HOW FLUCTUATIONS CONTINUE THROUGH AN X-POINT

The structure of waves around a magnetic X point is analyzed. A parado x is noted, in which theory implies that waves cannot propagate along the field past an X point, but experiment shows that they do anyway. T he paradox may arise from the theoretical ''eikonal in the perpendicul ar direction'' ansatz, in which waves follow field lines to lowest ord er. This paper demonstrates that waves can encounter a boundary layer in which this ansatz is violated. Such waves can propagate around the X-point region, thus avoiding the large wave number increase from magn etic shear, allowing them to correlate through such a region, This res ult has some unexpected implications concerning mode structure in the edge and scrape-off layer of a diverted tokamak, and possibly for the core as well. (C) 1995 American Institute of Physics.