Wake fields evaluation for beam collimators and the 60 pc electron beam at the compact ERL at KEK

In high-intensity particle accelerators, unwanted transverse and longitudinal wakefields arise when the high- charge particle beam passes through the narrow chambers or locations with small transverse apertures, such as collimator jaws. The transverse wake field may affect the beam emittance and the longitudinal wake field can cause the energy loss and the energy spread. In the present study we investigated the collimator’s impact to the beam performance. In this paper, we have shown numerical, analytical and measurement results on the collimator’s wakefields that will be important for the next step operation. Thus, considering future cERL upgrade to the IR-FEL, a possibility of consequent degradation of the FEL performance should be taken into account. The correspondent power loss was obtained as 13.7 W (81.25 MHz, 5 mA, 2 ps).