Periodic focusing and ponderomotive stabilization of sheet electron beams

Abstract

Particle simulations compare the behavior of nonrelativistic sheet electron beams in uniform static and nonuniform time-harmonic magnetic fields. The time-harmonic fields are equivalent to periodically cusped magnetic (PCM) focusing. While the sheet beam in a uniform field exhibits diocotron instability, the PCM-focused beam is stabilized by ponderomotive forces, in agreement with recent analytic predictions [J. Appl. Phys. 73, 4140 (1993)]. Mismatched Pcm-focused beams exhibit envelope oscillation and initially rapid emittance growth followed by a region of slower increase, in agreement with a recent semianalytic Fokker-Planck model.