Simulation analysis of coupling effect during multi-plate Blumlein lines loading high gradient insulator

Due to the coupling problem, the output efficiency of the accelerating unit for the dielectric wall accelerator is reduced. With electromagnetic field simulation software based on FDTD method, the multi-plate Blumlein lines loading the high gradient insulator(HGI) is analyzed. The simulation includes one and three groups of 1-stage and 15-stage Blumlein line(BL) respectively loading HGIs. The results show more parallel electrodes in multi-BLs bring itself a large coupling capacitance, which leads to a slower rising edge and a lower amplitude. The output efficiency drops when three groups of multi-BLs work together because the adjacent group of multi-stage-BLs become a coupling capacitor and split current seriously. At the same time, the adjacent group of multi-stage BLs also discharge and affect output efficiency. A preliminary optimization is studied. By rotating every BL stages a certain angle to reduce the effective opposite area of parallel electrodes, the group of multi-BLs decreases its own coupling capacitance, and some benefit achieved. However, it requires further verification whether the optimization can reduce the coupling capacitance between the BL modules. (authors)