Helical small period wiggler for the Raman free electron laser of SIOFM

The small period wigglers in recent years have been attracted by developing a compact free electron laser (FEL) device. A new small period wiggler configuration constructed by the bifilar helical sheets with ferromagnetic cores for the Raman FEL of Shanghai Institute of Optics and Fine Mechanics (SIOFM) is developed, and the performance characteristics of the wiggler with 10 mm period and 600 mm length are measured. It is similar to the bifilar helical wires wiggler, but in this configuration, there are the copper sheets instead of the wires, some ferromagnetic laminations between the copper sheets have been inserted in order to enhance the wiggler field. The field as high as 1500 G has been obtained with a large gap of 16 mm.