Two-dimensional spatial distribution and production mechanism of H− ions in cylindrical inductively coupled H2 discharges

Abstract

In this work, radio frequency (RF) inductively coupled hydrogen plasmas have been investigated using a two-dimensional (2D) hybrid model, consisting of a fluid module and an electromagnetic field module. This paper focuses on the effects of driver chamber radius, RF power, and gas pressure on the spatial distribution of H− density. The results show that H− ions are produced all over the driver chamber and exhibit a strong accumulation in the plasma center. Furthermore, this accumulation becomes much stronger with a smaller radius, due to the larger dc electric field intensity. While the H− density in the plasma center first increases and then decreases with the increasing radius. This is because the total production rate of H− has an opposite tendency to that of the dc electric field intensity. Therefore, the spatial distribution of the H− is governed by the dc electric field and the production mechanism. In addition, the accumulated area of H− at different powers is nearly invariable, whereas it spreads out with pressure. This can be attributed to the different spatial profiles of the dc electric field. To validate our model, the calculated electron density is compared with the experimental result, and a reasonable agreement is achieved. Hopefully, the results in this work could lead to a deeper insight into the variations of the spatial distribution of H− density on the driver chamber radius and discharge conditions, which is very important in the design of a high efficiency and compact negative hydrogen ion beam source.