A closed circular loop made of a superconducting material with zero electrical resistance (\(R = 0\)) is placed in a region of uniform external magnetic field perpendicular to the plane of the loop. Initially, both the external field and any current in the loop are zero. The external magnetic field is increased at a constant rate until it reaches a strength \(B_0\), after which it remains constant. While the external field is increasing, an induced current is established in the loop. Long after the external field has stabilized at \(B_0\), the current in the loop is observed to flow at a constant, non-zero magnitude. Which of the following best explains why this current persists indefinitely at a constant magnitude?