An Approach to Focus the Sheet Electron Beam in the Planar Microstrip Line Slow Wave Structure

Abstract

Planar microstrip line slow wave structures (PML-SWSs) have great prospects in the millimeter and terahertz wave fields. However, the development of the devices employing PML-SWSs is severely limited due to the focusing difficulties. Compared with the conventional sheet electron beam (SEB) SWS, the asymmetric boundary condition of PML-SWS and high local electric field further increase the instabilities of the SEB transport in PML-SWS. A new approach, named the uniform magnetic focusing system with the matching electric field (UMFS-MEF), is presented in this article, which can effectively solve these issues. The simulation results illustrate that the expansion rate of the SEB in UMFS-MEF is significantly lower than that in the conventional uniform magnetic focusing system (CUMFS) with the same magnetic field strength <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${B}_{z}$ </tex-math></inline-formula> . Moreover, the present calculation results show that the UMFS-MEF requires only 10.6% of the magnetic field strength of CUMFS for maintaining the same expansion rate. This means that the UMFS-MEF can effectively suppress the instabilities, and employ a very low magnetic field to maintain the stabilities of the SEB transport. Finally, we give several other schemes to realize the method.