Rotation studies in electron Internal Transport Barriers on TCV
This paper reports simultaneous measurements of intrinsic toroidal and poloidal plasma rotation during the evolution of electron Internal Transport Barriers (eITBs) on TCV. A CXRS diagnostic-beam system provides ion parameter profiles for stationary pre-barrier formation and eITB sustainment phases with a 15mm spatial resolution across the entire barrier width. This special configuration is used to assess the role of Er and E ×B shearing for the eITBs sustainment and formation in TCV. Two eITBs targets were developed either by applying central counter-ECCD with off-axis ECH, giving a central barrier, or off-axis co-ECCD with central ECH/counter-ECCD. The first target, characterized by a central Te barrier, is used to study the evolution of the rotation and Er with respect to the development of MHD modes, ECH power and plasma density. MHD modes cause a toroidal rotation reversal leading to increasingly positive Er. When applying central counter-ECCD, a peaked counter current rotation is sustained in the core with rotation values approximately doubled compared with the ECH phase where both cases have flat Er profiles. This shows experimentally for the first time on TCV that the E ×B shearing does not influence the eITB.