Optimized Design of Azimuthal Transmission Lines for the Cell Driven by Two PFLs in Induction Voltage Adders

In this paper, a full-size 3-D electromagnetic model (without electrons) and an equivalent circuit model of a single cell in magnetically insulated induction voltage adders has been established. The simulation results of these two models agree well with each other. On the basis of these two models, azimuthal transmission lines for a cell driven by two pulse forming lines (PFLs) have been optimized. The optimization process aims at matching the impedance to the feed PFLs, ensuring uniform potential distribution along the insulator-stack, maximizing the symmetric current flow around the bore, and minimizing the waveform distortion of the injected pulse. A formula is presented to estimate the azimuthal impedance and an asymmetric coefficient is also defined to quantify the asymmetric extent of the feed pulses. The profiles of the total four candidate azimuthal lines have been simulated and analyzed. The simulation results indicate a relatively low feed asymmetry for all the four profiles. However, considering the waveform quality of the cell output voltage, the azimuthal line profiles with four points connected or wholly connected to the cathode plate are the most suitable for induction cells with two PFL feeding. And the corresponding coefficients $\delta$ are 3.1% and 7.6%, respectively. It is concluded that, when optimizing azimuthal lines for cells with two PFL feeding, the principal consideration should be matching the impedance instead of symmetrizing the current flow.