Enhancement of the negative hydrogen ion generation by combining surface and volume production mechanisms: A simulation study

In negative hydrogen ion sources, the H− yield is a key parameter for the extracted negative ion and co-extracted electron currents. Generally, negative hydrogen ions are produced through two mechanisms: volume production and surface production. In this work, a global model is developed, which includes both the H− generation processes in the gas phase and its formation on the walls. The significant influence of the surface production mechanism on the H− density has been examined under different H temperatures, i.e., 500, 4000, and 8000 K, in a wide range of power (1–50 kW) and pressure (0.2–8 Pa). The results indicate that the H− density rises strikingly when surface production is included, especially at low pressure and high H temperature. This is because the H− formation induced by positive ions is comparable to the volume generation processes, and meanwhile the H− yield originated from the conversion of H atoms on the walls is strongly enhanced and dominates the discharge at high H temperature, i.e., the rate is dozens of times higher than the total volume production rate at 8000 K, 0.3 Pa. Moreover, the surface production mechanism also has a pronounced effect on the other plasma properties, and the influence depends on the H temperature and discharge conditions.