Transport Coefficients in the Jet Boundary

Abstract

AbstractLangmuir probes mounted in an antenna protection tiles have facilitated the comprehensive measurement of electron temperatures and densities in the JET scrape‐off layer (sol)2. The probes are close to the outside midplane and at radial positions of 15 and 28 mm behind the last closed flux surface. The data are from ohmic discharges with plasma currents between 1 and 5 MA and average electron densities between 8 × 1018 and 5 × 1019 m−3.Here we use these measurements in a simple diffusive model for the electrons to obtain empirical scalings of the transport coefficients with local parameters. The scalings are shown to be inconsistent with exponentially decaying profiles of electron temperature and density, such as are measured in the JET sol.In the apparent absence of a suitable model we are forced to scale directly the characteristic decay lengths in similar fashion. Finaally we use these dependences to campare models of global particle and power balance with the data.