Electron transport in the plasma edge with rotating resonant magnetic perturbations at the TEXTOR tokamak

Small three-dimensional (3D) magnetic perturbations can be used as a tool to control the edge plasma parameters in magnetically confined plasmas in high confinement mode (”H-mode”) to suppress edge instabilities inherent to this regime, the Edge Localized Modes (ELMs). In this work, the impact of rotating 3D resonant magnetic perturbation (RMP) fields on the edge plasma structure characterized by electron density and temperature fields is investigated. We study a low confinement (L-mode) edge plasma (r/a > 0.9) with high resistivity (edge electron collisionality ν$^{∗}_{e}$ > 4) at the TEXTOR tokamak. The plasma structure in the plasma edge is measured by a set of high resolution diagnostics: a fast CCD camera (Δt = 20μs) is set up in order to visualize the plasma structure in terms of electron density variations. A supersonic helium beam diagnostic is established as standard diagnostic at TEXTOR to measure electron density ne and temperature Te with high spatial (Δr = 2 mm) and temporal resolution (Δt = 20μs). The measured plasma structure is compared to modeling results from the fluid plasma and kinetic neutral transport code EMC3-EIRENE. A sequence of five new observations is discussed: (1) Imaging of electron density variations in the plasma edge shows that a fast rotating RMP field imposes an edge plasma structure, which rotates with the external RMP rotation frequency of |ν$_{RMP}$ | = 1 kHz. (2) Measurements of the electron density and temperature provide strong experimental evidence that in the far edge a rotating 3D scrape-off layer (SOL) exists with helical exhaust channels to the plasma wall components. (3) Radially inward, the plasma structure at the next rational flux surface is found to depend on the relative rotation between external RMP field and intrinsic plasma rotation. For low relative rotation the plasma structure is dominated by a particle and energy loss along open magnetic field lines to the wall components. For high relative rotation indications for a magnetic island acting as locally confining sub-volumes are found. (4) For high relative rotation, the entire measured edge plasma structure is shifted by $\pi$/2 toroidally with respect to the position modeled in vacuum approximation. The latter two experimental findings are compatible with modeling results of the underlying magnetic topology including plasma response obtained by a 4-field drift fluid transport model. (5) A smaller shift is measured in front of the RMP coils. This gives direct experimental evidence that the near field plasma structure is governed by the competition between the RMP near field and the local plasma structure at the next inward rational flux surface. The results obtained are essential input for benchmarking models, which include plasma response, in order to extrapolate the RMP imposed 3D plasma structure toward the next step fusion experiment ITER. The measurements of the plasma structure presented indicate that the underlying magnetic topology is rotation dependent and may therefore stimulate direct measurements of the components of the magnetic field in future