Variable-period electrostatic and magnetostatic undulator designs for generating polarized soft x rays at PEP (abstract)

It can been shown that the generation of soft x rays on high energy storage rings such as PEP is most effectively performed with low-field, variable-period insertion devices, in contrast to the fixed-period devices represented by conventional transverse magnetostatic (TM) technology. Moreover, variable-period undulators of arbitrary field strength can be shown to be preferable to variable-gap devices under all circumstances where the generation of excessive superfluous power is undesirable, or where the available range of tuning with a single device must be maximized. In this article, basic arguments for these claims are presented, and an electrostatic implementation of a variable-period polarizing undulator is described. Some attractive properties of a recently designed, higher-field magnetostatic analog of the electrostatic device are also mentioned.