Long-length YBCO coated conductors for ultra-high field applications: gaining engineering current density via pulsed laser deposition/alternating beam-assisted deposition route

Abstract

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 μm. Nevertheless, the reduction of substrate thickness in case of the applied processing technology that employs relatively thick (2–3 μm) 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 .

Development and large volume production of extremely high current density YBa2Cu3O7 superconducting wires for fusion

“…Indeed, our present J c (B) results are superior to many excellent results achieved with nano-columnar APC reported by other groups 7,26,[30][31][32][33][34] . We conclude, therefore, that nano-columnar defects are not indispensable for high critical current in magnetic field.…”

“…The samples differed in substrate thickness: 40, 60 and 100 µm and YBCO layer thickness: 2.55, 2.82 and 3.28 µm, respectively. In all three samples very high values of critical current were achieved, among the best reported to date for commercial 2G HTS wire 7,26,[30][31][32][33][34] . In particular, an I c at 20 K, 20 T in the 220-270 A/4 mm range and an I c at 4.2 K, 20 T in the 450-570 A/4 mm range were measured.…”

“…The progress of HTS technology has been especially impressive in the last decade, culminating recently in J E values in excess of 1000 A/mm 2 at 4.2 K in 18–20 T magnetic field 6 , 7 . While this is ample for some applications 8 , higher J E opens new frontiers in magnets for fusion reactors 9 , 10 , particle accelerators 11 – 13 , magnetic resonance imaging 14 , nuclear magnetic resonance spectroscopy 15 , 16 and space detectors 17 .…”

HTS Accelerator Magnets and Conductor development in Europe

“…Substantial progress was done in this direction by BHTS. A significant increase of Jc in high magnetic field was recorded in tapes manufactured employing the so-called double-disorder (DD) route [29,48,49], which creates intrinsic and extrinsic defects in the YBCO layer. The intrinsic disorder is caused by local stoichiometry deviations with respect to the nominal YBa2Cu3O7−x composition and is achieved through a tailored modulation of the oxygen pressure during the PLD process.…”

“…Nonetheless, the implementation of this strategy proved to be harder than expected. Major core steps in the ABAD and PLD processing routes had to be re-tuned because of a substantial variation of mechanical and thermal parameters of the thinner substrate [49]. In particular, the deposition of the relatively thick YSZ buffer layer on the 50 μmsubstrate determined a pronounced transverse bending of the tapes, a bow-shape that was traced back to the thermal contraction mismatch between the ceramic layer and the stainless steel (see Fig.…”