Study of the multi-driver decoupling model of RF negative ion source

According to the latest physics design of the China Fusion Engineering Test Reactor (CFETR), a radio-frequency (RF)-driven negative ion source was selected as the preferred ion source for the neutral beam injection (NBI) system. In order to solve the key problems of the CFETR, a project called the Comprehensive Research Facility for Fusion Technology (CRAFT) has begun. Since the RF-driven negative ion source of CRAFT is a high-current beam source with large area, a multi-driver negative beam source was employed. When multiple RF drivers of the same type are operated at the same time, there may be mutual coupling and interference between them. This results in an asymmetric distribution of the RF magnetic field in the driver, thereby affecting the extraction of ion current. This study investigates some possible solutions which would provide theoretical support for CRAFT's RF negative ion source to achieve stable operation.