On the Large Helical Device （LHD） where nested magnetic surfaces are surrounded by the ergodic field layer, edge transport barrier （ETB） was produced in neutral-beam-injection （NBI） heated plasmas through transi...On the Large Helical Device （LHD） where nested magnetic surfaces are surrounded by the ergodic field layer, edge transport barrier （ETB） was produced in neutral-beam-injection （NBI） heated plasmas through transition and non-transition processes. The former case is the ETB formation by L-Htransition, where characteristics of L-H transition observed in a tokamak plasma are clearly recognized. The confinement improvement is the modest （- 10%）, compared with the ISS95 international stellarator scaling. The threshold power for the transition is comparable or slightly lower than the ITER scaling law established by tokamaks and compact tori. The ETB is formed inside the ergodic field layer of the vacuum field. The ETB formation destabilizes edge coherent modes such as m/n = 1/1, 2/3 and 1/2, of which rational surfaces are in the magnetic hill. The formed ETB is partially and transiently destroyed by these coherent edge MHD modes and edge localized modes （ELMs） typically observed in Ha signals. The latter ETB is observed in a plasma with large reversed NBI-driven current more than 100 kA at Bt = 1 T. In these plasmas, the edge magnetic shear is enhanced by the current and the rotational transform in the core region is expected to be appreciably reduced. Thus reduced rotational transform in the plasma central region will enhance outward heat and particle fluxes toward ergodic edge layer. The ETB with steep electron temperature gradient up to - 5 keV/m is formed by blocking enhanced outward heat flux.展开更多
基金supported in part by the JSPS-CAS Core-University Program in the field of Plasma and Nuclear Fusion and the JSPS Grant-in-Aid for Exploratory Research(No.6656287)
文摘On the Large Helical Device （LHD） where nested magnetic surfaces are surrounded by the ergodic field layer, edge transport barrier （ETB） was produced in neutral-beam-injection （NBI） heated plasmas through transition and non-transition processes. The former case is the ETB formation by L-Htransition, where characteristics of L-H transition observed in a tokamak plasma are clearly recognized. The confinement improvement is the modest （- 10%）, compared with the ISS95 international stellarator scaling. The threshold power for the transition is comparable or slightly lower than the ITER scaling law established by tokamaks and compact tori. The ETB is formed inside the ergodic field layer of the vacuum field. The ETB formation destabilizes edge coherent modes such as m/n = 1/1, 2/3 and 1/2, of which rational surfaces are in the magnetic hill. The formed ETB is partially and transiently destroyed by these coherent edge MHD modes and edge localized modes （ELMs） typically observed in Ha signals. The latter ETB is observed in a plasma with large reversed NBI-driven current more than 100 kA at Bt = 1 T. In these plasmas, the edge magnetic shear is enhanced by the current and the rotational transform in the core region is expected to be appreciably reduced. Thus reduced rotational transform in the plasma central region will enhance outward heat and particle fluxes toward ergodic edge layer. The ETB with steep electron temperature gradient up to - 5 keV/m is formed by blocking enhanced outward heat flux.
