Effects of Magnetic Field Shielding on UED Ultrashort Electron Pulses

The magnetic simulation is carried out for four cases. The relative permeability of chamber is 1.04 with the magnetic shielding or not. The relative permeability of chamber is set to μr = 1000 or μr = 100 with the magnetic shielding. The focusing of electronic pulse by magnetic lens is simulated by the N-particle program with the magnetic field results. The electron pulses converges earlier with the magnetic shielding and divergences faster after the convergence. But the electron distribution is less affected. The magnetically conductive material chamber will affect the magnetic distribution of magnetic lens which delay and weaken the pulse convergence. If the magnetic permeability is too high, the magnetic lens will lose the convergence effect.