Experimental Study On The Plasma Characteristics In The Extraction Area Of Radio Frequency Negative Ion Source

With the development of fusion research,the neutral beam injection system,as one of the most important auxiliary heating methods in the magnetic confinement controllable fusion device,not only has a clear heating mechanism and high heating efficiency,but also can realize the current drive of the plasma.In recent years,the requirements of the strength and energy of the neutral beam are increasing.Hence,negative ion sources have gradually become the main research direction due to their high neutralization efficiency.Compared with filament source,the RF(Radio Frequency)negative ion source which generates plasma by RF coil has the advantages of long service life,convenient maintenance and no filament pollution,which has become the primary choice of NBI system.In order to study the key technology of RF negative ion source,ASIPP designed and built the prototype RF negative ion source in 2016.At present,it has the capability of stable operation with 100kW RF power,but there are still many deficiencies.Therefore,it is particularly important to study the behavior characteristics of plasma in the extraction area based on the prototype ion source.In this paper,relevant research results were fully investigated,and it was found that the magnetic field filter(MFF)was the key factor affecting the plasma in the extraction area.Firstly,the key parameters of the MFF that can affect the plasma are summarized from the experimental results of each research institute.The electromagnetic simulation calculation of the MFF is carried out with the finite element simulation analysis software to analyze its shortcomings.Secondly,the measurement experiment of the MFF was completed by the electric manipulator with Gauss meter,and the results are compared with the simulation results to comprehensively evaluate the status of the MFF.On this basis,the MFF of various configurations suitable for the prototype ion source are designed and simulated.The design of new MFF composed of permanent magnet and PG current with wire was determined.Finally,the influence of the MFF on the electron temperature and density and the uniformity distribution of plasma was investigated by using Langmuir probe and emission spectroscopy system to simultaneously diagnose the plasma behavior characteristics in the extraction area.The development of this subject has laid a certain theoretical and experimental foundation for the development of the prototype negative ion source at ASIPP.Experience has been gained in designing the MFF suitable for large size ion source,and the experimental research on the plasma parameters has promoted the development of diagnostic system,it also has certain reference value for the structure upgrading and optimization of RF negative ion source.