Permanent Helical Undulators with Strong Fields

Undulators containing magnetized rare-earth helices can provide a significantly higher oscillatory electron velocity than the widely used planar Halbach undulators. Using Wire Electrical Discharge Machining (WEDM), it is possible to manufacture NdFeB helices with a period of 1 mm or less with high accuracy. In this work, we describe the results of manufacturing and studying prototypes of undulators in the form of one or two axially and radially magnetized helices. More efficient hybrid systems of two axially oppositely magnetized and two steel non-premagnetized helices with a field on the axis of the order of 1 T are also shown. Micro-undulators of this type can significantly increase the efficiency of XFELs and Inverse FELs.