Circular-to-planar transformations of high-perveance electron beams by asymmetric solenoid lenses

The generation and transport of planar electron beams is a topic of increasing interest for applications to high-power, high-frequency microwave devices. This paper describes the use of solenoid lenses with elliptical pole apertures to transform a circular high-perveance beam to a planar configuration. The resulting transformation system has a short axial length and is easily fabricated. Furthermore, the approach allows use of a conventional electron gun. We designed lenses and simulated the dynamics of a beam system to drive a 95 GHz, traveling-wave tube experiment at Los Alamos National Laboratory. The three-dimensional self-consistent calculations indicate that a 0.5   μperv beam can be compressed to a height of less than 0.5 mm with sufficiently low emittance for transport through periodic-permanent-magnet or wiggler arrays.