Investigation on current loss of high-power vacuum transmission lines with coaxial-disk transitions by particle-in-cell simulations

Abstract

Coaxial-disk transitions can generate non-uniform magnetic fields and abrupt impedance variations in magnetically insulated transmission lines (MITLs), resulting in disturbed electron flow and non-negligible current loss. In this paper, 3D particle-in-cell simulations are conducted with UNPIC-3d to investigate the current loss mechanism and the influence of the input parameters of the coaxial-disk transition on current loss in an MITL system. The results reveal that the magnetic field non-uniformity causes major current loss in the MITL after the coaxial-disk transition, and the non-uniformity decreases with the distance away from the transition. The uniformity of the magnetic field is improved when increasing the number of feed lines of a linear transformer driver-based accelerator with coaxial-disk transitions. The number of input feed lines should be no less than four in the azimuthal distribution to obtain acceptable uniformity of the magnetic field. To make the ratio of the current loss to the total current of the accelerator less than 2% at peak anode current, the ratio of the current in each feed line to the total current should be no less than 8%.