A MODEL FOR THE PREDICTION OF NB3SN CRITICAL CURRENT AS A FUNCTION OF FIELD, TEMPERATURE, STRAIN, AND RADIATION-DAMAGE

Conductors designed for fusion machines must operate at high fields, under large mechanical loads, and in a high neutron flux. Present designs favor the use of Nb3Sn with force-cooling by supercritical-helium to extract large nuclear and ac loss heat loads. Consequently, the magnet designer must have a good knowledge of the critical current of the superconductor as a function of field, strain, temperature, and radiation damage. Expanding on work by Hampshire, et al. and Ekin, combined with radiation-damage studies of Nb3Sn, we express the critical field (B(c)20) as function of temperature, strain and damage energy (E(d)). Similarly, the zero-field critical temperature (T(c)0) is expressed as a function of strain damage energy. The expressions for B(c20) and T(c0) are combined into a functional form that allows an accurate and consistent estimate of the critical current density at the operating conditions of fusion magnet conductors.