In the Wendelstein 7-X stellarator, the vacuum rotational transform, iota, has a flat radial profile and does not cross any major rational resonance. Nevertheless, during plasma operation the iota profile can be strongly modified by electron cyclotron current drive (ECCD) in such a way that the resulting iota profile passes through low-order rational values, and this can trigger...
Radio frequency waves (RF) are scattered by filamentary structures which exist in the edge region of a tokamak plasma. The waves are reflected, refracted, and diffracted leading to a change in their spectral properties. The spatial profile of the launched power gets fragmented and part of the launched power can be coupled to an unwanted cold plasma wave. Consequently, the efficiency of heating...
Understanding the field excitation and power losses in the plasma edge from an ICRH antenna is of paramount importance to avoid impurity release from the edge in reactor conditions. The semi-analytical code ANTITER IV provides a complete description in plane geometry (z along the total B0 field in front of the antenna, x the radial component) in the cold plasma approximation and with...