A comprehensive study on impurity behavior in LHD long pulse discharges. (August 2017)

• Record Type: Journal Article
• Authors: Nakamura, Y.; Tamura, N.; Kobayashi, M.; Yoshimura, S.; Suzuki, C.; Yoshinuma, M.; Goto, M.; Motojima, G.; Nagaoka, K.; Tanaka, K.; Sakamoto, R.; Peterson, B.J.; Ida, K.; Osakabe, M.; Morisaki, T.
• Is Part Of: Nuclear materials and energy. Volume 12(2017)
• Page Start: 124
• Page End: 132
• Publication Date: 2017-08
• Subjects: Long pulse discharge -- Impurity accumulation window -- Radial electric filed -- Impurity screening -- Turbulent impurity transport; Nuclear energy -- Periodicals; Nuclear fuels -- Periodicals; Nuclear reactors -- Materials -- Periodicals; Radioactive substances -- Periodicals; 621.4833
• DOI: 10.1016/j.nme.2016.11.005
• Languages: English
• ISSNs: 2352-1791

Abstract

Highlights: ∙ Impurity behavior is investigated in a variety of LHD long pulse discharges (hydrogen or helium plasma, super dense core plasma and multi-species plasma). ∙ A comprehensive understanding of impurity behavior in steady state plasmas is provided on the basis of impurity transport theories. ∙ Mapping of impurity behavior on n-T space at the plasma edge provides operation scenarios to build up fusion-relevant plasmas. Abstract: Impurity behavior is studied in a variety of LHD (Large Helical Device) long pulse discharges, i.e. standard hydrogen plasmas, super dense core plasmas, helium plasmas with ICH (Ion Cyclotron Frequency Heating), multi-species plasmas mixed with H and He. Density scan experiments show a specific density range of impurity accumulation for only hydrogen discharges. Strong suppression of impurity accumulative behavior is observed in high temperature plasmas with high power heating. The main contributions to impurity transport are extracted by a comprehensive study on impurity behavior, i.e. investigating the critical conditions for impurity accumulation and the parameter dependences. It is found that the impurity behavior is determined by three dominant contributions, i.e. neoclassical transport mainly depending on radial electric field, turbulent transport increasing with heating power and impurity screening at high edge collisionality in the ergodic layer. The mapping of impurity behavior on n-T (electron density and temperature) space at the plasma edge shows a clear indication of the domain without impurity accumulation and provides operation scenarios to build up fusion-relevant plasmas.