Small period electromagnet higglers for free electron lasers

Small period wiggler magnets for Free Electron Lasers (FEL's) are currently a topic of considerable interest because a small wiggler period leads to a reduced electron energy requirement for a desired radiation wavelength. A great deal of effort has been expended on the design of permanent magnet wigglers in recent years,1and high quality wigglers of this type have been constructed with periods typically in the range 1–10 cm (although methods for constructing even shorter period wigglers are currently under development). Recently our group has reported2a technique for fabricating small period (1–10 mm) electromagnetic wigglers in which the magnetic field amplitude can be varied continuously by varying the current in the electromagnet “windings.” In addition, the proposed design is bilateral, thus increasing the magnetic field amplitude and reducing the transverse gradient in the magnetic field in the central region betwen the two magnetic structures. As these wiggler electromagnets are inexpensive and easily constructed, they might prove useful for studying FEL physics and for the development of practical, lower voltage, FEL devices. In this paper we present the initial results from a program to investigate the performance characteristics of such wiggler electromagnets, and gain and efficiency calculations for an FEL employing a small period electromagnet wiggler of this type.