Transport analysis in an electron cyclotron heating power scan of TJ-II plasmas

The response of transport in low density (line average ) plasmas to electron cyclotron resonance heating (ECH) power, 100 kW QECH 400 kW, is documented for the TJ-II Heliac-type stellarator. Radially resolved electron heat balance shows no significant differences between boron or lithium coating of the vacuum chamber walls. The main trends in electron heat transport are found to be similar to other stellarator/heliotron devices and are compatible with neoclassical calculations in the bulk of the plasma. According to our calculations the heat fluxes are anomalous near the edge, ρ 0.8 where ρ is the normalized minor radius, but the uncertainties there are large. Particle transport in the density gradient region, ρ ≈ 0.8, has little sensitivity to the variation of heating power and is compatible with neoclassical predictions. Neoclassical transport of particles and electron heat is found to be dominant in the gradient regions of typical ECH plasmas of the TJ-II Heliac.