Final design and manufacturing of the neutralizer for the negative ion-based neutral beam injector test facility of CRAFT

The Comprehensive Research Facility for Fusion Technology (CRAFT) is a highly integrated research and development base. It consists of 20 different demonstrating or testing facilities that address most of the critical technologies and systems for the fusion reactor in China. A negative ion-based neutral beam injector (NNBI) test facility is established in CRAFT. A gas neutralizer is applied to the CRAFT NNBI test facility for the neutralization of the negative hydrogen ion beam. The target of the neutralization efficiency is more than 50%. The length of the neutralizer is 3 m. The neutralizer is divided into two adjacent vertical channels and the total opening is 1.7 m x 0.32 m. The neutralizer is mainly composed of channel plate, support structure, beam scraper, cooling water pipes, and gas inlet pipes. Based on the design requirements of the neutralizer, the support structure and cooling water pipes were optimized, to reduce the total weight. The structural strength of all components was simulated and compared to the preliminary design. The manufacturing of the neutralizer is ongoing. Some manufacturing challenges have been overcome, such as deep hole drilling. Several 1.7 m long cooling channels were successfully drilled in a copper panel and the ratio of depth to diameter was 94.