Swiss Light Source

The Swiss Light Source (SLS) is a synchrotron located at the Paul Scherrer Institute in Switzerland for producing electromagnetic radiation of high brightness. Planning started in 1991, project was approved in 1997, and first light from the storage ring was seen at December 15, 2000. The experimental program started in June 2001 and it is used for research in materials science, biology and chemistry.

Main component of the SLS is the 2.4 GeV electron storage ring of 288 m circumference: The ring is formed by 36 dipole magnets of 1.4 tesla magnetic field, combined in 12 groups of three (triple bend achromat, TBA) for achromatic deflection of the electron beam. 12 straight sections between the TBAs of different lengths (3×11.5 m, 3×7 m, 6×4 m) accommodate the undulator magnets to generate ultraviolet and X-ray light of extreme brightness. 3 of the dipoles have an increased center field of 3 tesla to produce hard X-rays. A total of 177 quadrupole magnets (magnetic lenses) focuses the beam to provide a beam emittance of 5.5 nm rad. 120 sextupole magnets correct the chromatic focusing errors of the quadrupoles. 73 horizontal and vertical beam steerers are used to continuously correct the position of the electron beam. Finally 24 skew quadrupole magnets are adjusted to correct any torsion of the beam and to minimize the vertical emittance: a world record low value of 3 pm rad has been achieved in 2008.

The SLS has achieved a photon beam stability of 1 micrometre: the ring is operated in top-up mode, i.e. the stored current of 400 mA is kept constant to 1 mA by frequent (1–2 minutes) injections. This maintains a constant thermal load from synchrotron radiation. A fast orbit feedback system controlling the 73 beam position monitors and the 73 horizontal and vertical steeres corrects the position of the electron beam 100 times per second to suppress any distortions from ground vibrations etc. Beam distortions from changing the undulator status as done during experiments are minimized by application of a set of feed forward corrections measured once for the undulators, the orbit feedback takes care of the rest. Finally X-ray beam position monitors measuring the location of the synchrotron radiation itself perform the final adjustment in front of the experiment.

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