分析了采用单一同轴磁场时强流相对论多注阴极的侧端发射问题，研究了在不同磁场内半径和多注漂移管长度情况下多注电子束的传输效率。研究发现：由于引导磁场尺寸有限，高压下多注阴极杆及多注阴极柱的电子束发射是影响多注电子束传输效率的主要因素，且该部分电子束对多注漂移管入口管壁的轰击直接影响了多注速调管的重频能力。设计了采用永磁铁和同轴磁场组合工作的强流相对论多注二极管，理论分析和模拟计算证明：基于组合磁场的多注二极管可明显减弱甚至抑制多注阴极发射球头以外的电子束发射，并且组合磁场的磁场位形和强度可满足强流相对论多注电子束的高效、稳定传输。

This paper analyses the electron emission from cathode stick and multi-beam cathode rod of MBK and investigates the transport efficiency with different radius and drift tube length. The results show that with compact constructure the electron emission from cathode stick and rod under high voltage affect the multi-beam transmission efficiency obviously. Especially, the beam bombing on the wall of tube will degenerate the repetition capacity of multi-beam klystron. To resolve these problem, a combined magnetic system is designed and fabricated, which can reduce the stick and rod emission by pulling the multi-beam cathode out of the high electric zone. Then a multi-beam diode with combined magnetic system is designed. Calculation and simulation results show that beam emission from the cathode stick and the rod can be decreased evidently, furthermore the cathode stick can be removed. In addition, the magnetic distribution can ensure high efficiency and stability of multi-beam transport. At present, the multi-beam diode with combined magnetic system is being experimented.