Focal Lengths of High-Tc Sintered Superconducting Lenses (Supertrons) for Intense Electron Beams

Abstract
To determine the optimum dimensions of high-critical-temperature (T c) sintered superconducting lenses (Supertrons), we observed intense electron beams (~340 keV, ~1 kA, ~10 ns) which were focused using axial-length-variable Bi(2223)-based lenses, with a Faraday cup at the exit of the lenses. The lens pipes examined were 13, 28, and 50 mm long and had a wall thickness of 1.5 mm and an inner diameter of 20 mm. Among the lenses, the 50-mm-long lens exhibited the best performance and was found to have the optimum dimensions by comparing the experimental results with electron trajectories simulated for single electrons injected in parallel to the axis of the lenses under a condition of space-charge neutralization. The simulation seems to be a useful method for designing Supertrons.