Measurements of hydrogen negative ion and its comparison with the molecular hydrogen spectra in divertor simulator MAP-II

Abstract Negative ion density and vibrationally excited molecular hydrogen were compared in divertor simulator MAP-II. Laser photo-detachment technique was used for the negative ion measurement, and Fulcher- α band ( d 3 Π u → a 3 Σ g + ) spectra were used to determine the vibrational distribution of excited hydrogen molecules in the electronic ground state. As the hydrogen gas pressure increased, the negative ion density increased at first, then started to decrease as the hydrogen pressure exceeded 10 mTorr. On the other hand, the vibrational temperature measured in the same condition decreased when the hydrogen gas pressure became higher than 10 mTorr. We found that the decrease in the vibrational temperature resulted in the decrease in the negative ion density.