Direct method of measuring ac losses in superconducting tapes, simultaneously subjected to ac current and ac magnetic field

A novel technique for measuring ac losses in short lengths of high-temperature-superconductor tapes is presented. The principle of operation is based on the direct detection of the heating produced by the losses. In the presented system a tape can be subjected to current up to 40 A rms and ac magnetic field up to 600 mT rms, with an arbitrary phase between them; the measurements are made at 77 K. The noise floor is of the order of 1 /spl mu/W/cm. A number of test experiments are presented, which prove the validity of the technique.