Influence of component structure on RF power coupling and plasma parameters in a dual-driver RF negative ion source

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Abstract
Radio-frequency (RF) negative ion sources are essential component for neutral beam injection systems in magnetic confinement fusion devices. In this work, the RF power coupling efficiency of the Comprehensive Research Facility for Fusion Technology dual-driver RF negative ion source was experimentally measured on the Hefei Open-facility for Negative-ion Source Research test facility. The effects of selected external configurations were evaluated, including the relative RF coil current direction, the diameter of the electromagnetic shielding (EMS) for the RF driver coil, and the cusp magnet configuration. Under the reference configuration without EMS or cusp magnet systems, the RF power coupling efficiency was approximately 55%. Changing the relative RF coil current direction had only a marginal effect on the coupling efficiency and electron density. The installation of EMS improved the plasma density uniformity in front of the plasma grid (PG), while the EMS diameter affected both network resistance and RF coupling efficiency. The cusp magnet system mounted on the backplate of the RF driver reduced the RF coupling efficiency and electron density near the extraction region, whereas the additional sidewall cusp magnet system increased the electron density in front of the PG despite a further decrease in coupling efficiency. The results show that the evaluated external configurations can increase the RF power coupling efficiency by up to approximately 10% and increase the plasma density in the extraction region by about 6%.
Funding Information
  • National Natural Science Foundation of China (No.U2341250)
  • Comprehensive Research Facility for Fusion Technology of China (No. 2018-000052-73-01-001228)
  • Science Foundation of Institute of Plasma Physics, Chinese Academy of Sciences (No. DSJJ-2024-03)

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