Zonal flows and long-distance correlations during the formation of the edge shear layer in the TJ-II stellarator

12 pages, 7 figures.-- PACS nrs.: 52.55.Hc, 52.30.-q, 52.40.Hf, 52.25.Fi, 52.35.Ra, 52.25.Gj.-- ArXiv pre-print available at: http://arxiv.org/abs/0904.2551A theoretical interpretation is given for the observed long-distance correlations in potential fluctuations in TJ-II. The value of the correlation increases above the critical point of the transition for the emergence of the plasma edge shear flow layer. Mean (i.e. surface averaged, zero-frequency) sheared flows cannot account for the experimental results. A model consisting of four envelope equations for the fluctuation level, the mean flow shear, the zonal flow amplitude shear and the averaged pressure gradient is proposed. It is shown that the presence of zonal flows is essential to reproduce the main features of the experimental observations.Part of this research was sponsored by the Dirección General de Investigación of Spain under project ENE2006-15244-C03-01. BAC acknowledges the financial support of Universidad Carlos III and Banco Santander through a Cátedra de Excelencia.Publicad