Impact study of beam losses in TRIUMF’s BL4N proton cave and ARIEL tunnel

Abstract

As part of the ARIEL project, currently under construction at TRIUMF, a new proton beam line will be installed to transport up to 100 µA of nominal beam energy 480 MeV protons from the main cyclotron extraction port to an isotope separator on-line (ISOL) proton target station. This new beam line, approximately 80 m long, designated beam line 4-North (BL4N), will connect the cyclotron to the ARIEL facility via a tunnel. The proton beam line is designed for beam losses lower than 1 nAm−1 and will feature a collimator to remove the beam halo produced by large-angle scattering in the cyclotron extraction foil.The tunnel will be shared with an electron beam line with its own specific requirements for beam loss mitigation and machine protection, leading to another ISOL electron target station. The electron beam is generated by an e-linac with capacity for 500 kW beam power operation, but is ultimately expected to operate at 100 kW with losses not exceeding 20 nAm−1. After an initial stage of operation at 25 MeV the beam energy will be upgraded to 50 MeV.In this work, the effect of the beam losses, both chronic and catastrophic, in the tunnel and adjacent areas were studied. The FLUKA particle transport and interaction code was employed to estimate the impact of the combined proton and electron beam losses to the shielding, including as well the reflection of radiation from the target stations into the tunnel during ARIEL operation. This analysis resulted into a better assessment of the damage to equipment in the tunnel and the impact on maintenance due to activation of elements of the beam line. Maximum credible accidental scenarios were also detailed to validate the shielding configuration and the safety systems location.