Fluid velocity and electromagnetic forces measured by a rotating Langmuir probe in the scrape-off layer of JFT-2M

Measurements obtained by the novel technique of an assembly of planar Langmuir probes rotating in the scrape-off layer of JFT-2M are described. The probes scan the radial direction and rotate 360 deg. so measuring the direction of the magnetic field and the density of current in the magnetic surfaces. Experiments carried out with and without divertor biasing lead to the following main results: (1) The direction of the ion flow has been measured. (b) It has been found that j x B ≠ 0 with the resulting force always directed towards the magnetic axis. (c) By applying a negative divertor bias a narrow layer appears where the current flows in a direction opposite to the main plasma current. (author). 18 refs, 9 figs