An analysis of the international tokamak physics activity (ITPA) H-mode power threshold database is advanced to study the roles of the aspect ratio, A, the absolute magnetic field and the effective charge number, Zeff. A new scaling expression for the power threshold, Pthr, is presented. The absolute B at the outer surface is used instead of Bt in the scaling, and the Ip dependence of Pthr in low-A tokamaks is described without the explicit use of the Ip variable. A clear and strong dependence on Zeff is found; . Both the scattering nature in the data fitting and the 'low-density anomaly' can be reduced. A nonlinear A dependence is also suggested. The Pthr in ITER is predicted on the basis of the present scaling.
Empirical scaling of the L–H threshold power for metal wall tokamaks using a multi-device database