Design of W-Band Planar Distributed Three-Beam Gun with Uniform Magnetic Focusing

In this paper, a novel planar distributed three-beam electron optics system is proposed for W-band high power Staggered double vane TWT. First, the three-beam gun is designed and optimized based on Pierce theory. The three-beam gun model is constructed sing CST to verify the correctness of the theoretical design with the beam voltage of 22 kV and the current of
$3\times 0.15$
A. Simulation results show that the beam radius of 0.08 mm at each beam waist is obtained with the compression factor of 5 for the 0.18 mm beam tunnel radius, and the axis separation of the adjacent electron beams is 0.46 mm. Then, a uniform magnetic focusing structure used for constraining the three-beam array is designed to make sure that the three-beam array can be transmitted stably. The magnetic saturation analysis of the pole piece and the optimization of the structural parameters of the magnet are fully considered to ensure the transmission stability of the three-beam array and reduce the volume of the magnet. Simulation results show that the three-beam gun matches well with the uniform magnetic focusing structure, and the three-beam array can be stably transmitted 70 mm in this focusing structure with the thickness pole piece
$\mathrm{T}_{pp}$
of 4 mm, the axial length of the magnetic shield
$\mathrm{Z}_{MS}$
of 15 mm and the diameter of the pole piece aperture
$\mathrm{d}_{h}$
of 2.16 mm.