PRACTICAL SOLENOID-DERIVED WIGGLER

Theoretical model and experimental results of a simple wiggler for fre e electron lasers with axial magnetic field are presented. The wiggler consists of a staggered array of iron rods placed inside the bore of a solenoid. The high-permeability rods deflect the nearby magnetic fie ld, which thus acquires a periodic transverse component in addition to the longitudinal guiding field. The conversion ratio of the axial mag netic field to the transverse field depends on the geometry only, and is given by a simple analytical expression derived from a dipole-array model. The experimental results agree with the theoretical model. The solenoid derived wiggler with iron rods has the advantage of simplici ty and accuracy. It is used in the traveling-wave free-electron maser (TWFEM) experiment at Tel-Aviv University.