The design of boronization coating system using deuterated diborane in EAST

• A new boronization system using B₂D₆ is developed for EAST. • The system features comprehensive safety designs for toxic B₂D₆. • Purity tests confirm B₂D₆ with <0.01% impurities, suitable for experiments. • B₂D₆ eliminates hydrogen and carbon impurities compared to carborane. • The system supports ITER-relevant research and future full-metal wall devices. Boron coating on plasma-facing components (PFCs) surface is widely used in fusion devices to suppress the oxygen impurities and form a protective layer for metal walls, which is chosen as new research plan of ITER. In EAST, a new boronization coating system which introduces deuterated diborane (B 2 D 6 ) as the working material is developed to support ITER. Due to the strong toxicity and flammability of B 2 D 6 , the main work focus on the safety design of the gas introduction and off gas exhaust. The new developed boronization system includes six main components, such as special gas safety cabinet, double-locked gas introduction pipes, vacuum pumps, off gas exhaust, gas monitoring system and interlocking control system. In order to maximize the uniformity of boron film on first walls surface, three gas injection ports were toroidally placed in EAST mid-plane ports. Finally, a specific deuterated diborane detection system was developed to detect the hydrogen contents in diborane gas which manufactured by Spectrum Materials company in China. The results showed that deuterium diborane was truly existed, even though there were still some hydrogen species existed. This new developed boronization coating system and deuterated diborane gas will provide valuable technical support for EAST 's future plasmas operation on the full metal walls.