KMC-1: A high resolution and high flux soft x-ray beamline at BESSY

• Published in: Review of scientific instruments 2007-12, Vol.78 (12), p.123102-123102-14
• Main Authors: Schaefers, F., Mertin, M., Gorgoi, M.
• Format: Article
• Language: English
• Subjects: ABSORPTION; ABSORPTION SPECTROSCOPY; BESSY STORAGE RING; CRYSTALS; FINE STRUCTURE; FLUORESCENCE SPECTROSCOPY; HARD X RADIATION; INDIUM ANTIMONIDES; INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; KEV RANGE; KINETIC ENERGY; MAGNETS; MEV RANGE; MONOCHROMATORS; PHOTONS; RESOLUTION; SOFT X RADIATION; X-RAY FLUORESCENCE ANALYSIS; X-RAY PHOTOELECTRON SPECTROSCOPY; X-RAY SPECTROSCOPY
• ISSN: 0034-6748; 1089-7623
• DOI: 10.1063/1.2808334

The crystal monochromator beamline KMC-1 at a BESSY II bending magnet covers the energy range from soft ( 1.7 keV ) to hard x-rays ( 12 keV ) employing the ( n , − n ) double crystal arrangement with constant beam offset. The monochromator is equipped with three sets of crystals, InSb, Si (111), and Si (422) which are exchangeable in situ within a few minutes. Beamline and monochromator have been optimized for high flux and high resolution. This could be achieved by (1) a windowless setup under ultrahigh-vacuum conditions up to the experiment, (2) by the use of only three optical elements to minimize reflection losses, (3) by collecting an unusually large horizontal radiation fan ( 6 mrad ) with the toroidal premirror, and (4) the optimization of the crystal optics to the soft x-ray range necessitating quasibackscattering crystal geometry ( θ Bragg , max = 82 ° ) delivering crystal limited resolution. The multipurpose beamline is in use for a variety of user facilities such as extended x-ray absorption fine structure, ((Bio-)EXAFS) near-edge x-ray absorption fine structure (NEXAFS), absorption and fluorescence spectroscopy. Due to the windowless UHV setup the k edges of the technologically and biologically important elements such as Si, P, and S are accessible. In addition to these experiments this beamline is now extensively used for photoelectron spectroscopy at high kinetic energies. Photon flux in the 10 11 - 10 12 photons ∕ s range and beamline resolving powers of more than E ∕ Δ E ≈ 100.000 have been measured at selected energies employing Si ( n n n ) high order radiation in quasibackscattering geometry, thus photoelectron spectroscopy with a total instrumental resolution of about 150 meV is possible. This article describes the design features of the beamline and reports some experimental results in the above mentioned fields.