Modeling and analysis of a high current electron beam focused by a permanent-magnet quadrupole lattice in a helical traveling-wave circuit

In comparison to conventional periodic permanent-magnet (PPM) lattices, the periodic permanent-magnet quadrupoles (PMQ) lattices have the potential to provide the strong focusing required to transport higher current electron beams. Here, analyses of the interaction between the elliptical beam formed by the PMQ lattice and a helical traveling-wave circuit are presented. The large-signal traveling-wave tube (TWT) code, CHRISTINE 1-D, have used to explore the sensitivity of the amplifier performance to variations in beam radius. In addition to enabling higher rf power operation, also showed the higher beam currents afforded by PMQ focusing enable a higher power gain per unit length and the result in more compact form factors and higher amplifier power densities compared with PPM-focused circuits.