and versatile Stewart platform. The motion control system consequently uses absolute encoders for length and angle measurements.

enlarged view

Figure 1 layout for the soft X-ray beamlines.

enlarged view

Figure 2 layout for the hard X-ray beamlines.