Diagnostics of recombining plasmas in divertor simulator MAP-II

Atomic and molecular processes in volumetric recombination phenomena relevant to divertor detachment are investigated in a divertor simulator MAP (Material and Plasma)-II. In the recombining plasmas, quantitative measurements of parameters, especially using a Langmuir probe, are difficult, so that the development of alternative diagnostics is important. Recombination can be induced in He plasma by puffing of He or H2. In the He puffing case, the Rydberg spectra show an electron temperature of lower than 0.1 eV, while in the H2 puffing case, the Rydberg spectra disappear even though the reduction of the ion flux is apparent, showing that another type of recombination occurs. Negative hydrogen ions are observed in the peripheral region of the plasma column. (author)