Thermonuclear device

In a thermonuclear device, since neutrons formed by nuclear reactions deteriorate the property of the constituents materials for toroidal coils and colloidal coils, superconducting property of the superconductors and the strength property of the insulators suffer from remarkable adverse effects. In view of the above, in the present invention, small pieces made of an oxide conductor are attached near the superconductor coils, to which a current supply terminal and an output voltage terminal are disposed to supply a weak current and the output voltage therefrom is monitored. The superconducting property of the oxide superconductors is changed due to the irradiation amount of radiation rays to generate electric resistance. By monitoring the generated voltage, the irradiation amount of radiation rays can be recognized previously. In a case of cooling with liquid helium, the critical magnetic field is high and the material is substantially free form the effect. Thus, maintenance and checking can be conducted previously and it is also possible to prevent such a trouble that the superconductor coils are damaged by irradiation rays to cause quench. (N.H.)