Gas puff fueled H-mode discharges with good energy confinement above the Greenwald density limit on DIII-D

T. H. Osborne, A. W. Leonard, M. A. Mahdavi, M. Chu, M. E. Fenstermacher, R. La Haye, G. McKee, T. W. Petrie, E. Doyle, G. Staebler, M. R. Wade

Research output: Contribution to journalConference articlepeer-review

30 Citations (Scopus)

Abstract

ELMing (edge-localized) H-mode discharges with densities as high as 40% above the Greenwald density and good energy confinement, HITER-89P = 2, were obtained with D2 gas puffing on DIII-D [Chan et al., Proceedings of the 16th IAEA Conference, Montreal (International Atomic Energy Agency, Vienna, 1996), Vol. 1, p. 95]. These discharges have performance comparable to the best pellet fueled DIII-D discharges. Spontaneous peaking of the density profile was an important factor in obtaining high energy confinement. Without density profile peaking, the energy confinement at high density degraded with reduction in the H-mode pedestal pressure under the stiff temperature profile conditions observed at high density on DIII-D. Reduction in the pedestal pressure was associated with loss of access to the second stable regime for ideal ballooning modes at the edge, and change in the edge-localized mode (ELM) instability from a low to high toroidal mode number. Gyrokinetic stability calculations indicate that the core of the high-density discharges is dominated by ion temperature gradient mode turbulence. A turbulent transport simulation with the GLF23 [Waltz et al., Phys. Plasmas 4, 2482 (1997)] code produced stiff temperature profiles in agreement with the experiment and did not indicate the formation of an internal transport barrier. Helium transport studies showed an anomalous inward particle pinch at high density. The highest density discharges were terminated by onset of a magnetohydromagnetic instability, which is consistent with destabilization of neoclassical tearing modes through peaking of the pressure profile.

Original languageEnglish
Pages (from-to)2017-2022
Number of pages6
JournalPhysics of Plasmas
Volume8
Issue number5 II
DOIs
Publication statusPublished - 2001 May
Event42nd Annual Meeting of the APS Division of Plasma Physics - Quebec, Que, Canada
Duration: 2000 Oct 232000 Oct 27

All Science Journal Classification (ASJC) codes

  • Condensed Matter Physics

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