Conventional Practical Superconductors

All superconductors exhibit thermal and EM instabilities because of their poor thermal conductivity and worst electrical conductivity in their normal state. These instabilities lead to premature quench in superconducting magnets. To circumvent the problem, practical superconductors are produced in the form of fine filaments in high conductivity copper matrix. Most popular superconductor Nb-Ti had been produced this way by co-processing it with Cu and used universally up to a field of 8–9 T. To meet the stringent requirement of high \(J_{\text{c}}\) and low AC losses for accelerator and fusion reactor magnets, impressive improvements have been made in the production techniques of Nb-Ti. Conductors with fine filaments 1–5 µm diameter cladded with diffusion barriers, with low filament spacing to dia. ratio (~ 0.15), resistive matrix to reduce filament coupling and low fraction of Cu have been produced. Conductors carrying large \(J_{\text{c}}\) of 50–70 kA in Rutherford and cable-in-conduit conductor (CICC) configuration have been produced. For future accelerators and fusion reactors, high-field A-15 Nb3Sn superconductor cables with high \(J_{\text{c}}\) have been produced by bronze technique, internal tin (IT) method, improved distributed tin (DT) method, RRP and the jelly roll (JR) methods. The DT technique has yielded Nb3Sn wire with 2–3 µm filament dia. with \(J_{\text{c}}\) = 105 A/cm2 (12 T, 4.2 K) and AC loss = 300 kJ/m3 (± 3 T, 4.2 K) suitable for ITER application. JAERI has produced CICC Nb3Al cable by JR technique, which produces a field of 13 T at a current of 46 kA. NRIM, KEK and FNAL have jointly developed Nb3Al Rutherford cable (14 × 1.84 mm) using 27 strands prepared by the so-called rapid heating quench technique (JR-RHQT) for the luminosity upgradation of the LHC. V3Ga conductors too are being developed by PIT technique for the future DEMO fusion power reactor to take care of the induced radioactivity by the 14 MeV neutrons released by the D + T reaction.