Poincaré plots showing vacuum calculations of the magnetic flux surfaces, including the internal magnetic island chain for the bean-shaped cross-section of W7-X for different values of iota, increasing from left to right. Corresponding details of these configurations are given in table 1. For the high-confinement configuration (in the middle), the island chain is already inside the confinement region as the last closed flux surface (LCFS) occurs outside.
Stochastic perturbed magnetic field lines that approach each other at a decorrelation distance l_{\perp c} generally of the order of the electron Larmor radius ρe allowing an electron the possibility to jump from one line to another line via collisional process. The maximum distance between the magnetic field line is represented by Δr.
(a) Buildup of a transport barrier (marked with black dashed line) is shown in high confinement configuration, where the internal 5/5 island-chain is inside the LCFS, with the T_{\mathrm e} (important to note that the radiation temperature of ECE is taken as T_{\mathrm e} for these figures, and hence, the radial location and relative trends are of more importance than absolute values) at different plasma radius, the line integrated plasma density n_{\mathrm e}, the stored diamagnetic energy W_{\mathrm{dia}} and the H_{\mathrm{alpha}} radiation levels. (b) The high field side T_{\mathrm e} profiles from ECE for the high iota configuration scan at the heating power of 2 MW and a plasma density of ≈3.5 \times 10^{19} m−3. The profile mapping is done with HINT equilibrium, including the island in the calculation. The magnetic island is ≈8 cm wide for high confinement configuration (\iota_{0} = 0.911, FMM002, shaded in red) and is located around 0.416–0.496 m.
