ABSTRACT
In Chapter 8, the influence of the voltage-current characteristic of a superconductor on the conditions of the occurrence and development of thermal instabilities in technical superconductors is studied. The obtained results are compared with the conclusions of the thermal stabilization theory based on the model with the ideal voltage-current characteristic. It is shown that it leads to overestimated values of the Joule heat release in a wide range of the temperature changes of the composite. Moreover, it appears that when used in the thermal stabilization theory, the concepts of the critical current, defining the maximum value of a transport current and the temperature of the resistive transition beyond which the current starts to share between the superconducting core and matrix have no physical meaning for technical superconductors. As a result, the stable states are possible at currents that are higher than the conditionally set value of the critical current of the composite, which is the ideal voltage-current characteristic.
The analysis of dissipative processes is carried out that occurs in superconducting composites as a result of the redistribution of the current across the composite, which occurs as a response to the action of an external disturbance, taking into account the emergence of a stable value of the electric field due to the existence of voltage-current characteristic. It is shown that regardless of the nature of disturbances initiating current diffusion, the induced additional heat dissipation can significantly exceed the Joule losses determined in the approximation based on the constant current distribution over the entire cross-section of the composite. As a consequence, dissipative phenomena occurring in superconducting composites in response to external disturbances can lead to a significant reduction in the boundary of stable states.
