Analysis of plasma characteristics of a high-power radio frequency negative ion source based on Langmuir probe

The plasma parameters of the radio frequency (RF) negative ion source directly affect the density of negative ions and the uniformity of the plasma in the extraction area. In order to understand the behavior of the plasma inside the RF negative ion source, a system of planar and cylindrical Langmuir probes was developed. The system was tested on the RF ion source test facility at the Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP). The Langmuir probe was used to measure the spatial distribution of the plasma parameters in the extraction area and the axial distribution of the plasma parameters in the expansion area. In the experiment, the relationship between the density parameters and the RF power and source pressure is explored. Experimental results show that the plasma parameters present better uniformity, whilst the electron temperature is maintained at a lower level (about 0.8eV) due to the filter magnet field in the extraction area. Also, it has been measured that the electron density can reach up to 6 × 1016 m−3 at 55 kW of RF power. Considering the production of negative ions in the extraction area, the Electron Energy Probability Function (EEPF) is also given at different operational parameters. This article helps us to understand the plasma characteristics and provide technical support for experimental studies of negative ion production and extraction.