A facility for cryogenic ion irradiation and in situ characterization of rare-earth barium copper oxide superconducting tapes.

Superconducting magnets based on Rare Earth Barium Copper Oxides (REBCO) offer transformative capabilities in the fields of fusion energy, high energy physics, and space exploration. A challenge shared by these applications is the limited lifetime of REBCO due to radiation damage sustained during operation. Here we present a new ion-beam facility that enables simultaneous cryogenic irradiation and in situ characterization of commercial REBCO tapes. The ion source provides spatially uniform fluxes up to 1018 protons/m2s with kinetic energies up to 3.4 MeV, in addition to helium and higher-Z species. Using this facility, we can induce uniform damage profiles in the first 10-20 µm of REBCO tapes with less than 0.25 appm of hydrogen implanted in REBCO after a dose of 1020 protons/m2. The tape can be held between 20 and 300 K with an accuracy of ±0.1 K and is connected to a four-point probe measuring the critical current, Ic, and critical temperature, Tc, before, during, and after irradiation with transport current ranging from 100 nA to 100 A, and a typical voltage noise less than 0.1 µV. These capabilities are presently used to study the effect of irradiation temperature on REBCO performance change during and after proton bombardment, to assess the possibility of Ic and Tc recovery after irradiation through thermal annealing, and to explore the instantaneous and recoverable suppression of Ic and Tc observed during irradiation.

Simulated plasma facing component measurements for an in situ surface diagnostic on Alcator C-Mod.

The ideal in situ plasma facing component (PFC) diagnostic for magnetic fusion devices would perform surface element and isotope composition measurements on a shot-to-shot (∼10 min) time scale with ∼1 µm depth and ∼1 cm spatial resolution over large areas of PFCs. To this end, the experimental adaptation of the customary laboratory surface diagnostic--nuclear scattering of MeV ions--to the Alcator C-Mod tokamak is being guided by ACRONYM, a Geant4 synthetic diagnostic. The diagnostic technique and ACRONYM are described, and synthetic measurements of film thickness for boron-coated PFCs are presented.