Busbar arcs at large fusion magnets: Model experiments on busbar arcing in a double-walled feeder tube with the LONGARC device

Electric arcs moving along the power cables (the so-called busbars) of the toroidal field (TF) coils of large fusion devices like DEMO and ITER may reach and penetrate the cryostat wall. The present work concludes a series of model experiments studying the propagation and destruction mechanisms of such busbar arcs in small scale. While it went clear from previous findings that the inner feeder tube of a busbar would not withstand a powerful arc, the present work investigated the impact of the arc on the second, coaxial outer feeder tube. The key finding is that the outer feeder tube will stay intact in any case, proving the robustness of the ITER TF busbar confinement concept. As the basic DEMO magnet concept will be “ITER-like”, the knowledge of weaknesses and strengths of the ITER TF busbar feeder design may be helpful in the preparation phase of a detailed DEMO magnet feeder design.