Observation of molecular assisted recombination via negative ions formation in a divertor plasma simulator, TPDSHEET-IV

Abstract

Molecular assisted recombination (MAR) via negative ions formation has been observed in a linear plasma simulator. A small amount of hydrogen gas puffed into a hydrogen plasma strongly reduced the heat flux to the target and rapidly increased the density of negative ions of hydrogen atom, n H − , in the circumference of the plasma, while the conventional radiative and three-body recombination processes disappeared. n H − is localized in the outer region where electrons exist ( n e∼5×10 17 m −3, T e=3–5 eV). The peak value of n H − is 1.2×10 17 m −3 and the ratio of n H − / n e in the outer region goes up to over 20%. These results can be well explained by taking the mutual neutralization between the negative and positive ions of MAR in the detached plasma into account.