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Published online by Cambridge University Press: 09 October 2009
Introduction
A wiggler is a set of dipole magnets located in a straight section that has a different field strength Bw from that of the bending magnets of the ring. They are arranged and powered in such a way that the overall bending and displacement of the electron orbit vanishes, a condition that is also realized in undulators. For this reason undulators and wigglers are often referred to as insertion devices since they are located in a straight section and can be powered at different field levels without disturbing the orbit in the rest of the machine. However, they provide some focusing of the electron beam, which might have to be corrected.
We distinguish basically between two types of wigglers: wavelength shifters, having only one period, and multipole wigglers with many periods. The wavelength shifter has a short and strong dipole magnet in the center, which is used as the main source of radiation, with longer and weaker magnets on each side to make the overall bending vanish, as illustrated in Fig. 10.1. Varying the field strength changes the critical energy and the radiated power. Usually the central field is much larger than that of the lattice bending magnets and has the purpose of providing very-short-wavelength radiation.
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