JANUS: A Robust ReBCO Tape Design for Increased Performance in Magnetic Fields

We propose the
JANUS
(Joint ANgled Unconventional Superconductor) compound tape design with two oppositely tilted c-axes. This design takes advantage of the 30° inclination of the c-axis to the substrate normal to broaden the angle dependence of the critical current. The minimal critical current along the coil is raised and the amount of ReBCO tape required for a given field strength is reduced. For 8 T and 20 K, the averaged minimum
$I_{c}$
of the two tapes is raised by 14%. By restricting the angle to
$\pm$
60° between field and the tape binormal direction, the local
$I_{c}$
minimum is even 20% higher. Furthermore,
JANUS
shows an increased robustness to manufacturing errors. The maximum
$I_{c}$
drop for a 5° deviation in the angle between ReBCO tape and magnetic field is reduced from 18% to 13%. The use of
JANUS
in an exemplary stellarator coil also shows an increase of 10% in
$I_{c}$
and encourages numerical optimization of the tape orientation for a further performance increase.