Theory of superpinched relativistic electron beams

Numerical simulation and analytic theory are used to study the z-dependent equilibria of a charge neutralized, relativistic electron beam, subject to an applied axial electric field. The analytic theory consists of nonparaxial envelope equations derived from a finite temperature fluid model for relativistic beams. The application of the theory to the calculation of beam pinching in high-current relativistic electron beam accelerator diodes is discussed. An effect of the applied electric field in the diode is to enhance beam pinching, for configurations relevant to both low- and high-impedance diodes. In certain cases, the highly-pinched beams have more energy in the random motion of the beam particles than in the longitudinal flow.