Experimental Setup and Results of a Radio Frequency Ion Source for Fusion Research Applications

The 13.56 MHz radio frequency ion source test bed (RFISTB) has been designed and constructed to evaluate the instruments used in fusion and plasma physics experiments at the Physics and Accelerator Research School in Tehran, Iran. This test bed enables the integration of advanced diagnostic tools for a comprehensive analysis and characterization of ion beam dynamics utilized in energy analyzers and neutral beam injectors. In this article, both theoretical and experimental details of the RFISTB system are presented. Subsequently, the operational capabilities of radio frequency (RF) ion sources have been examined. For this purpose, the effects of various system components, such as applied RF power, probe voltage and focusing voltage, are analyzed and characterized through experiment. To our knowledge, the Thonemann ion source type has only been tested in direct mode and up to 5 keV. Higher voltages cannot be attained due to arc discharge. In this study, we have investigated the pulse performance of the system in addition to the direct mode, reaching up to 12 keV. In addition, since the impedance varies with fluctuations in discharge pressure and input power, accurately calculating the equivalent impedance of plasma during discharge is challenging. To optimize the transfer of maximum output power from the RF power source to the antenna of the ion source an impedance-matching circuit has been designed.