Research teams from the Southwestern Institute of Physics (SWIP), a subsidiary of China National Nuclear Corporation (CNNC), have made tremendous progress in the research and development of wall-treatment technology for the International Thermonuclear Experimental Reactor (ITER), a large scientific project that aims to replicate the sun's fusion process to produce clean energy.

Research workers of the SWIP have passed the delta final design review (Delta FDR) for the supplementary design of permanent electrode project of the glow discharge cleaning (GDC) system. They have also won the bid and clinched a deal for the design and production of the boronization system and the gas supply system for the X-ray crystal spectrometer (XRCS) in collaboration with counterparts from China Nuclear Industry 23 Construction Company, Ltd.

These remarkable achievements have further consolidated the presence of Chinese researchers in the ITER's core wall-treatment technology. Their business scopes have extended from the existing GDC system to boronization wall treatment, building a complete technical chain from impurity removal to surface pre-treatment. It also provides critical support for the operation of the ITER's full-tungsten first wall.

These two specific research tasks are directly connected with strategic design changes taken by the ITER in 2023, which required the replacement of first-wall materials from beryllium metal to tungsten metal. Although tungsten is reputed for its high-temperature resistance, its impurities can severely pollute plasma.

For instance, it has been found that even a small amount of impurities can lead to uncontrolled energy radiation during the sensitive discharge start-up phase. The GDC system, which is undertaken by the SWIP's research personnel and known as the powerful vacuum cleaner for the ITER's vacuum vessel, generates cold plasma via glow discharge to bombard and remove residual gases and impurities attached on the vessel wall. This Delta FDR has tackled the challenges of electrode manufacturing feasibility in complex spatial environments and cleaned final hurdles for the transition of the GDC system from design drawings to engineering and manufacturing.

Meanwhile, the newly-awarded boronization system acts as a sophisticated "surfaced coater". It adopts glow discharge-assisted deposition to deposit a boron film merely 10 to 100 nanometers thick on all plasma-facing surfaces, addressing the impurity risks posed by full-tungsten walls. This low-Z boron film serves as a physical barrier to effectively suppress the sputtering release of high-Z tungsten impurities. On the other hand, it works much like a sponge to capture and absorb impurities such as oxygen and carbon escaping from vessel walls, preventing them from entering the plasma core and causing radiative cooling.

Notably, this boronization system will draw on test experience from multiple existing tokamak facilities in the application into large-scale ITER devices for the first time. It is also compatible with future tritium-containing operating environments, providing the experimental operation of the ITER facility with assurance.

According to the newly-signed deal, the SWIP and China Nuclear Industry 23 Construction Company will be responsible for detailed design, equipment manufacturing and on-site installation, fully showcasing the comprehensive capabilities of Chinese researchers in the integration of complex fusion-engineering systems.

Luo Delong, deputy director-general of the ITER Organization, gave high praise to the coordinated development of the GDC and boronization project. In the next step, the Chinese side will strictly follow the overall ITER plan, accomplish the production and delivery of GDC electrodes, and contribute Chinese wisdom as well as strength to the international fusion energy development with solid technical expertise and outstanding engineering practices.