Application of magnetic flux conservation law in research of critical states of htsc ring-shaped sample

Objective of the work is to study the magnetization curve as a function of the magnetic field of a superconducting ring $B_K(i)$ on the magnetic field of the solenoid $B_C(i)$ on the velocity of change of magnetic flux through the hole of the ring. Material and Methods: Experiments were conducted to measure the critical current of HTSC ring inductive method. The main feature of the inductive method of magnetization curves removal is that HTSC ring interacts only with its own magnetic field and there is no direct effect of the external magnetic field on the sample. The authors measure the magnetic field generated by HTSC ring, which is induced by administration of the external magnetic flux in the ring hole by means of solenoid with constant current. One of the advanteges of the conducted experimental work is the fact that the experiment clearly demonstrates the action of two laws describing the inductive currents and the ranges of these laws. It is shown, for HTSC samples at currents $I < I_{2c}$ – it is the law of conservation of magnetic flux, and for the samples in the resistive (or partially resistive) state, with the currents $I\geq I_{2c}$ – it is the law of electromagnetic induction. As the material of the ring is not a directly effected by the external magnetic field of the magnetization curve, the curve of the magnetic field extends parallel to the ring axis of the external magnetic field and depends on the velocity of change of magnetic flux. By means of the magnetization curve study to velocity of magnetic flux change the researchers determined the phenomenon of equidistance of magnetization curve on the multiple velocities of magnetic flux change. As a result the authors discovered a new correlation for the voltage-current characteristic of HTSC for area of near-critical current. Thus the most important fact is that nature of transition doesn't depend on type and structure and superconductor microstructure, and is defined only by the law of magnetic flux conservation.