  Fusion reactors are limited by the magnetic field available to confine their
plasma. The commercial fusion industry uses the larger magnetic field and
higher operating temperature of the cuprate superconductor
$\mathbf{YBa_{2}Cu_{3}O_{7-\delta}}$ (YBCO) in order to confine their plasma
into a dense volume. A superconductor is a macroscopic quantum state that is
protected from the metallic (resistive) state by an energy gap. Unfortunately,
YBCO has an anisotropic gap, known as D-wave because it has the shape of a
$\mathbf{d_{x^2-y^2}}$ chemical orbital. This D-wave gap means that
poly-crystalline wire cannot be made because a few degree misalignment between
grains in the wire leads to a drastic loss in its supercurrent carrying
ability, and thereby its magnetic field limit. The superconductor industry has
responded by growing nearly-single-crystal superconducting YBCO films on
carefully prepared substrate tapes kilometers in length. Heroic development
programs have made such tapes commercially available, but they are very
expensive and delicate. MRI magnet superconductors, such as $\mathbf{NbTi}$ and
$\mathbf{Nb_{3}Sn}$, are formed into poly-crystalline wires because they have
an isotropic gap in the shape of an s chemical orbital (called S-wave) that
makes them insensitive to grain misalignment. However, these materials are
limited to lower magnetic fields and liquid-He temperatures. Here, we modified
YBCO by doping the Y site with Ca and Ce atoms to form
$\mathbf{(Y_{1-x-y}Ca_{x}Ce_{y})Ba_{2}Cu_{3}O_{7-\delta}}$, and show evidence
that it changes to an S-wave gap. Its superconducting transition temperature,
$\mathbf{T_c}$, of $\mathbf{\sim 70K}$, while lower than that of D-wave YBCO at
$\mathbf{\sim 90K}$, is easily maintained using common, economic cryogenic
equipment.
