A research group led by Associate Prof. LI Hua from the Hefei Institutes of Physical Science of the Chinese Academy of Sciences, along with Dr. TONG Wei's research group from Hefei University of Technology, revealed the neutrons irradiation damage mechanism of high-power thyristors used in quench protection system.

High-power semiconductors, especially thyristors, are the key components of the power supply system in the Tokamak fusion device. Some extremely important power equipment must be placed close to the superconducting Tokamak to protect the safety of the reactor. The neutron produced by the Deuterium Tritium fusion reaction could change the material properties of the p-n junction. Hence the electrical performance changes of the thyristor after neutron irradiation should be studied.

In this study, the researchers established the relationship between physical and electrical characteristics of high-power thyristors under 14 MeV neutron irradiation. A mathematical correlative model was built after considering various key parameters of thyristors including carrier lifetime, mobility, reverse/forward blocking voltage, and reverse recovery charge. The simulations and experiments were carried out to reveal the electrical parameters degradation of thyristor under neutron irradiation.

Moreover, the team studied the effect of performance change of irradiated thyristors on the security protection system, which indicated that the increasing leakage current of irradiated thyristors could lead to the failure of the protection system. Therefore, the degradation of thyristor performance after neutron irradiation will raise the risk of damage to the superconducting Tokamak.

"Our research provides basis support and further study directions for improving the reliability of fusion reactor protection system," said LI Hua.

This study was published in Nuclear Science and Techniques.

Schematic diagram of neutron irradiation experiment. (Image by LI Hua)

The change in each thyristor parameter before and after neutron irradiation. (Image by LI Hua)