Electron beam propagation through a magnetic wiggler with random field errors
Abstract
The effects of random field errors on the propagation of a relativistic electron beam through a wiggler magnet is analyzed both theoretically and numerically. Random field errors give rise to detrimental effects such as a random walk in the transverse position of the beam centroid as well as fluctuations in the parallel energy of the electron beam. This random beam motion is analyzed both for a single realization of a wiggler magnet (a particular arrangement of field errors) and for an ensemble of wiggler magnets with identical statistical properties. Both helical and planar wiggler configurations are studied, with and without the effects of transverse focusing forces. Theoretical expressions are derived for the random electron motion and these results are then confirmed through 3D particle simulations of electron beam transport including the effects of finite emittance. Without transverse focusing, the rms transverse centroid displacement scales as z to the 3/2 power and the variance of the parallel energy deviation scales as the square root of z, z being the axial propagation distance. Transverse focusing inhibits the random walk of the centroid so that its rms value scales as the square root of z, but the variance of the parallel energy is only reduced by a factor of the square root of 2. In a free electron laser (FEL) it may be possible for the random walk of the electrons to become large enough so that the centroids of the radiation and electron beams no longer overlap, thus destroying the FEL interaction and reducing the FEL gain.
 Publication:

Naval Research Lab. Report
 Pub Date:
 August 1989
 Bibcode:
 1989nrl..reptQ....E
 Keywords:

 Electron Accelerators;
 Focusing;
 Free Electron Lasers;
 Magnetic Fields;
 Random Errors;
 Random Walk;
 Relativistic Electron Beams;
 Wave Propagation;
 Wiggler Magnets;
 Center Of Gravity;
 Displacement;
 Electron Energy;
 Emittance;
 Position Errors;
 Electronics and Electrical Engineering