Scaling of H-mode edge pedestal pressure for a Type-I ELM regime in tokamaks

Scaling of H-mode edge pedestal pressure for a Type-I ELM regime based on a simple analytical formula (Hatae T et al 2001 Nucl. Fusion41 285) can be significantly improved by introducing shaping factors into the scaling, which is motivated by a recent development of the MHD model for the critical pressure gradient (Snyder P B et al 2002 Phys. Plasmas5 2037, Lao L L et al 2002 ITPA H-mode Edge Pedestal Physics Topical Group Meeting (San Diego)). The physics basis of these shaping factors is an enhancement of the critical pressure gradient determined by a high toroidal mode number, n, ideal ballooning mode through the effect of the magnetic well. On an increase in the magnetic well, peeling and ballooning modes decouple and the critical gradient is determined by the intermediate n mode, which enhances the critical gradient substantially. The improved scaling can reproduce the pedestal pressure reasonably well for ASDEX-U, JET and JT-60U Type-I ELMy data archived in the International Pedestal Database version 3.