Charged-Particle Motion in Large-Amplitude Electromagnetic Fields

Abstract

The relativistic motion of a charged particle in large amplitude, inhomogeneous electromagnetic fields is studied for several situations. This study involved the numerical integration of the equations of motion including the relativistic mass correction and the nonlinear rf v×B force term. The cases studied include particle motion in linearly and circularly polarized, homogeneous plane waves with a homogeneous steady magnetic field parallel to the direction of propagation; particle motion in linearly and circularly polarized TE-11 modes in waveguides of circular cross section immersed in a uniform steady axial magnetic field; and particle motion in cavity resonators of circular cross section (TE-111 mode) immersed in a nonuniform steady axial magnetic field. This study is concerned with the maximum energy gains possible in the above situations with field amplitudes appropriate to high-power microwave experiments. To verify the features of the particle motion as predicted in the numerical study, and to investigate effects which could not be easily included in the analysis, such as space charge from the electron beams, beam-induced cavity fields, and ionization of residual gas in a cavity resonator, certain experiments were performed. These involved the injection of 1–100-mA electron beams at 100–1000 V on the axis of circular cross-section cavity resonators (10 GHz and 1.0 GHz) immersed in a steady axial magnetic field. With pulsed operation, an energy increase of 460 keV was obtained for a drive power of 46 kW at an over-all efficiency of acceleration of approximately 10%. Higher-efficiency pulsed operation and continuous operation at lower power levels were also investigated experimentally.