  We report here that magnetic fields of almost 34 T, far above the upper 24 T
limit of Nb3Sn, can be generated using a multifilament round wire conductor
made of the high temperature cuprate superconductor Bi2Sr2CaCu2O8-x (Bi-2212).
A remarkable attribute of this Bi-2212 conductor is that it does not exhibit
macroscopic texture and contains many high angle grain boundaries but
nevertheless attains very high superconducting critical current densities Jc of
2500 A/mm2 at 20 T and 4.2 K. This Bi-2212 conductor does not possess the
extreme texture that high Jc coated conductors of REBa2Cu3O7-x (REBCO) require,
avoiding also its high aspect ratio, large superconducting anisotropy and the
inherent sensitivity to defects of a single filament conductor. Bi-2212 wires
can be wound or cabled into almost any type of superconducting magnet and will
be especially valuable for very high field NMR magnets beyond the present 1 GHz
proton resonance limit of Nb3Sn technology. This demonstration that grain
boundary limits to high Jc can be practically overcome suggests the huge value
of a renewed focus on grain boundary properties in non-ideal geometries,
especially with the goal of translating the lessons of this Bi-2212 conductor
into fabrication of multifilament round wire REBCO or Fe-based superconductors.
