STUDIES ON PLASMA EDGE TRANSPORT AND LAYER DEPOSITION BY LOCAL INJECTION OF REACTIVE GASES DURING TEXTOR-94 DISCHARGES

To study local particle transport, silane was injected through a hole in a test limiter surface during discharges in TEXTOR-94. The gas inje ction lead to the deposition of a thin layer around the injection hole which was close to the area of the highest heat load. The layer was e roded in discharges without silane injection. The layer was not only f ormed by the injected silicon but also by a large amount of carbon whi ch must originate from other plasma facing components. The preferentia l direction (symmetry line) of the deposition pattern is tilted by sim ilar to 25 degrees relative to the magnetic field lines. Calculations with the ERO-TEXTOR code recover the general shape of the Si-depositio n pattern. To get accordance between the calculations and the experime ntal results a strong electric field parallel to B and a sticking coef ficient much smaller than I has to be considered to reproduce the low silicon deposition efficiency, whereas the tilting of the symmetry lin e can be explained by the existence of a radial electric field.