The integrating current transformer (ICT, and sometimes also nicknamed the 'AC-Trafo') has two measurement ranges with either 10 or 100 μA maximum. The beam current is transformed into a voltage signal, which itself is transformed to a frequency with the following calibration:
The frequency at the maximum is 23.5 MHz.
Clarify with the machine experts, which range is in use, if you record only the frequency signals. The range is available as LSA parameter.