Measuring AC losses and critical current of high pressure synthesized MgB2 bulk rings by the transformer method

The results of experimental study of the critical current and AC losses in high pressuresynthesized MgB2 bulk superconductors are presented. The method is based on the use of the transformer configuration and suitable for samples in the form of hollow superconducting cylinders and rings. It was shown that the critical current measured by the transformer method is an order of magnitude lower than the value given by the magnetization technique. The obtained dependencies of the losses on current and frequency reveal the deviations from the critical state model behavior and reflect structural peculiarities of the investigated MgB2 samples.