Axially polarized wiggler radiation from a toroidal electron beam source

Abstract

Recent work has described wigglers in which the radiating electron beam circulates azimuthally within a toroidal tube where a surrounding permanent magnet structure keeps the beam on a mean circular path and simultaneously provides the field periodicity for wiggler action. Both the mean field and the periodic field are in the axial direction so that the resulting synchrotron and wiggler radiations are both polarized in the principal toroidal plane. The present work analyzes a structure in which the synchrotron and wiggler polarizations are mutually orthogonal so that one or the other can be easily eliminated to provide essentially monochromatic radiation. This is accomplished by an azimuthally periodic arrangement of magic ring sections that form a toroidal tube. These are oriented with their axial field components constant and equal and their radial components equal but alternating radially outward and inward in direction. The constant axial field holds the electron beam in a circular path while the alternating radial field provides the wiggler action. The wiggler radiation has n times the frequency of the synchrotron radiation where n is the number of azimuthal periods per circuit.