Empirical scaling law for the effective heat diffusivity in ELMy H mode plasmas

Predictive code simulations of high density scenarios of ITER and other reactor-grade devices require an experimentally validated scaling relation for the one-fluid effective heat diffusivity χ in the ELMy H mode regime. A comprehensive empirical χ scaling compatible with the ITERH92-P ELMy H mode scaling of the thermal energy confinement time is presented. It follows from a power law ansatz for χ and integration of the single-fluid energy equation and recovers all the exponents of the global confinement law. The numerical factor of the global scaling is used to calibrate the heat diffusivity. The dependences of χ on the temperature and temperature gradient, connected with the power degradation of confinement, are inferred from profile information of a high density H mode discharge. The scaling law obtained is successfully tested against JET, ASDEX and ASDEX Upgrade H mode discharges covering a wide parameter range. It is found to predict the strong rise of the experimental χ profiles with increasing effective radius. (author). Letter-to-the-editor. 8 refs, 2 figs, 1 tab