New insights into neutron irradiation damage in high-power thyristors enhance fusion reactor safety

Recently, a research group led by Associate Prof. LI Hua from Institute of Plasma Physics, 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.

The research results were published in Nuclear Science and Techniques.

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

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

What’s more, the effect of performance change of irradiated thyristor on the security protection system is studied. The result indicates the increasing of leakage current of irradiated thyristors could lead to the failure of protection system. The degradation of thyristor performance after neutron irradiation will raise the risk of damage of superconducting Tokamak.

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