Long-length YBCO coated conductors for ultra-high field applications: Gaining engineering current density via PLD/ABAD route

Gaining engineering critical current density (J(e)) in high-temperature superconducting (HTS) coated conductors based on double-disordered YBCO for operation at high fields is one of the key requirements in upcoming magnet/accelerator projects. Currently, the development of a tape with advanced J(e)-s is performed based on an alternating beam-assisted deposition-pulsed laser deposition (ABAD-PLD) manufacturing route. An obvious way to improve J(e)-s is to reduce substrate thickness. A 40% J(e) increase is expected owing to the thickness reduction from 100 to 50 mu m. Nevertheless, the reduction of substrate thickness in case of the applied processing technology that employs relatively thick (2-3 mu m) yttria-stabilized zirconia buffer layers leads to the manifestation of considerable strain in the tape resulting in strong tape bowing. Advanced processing routes have been developed to suppress this effect. The highest engineering current density was recorded at well above 1000 A mm(-2) under an ultra-high field of 18 T at 4.2 K, B // c. Influence of tape bowing and the impact of longitudinal defects are studied via V-I measurements at 77 K and a moderate magnetic field with intrinsic edge gradients. Potential for further gaining of J(e) was found employing mechanisms of (i) film nucleation from lateral flows that provide material transfer during the PLD process. Further steps include suppressing the instability of instantaneous temperature via quasi-adiabatic pulsed heating of the growing HTS film via (ii) control of laser plume energy, and (iii) energy release during film condensation (condensation enthalpy). These effects disturb the instantaneous temperature of the growing HTS layer, which exhibits very limited capability of heat transfer. Temperature pulses reaching 30-40 K were evaluated via heat transfer modeling. Stabilization of the level of pulsed temperature during layer growth is anticipated to result in a further increase in J(e).