Session NP1 - Poster Session VIII.
POSTER session, Wednesday afternoon, October 25
Exhibit Hall AB, Qu\'{e}bec City Convention Centre
The observed dependence on discharge shape of the edge-localized-mode (ELM) amplitude and frequency in DIII-D tokamak H-mode plasmas has been shown to be consistent with a model for the pressure gradient (P^\prime_edge) stability threshold as a function of toroidal mode number (n).(J.R.\ Ferron et al., Phys. Plasmas 7), 1976 (2000). In this model, based on ideal MHD stability theory, the instability responsible for triggering a Type~I ELM is a coupled kink/ballooning mode with n near the largest value without access to a second stability regime. Here we add to the understanding of this model through additional parameter scaling studies. The calculated sensitivity to the edge current density (J_edge) of the P^\prime_edge stability threshold versus n is used to determine the importance of the uncertainty in the measurement of J_edge. The dependence of the P^\prime_edge threshold on the pressure pedestal width and the total plasma current are compared to experiment. Equilibria characteristic of those at the end of the VH-mode ELM-free phase, when the observed P^\prime_edge can be especially large, are tested for second stability regime access at low values of n.