InternationalCrystallography of biological macromoleculesTables for Crystallography Volume F Edited by E. Arnold, D. M. Himmel and M. G. Rossmann © International Union of Crystallography 2012 |
International Tables for Crystallography (2012). Vol. F, ch. 8.1, pp. 190-191
## Section 8.1.3. Insertion devices (IDs) |

These are multipole magnet devices placed (inserted) in straight sections of the synchrotron or storage ring. They can be designed to enhance specific characteristics of the SR, namely

The classification of a periodic magnet ID as a wiggler or undulator is based on whether the angular deflection, δ, of the electron beam is small enough to allow radiation emitted from one pole to interfere directly with that from the next pole. In a wiggler, , so the interference is negligible and the spectral emission (Fig. 8.1.2.2*a*) is very similar in shape to, but scaled up from, the universal curve (*i.e.* bending magnet spectral shape). In an undulator and the interference effects are highly significant (Fig. 8.1.2.2*b*). If the period of the ID is (cm), then the wavelengths (*i* integer) emitted are given by where .

The spectral width of each peak is where *N* is the number of poles. The angular deflection, δ, is changed by opening or closing the gap between the pole pieces.