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Description
The plasma parameters of the radio frequency (RF) negative ion source directly affect the density of negative ion and the uniformity of the plasma in the extraction zone. In order to understand the behavioral characteristics of the plasma inside the RF negative ion source, a set of Langmuir probe system (plate probe and cylindrical probe) was developed and 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 zone and the axial distribution of the plasma parameters in the expansion zone. In the experiment the relationship between the density parameters and the RF power, source pressures is explored. Experimental results show that the plasma parameters presents better uniformity and the electron temperature is maintained at a lower level (Te<2eV) due to the filter magnet field in the extraction zone and the electron density can reach up to $10^{17}/m^3$ at the 60kW RF power. Considering the production of negative ions in the extraction zone, the Electron Energy Distribution Functions（EEDF) is also given at different operational parameters. This article helps us to understand the plasma characteristics and provide technical support for experimental study of negative ion production and extraction.
