Fabrication and Experimental Study of Prototype NdFeB Helical Undulators

An experiment with short prototypes of helical undulators, comprised of longitudinally magnetized helices made from a single piece of a rare-earth magnet, is described. Wire electrical discharge machining (WEDM) in combination with a flat tool and the rotary movement of the workpiece made it possible to achieve high precision in the manufacture of NdFeB helices. An assembly of two oppositely longitudinally magnetized helices with a period of 20 mm and a relatively large inner diameter of 8 mm creates a field of 0.53 T on the axis of the system, which ensures the value of the undulator parameter K close to unity. According to the calculation, Halbach-type helical micro-undulators with periods of (3-6) mm of four helices can provide a field of 1 T and K = 0.28-0.6 at the axis.