Beam current in extraction system of neutral beam ion source on HL-2A

In the extraction process of neutral beam ion source, the production of extraction current and deceleration current is analyzed and it is helpful for obtaining reliable extraction power and heat deposition power on the grids surface. Based on the electric connection way of the extraction grids of neutral beam ion source on HL-2A and the basic physical process during ion beam extraction, beam extraction process is analyzed and the principle sources of deceleration current are given. Through analyzing the results in gas pressure scanning experiment, it is found that with gas pressure increasing, deceleration current increases, and the ratio of deceleration current to extraction current increases approximately linearly. A physical model is set up based on the process of extracted ion beam coming through the extraction grids. The dependence of the ratio of deceleration current to the acceleration current on the discharge gas pressure is calculated, and the result is consistent with the experimental result which shows the rationality of the analysis method.