Dependence of H-mode power threshold on global and local edge parameters

Measurements of local electron density n(e), electron temperature T-e and ion temperature T-i have been made at the very edge of the plasma just prior to the transition into H-mode for four different single parameter scans in the DIII-D tokamak. The means and standard deviations of n(e), T-e and T-i under these conditions for a value of the normalized toroidal Bur of 0.98 are, respectively, (1.5 +/- 0.7) x 10(19) m(-3), 0.051 +/- 0.016 keV, and 0.14 +/- 0.03 keV. The threshold condition for the transition is more sensitive to temperature than to density. The data indicate that the dependence is not as simple as a requirement for a fixed value of the ion collisionality.