ABSTRACT
Imperfections are the discrepancies of a real, as-built accelerator from the ideal computer model we discussed in Chapter 3. The model typically describes a lattice in which all magnets are perfectly placed at their reference location, and all magnets are powered with their design currents. Moreover, typically only beamline elements for the accelerator are taken into account, and magnetic fields that are not part of the bare lattice are omitted; examples for the latter are the solenoid magnets that are part of the detectors in high-energy accelerators or in electron coolers, but also the additional fields from undulator magnets in synchrotron light sources. In short, all influences that make a real accelerator deviate from its ideal behavior we call “imperfection.” In the section on corrections, we also address the compensation of chromatic effects, even though they are inherently caused by the finite momentum spread of the beam, rather than imperfections.
