(TH/P8-4) Second Ballooning Stability Effect on H-mode Pedestal Scalings

T. Onjun1), A.H. Kritz2), G. Bateman2), A. Pankin2)
 
1) Sirindhorn International Institute of Technology, Pathumthani, Thailand
2) Department of Physics, Lehigh University, Pennsylvania, USA

Abstract.  Edge localized modes (ELMs) have a strong effect on the plasma at the edge of H-mode tokamak discharges. Robust models for triggering ELM crashes are needed for predictions of the pedestal height. In this study, the transition from the first ballooning mode stability to the second stability is included in the determination of scalings for the height of the temperature pedestal of type-I ELMy H-mode discharges. The ballooning threshold, derived from MHD stability calculations obtained using the HELENA and MISHKA codes, together with six theoretical-based models for the pedestal width, are implemented to derive scalings for the pedestal temperature height. These pedestal height scalings include the effects of plasma shaping, separatrix, bootstrap current, and the effect of access to the second ballooning stability. Each pedestal model is calibrated using experimental data obtained from the latest public version of the International Tokamak Physics Activity (ITPA) Pedestal Database (Version 3.2). In addition, an improved empirical model is developed for the height of the density pedestal. Statistical measures are used to show that the new models using the ballooning stability threshold that takes into account a possible access to the second stability region agree with experimental data about equally well and yield better agreement with experimental data than previous models. Results are presented for the pedestal height expected in ITER discharges based on the new scalings.

Full paper available (PDF)