AXIALLY POLARIZED WIGGLER RADIATION FROM A TOROIDAL ELECTRON-BEAM SOURCE

Recent work has described wigglers in which the radiating electron bea m circulates azimuthally within a toroidal tube where a surrounding pe rmanent magnet structure keeps the beam on a mean circular path and si multaneously provides the field periodicity for wiggler action.(1,2) B oth the mean field and the periodic one are in the axial direction so that the resulting synchrotron and wiggler radiations are both polariz ed in the principal toroidal plane, The present work analyzes a struct ure in which the synchrotron and wiggler polarizations are mutually or thogonal so that one or the other can be easily eliminated to provide essentially monochromatic radiation. This is accomplished by an azimut hally periodic arrangement of magic ring sections that form a toroidal tube. These are oriented with their axial field components constant a nd equal and their radial components equal but alternating radially ou tward and inward in direction. The constant axial field holds the elec tron beam in a circular path while the alternating radial field provid es the wiggler action. The wiggler radiation has n times the frequency of the synchrotron radiation where n is the number of azimuthal perio ds per circuit.