A novel discharge control method for megawatt-level NNBI RF ion sources

High-power efficient coupling and high-density negative ion beam extraction are critical challenges urgently requiring solutions for the Radio Frequency (RF) driven Negative ion based Neutral Beam Injection (NNBI) systems. To improve the power transfer efficiency of the RF ion source power supply and simultaneously simplify the design of the NNBI filter magnetic field, this paper proposes a novel discharge control method for NNBI RF ion sources. The design scheme of the RF ion source inverter power supply is analyzed. The principle of a frequency-tuning-based impedance matching control method for the inverter power supply is investigated, and its simulation verification is completed. Based on the operational mechanism of the power supply, a control method utilizing pulsed power modulation to optimize the electron temperature distribution within the ion source is proposed. The inverter power supply exhibits fast frequency adjustment, enabling dynamic impedance matching. This facilitates efficient RF power coupling into the ion source and improves electromagnetic compatibility, thereby reducing arcing incidents in the excitation coil. The method of modulating the electron temperature distribution within the ion source via pulsed power is beneficial for simplifying the design and reducing the engineering complexity of the NNBI filter magnetic field.