Abstract
In reduced recycling discharges using a local island divertor in the Large Helical Device [O. Motojima, H. Yamada, A. Komori et al., Phys. Plasmas 6, 1843 (1999)], a stable high-density plasma develops in the core region when a series of pellets is injected. A core region with ∼5×1020m−3 and temperature of 0.85keV is maintained by an internal diffusion barrier (IDB). The density gradient at the IDB (r∕a∼0.6) is very high, and the particle confinement time in the core region is ∼0.4s. Because of the increase in the central pressure, a large Shafranov shift up to ∼0.3m is observed. The critical ingredients for IDB formation are a strongly pumped divertor to reduce edge recycling, and multiple pellet injection to ensure efficient central fueling. No serious magnetohydrodynamics activity and impurity accumulation have been observed so far in this improved discharge.
Highlights
To achieve a burning plasma is the final goal for the toroidal magnetic confinement fusion research.1 Much effort and time have been paid to discover a breakthrough toward this goal
In the Large Helical DeviceLHDproject,7 one of the most important research goals is to realize a reactor-relevant plasma through effective edge control with divertors
A superdense plasma with the central density of ϳ5 ϫ 1020 m−3 is maintained by the formation of an IDB with extremely high-density gradient
Summary
To achieve a burning plasma is the final goal for the toroidal magnetic confinement fusion research. Much effort and time have been paid to discover a breakthrough toward this goal. In the Large Helical DeviceLHDproject, one of the most important research goals is to realize a reactor-relevant plasma through effective edge control with divertors. A superdense coreSDCmode, achieved with the formation of an internal diffusion barrierIDB, was discovered on the LHD in the LID configuration with a central fueled condition by the repetitive pellet injection.. A superdense coreSDCmode, achieved with the formation of an internal diffusion barrierIDB, was discovered on the LHD in the LID configuration with a central fueled condition by the repetitive pellet injection.15 In this mode, a superdense plasma with the central density of ϳ5 ϫ 1020 m−3 is maintained by the formation of an IDB with extremely high-density gradient. The characteristics of the IDB-SDC mode are mainly described, together with its future aiming at the reactor plasma.
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