Rotating Quadrupole Undulators Formed By Magnetized Helices

To create a rotating quadrupole field a system of two magnetized helices is proposed. The simplest shape of undulator trajectories in such a field is provided when electrons are injected into a quasi-homogeneous region of the azimuthal component. Such systems can be used to implement high-power FEL-like sources of coherent radiation from short electron bunches.