Irradiation effects on magnetic probes made of mineral insulated cable

A magnetic probe made of mineral insulated (MI) cable in Japan Material Testing Reactor (JMTR) was irradiated as one of the irradiation tests on diagnostics components for experimental thermonuclear reactors such as International Thermonuclear Experimental Reactor (ITER). Magnetic probes have to be installed inside the vacuum vessel to measure the magnetic field, which is very important for the position control of the plasma. The magnetic probe made of MI cable is regarded as the most reliable magnetic sensor, and proposed to ITER. The irradiated coil of the magnetic probe was made of MI cable with 1.6 mm outer diameter, 0.5 mm center conductor diameter and MgO insulator. The fast neutron flux (>1 MeV) and fast neutron fluence were 9×10¹⁶ n m^-2 s^-1 and 6×10²³ n m^-2, respectively. The probe inductance was analyzed with the equivalent circuit where the sheath is modeled as a secondary coil in order to remove the shielding effect of the sheath. A weak dependence of the inductance on the temperature was found, which is explained by the thermal expansion of the coil. There is no irradiation effect on the electrical characteristics of the probe up to the fluence of 6×10²³ n m^-2, except RIEFM of 5-6 V between the sheath and the center conductor.