Electron energy transport in the presence of rational surfaces in the wendelstein 7-AS stellarator

摘要

Electron energy transport in the Wendelstein 7-AS stellarator exhibits a strong sensitivity to the boundary value of the rotational transform when the magnetic shear is low. Pronounced confinement maxima close to the low order rational i values correlate with a low density of other rational numbers in these favourable i ranges. The i dependence is lost if magnetic shear is increased by large plasma currents. The hypothesis is proposed that, at rational flux surfaces, electron energy transport is increased above the already anomalous level and that magnetic shear reduces the additional enhancement.