Design of a Sheet Beam Electron Optics System for a 140-GHz Traveling Wave Tube

An integrated sheet beam electron optics system that employs a sheet beam gun together with a uniform permanent magnetic focusing structure was thoroughly analyzed and designed, for a 140-GHz staggered double vane traveling wave tube (TWT). First, a laminar quasi-elliptical beam with a 25 kV, 0.25 A, and a cross-section of $0.75\times0.15$ mm was obtained via theoretical analysis and CST simulation, featuring a current density of $\sim $ 222 A/cm2 at the beam waist. Then, a compact uniform magnetic structure was employed, conveying the sheet beam stably over a distance of 100 mm, with no beam interception. Furthermore, simulated stability analysis showed that the electron optics system could allow enough tolerances for assembly errors, magnetization errors, and operating voltage variation.