An electron accelerator is provided. The electron accelerator comprises a resonant cavity comprising a hollow closed conductor, an electron source configured to inject a beam of electrons, and an RF system. The electron accelerator further comprises a magnet unit, comprising a deflecting magnet. The deflecting magnet is configured to generate a magnetic field in a deflecting chamber in fluid communication with the resonant cavity by a deflecting window. The magnetic field is configured to deflect an electron beam emerging out of the resonant cavity through the deflecting window along a first radial trajectory in the mid-plane (Pm) and to redirect the electron beam into the resonant cavity through the deflecting window towards the central axis along a second radial trajectory. The deflecting magnet is composed of first and second permanent magnets positioned on either side of the mid-plane (Pm).