Undulators Consisting of Magnetized Helices

A ferromagnetic helix magnetized axially or radially is apparently the simplest helical undulator. Four helices with alternating magnetization can provide a stronger helical field than a pair of conventional planar Halbach arrays. Such undulators and microundulators seem promising for various powerful high frequency sources. The fields of infinite helices uniformly magnetized in the longitudinal and radial directions are found analytically by integration of contributions from elementary dipoles. The analytical values of the field magnitudes are close to the numerically calculated ones for a helix with a relatively small number of periods five-ten. According to simulation, a magnitude of about 1 T can be obtained on the axis of a system of helices with small inner radii.