Tolerable ELMs at high density in DIII-D

The energy released at each edge-localized mode (ELM) is found to decrease in relation to the pedestal pressure, by more than a factor of five, as the line-averaged density in DIII-D H-mode is raised from about half the Green wald density limit to near the Greenwald limit. The pedestal pressure remai ns nearly constant over this range demonstrating an attractive regime for f uture larger tokamaks. The reduction in ELM energy, in both low and high tr iangularity configurations, is seen to scale more with the pedestal electro n temperature than the pedestal density. At low density both the electron d ensity and temperature inside the separatrix drop due to the ELM instabilit y; however at high density the density perturbation remains similar while t he temperature profile is unaffected. ELMs at high density are also charact erized by smaller magnetic fluctuations consistent with a higher toroidal m ode number ELM instability. (C) 2001 Elsevier Science B.V. All rights reser ved.