The New Approach to Focus High-Current-Density Sheet Electron Beam by Rotated Reversed Magnetic Field

The difficulty of focusing high-current-density sheet electron beams (SEBs) significantly limits the development of SEB devices. To address this problem, this article studies the cause of the collapse of the SEB in the reversed magnetic field (RM). Based on this analysis, a new approach, named SEB rotated reversed magnetic field (SEB-RRM), is proposed in this article. This new approach is rotating the transverse magnetic field of RM along the z-axis in the reversed region to a specific angle. Simulation confirms that the SEB-RRM can effectively solve the issue of SEB's collapse in RM. The analysis shows that the SEB's instability would be continuously decreased after passing through the reversed region of the SEB-RRM. Compared with the uniform magnetic field (UM), roughly twice the maximum beam current density can be transported by the SEB-RRM, with the same magnetic strength as the UM. In addition, this article gives a design of an electron optical system (EOS) with this new method, to verify the feasibility of the SEB-RRM. The simulation illustrates that the 600-A/cm(2) SEB can be well focused by a 0.74-T SEB-RRM in a 40-mm tunnel. While the UM needs to increase to 1.4 T to reach the same expansion degree as the SEB-RRM. Moreover, with the same peak magnetic value and tunnel length, the size of the SEB-RRM system is only 11.4% of that of the UM. Therefore, SEB-RRM can substantially increase the transmissible current density of SEB to improve the output level of devices while greatly reducing the system's dimension.