Effect of pre-irradiation on corrosion performance of beryllium in BEPC II/BES III and CEPC beam pipe

Abstract

Abstract Beryllium is one of the most important materials in high energy physics and nuclear physics experiments. Beam pipe, which lies at the centre of the second-generation Beijing Electron Positron Collider (BEPC II) and its detector Beijing Spectrometer III (BES III), is made of beryllium and the electron–positron beam collision occurs in it. China is planning to build a Circular Electron Positron Collider (CEPC) with higher brightness, in which the beryllium beam pipe will inevitably be used. High-speed particles will produce a lot of γ -rays and neutron irradiation and heat loads on the beryllium beam pipe in the collision. In order to ensure the normal particle detection of BES III, a coolant must be used to take away the excess heat to maintain the constant temperature of the outer wall of the beam pipe. Researches, however, have shown that the coolant can cause some corrosion of beryllium and affect the normal operation of the beam pipe in the irradiation environment. Therefore, this paper intends to study the influences of different irradiation types and doses on the corrosion performance of beryllium in EDM-1, by using No.1 Electrical Discharge Machining Oil (EDM-1) to scour the beryllium sample after γ and neutron pre-irradiation, according to the working condition of BEPC II/BES III. It is found that pre-irradiation promotes the formation of pitting nuclei and corrosion holes on the beryllium surface. The corrosion effect of γ pre-irradiation on beryllium in EDM-1 is much more significant than that of γ and neutron pre-irradiation and the corrosion strengthens with the increase of irradiation dose. Impurity elements in beryllium play an important role in inducing pitting corrosion and promoting the formation and expansion of corrosion holes. S 2 − in EDM-1 may adsorb on the surface and further be oxidized to SO2 and SO 4 2 − , which can be incorporated into the oxide–metal interface and change its composition. In conclusion, irradiation enhanced the corrosion of beryllium in EDM-1.