Geometric dependence of the energy confinement time scaling for H-mode discharges

The dependence of the H-mode energy confinement time τE on the plasma elongation and the divertor configuration is studied. A regression analysis of the H-mode database is presented in which the dependence on the closed/open divertor configuration, estimated from the ASDEX experiments, is included. The dependence of τE on the elongation factor k is found to be positive (approximately k0.6) for ELM-free H-mode discharges, in accordance with experimental results for ELM-free limiter H-mode plasmas in JFT-2M. In addition, the influence of the X-point configuration (single null or double null) on the confinement time is briefly addressed. (author). Letter-to-the-editor. 11 refs, 6 figs