Design of a Tunable PCM-QM Focusing System for a 220 GHz Sheet Beam Traveling-Wave Tube

In this paper, the design and simulation of a tunable periodic cusped magnet-quadrupolar magnet (PCM-QM) focusing system for a 220 GHz sheet beam traveling-wave tube (SB-TWT) is presented. Simulation results show that a 0.1 A, 30 kV sheet electron beam with a cross-sectional size of
$\mathbf{0.6} \mathbf{mm} \times \mathbf{0.1}\ \mathbf{mm}$
can be transported smoothly through a 75 mm-long drift tube with a beam tunnel size of
$\mathbf{0.826}\ \mathbf{mm} \times \mathbf{0.143} \mathbf{mm}$
under the focusing of this PCM-QM. The transmission rate of the sheet beam is up to 100%. The quality of the sheet beam at the end of the drift tube is acceptable.