Critical current and cryogenic stability modelling of filamentary MgB2 conductors

The modelling of a single filament, 6 filaments and 19 filaments MgB(2) conductors was performed for two limiting cases: a) isothermal conditions considering J(c)(B) dependence, b) considering heating effects but with J(c) magnetic field independent. As a starting point of the modelling in case a) we used experimental dependence of J(c)(B,4.2 K) for the best wire. Then Poisson equation for magnetic vector potential was solved by finite element method and self-field critical current densities of the wires with different diameter were calculated. There is no significant dependence of J(c) in range of electric fields E % 10 mu V/cm. The isothermal modelling with J(c) independent on magnetic field, case b), gave the results more close to the experimental ones. From the modelling of the heating effects we conclude that the cryogenic stability of the used Cu/SUS316/MgB(2), Fe/MgB(2) and Cu/MgCu(2)/MgB(2) wires is adequate. The stabilizing copper layer can take all the current up to the onset of film boiling of LHe where the current starts to decrease with increasing electric field, i.e. at this point the differential resistivity of the Cu/SUS316/MgB(2) wire starts to become negative (indicating the onset of instability). Analysis of mechanically induced defects limiting the J(c) in 6 filaments conductor is presented.