Effect of irradiation of silicon photodiode arrays for ITER radial x-ray camera investigated by measuring response and current–voltage characteristics

The response and current–voltage (I–V) characteristics of irradiated and non-irradiated silicon photodiode arrays (SPDAs) for use in the International Thermonuclear Experimental Reactor camera are measured and compared. Irradiation experiments are carried out using a uranium–zirconium hydride pulsed reactor. The total equivalent 1 MeV neutron fluence with energy above 0.01 MeV is ∼9.89 × 10¹³ n cm⁻². The output signal of the irradiated SPDA (XD2) shows a nonlinear trend during the irradiation experiment. The final signal is about 5.6% of the original one in the visible light region. Tests on the Experimental Advanced Superconducting Tokamak (EAST) show that the XD2 signal is 70%–80% of that of a non-irradiated SPDA (XD3). This indicates that irradiated SPDAs can still observe plasma radiation after exposure to 9.89 × 10¹³ n cm⁻² neutron fluence. However, because the neutron fluence of external camera detectors will reach 1.4 × 10¹⁶ n cm⁻² in D-T phase, the SPDAs might become unusable at some point. The responsivity ratio of irradiated and non-irradiated SPDAs is about 4%–20% from 7 to 13 keV. The degradation of responsivity is related to the energy level. After irradiation, the reversed dark current rises from 0.1 to 10 nA to a level of around 1 µA. In terms of tests of XD2 on EAST, zero bias is a good working condition for irradiated SPDAs.