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

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, nH−, in the circumference of the plasma, while the conventional radiative and three-body recombination processes disappeared. nH− is localized in the outer region where electrons exist (ne∼5×1017 m−3, Te=3–5 eV). The peak value of nH− is 1.2×1017 m−3 and the ratio of nH−/ne 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.