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Title: Transport implications of non-monotonic-q tokamak configurations

Abstract

Advanced tokamak configurations attempt to make use of cross-sectional shaping and profile control to enhance the stability properties of the plasma. A comprehensive kinetic toroidal eigenvalue calculation which implements the ballooning formalism is employed to investigate this for high-n instabilities such as the toroidal drift mode destabilized by the combined effects of ion temperature gradients and trapped particles. An approach being pursued in advanced tokamak configurations is profile control for the current and/or pressure. In particular, it may be possible to produce regions of reversed shear (dq/dr < 0), as has been observed in the JET tokamak in PEP mode discharges. If sufficiently large, this reversal has the effect of reversing the ``bad curvature`` of the trapped particles and thereby suppressing the collisionless trapped-electron mode instability mechanism of magnetic-drift precession resonance. At the same time, temperature and density profiles which optimize the bootstrap current can also correspond to regions with {eta}{sub i} {equivalent_to} dln T{sub i}/dln n < {eta}{sub i}{sup crit}, so that the ion-temperature-gradient-mode instability mechanism is also suppressed. If these regions overlap, as has happened in the plasma interior for a particular operating mode for a TPX design, then the toroidal drift mode can be completely stabilized. Ifmore » this mode is responsible for the experimentally-observed anomalous transport in tokamaks, then this situation can lead to a ``transport barrier`` in the plasma interior. The stability properties of such configurations with respect to low-n ideal MHD modes will also be discussed.« less

Authors:
; ; ;
Publication Date:
Research Org.:
Princeton Univ., NJ (United States). Plasma Physics Lab.
Sponsoring Org.:
USDOE, Washington, DC (United States)
OSTI Identifier:
10182746
Report Number(s):
PPPL-CFP-2957; CONF-920813-7
ON: DE93019821; TRN: 93:022834
DOE Contract Number:  
AC02-76CH03073
Resource Type:
Conference
Resource Relation:
Conference: Joint Varenna-Lausanne international workshop on theory of fusion plasmas,Varenna (Italy),24-28 Aug 1992; Other Information: PBD: [1992]
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; TOKAMAK DEVICES; PLASMA INSTABILITY; SHEAR PROPERTIES; MHD EQUILIBRIUM; EIGENVALUES; ION TEMPERATURE; CURRENT DENSITY; PLASMA PRESSURE; BOOTSTRAP CURRENT; PLASMA CONFINEMENT; 700340; 700310; PLASMA WAVES, OSCILLATIONS, AND INSTABILITIES

Citation Formats

Rewoldt, G, Tang, W M, Manickam, J, and Kessel, C. Transport implications of non-monotonic-q tokamak configurations. United States: N. p., 1992. Web.
Rewoldt, G, Tang, W M, Manickam, J, & Kessel, C. Transport implications of non-monotonic-q tokamak configurations. United States.
Rewoldt, G, Tang, W M, Manickam, J, and Kessel, C. 1992. "Transport implications of non-monotonic-q tokamak configurations". United States. https://www.osti.gov/servlets/purl/10182746.
@article{osti_10182746,
title = {Transport implications of non-monotonic-q tokamak configurations},
author = {Rewoldt, G and Tang, W M and Manickam, J and Kessel, C},
abstractNote = {Advanced tokamak configurations attempt to make use of cross-sectional shaping and profile control to enhance the stability properties of the plasma. A comprehensive kinetic toroidal eigenvalue calculation which implements the ballooning formalism is employed to investigate this for high-n instabilities such as the toroidal drift mode destabilized by the combined effects of ion temperature gradients and trapped particles. An approach being pursued in advanced tokamak configurations is profile control for the current and/or pressure. In particular, it may be possible to produce regions of reversed shear (dq/dr < 0), as has been observed in the JET tokamak in PEP mode discharges. If sufficiently large, this reversal has the effect of reversing the ``bad curvature`` of the trapped particles and thereby suppressing the collisionless trapped-electron mode instability mechanism of magnetic-drift precession resonance. At the same time, temperature and density profiles which optimize the bootstrap current can also correspond to regions with {eta}{sub i} {equivalent_to} dln T{sub i}/dln n < {eta}{sub i}{sup crit}, so that the ion-temperature-gradient-mode instability mechanism is also suppressed. If these regions overlap, as has happened in the plasma interior for a particular operating mode for a TPX design, then the toroidal drift mode can be completely stabilized. If this mode is responsible for the experimentally-observed anomalous transport in tokamaks, then this situation can lead to a ``transport barrier`` in the plasma interior. The stability properties of such configurations with respect to low-n ideal MHD modes will also be discussed.},
doi = {},
url = {https://www.osti.gov/biblio/10182746}, journal = {},
number = ,
volume = ,
place = {United States},
year = {Thu Dec 31 00:00:00 EST 1992},
month = {Thu Dec 31 00:00:00 EST 1992}
}

Conference:
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