Permanent magnet undulator with a variable gap for a free electron laser

A permanent magnet undulator with a variable gap serves to generate coherent X-ray radiation. The length of the undulator magnetic system is 5 m, period T = 32 mm, and magnetic field amplitude B is 0.75 T at interpole gap h = 9 mm. The magnetic and mechanical structures of the undulator and an innovative technique for mounting movable girders with permanent magnets are described. A technique for adjusting the undulator and the results of magnetic measurements are also described.