Dose dependences of the superconducting transition temperature and collision cascades of Nb3Sn

The concept of the cascade defective regions as inclusions of a disordered phase with the specific physico-chemical properties is used to interpret the doses dependences of the superconducting transition temperature as an equivalent of the composition-property diagram for the mixture of ordered and disordered phases. The experimentally measured dose dependences of the critical temperature of Nb3Sn irradiated with protons and helium ions with an energy of the order of 100 kev were used to estimate the volumes of the displacement cascades. The experimental and theoretical values of the cascade volumes were in satisfactory agreement. A criterion of equivalence of irradiation doses which can be used to predict the extent of damage in superconducting materials is proposed. Recommendations are given for the characteristics of protection of these materials in controlled thermonuclear reactors with magnetic plasma retention. (author)