Width of turbulent SOL in circular plasmas: A theoretical model validated on experiments in Tore Supra tokamak

Abstract

The relation between turbulent transport and scrape off layer width is investigated in circular plasmas toroidally limited on the inner wall. A broad set of experimental observations collected in the Tore Supra scrape off layer is detailed and compared to turbulent interchange models. Blob E × B drift velocities measured in experiments agree reasonably well with an analytical model derived for isolated blobs. Based on a time averaged particle flux balance, it is also shown that the SOL width depends on both the blob drift velocity and a blob intermittency parameter, which is so far not predicted by isolated blob models. A set of 2D isothermal turbulence simulations are used to derive a power law regression of the density width function of global control parameters. Quantitative agreement is found between this regression and experimental density widths measured in Tore Supra, over a large set of plasma conditions. The sensitivity to control parameters (major radius, safety factor and normalized Larmor radius) is roughly explained by the sensitivity of the blob velocity model. The predictions are also extended to power decay length in limited plasma configurations. For ITER start-up phases, the predicted power decay length fall in the range of extrapolations based on multi-machine regressions.