Observations of fast anisotropic ion heating, ion cooling, and ion recycling in large-amplitude drift waves

Large-amplitude drift wave fluctuations are observed to cause severe ion temperature oscillations in plasmas of the Caltech Encore tokamak @J. M. McChesney, P. M. Bellan, and R. A. Stern, Phys. Fluids B 3, 3370 ~1991!#. Experimental investigations of the complete ion dynamical behavior in these waves are presented. The wave electric field excites stochastic ion orbits in the plane normal (') to B, resulting in rapid ' heating. Ion–ion collisions impart energy along (i) B, relaxing the '-i temperature anisotropy. Hot ions with large orbit radii escape confinement, reaching the chamber wall and cooling the distribution. Cold ions from the plasma edge convect back into the plasma ~i.e., recycle!, causing further cooling and significantly replenishing the density depleted by orbit losses. The ion–ion collision period t ii;T /n fluctuates strongly with the drift wave phase, due to intense ('50%! fluctuations in n and T . Evidence for particle recycling is given by observations of bimodal ion velocity distributions near the plasma edge, indicating the presence of cold ions ~0.4 eV! superposed atop the hot ~4–8 eV! plasma background. These appear periodically, synchronous with the drift wave phase at which ion fluid flow from the wall toward the plasma center peaks. Evidence is presented that such a periodic heat/loss/recycle/cool process is expected in plasmas with strong stochastic heating. © 1998 American Institute of Physics. @S1070-664X~98!01603-6#