The recovery of superconducting systems

Superconducting systems, as proposed for fusion reactors and alternators, must if possible be encouraged to return to operating conditions after a transient fault. Electric ac power systems de-energise a faulty section of line, then re-close. The analogy is useful. The paper describes measurements and calculations for superconductors under fault and recovery conditions. In the laboratory, as in the final installation, recovery may be initiated in a number of ways; for example the removal of a continuous heat input could be considered as equivalent to the removal of external heat flux in a fusion reactor toroidal field winding. More realistic would be the reduction of conductor current, simulating the effect of protective action in a large installation. Laboratory observations are correlated with computer calculations in which detailed thermo-dynamic properties of superconductors are used. The conditions under which the recovery of a large system is possible are discussed.