Parametric study of 2D potential structures induced by RF sheaths coupled with transverse currents in front of ICRH antenna

Hot-spot formation on the corners of the ICRH antenna can be explained by high DC potential structures, which accelerate ion fluxes and generate strong convective fluxes to the antenna surface. This comes from RF sheaths at the end of open magnetic lines, which rectify RF potential resulting from parallel electric fields. As these electric fields are not homogeneous in front of the antenna, transverse potential gradients generate transverse polarization currents which modify the potential structure. These potentials are studied with a simple flux-tube model and then a 2D-fluid model was elaborated to obtain analytical expressions for rectified potential with respect to these transverse currents. We compare them to numerical results coming from a 2D-fluid code executed in a poloidal plane in front of the antenna. Then we build a potential peak criterion to determine the peaking of DC-potential structures for typical parameters in Tore Supra. Finally, current interaction between different magnetic line lengths is approached.Presented at the Workshop Electric Fields Structures and Relaxation in Edge Plasmas, Nice, France, October 26–27, 2004.