Electron source model responsible for low power beam losses of 1 W/m along the entire PolFEL superconducting electron linear accelerator

The National Centre for Nuclear Research is planning to build a facility based on a free-electron laser (FEL) photon source. It is the first center to build this kind of facility in Eastern Europe. The laser radiation source relies on a superconducting linear electron accelerator. Ultimately, electrons are to be accelerated to energies of 72 MeV, 187 MeV and 280 MeV. To safely operate such kind of accelerator, the design of a shielding bunker is required, capable of attenuating the secondary radiation generated by electrons lost from the beam. This paper proposes a model for the energy and spatial distribution of such electrons. The proposed model will be used in subsequent calculations of the distribution of secondary radiation emitted by both the beamline and some devices essential for the operation of the PolFEL accelerator, such as superconducting niobium accelerating cavities, titanium liquid helium tanks filled with liquid helium, surrounded by μ-metal steel cryomodules containing a steel tube filled with liquid nitrogen, mirrors reflecting the resulting laser beams based on copper blocks, and electron beam deflecting electromagnets made of iron and copper. It was calculated that to reproduce a complex beam loss of 1 W/m, the total lost electron flux as a source of secondary radiation should be 1.7991 × 10¹³ e/s for 72 MeV, 1.1537 × 10¹³ e/s for 187 MeV and 1.1012 × 10¹³ e/s for 280 MeV. Preliminary Monte Carlo calculations of the designed source were performed, obtaining the energy and spatial distributions of the lost electrons.