Study on irradiation effect of insulating materials for fusion superconducting magnet: change in electric insulation performance by irradiation

In the fusion reactor, hybrid composite material composed of glass fiber reinforced plastic (GFRP) and polyimide film is used for insulation material of superconducting magnets. The insulation material is used in severe environments of fast neutron fluence of 10(22) n/m(2) (E > 0.1 MeV), cryogenic temperature, large mechanical stress (43 MPa of interlaminar shear stress) and high voltage of 20 kV. Thus, insulation material is required to maintain its insulation performance even in such environments. In the previous study about irradiation effect on insulation material, interlaminar shear strength was used to evaluate the radiation resistance. However the insulation performance can be degraded by microscopic cracks even if it is not fractured. In order to investigate the effect of mechanical deterioration on the insulation performance, a dielectric breakdown test was conducted under shear stress at 77 K on irradiated hybrid composite of GFRP and polyimide film.