Modification of high mode pedestal instabilities in the DIII-D tokamak

J. R. Ferron, M. S. Chu, G. L. Jackson, L. L. Lao, R. L. Miller, T. H. Osborne, P. B. Snyder, E. J. Strait, T. S. Taylor, A. D. Turnbull, A. M. Garofalo, M. A. Makowski, B. W. Rice, M. S. Chance, L. R. Baylor, M. Murakami, M. R. Wade

Research output: Contribution to journalConference articlepeer-review

70 Citations (Scopus)

Abstract

The amplitude and frequency of modes driven in the edge region of tokamak high mode (H-mode) discharges [type I edge-localized modes (ELMs)] are shown to depend on the discharge shape. The measured pressure gradient threshold for instability and its scaling with discharge shape are compared with predictions from ideal magnetohydrodynamic theory for low toroidal mode number (n) instabilities driven by pressure gradient and current density and good agreement is found. Reductions in mode amplitude are observed in discharge shapes with either high squareness or low triangularity where the stability threshold in the edge pressure gradient is predicted to be reduced and the most unstable mode is expected to have higher values of n. The importance of access to the ballooning mode second stability regime is demonstrated through the changes in the ELM character that occur when second regime access is not available. An edge stability model is presented that predicts that there is a threshold value of n for second regime access and that the most unstable mode has n near this threshold.

Original languageEnglish
Pages (from-to)1976-1983
Number of pages8
JournalPhysics of Plasmas
Volume7
Issue number5 II
DOIs
Publication statusPublished - 2000 May
Event41st Annual Meeting of the Division of Plasma Physics of the Ameircan Physical Society - Seattle, WA, United States
Duration: 1999 Nov 151999 Nov 19

All Science Journal Classification (ASJC) codes

  • Condensed Matter Physics

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