Experimental study of the stability of a superconductor cooled by a limited volume of superfluid Helium

Stability experiments have been carried out to confirm the validity of a theoretical model which provides us with the conditions of stability of a superconductor cooled by a confined volume of superfluid helium at atmospheric pressure, and subjected to short duration high energy disturbances affecting a large length of conductor. The conductor is quenched by a high power (typically 10 W/cm²per unit of cooled surface area) injected in a short time (540 μs) by the discharge of a capacitor bank. Experimental results suggest that transient phase transitions occur at the interface conductor-helium during the heat exchange. Dynamic studies of the superconductor and superfluid states are performed. A good agreement is found between the theoretical analysis and the experimental results which allows to give a useful relationship among the maximum current density, the disturbance energy, the cooling channel configuration, and the bath temperature.