Radiation-resistant C-type dipole dump magnet for MIR/THz FEL applications at TARLA

Abstract

Radiation-induced degradation is a key challenge for dipole magnets used in beam dump systems of free-electron laser (FEL) facilities. This study presents the design and experimental validation of a compact, radiation-resistant C-type dipole dump magnet developed for the MIR/THz FEL at the Turkish Accelerator and Radiation Laboratory (TARLA). The magnet deflects electron beams of up to 45 MeV by 42°, enabling safe beam disposal under radiation-intensive conditions. A radiation-informed design approach combining magnetic material characterization, electromagnetic modeling, and Monte Carlo radiation transport simulations was employed. Electrical steel with high iron content was selected to ensure sufficient saturation margin and magnetic stability in the fringe-field-dominated geometry. Coupled MCNP–COMSOL analyses showed that the combined radiation and resistive heating leads to a maximum coil temperature rise of only 18.7 °C, allowing reliable air-cooled operation. A parallel winding scheme was adopted to reduce Joule losses and enhance thermal margins. Neutron shielding experiments using a locally developed composite material achieved up to 99% attenuation, confirming the effectiveness of the shielding design. The proposed magnet provides a compact and radiation-tolerant solution for FEL beam dump systems.