It is important to construct superconducting magnets as cheap as possible. One of the methods to achieve such a purpose is to save the supercondcting material and operate the magnets at a high current density. Therefore it is useful to investigate the requirements for the operation of metastable superconducting magnets which can work at a current higher than the recovery current.
Using the theory of flux jump, we introduce a “stable current” below which no flux jump can occur. On a rough approximation, it is given byIs=√A PiheTof(x)/ρ where A: cross-section of the composite conductor. Pi: total perimeter of all the superconducting cores. he: effective heat transfer coefficient to the liquid helium through the stabilizer. To: a characteristic temperature of the superconducting cores. f(x): a characteristic function for the relative core radius x. ρ: effective resistivity of the composite. Then it is shown that superconducting magnets can operate without unexpected normal transitions in the region enclosed by the two curves of Is and Ic.
Next, we discuss the characteristics of our saddle shaped superconducting magnet for an one-KW MHD generator. We found that,
1) the magnet does safely operate in the metastable state;
2) the characteristics of the magnet are consistent with our theoretical results.
