Properties of the LHD plasmas with a large island—super dense core plasma and island healing

In local island ( m / n = 1/1) divertor discharges in the large helical device a stable super dense core plasma develops when a series of pellets are injected. A core region with a density as high as 4.6 × 10 20 m −3 and a temperature of 0.85 keV is maintained by an internal diffusion barrier with a very high density gradient. In a study of island dynamics, we find that an externally imposed large island ( m / n = 1/1) as large as 15% of the minor radius is healed when beta at the island exceeds a critical value.