Neutron Irradiation Tolerant REBCO Tapes for Compact Fusion Reactors

The ultra-high critical magnetic fields of RE-Ba-Cu-O (REBCO RE=rare earth) High Temperature Superconductors (HTS) are very attractive for compact fusion energy systems that can operate over a temperature range of 4 – 50 K in magnetic fields beyond the realm of Nb3Sn wires. REBCO tapes are now being manufactured in piece lengths up to a kilometer with engineering current densities above 500 A/mm2 at 77 K, 0 T. Several designs of high-current cables are now being developed for fusion energy systems using stacks of REBCO tapes. A major concern is that the neutron flux typical of a compact fusion reactor may lead to significant degradation of REBCO tape performance during use. This sets a minimum amount of shielding and a minimum device size and cost; or, equivalently, for a given size, it sets device lifetime. Despite its importance, a systematic study of the effects of tape composition and structure on tape robustness under neutron irradiation has not been carried out. Commercial REBCO tapes, originally developed for electric power applications have not been properly optimized for high magnetic field applications and not at all designed for neutron irradiation tolerance. In the proposed project, AMPeers and the University of Houston will systematically investigate the influence of composition and structure of REBCO tapes on tolerance to fast neutron irradiation. The tapes will be tested at increasing levels of neutron fluence at Massachusetts Institute of Technology followed by critical current testing over a temperature range of 4.2 K – 77 K in magnetic fields up to 14 T. We will determine the film composition and tape structure that yields the least degradation in critical current or the highest neutron fluence with less than 10% reduction in critical current.