Article révisé par les pairs
Résumé : The effect of boundary conditions at the last closed magnetic surface (LCMS) on the formation of the edge transport barrier (ETB) in tokamaks is investigated by one-dimensional transport calculations for the radial profiles of plasma parameters. For a given heating power the transition from the low confinement mode (L mode) to the high confinement mode (H mode) can be triggered by increasing the density e -folding length, δn, or reducing the temperature e -folding length, δT, at the LCMS. This is explained by the decrease of heat losses from the confined plasma with the convection of charged particles and changeover to the case where losses are mostly due to heat conduction. In such a case, corresponding to a divertor configuration, the computed power threshold for the L - to H -mode transition (L - H transition) is in a good agreement with the experimental multimachine scaling. © 2006 American Institute of Physics.