Theoretical study on temporal and spatial performance of magnetic solenoid used in dilation x-ray imager

In the Dilation X-ray Imager (DIXI), which is characterized by an ultra-short gating time, a magnetic solenoid is used to keep the photoelectrons from defocusing during the drift process. The performance of the magnetic solenoid has an important influence on the performance of the DIXI. We present in this paper the efforts on studying the spatial and temporal performance of the magnetic solenoid used in the DIXI by tracking the photoelectrons with the particle-in-cell method. The initial parameters of the photoelectrons of the Au cathode were sampled with a Monte Carlo code. A novel magnetic solenoid with a shielding shell made of soft iron was proposed. We compared the performance of this solenoid with a normal solenoid. The simulation results of magnetic field distribution, spatial resolution, transit time spread, and temporal distortion were presented in detail to demonstrate that the performance of the DIXI can be significantly improved by using the magnetic solenoid with the proposed iron shell.