Profile control and its effects on plasma confinement in Heliotron E

The effects of the plasma profile on the global energy confinement have been studied in Heliotron E with special regard to differences between heating methods (ECH, NBI and NBI + ECH). With high power NBI, peaked T i and peaked n e profiles (T i (0)/⟨T i ⟩ ≲ 2.7, n e (0)/⟨n e ⟩ ≲ 4.5) were simultaneously achieved under low recycling conditions. A peaked n e profile (n e (0)/⟨n e ⟩ ≳ 2.5 ) could lead to the high T i mode where the ion heat transport in the central region is substantially reduced. By changing the ECH launching condition (on-axis, off-axis and toroidally oblique injection), the peakedness of the T e profile could be controlled in the range 1.3 ≲ T e (0)/⟨T e ⟩ ≲ 4.5. A peaked T e profile and a flat n e profile (3.5 ≲ T e (0)/⟨T e ⟩, n e (0)/⟨n e ⟩ ≲ 1.8) were brought about by the well focused on-axis ECH. The ECH plasma with a peaked T e profile has higher stored energy than that with a moderately peaked T e profile for the same injected ECH power and the same density region. The global energy confinement time normalized by the LHD scaling, τ E G /τ E LHD , showed n e (0)/⟨n e ⟩ dependence for the low T i mode NBI plasmas. For the high T i mode, the n e (0)/⟨n e ⟩ dependence of τ E G /τ E LHD was weak. These findings suggest that the LHD scaling should be modified to scale the global energy confinement of the helical plasmas in a wide range of n e (0)/⟨n e ⟩.