A universal classification of optimal undulator types and parameters for arbitrary storage ring environments

Abstract

Prevailing insertion device technology utilizes transverse magnetostatic (TM) field configurations with fixed periods to induce periodic deviations in relativistic charged particle trajectories. Such devices are invariably tuned by varying the field strength in the region encompassing the trajectory. As a consequence, the highest first harmonic frequencies generated by such structures are limited by their period lengths, while the generation of lower first harmonics quickly leads to the production of excessive amounts of out-of-band radiation. In the spontaneous emission regime, this superfluous power varies directly with the length of the device. In view of this, recent access to straight sections in high energy storage rings exceeding lengths of 100 m has raised the undesirable prospect of unmanageable power levels limiting the utility of such facilities. In this article a general study of a set of major types and classes of transverse insertion devices operating on storage rings of arbitrary energy and current is made and the results are represented with a set of universal performance curves. The graphical tabulation enables easy identification of optimum undulator types and operating parameters for any storage ring environment; in particular, optimal devices which do not suffer from excessive power generation on high energy storage rings are defined.