Experimental study of negative ion profiles in H2-MAR plasmas in divertor simulator MAP-II

The negative hydrogen ion density profile is measured in hydrogen molecular assisted recombination (MAR) plasmas in the steady-state linear divertor/edge plasma simulator material and plasma (MAP)-II device. Fulcher band spectroscopy is also performed for the measurement of the ro-vibrational distribution of hydrogen molecules and the degree of dissociation. We have developed negative ion diagnostics using a combined scheme of an ‘eclipse’ laser photo-detachment system and a double probe. The former is to avoid probe surface ablation phenomena while the latter is to avoid the anomaly in the Langmuir probe characteristics in recombining plasmas, which leads to an overestimation of Te. Negative hydrogen ions are detected in the peripheral regions of the hot plasma column while vibrationally excited molecules exist in the plasma core. Based on the rate equation, the measured negative ion density is compared with the results of model calculations.