Beam Charge Monitor for quantitatively measuring electron bunch of very Low-charge pulse and Ultra-short pulse

The X-ray free-electron laser (XFEL) system of the Pohang accelerator laboratory (PAL) makes short electron beams with very low quantities of electric charge. It is difficult to measure bunch charge with very low-charge pulses and ultra-short pulses using an ordinary integrating current transformer (ICT). When there is a klystron modulator or a pulse power supply generating electromagnetic noise and ground noise in the surrounding area, it becomes especially difficult to measure the quantity of electric charge. In this paper we report on charge measurements performed at PAL-XFEL using a Turbo-ICT from Bergoz Instrumentation, which was developed to overcome various kinds of noise occurring in the surrounding areas.