Deuterium experiment with large-scale negative ion source for large helical device

The deuterium experiment with various source plasma diagnostics was conducted at the research and development negative ion source at National Institute for Fusion Science, which is a cesium-seeded large-scale negative hydrogen-ion source with half discharge volume and the same type of ion source for large helical device. A change of filling gas from hydrogen to deuterium increased line-averaged negative ion density by a factor of 1.3 in beam extraction region as a result of flattened profile with keeping central density. Positive ion and electron densities increased threefold. This was influenced by the increase of plasma density in the plasma generation region. The plasma space potential varied as equivalent of the collisionless sheath theory in electro-positive plasma expected by the hydrogen isotope gas species, although the negative ion could affect sheath formation. Higher atomic cesium density was observed because of higher sputtering yield due to higher momentum of deuterium. (C) 2020 The Japan Society of Applied Physics