New varieties of helical undulators

A helix magnetized along the axis can be used as an undulator with a fairly strong transverse field. Two such helices with the opposite direction of magnetization and shifted relative to each other create a field that is twice as strong. It has been shown, both theoretically and experimentally, that helical undulator fields can also be created due to the redistribution of the uniform magnetic field of the solenoid by ferromagnetic or well-conducting insertions as well as by various combinations of these elements. Use of such undulators in electron sources of terahertz radiation is promising for a significant enhancement of both emitted power and frequency.