Toweards improved confinement: analysis of the radial electric field in LHD

摘要

the radial electric field (E_r) properties in LHD have been investigated to give guidance towards improved confinement with a possible E_r transition and bifurcation. The ambipolar E_r is calculated from the neoclassical flux on the basis of analytical formulas. This approach is appropriate to clarifying the E_r properties over a wide parameter range in a more transparent way. A comparison between calculated E_r and the experimental values has shown a qualitatively good agreement, for example, for the threshold density for the transition from the ion root to the electron root.