Characterizing electron beams using microwave cavity resonance spectroscopy

In state-of-the-art electron microscopes and research facilities, electron beam parameter measurements are typically performed using interceptive diagnostics, such as Faraday cups. In this work, microwave cavity resonance spectroscopy (MCRS) is introduced as a non-invasive alternative for electron beam characterization. To showcase the potential of this method, an electron beam with an energy of 15 keV and currents up to 350 μA was passed through a cylindrical hollow metal pillbox microwave cavity, and the resulting shift of its resonance frequency was measured with high precision. After correction for cavity temperature effects, the expected linear relation between frequency shift and beam current was observed. Beam profile measurements obtained using a knife-edge method were used to convert the measured frequency shift into an equivalent current density. Comparison with (invasive) collector-plate measurements demonstrates good agreement between the two techniques. In its current implementation, the method achieves a lower current-density detection limit of ∼1 μA/mm2. These results show that MCRS is a promising diagnostic method for real-time, non-invasive electron beam current monitoring.