Undulators in the form of Permanently Magnetized Helices

A ferromagnetic heix magnetized axially or radially is apparently the simplest helical undulator. Four helices with alternating magnetization can provide a stronger helical field than the conventional planar Halbach arrays. Such undulators and micro undulators seem promising for various powerful HF sources. The method of direct integration of the fields of elementary magnets is used for analytical calculation of the fields of infinitely thin, longitudinally and radially uniformly magnetized helices of arbitrary length. Subsequent integration allows finding the field of a helix with finite transverse dimensions. The analytical magnitude of the field for an infinite helix is close to the numerically calculated one for a helix with a relatively small number of periods 5-10.