A new approach of using low magnetic field to focus SEB

The transport of sheet electron beam (SEB) is of critical importance for the success of a number of high-power millimeter wave and terahertz vacuum devices. In this paper, the condition to achieve the SEB's stable transport in uniform longitudinal magnetic field is studied. Based on this stability condition, a new approach, named sheet electron beam matching focusing magnetic (SEB-MFM) field, which consists of a longitudinal component and a tiny transverse component, is presented. The SEB-MFM field can be generated by adding extra transversely magnetized magnets to the conventional uniform magnetic (UM) system. For demonstrating the effect of the SEB-MFM field, the simulation work of the SEB-MFM field and conventional UM field is carried out for an electron optical system employing a SEB. The simulation results show that the SEB-MFM field effectively eliminates the instabilities, such as distortion and deformation, arising from the longitudinal magnetic field. In addition, comparing with conventional UM field, the SEB-MFM can achieve the stable and long-distance transport of a SEB with a pretty low magnetic field strength. Finally, a new magnetic system generating SEB-MFM field is designed, fabricated, and measured.