1983 年 18 巻 6 号 p. 317-323
The neutron irradiation effects on cryostability of composite superconductors for fusion reactor are studied based on Maddock's condition. In particular, to estimate the effects of 14MeV neutrons we assumed that the irradiation-induced degradation of critical temperature, critical current density and conductivity of stabilizer are determined by the damage energy depending on the neutron energy spectrum. The cryostability is found to decrease sensitively with increasing the fraction α of fusion neutrons with energy of 10-14MeV to the total neutrons;
(1) The Cu/superconductor ratio Rns, to stabilize the conductor, must be increased remarkably with increasing α as well as the total dose of the neutron fluence. The optimized Rns has a maximum value of about 80 in case of Nb3Sn with transition temperature Tc=15K, critical current density Jc=105A/cm2 and stabilizer resistivity ρ=5×10-8Ωcm. The fluence to give the maximum Rns shifts to the lower one with increasing α. In order that the composite conductor is fully stabilized under the irradiation (<1018n/cm2), one must choose the larger Rns than the maximum one.
(2) For the small Rns (-4), the stabilized overall current density decreases by several ten percents even at the fluence where Tc and Jc change only a few percent. This effect is dominated by the severe increase of ρ.